WO1998041664A1 - Dual-phase high-strength steel sheet having excellent dynamic deformation properties and process for preparing the same - Google Patents

Dual-phase high-strength steel sheet having excellent dynamic deformation properties and process for preparing the same Download PDF

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Publication number
WO1998041664A1
WO1998041664A1 PCT/JP1998/001101 JP9801101W WO9841664A1 WO 1998041664 A1 WO1998041664 A1 WO 1998041664A1 JP 9801101 W JP9801101 W JP 9801101W WO 9841664 A1 WO9841664 A1 WO 9841664A1
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Prior art keywords
steel sheet
strength
deformation
dual
temperature
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PCT/JP1998/001101
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French (fr)
Japanese (ja)
Inventor
Akihiro Uenishi
Manabu Takahashi
Yukihisa Kuriyama
Yasuharu Sakuma
Osamu Kawano
Junichi Wakita
Hidesato Mabuchi
Original Assignee
Nippon Steel Corporation
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Priority claimed from JP19029797A external-priority patent/JP3530347B2/en
Priority claimed from JP22300897A external-priority patent/JP3936440B2/en
Priority claimed from JP25893897A external-priority patent/JP3839928B2/en
Application filed by Nippon Steel Corporation filed Critical Nippon Steel Corporation
Priority to EP98907247.5A priority Critical patent/EP0969112B2/en
Priority to CA002283924A priority patent/CA2283924C/en
Priority to AU63118/98A priority patent/AU717294B2/en
Publication of WO1998041664A1 publication Critical patent/WO1998041664A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to a dual-phase high-strength steel sheet for automobiles having excellent dynamic deformation characteristics and excellent collision safety, which is intended to be mainly used for structural members of automobiles and reinforcing materials. It is about methods. Background art
  • high-strength steel has been expanding for the purpose of reducing vehicle body weight in the context of automobile fuel efficiency regulations, but recently, laws and regulations regarding collision safety assuming an automobile accident have been rapidly expanding and strengthening in Japan and overseas.
  • Expectations for high-strength steel are increasing. For example, in a frontal collision of a passenger car, if a material with high shock absorption performance is applied to a member called the front side member, the shock energy is absorbed by the crushing of this member, which affects the occupant. Shock can be reduced.
  • a collision safety member when forming a collision safety member, it has excellent shape freezing properties, excellent stretchability (tensile strength X total elongation ⁇ 18,800), and excellent elongation flangeability (hole expansion ratio ⁇ It is desired that the combination of 1.2) is satisfied, but it has not been found that there is a material that has both excellent collision safety and excellent formability. Disclosure of the invention
  • the present invention has been proposed to solve the above-described problems, and provides a dual-fused high-strength steel sheet for an automobile having excellent collision safety and excellent dynamic deformation characteristics, and a method for producing the same. is there.
  • the present invention relates to a high-strength steel sheet used for a molded automotive part such as a front side member and the like, which is selected based on appropriate characteristics and criteria for absorbing impact energy in a collision.
  • Another object of the present invention is to provide a dual-phase high-strength steel sheet for automobiles having excellent dynamic deformation characteristics that can surely contribute to ensuring safety and a method for producing the same.
  • the present invention provides a dual-fuse type vehicle having excellent dynamic deformation characteristics having excellent shape freezing properties, excellent overhanging properties, and excellent elongation flangeability suitable for forming a collision safety member. It provides high-strength steel sheets and methods for manufacturing them.
  • the present invention has been made to achieve the above object, and specific means thereof are as follows.
  • the main phase is flat and the second phase is 5% with the equivalent strain of the steel sheet.
  • the martensite is reduced to 3 to 50% by volume fraction.
  • This is a composite structure with other low-temperature-producing phases containing, and after applying a pre-deformation of more than 0% to 10% or less at equivalent strain, 5 X 10 " 4 to 5 X 10 — 3 (s — ')
  • the difference ( ⁇ ) between the shape strength s and the dynamic deformation strength ⁇ d when deformed in the strain rate range of 5 ⁇ 10 2 to 5 ⁇ 10 3 (s ′′ ′) after the pre-deformation is applied.
  • (3- ⁇ s) satisfies 6 OMPa or more, and a work hardening index at a strain of 5 to 10% satisfies 0.13 or more.
  • the main phase is ferrite and the second phase is 5% with the equivalent strain of the steel sheet.
  • the martensite is converted to a volume fraction of 3 to 50%. This is a composite structure with other low-temperature generation phases containing 5% after applying a predeformation of more than 0% to 10% or less at equivalent strain.
  • the average crystal grain size of the martensite satisfies 5 m or less and the average crystal grain size of the fly satisfies 10 m or less.
  • Dual-pipe high-strength steel sheet with excellent dynamic deformation characteristics ⁇ ⁇ ⁇ ⁇ In any of 1, 2, 3 or 2 above, tensile strength (MPa) X total elongation (%) ⁇ 18,000 and hole expansion ratio (d / do) ⁇ 1.2
  • MPa tensile strength
  • X total elongation (%) ⁇ 18,000
  • a dual-phase high-strength steel sheet with excellent dynamic deformation characteristics characterized by satisfying
  • the amount of plastic deformation (T) at the time of pre-deformation by either or both of the temper rolling and the tension leveler is expressed by the following formula:
  • a dual-phase high-strength steel sheet having excellent dynamic deformation characteristics characterized by satisfying the following requirements.
  • the dual-phase high-strength steel sheet having excellent dynamic deformation characteristics according to the present invention is characterized in that, in the above-mentioned 1 to 6, C: 0.02 to 0.25% by weight as a material component, 0.15 to 3.5% in total of one or more of Mn and Cr, 0.02 to 4.0 in total of one or more of Si, Al, P %, And if necessary, one or more of Ni, Cu and Mo in a total of 3.5% or less, and one or more of Nb, Ti and V in total 0.3% or less, one or more of Ca and REM, 0.05 to 0.01% for Ca, and 0.05 to 0.05 for REM %, With the balance being Fe as the main component.
  • the dual-phase high-strength steel sheet having excellent dynamic deformation characteristics according to the present invention further comprises B ⁇ 0.0I%, S ⁇ 0.01 N ⁇ 0.0 A dual-phase high-strength steel sheet with excellent dynamic deformation characteristics characterized by the addition of one or more of 2% or more as required.
  • ⁇ ⁇ ⁇ ⁇ As a method for producing a dual-phase high-strength hot-rolled steel sheet having excellent dynamic deformation characteristics in the present invention, a continuous forged slab is directly sent to a hot-rolling process as it is, or after being cooled once.
  • the metallurgical parameters A force The hot rolling that satisfies the formulas (1) and (2) is performed, and in the subsequent runtable The average cooling rate was set to 5 ° C / sec or more, and the relationship between the above-mentioned metal parameter: A and the winding temperature (CT) was (
  • a continuous production slab is directly sent to a hot-rolling process as it is produced.
  • hot-rolled, hot-rolled and rolled hot-rolled steel sheet is pickled, cold-rolled, and annealed in a continuous annealing process to obtain a final product, A c, ⁇
  • cooling is performed at a cooling rate of 5 ° C./second or more.
  • the cold-rolled steel sheet is heated to a temperature of A c, to A c 3 (T o), and annealed for more than 10 seconds within this temperature range.
  • FIG. 1 is a view showing the relationship between the absorbed energy (E ab) of the molded member and the material strength (S) at the time of collision in the present invention.
  • Fig. 2 Perspective view showing the molded member for measuring the shock absorption energy in Fig. 1.
  • Fig. 3 Diagram showing the relationship between the work hardening index of steel sheets and the amount of dynamic energy absorption.
  • Fig. 4 A graph showing the relationship between the yield strength of a steel sheet X work hardening index and the amount of dynamic energy absorption.
  • Fig. 5 Schematic view of the (hat model) used in the impact crush test method related to Figs.
  • Fig. 6 Sectional view of the test piece shape of Fig. 5.
  • Fig. 7 Schematic diagram of the impact crush test method related to Figs.
  • Fig. 8 Equivalent strain of 3 to 10% when deformed at a strain rate of 5 ⁇ 10 2 to 5 ⁇ 10 3 (1ZS), which is an index of the impact energy absorption capacity at the time of collision in the present invention.
  • the figure which shows the relationship between the average value of deformation stress dyn-TS and TS in the range.
  • Fig. 9 Shows the change in static-dynamic ratio due to temper rolling in the present invention example and the comparative example. Graph.
  • FIG. 10 is a view showing the relationship between ⁇ ⁇ ⁇ ⁇ ⁇ and metal parameter: A in the hot rolling process according to the present invention.
  • FIG. 11 is a view showing the relationship between the winding temperature and the metallurgical parameter: A in the hot rolling process according to the present invention.
  • FIG. 12 is a schematic view showing an annealing cycle of continuous annealing according to the present invention.
  • Shock absorbing members such as front side members of automobiles are manufactured by bending and pressing steel plates. Since the impact at the time of vehicle collision is applied to these formed members, it is necessary to have a high shock absorbing capacity in a state after pre-deformation corresponding to such forming.
  • attempts have been made to obtain a high-strength steel sheet having excellent shock absorption properties as a real member by simultaneously considering the increase in deformation stress due to forming and the increase in deformation stress due to increase in strain rate. That is not described above.
  • the present inventors have conducted various experiments and studies in order to achieve the above object, and as a result, as a high-strength steel sheet having excellent shock absorption characteristics in the above-formed real member, a dual phase steel plate (DP)
  • a steel sheet with a structure was optimal.
  • the steel sheet having this dual-phase structure is a composite structure with the ferrite phase, which plays a role in increasing the deformation resistance due to the increase in deformation speed, as the main phase, and the second phase including a hard martensite phase. It was found to be excellent in dynamic deformation characteristics.
  • the microstructure of the finally obtained steel sheet has a ferrite phase as a main phase and a hard martensite phase with a volumetric equivalent of the above steel sheet of 3% by volume after forming by 5%. It was found that the composite showed high dynamic deformation resistance when it had a composite structure with other low-temperature generation phases containing up to 50%.
  • the volume fraction of the hard martensite phase 3 to 50%, if the martensite phase is less than 3%, a high-strength steel sheet cannot be obtained, and the dynamic deformation strength cannot be increased. Since a high steel sheet cannot be obtained, the volume fraction of the martensite phase must be 3% or more.
  • the volume fraction of the ferrite phase which should be responsible for the increase in deformation resistance due to the increase in deformation speed, decreases, and the dynamic deformation strength becomes smaller than the static deformation strength. It has also been found that it is not possible to obtain a steel sheet excellent in quality and the formability is impaired, so that the volume fraction of the martensite phase must be 3 to 50%.
  • the present inventors found that the amount of pre-deformation corresponding to the forming process of a shock absorbing member such as a front side member was up to 2 parts depending on the part.
  • the force can reach 0% or more, and it is also found that the equivalent strain is mostly in the range of 0% to 10%, and by grasping the effect of pre-deformation in this range, We also found that it was possible to estimate the behavior after pre-deformation as a whole. Therefore, in the present invention, a deformation of 0% to 10% was selected as an equivalent strain as an amount of pre-deformation to be given to the member during processing.
  • FIG. 1 shows the relationship between the absorbed energy (E ab) of the formed member and the material strength (S) at the time of collision for each of the steel types in Table 5 in the examples described later.
  • the material strength S is the tensile strength (TS) from a normal tensile test.
  • the material absorption energy (E ab) is calculated by colliding a weight of 400 kg with a velocity of 15 m / s in the length direction (the direction of the arrow) of the molded member as shown in Fig. 2 and crushing it. Absorbed energy up to 100 mm.
  • the formed member shown in Fig. 2 is made by joining a steel plate with a thickness of 2.0 mm to the hat-shaped part 1 and a steel sheet 2 of the same thickness and the same steel type by spot welding.
  • the work hardening index of the steel specifically, 0.13 or more, preferably 0.16 or more.
  • the work hardening index and the work hardening index By controlling the work hardening index and the work hardening index to a specific range, it is possible to achieve excellent collision safety, and to improve the formability, effects such as incorporating the volume fraction and the particle size of the martensite in a specific range. There is.
  • Figure 3 shows the relationship between the dynamic energy absorption, which is an index of the collision safety of the member, and the work hardening index of the steel sheet, for the same yield strength class.
  • the collision safety (dynamic energy absorption) of the members is improved due to the increase in the work hardening index of the steel sheet, and the work hardening of the steel sheet with the same yield strength class is used as an index of the collision safety of the member. This indicates that the index is valid.
  • the yield strength X work hardening index can be used as an index of the collision safety of the member.
  • the work hardening index is represented by an n value of 5% to 10% in consideration of the fact that the member is subjected to distortion during molding. From the viewpoint of improving the dynamic energy absorption, the work hardening index is expressed as 5%. It is preferable that the work hardening index is less than 10% and the work hardening index is more than 10%.
  • Figure 7 shows a schematic diagram of the test method. In Fig.
  • the steel sheet used was 1.2 mm in thickness, and the composition of the steel sheet was C: 0.02 to 0.25% by weight, and the total of one or more of 1 ⁇ 1 and ⁇ r was 0.15%. To 3.5% by weight, the total amount of one or two of Si, Al, and P is from 0.02 to 4.0% by weight, and the balance is Fe.
  • FIG. 8 is an index of the impact energy absorbing ability at the time of collision according to the present invention, which is equivalent to 3 to 10% when deformed in a strain rate range of 5 ⁇ 10 2 to 5 ⁇ 10 3 (s- 1 ).
  • TS maximum stress
  • MPa maximum stress
  • the shock absorbing member such as the front side member has a hat-shaped cross-sectional shape
  • the present inventors have analyzed the deformation of such a member during high-speed collision crushing.
  • deformation is progressing up to a high strain of 40% or more at the maximum, 70% or more of the total absorbed energy is absorbed in the strain range of 10% or less in the high-speed stress-strain diagram. I found it. Therefore, the dynamic deformation resistance at the time of high-speed deformation of 10% or less was adopted as an index of the absorption capacity of the collision energy at high speed.
  • CT dyn are the static tensile strength of the steel sheet before pre-deformation and baking treatment is carried out (5 X 1 0 "4 ⁇ 5 X 1 0 - 3 ( s'), which generally increases with an increase in the maximum stress (TS: MPa) ⁇ in the static tensile test measured in the strain rate range of Increasing the tensile strength (which is synonymous with the static material strength) directly contributes to the improvement of the impact energy absorption capacity of the member. Deterioration of the formability makes it difficult to obtain the required member shape, therefore, it is desirable to use a steel plate with the same tensile strength: TS and a high CT dyn.
  • the dynamic deformation strength is usually expressed as a power of the static deformation strength. As the static deformation strength increases, the difference between the dynamic deformation strength and the static deformation strength decreases. It becomes bad. However, when considering the weight reduction by increasing the strength of the material, it is not expected that if the difference between the dynamic deformation strength and the static deformation strength becomes smaller, the improvement in the shock absorption capacity by replacing the material will not increase. It is difficult to achieve weight reduction.
  • the (d — CTS) value is (d — CTS) ⁇ 4.1 X CT S. ' 8 — It is preferable that the range satisfy s.
  • the martensite has a volume fraction of 3 to 50%, preferably 3 to 30%.
  • the average crystal grain size of the martensite is preferably 5 m or less, and the average crystal grain size of the ferrite is preferably 10 zm or less.
  • martensite is hard and contributes to the reduction of the yield ratio and the improvement of the work hardening index by generating mobile dislocations mainly in the surrounding ferrite. It is possible to disperse fine martensite, and the effect of improving its properties extends to the entire steel sheet.
  • the volume fraction of the martensite When the volume fraction of the martensite is less than 3%, the yield ratio is increased and the work hardening ability (the work hardening index ⁇ 0.130) when the molded member is subjected to collision deformation is increased. It is not possible to exert it, the deformation resistance (load) remains at a low level, and the deformation work becomes small, so that the dynamic energy absorption is low and the improvement in impact safety cannot be achieved.
  • the volume fraction of the martensite exceeds 50%, the yield ratio increases and the work hardening index decreases, and further, the tensile strength X total elongation and the hole expansion ratio deteriorate. From the viewpoint of moldability, it is preferable that the volume fraction of the martensite be 30% or less.
  • ferrite is contained in a volume fraction of preferably 50% or more, more preferably 70% or more, and its average crystal grain size (average equivalent circle diameter) is preferably 10% or more. It is preferred that the length be less than 2 m, more preferably less than 5 m, and that the martensite be adjacent to the ferrite. This not only promotes the fine dispersion of the martensite in the ground, but also works effectively so that the above-mentioned effect of improving the properties extends not only to the local influence but also to the entire steel sheet.
  • the remaining structure other than martensite-filled light may be one or a combination of two or more of perlite, bainite, residual iron, etc., but when hole-expanding properties are required Although it is preferable to mainly use bainite, it is preferable that a small amount (5% However, experiments have shown that this is effective.
  • the ratio of the particle size of the martensite to the ferrite be 0.6 or less and the hardness ratio be 1.5 or more.
  • the dual-phase high-strength steel sheet having excellent dynamic deformation characteristics used in the present invention has a C: 0.02 to 0.25% by weight as a material component, and a content of Mn and Cr. 0.15 to 3.5% in total of 1 or 2 or more, 0.02 to 4.0% in total of 1 or 2 or more of Si, A1, P
  • one or more of Ni, Cu, and Mo are 3.5% or less in total
  • one or more of Nb, Ti, and V are 0.30% or less in total
  • C a, REM one or more of them
  • C a is 0.0 0 0 5 to 0 .01%
  • the length is 0.05 to 0.05. %, With the balance being Fe.
  • B ⁇ 0.01% S ⁇ 0.01% and N ⁇ 0.02% dual phase type with excellent dynamic deformation characteristics It is a high strength steel plate.
  • C is an element that strongly affects the structure of the steel sheet, and when its content is low, it becomes difficult to obtain the desired amount and strength of the martensite phase. If the amount of addition increases, unnecessary precipitation of carbides is caused, which hinders an increase in deformation resistance due to an increase in strain rate, increases the strength too much, and further deteriorates formability and weldability. ⁇ 0.25% by weight.
  • Mn, Cr Since Mn and Cr act to stabilize austenite and secure martensite and are also strengthening elements, the lower additive amount is 0.15% by weight. On the other hand, excessive addition saturates the above effects and adversely affects ferrite transformation, etc., so the upper limit is 3.5% by weight.
  • S i, A l, P S i, A l are useful elements for forming martensite, and promote martensite formation by promoting ferrite formation and suppressing carbide formation. It has the effect of securing and has the effect of strengthening the solid solution and the effect of deoxidation. P, like Al and Si, also has the ability to promote martensite formation and strengthen solid solution.
  • the lower limit of the addition of Si + A1 + P needs to be 0.02% by weight or more.
  • the upper limit of the addition is set to 4.0% by weight or less.
  • the Si content is reduced to 0.1% by weight or less to avoid the Si scale, and conversely to 1.0% by weight or more. Therefore, it is desirable that the Si scale be generated over the entire surface to make it inconspicuous.
  • the P content should be 0.05% or less, preferably 0.02% or less. I do.
  • Ni, Cu, Mo These elements are austenite stabilizing elements as well as the force Mn that is added as needed, enhance the hardenability of steel, facilitate the formation of martensite, It is also an effective element for adjusting the strength. From the viewpoint of weldability and chemical conversion treatment, it can be used when there are restrictions on the amounts of C, S i, A 1, and M n, but the total amount of these elements added is 3.5% by weight. Exceeding this causes the ferrite phase, which is the parent phase, to be hardened, hinders the increase in deformation resistance due to the increase in strain rate, hardens the parent phase, and also increases the cost of steel sheets. 50% by weight or less.
  • Nb, Ti, V These elements are added as necessary, but form carbides, nitrides, and carbonitrides, and are effective elements for increasing the strength of steel sheets.
  • carbides, nitrides, and carbonitrides are formed in the ferrite phase, which is the parent phase, or in the grain boundaries. It precipitates and becomes a source of mobile dislocations during high-speed deformation, hindering an increase in deformation resistance due to an increase in strain rate.
  • the upper limit of the addition amount is set to 0.3% by weight.
  • B is an element that is effective for increasing the strength because it improves the hardenability of steel by suppressing the formation of frit, but the effect is saturated when the added amount exceeds 0.01% by weight. Therefore, the upper limit of the amount of B added is set to 0.01% by weight.
  • Ca is added in an amount of 0.0005% by weight or more in order to further improve the formability (particularly the hole expansion ratio) by controlling the shape (spheroidization) of sulfide-based inclusions.
  • the upper limit of the addition amount is set to 0.01% by weight from the viewpoint of saturation of the effect and adverse effects (deterioration of the hole expansion ratio) due to the increase of inclusions.
  • the addition amount of REM is set to 0.005 to 0.05% by weight.
  • S should be 0.01% by weight or less, preferably 0.03% by weight or less, from the viewpoint of deterioration of formability (particularly hole expansion ratio) by sulfide-based inclusions and deterioration of spot weldability. .
  • the pre-deformation may be a forming process for forming a member, or may be a temper rolling applied to a steel sheet material before the forming process or a process performed by a tension leveler.
  • one or both of the temper rolling and the tension leveler can be used. That is, any of the means of the temper rolling, the tension leveler, the temper rolling and the tension leveler may be used.
  • a forming process may be added to the steel sheet material processed by the temper rolling or the tension leveler.
  • the amount of plastic deformation ( ⁇ ) is the yield strength: YS (0) and the static deformation after the pre-deformation of 5% at the equivalent strain or after further baking hardening treatment ( ⁇ ⁇ treatment). It was also found that the maximum strength in the tensile test was determined according to the ratio to TS ′ (5), ⁇ S (0) / TS ′ (5).
  • YS (0) ZT S ′ (5) is an index indicating the sum of the initial dislocation density and the dislocation density introduced by the 5% deformation, and the amount of solid-solution elements. It can be said that the smaller the value of S ′ (5), the higher the initial dislocation density and the more solid solution elements. Therefore, YS (0) / TS '(5) is set to 0.7 or less, and the following equation:
  • the upper limit of T is determined from the viewpoint of formability such as impact absorption capacity and bendability.
  • the as-fabricated product is directly sent to a hot rolling step, or is cooled once and then heated again, and then hot-rolled.
  • a hot rolling step in addition to normal continuous forming, thin-wall continuous forming and hot-rolling continuous forming technology (end rolling) can be applied, but the volume fraction of the light is reduced, and Considering the coarsening of the average crystal grain size of the structure, it is preferable that the slab ( ⁇ ) thickness (initial slab thickness) on the hot-rolled side of the finish be 25 mm or more.
  • the thickness is less than 25 mm, the space factor of the steel sheet decreases and the average equivalent circle diameter of the microstructure of the steel sheet becomes coarse, and it is disadvantageous to obtain a desired martensite.
  • the final pass rolling speed was 500 mpm or more due to the above problem.
  • hot rolling is performed at 600 mpm or more. If it is less than 50 O mpm, a decrease in the space factor of the light and an increase in the average equivalent circle diameter of the microstructure of the steel sheet occur, and it is disadvantageous to obtain a desired martensite.
  • the average cooling rate of hot run staples should be 5 ° C Z seconds or more. If it is less than 5 ° C Z seconds, it is difficult to obtain a desired martensite.
  • the winding temperature shall be 350 ° C or less. Above 350 ° C, it is difficult to obtain the desired martensite.
  • the finishing temperature in the hot rolling process there is a correlation between the finishing temperature in the hot rolling process, the finishing inlet temperature and the winding temperature. That is, as shown in FIGS. 10 and 11, there are specific conditions uniquely determined between the finishing temperature, the finishing inlet temperature, and the winding temperature.
  • the finishing temperature of hot rolling is in the temperature range of Ar 3 — 50 ° C to Ar 3 + 120 ° C
  • the metallurgical parameter: A is strong, and the equations (1) and (2) are Hot rolling is performed to satisfy the condition.
  • the above-mentioned meta-parameter: A can be expressed as follows.
  • Thickness of the final pass entrance side h 2 Thickness of the final pass exit side r: (hi-h) / h, R: Roll diameter
  • Finishing temperature finish final pass outlet temperature
  • finishing inlet temperature finish final pass outlet temperature
  • a r 90 1-32 5 C% + 33 S i%-92 M n eq Then, set the average cooling rate in the run-out table to 5 ° C / sec or more, and furthermore, One: It is preferable to wind under the condition that the relationship between A and the winding temperature (CT) satisfies the expression (3).
  • the winding temperature does not satisfy the relationship of the formula (3), there is an adverse effect on securing the amount of martensite. Even when a residual 7 is obtained, the residual resistance becomes excessively stable, the desired martensite during the deformation cannot be obtained, and the dynamic deformation resistance dyn, 5 to 10% work hardening Deterioration of performance.
  • the limit of the winding temperature is relaxed by increasing 10 gA.
  • the cold-rolled steel sheet according to the present invention is subjected to cold rolling and annealing of the steel sheet that has undergone each step of hot rolling and winding.
  • continuous annealing having an annealing cycle as shown in Fig. 12 is optimal.
  • a c, ⁇ A c 3 It is necessary to hold for 10 seconds or more in the temperature range. Since A c, the Osutenai I below does not generate, then it is impossible to obtain martensite, since the single phase structure of coarse austenite Bok in A c 3 greater, then the desired Marte Nsai Bok of occupying Ratio and its average particle size cannot be obtained.
  • the upper limit of the staying time is preferably 200 seconds or less from the viewpoint of avoiding lengthening of equipment and coarsening of microstructure.
  • the average cooling rate must be 5 ° C / sec or more. If it is less than 5 ° C / sec, the desired martensite space factor cannot be obtained.
  • the upper limit is not particularly set, but is preferably 300 ° C./sec from the viewpoint of temperature controllability during cooling.
  • the steel sheet after cold rolling is heated to a temperature To of A c, to A c 3 , and the cooling conditions are as follows. Cool at the primary cooling rate of 1 to 10 ° CZ seconds to the secondary cooling start temperature Tq in the range of 550 to T0, and then at the secondary cooling rate of 10 to 200 ° C / sec. Temperature determined by steel material composition and annealing temperature T 0: This is a method of cooling to the secondary cooling end temperature Te below T em. This is due to the quenching end point temperature T e in the continuous annealing cycle shown in Fig. 12.
  • T 1 is a temperature calculated by the concentration of a solid solution element other than C
  • T 2 is a temperature determined by A c, and A c 3 determined by the composition of the steel sheet, and a TQ determined by the annealing temperature T o. This is the temperature calculated from the C concentration in the residual austenite.
  • C eq * is the carbon equivalent in the austenite remaining at the annealing temperature To. Therefore, T 1 is
  • T 1 5 6 1 — 3 3 X ⁇ M n% + (N i + C r + C u + M o) / 2 ⁇ ,
  • a c, 7 2 3-0.7 X M n%-1 6.9 x N i% + 2 9.1 x S i% + 1 6.9 x C r%, and
  • a c 3 9 1 0-2 0 3 x (C%) , 2-1 5.2 x N i% + 4
  • T 2 4 7 4 x (A c-A c,) x C / (T o-A c.),
  • the microstructure of the steel sheet has a main phase of ferrite, and a volumetric fraction of 3% after forming with 5% with equivalent strain. It is a composite structure with other low-temperature generation phases containing 50% martensite, and after giving a predeformation of more than 0% and 10% or less with equivalent strain, 5X10 to 5X10 — Quasi-static deformation strength ( ⁇ s) when deformed within the strain rate range of 3 (1 / s) and 5 X 10 2 to 5 X 10 3 (1 / s) ) With the dynamic deformation strength (CT d) measured in the strain rate range (d – CTS) of 60 MPa or more, and a work hardening index of 0.1% at a strain of 5 to 10%.
  • CT d dynamic deformation strength
  • the steel sheet according to the present invention can be subjected to annealing, temper rolling, electric plating, etc. to obtain a target product.
  • the 26 types (steel numbers 1-26) shown in Table 1 were heated to 150-125 ° C and hot rolled, cooled, and wound under the manufacturing conditions shown in Table 2.
  • Table 3 the steel sheet satisfying the component conditions and the production conditions according to the present invention has a dual-phase structure containing a martensite volume fraction of 3% or more and 50% or less.
  • the mechanical properties of the steel sheet are such that the work hardening index at a strain of 5 to 10% is 0.13 or more, CT d — CT S force is 6 OMPa or more, ⁇ dy ⁇ ⁇ 0.76 It is clear that it has excellent impact resistance of 6 x TS + 250 and also has both formability and weldability.
  • the 22 types (steel numbers 27-48) shown in Table 5 were heated to 105-125 ° C, hot-rolled, cooled, rolled up, and pickled.
  • Cold rolled steel sheets were produced by cold rolling under the conditions shown in Table 6. After that, the temperatures of A c, A c 3 were determined from the components of each steel, and heating, cooling, and holding were performed under the annealing conditions shown in Table 6, and then cooled to room temperature.
  • the steel sheet satisfying the component conditions and the production conditions according to the present invention has a dual-phase structure containing 3% to 50% by martensite volume fraction as shown in Table 7, As shown in Table 8, the mechanical properties of the rolled steel sheet are such that the work hardening index at a strain of 5 to 10% is 0.13 or more, (7 d — ⁇ s force is more than 60 MPa, and dyn ⁇ It is clear that it has excellent impact resistance of 0.766 XTS + 250 and also has both formability and weldability.
  • Dynamic tension (strain rate 0.000 ⁇ ) Pre-deformation and BH treatment Pre-deformation ⁇ Static after BH treatment.
  • Dynamic tension (strain rate 100 plastic deformation Steel No. TS YS T. ⁇ 5-103 ⁇ 4
  • Pre-deformation form-equivalent strain BH 5XWH t] ⁇ YS * 2 ⁇ sad ⁇ ⁇ - as cr dyn
  • WH indicates the rise S of YS by giving 5X pre-deformation with the equivalent strain in the table.
  • AYS gives the pre-deformation shown in the table and indicates the amount of increase in YS when heat treatment equivalent to paint baking is performed at 170 ° C for 20 minutes.
  • the microstructure was evaluated by the following method.
  • the characteristic evaluation was performed by the following method.
  • Tensile tests were conducted using JIS No. 5 (gauge length 50 mm, parallel part width 25 mm) at a strain rate of 0.001 Zs.
  • Tensile strength (TS), yield strength (YS), total elongation ( T. El) and work hardening index (n value of strain 1% to 5%) were calculated, and YSX work hardening index, TSX T. E1 was calculated.
  • Stretch flangeability is obtained by pushing a 20-nun punched hole out of a burr-free surface with a 30-degree circular cone punch, and when the crack penetrates the plate thickness (d) and initial hole diameter (d) , 20 mm) and the spot weldability was found to be 0.9 times the current generated by dust with an electrode having a tip diameter 5 times the square root of the steel sheet thickness. If so-called peel rupture occurs when the spot welding test piece joined by
  • the present invention makes it possible to provide high-strength hot-rolled steel sheets and cold-rolled steel sheets for automobiles, which have both unprecedented excellent collision safety and formability, at low cost and stably. As a result, the uses and conditions of use of high-strength steel sheets will be greatly expanded.

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Abstract

A dual-phase high-strength steel sheet for automobiles, which possesses excellent collision safety and excellent dynamic deformation properties and is used mainly for structural members and reinforcements of automobiles, and a process for preparing the same. The steel sheet is characterized in that the microstructure of the finally obtained steel sheet is a composite texture comprising a main phase of ferrite and a secondary phase of other low-temperature formed phase containing 3 to 50 %, in terms of volume fraction, of martensite after 5 % forming of the steel sheet, that the difference between the quasistatic deformation strength σs upon deformation in the strain range of from 5 x 10-4 to 5 x 10-3 (s-1) after application of predeformation of more than 0 to not more than 10 % in terms of corresponding strain and the dynamic deformation strength σd upon deformation in the strain range of from 5 x 102 to 5 x 103 (s-1) after the application of the predeformation, that is, σd-σs, is not less than 60 MPa, and that the work hardening index at a strain of 5 to 10 % is not less than 0.13.

Description

明 細 書 動的変形特性に優れたデュアルフ ェーズ型高強度鋼板とその製造方 法 技術分野  Description Dual-phase high-strength steel sheet with excellent dynamic deformation characteristics and manufacturing method
本発明は、 主と して自動車の構造部材ゃ補強材に使用することを 目的と した優れた耐衝突安全性を有する動的変形特性に優れたデュ アルフ ェーズ型自動車用高強度鋼板とその製造方法に関するもので ある。 背景技術  The present invention relates to a dual-phase high-strength steel sheet for automobiles having excellent dynamic deformation characteristics and excellent collision safety, which is intended to be mainly used for structural members of automobiles and reinforcing materials. It is about methods. Background art
自動車の燃費規制を背景と した車体軽量化を目的に、 高強度鋼の 適用が拡大してきたが、 直近では自動車事故を想定した耐衝突安全 性に関する法規制が国内外で急速に拡大 · 強化されつつあり、 高強 度鋼への期待が益々高ま っている。 例えば、 乗用車の前面衝突にお いては、 フロ ン トサイ ドメ ンバと呼ばれる部材に高い衝撃吸収性能 を持つ材料を適用すれば、 この部材が圧潰するこ とで衝撃エネルギ —が吸収され、 乗員にかかる衝撃を緩和することができる。  The application of high-strength steel has been expanding for the purpose of reducing vehicle body weight in the context of automobile fuel efficiency regulations, but recently, laws and regulations regarding collision safety assuming an automobile accident have been rapidly expanding and strengthening in Japan and overseas. Expectations for high-strength steel are increasing. For example, in a frontal collision of a passenger car, if a material with high shock absorption performance is applied to a member called the front side member, the shock energy is absorbed by the crushing of this member, which affects the occupant. Shock can be reduced.
しかし、 従来の高強度鋼は成形性の向上を主眼と して開発された ものであり、 耐衝突安全性の観点では適用が疑問視されている。 耐 衝突安全性に優れた自動車用鋼板およびその製造方法に係わる従来 技術と しては、 特開平 7 — 1 8 3 7 2号公報に開示されたように、 耐衝突安全性の指標と して鋼板の高歪速度下における降伏強さを高 めることが開示されているが、 部材は成形加工時および衝突変形時 に歪を受けるため、 耐衝撃性の指標と しては降伏強さに加工硬化分 を加味するこ とが必要であり、 前述のような従来技術では耐衝突安 全性と しては不十分である。 However, conventional high-strength steels were developed with an emphasis on improving formability, and their application is questioned from the perspective of crashworthiness. As a prior art relating to an automobile steel plate having excellent collision safety and a method for manufacturing the same, as disclosed in Japanese Patent Application Laid-Open No. 7-183732, as an index of collision safety, It is disclosed that the yield strength of steel sheets at high strain rates is increased.However, since members undergo strain during forming and collision deformation, yield strength is used as an index of impact resistance. It is necessary to take into account the work hardening component. The whole is not enough.
また、 自動車衝突時に各部位が受ける歪速度は 1 0 3 ( s 程 度に達するため、 材料の衝撃吸収能を考える場合、 このような高歪 速度域での動的変形特性の解明が必要でもある。 そ して、 自動車の 軽量化と衝突安全性向上を両立させることのできる、 動的変形特性 に優れた高強度鋼板が必要とされ、 最近この点に関する報告がある 例えば、 本発明者らは、 CAMP- IS I J Vol.9(1966) ?.1112〜1115に おいて、 高強度薄鋼板の高速変形特性と衝撃エネルギー吸収能につ いて報告し、 その中で、 1 0 3 ( s — ') の高歪速度での動的強度は 、 1 0 '3 ( s の低歪速度での静的強度と比較して大き く上昇す ること、 鋼材の強度上昇により クラ ッ シュ時の吸収エネルギーが向 上すること、 材料の歪速度依存性は鋼の組織に依存すること、 T R I P型の鋼 （加工誘起変態型の鋼） およびデュアルフ ェーズ （以下 D P という） 型の鋼は優れた成形性と高い衝撃吸収能を兼ね備える ことを述べている。 また、 この D P型の鋼に関し、 本発明者らは先 に特願平 8 — 9 8 0 0 0号および特願平 8 - 1 0 9 2 2 4号を出願 し、 その中で自動車軽量化および衝突安全性向上の双方を達成する のに適した静的強度に対し動的強度が高い高強度鋼板とその製造方 法を提案している。 In addition, since the strain rate applied to each part during a car collision reaches about 10 3 (s), considering the shock absorption capacity of the material, it is necessary to clarify the dynamic deformation characteristics in such a high strain rate range. There is a need for a high-strength steel sheet having excellent dynamic deformation characteristics, which can achieve both a reduction in the weight of a car and an improvement in collision safety, and there has been a recent report on this point. ? is, cAMP-Oite the iS IJ Vol.9 (1966) .1112~1115, and report on high-speed deformation properties and impact energy absorption capability Nitsu high strength thin steel sheet, in which, 1 0 3 (s - 'dynamic strength at high strain rate) is 1 0' 3 (Rukoto to increase rather large compared to the static strength at a low strain rate of the s, the absorption at class Tsu shoe by increasing strength of the steel Energy increase, material strain rate dependence depends on steel structure, TRIP type steel Transformation type steel) and dual phase (hereinafter referred to as DP) type steels have both excellent formability and high shock absorption capacity. Application for Japanese Patent Application Nos. Hei 8 — 9800 and No. 8-109224, in which statics suitable for achieving both vehicle weight reduction and improved collision safety We have proposed a high-strength steel sheet with high dynamic strength compared to its strength and a manufacturing method.
上記のように、 高強度鋼板について自動車衝突時の高歪速度にお ける動的変形特性が解明されつつある ものの、 衝撃エネルギー吸収 のための自動車部材と して、 鋼板のどのような特性に注目 し、 どの ような基準で材料選定をおこなえば良いかについては明らカ、にされ ていない。 また、 上記自動車部材は、 鋼板に曲げやプレス等の成形 を施して製造され、 衝突時の衝撃は、 これら加工された部材に対し て加えられる。 しかし、 このような成形加工後における衝撃エネル ギー吸収能を解明した、 実部材と しての動的変形特性に優れた高強 度鋼板については、 従来知られていない。 As mentioned above, although the dynamic deformation characteristics of high-strength steel sheets at high strain rates during automobile collisions are being elucidated, attention is paid to what properties of steel sheets as automobile members for absorbing impact energy However, it is not clear what criteria should be used for material selection. Further, the automobile member is manufactured by subjecting a steel sheet to bending or pressing, etc., and the impact at the time of collision is applied to these processed members. However, the impact energy absorption capacity after such a forming process has been elucidated, and a high-strength material with excellent dynamic deformation characteristics as a real member. Conventional steel sheets have not been known.
更に、 衝突安全用部材の成形に際しては、 優れた形状凍結性、 優 れた張出し性 （引張強さ X全伸び≥ 1 8， 0 0 0 ) 、 優れた伸びフ ラ ンジ性 （穴拡げ比≥ 1 . 2 ) を兼ね備えることが望まれているが 、 優れた耐衝突安全性と優れた成形性を両立する ものは見当たらな いのが実情である。 発明の開示  Furthermore, when forming a collision safety member, it has excellent shape freezing properties, excellent stretchability (tensile strength X total elongation ≥ 18,800), and excellent elongation flangeability (hole expansion ratio ≥ It is desired that the combination of 1.2) is satisfied, but it has not been found that there is a material that has both excellent collision safety and excellent formability. Disclosure of the invention
本発明は上述した問題を解決すべく提案されたもので、 優れた耐 衝突安全性を有する動的変形特性に優れたデュアルフ —ズ型自動 車用高強度鋼板とその製造方法を提供する ものである。  The present invention has been proposed to solve the above-described problems, and provides a dual-fused high-strength steel sheet for an automobile having excellent collision safety and excellent dynamic deformation characteristics, and a method for producing the same. is there.
また、 本発明は、 フロ ン トサイ ドメ ンバ等の成形加工された自動 車部品に使用する高強度鋼板であって、 衝突時の衝撃エネルギー吸 収用と して、 適正な特性および基準に基づいて選定され、 安全確保 に確実に寄与することができる動的変形特性に優れたデュアルフエ —ズ型自動車用高強度鋼板とその製造方法を提供する ものである。 更に、 本発明は、 衝突安全用部材の成形に適した優れた形状凍結 性、 優れた張出 し性、 優れた伸びフラ ンジ性を兼ね備えた動的変形 特性に優れたデュアルフ 一ズ型自動車用高強度鋼板とその製造方 法を提供する ものである。  Further, the present invention relates to a high-strength steel sheet used for a molded automotive part such as a front side member and the like, which is selected based on appropriate characteristics and criteria for absorbing impact energy in a collision. Another object of the present invention is to provide a dual-phase high-strength steel sheet for automobiles having excellent dynamic deformation characteristics that can surely contribute to ensuring safety and a method for producing the same. Further, the present invention provides a dual-fuse type vehicle having excellent dynamic deformation characteristics having excellent shape freezing properties, excellent overhanging properties, and excellent elongation flangeability suitable for forming a collision safety member. It provides high-strength steel sheets and methods for manufacturing them.
本発明は、 上記目的を達成するためになされたもので、 その具体 的手段は以下に示す通りである。  The present invention has been made to achieve the above object, and specific means thereof are as follows.
① 最終的に得られる鋼板の ミ ク ロ組織において、 主相がフ ヱラ イ トで第 2相が前記鋼板の相当歪で 5 %成形加工後にマルテンサイ トを体積分率で 3〜 5 0 %を含むその他の低温生成相との複合組織 であり、 相当歪にて 0 %超〜 1 0 %以下の予変形を加えた後、 5 X 1 0 " 4 ~ 5 X 1 0 —3 ( s — ' ) の歪速度範囲で変形した時の準静的変 形強度ひ s と、 前記予変形を加えた後、 5 x 1 0 2 〜 5 x 1 0 3 ( s "') の歪速度範囲で変形した時の動的変形強度 σ d との差 （ σ (3 - σ s ) が 6 O M P a以上を満足し、 かつ歪 5〜 1 0 %の加工硬化 指数が 0. 1 3以上を満足することを特徴とする動的変形特性に優 れたデュアルフ ヱ一ズ型高強度鋼板、 ① In the microstructure of the finally obtained steel sheet, the main phase is flat and the second phase is 5% with the equivalent strain of the steel sheet. After forming, the martensite is reduced to 3 to 50% by volume fraction. This is a composite structure with other low-temperature-producing phases containing, and after applying a pre-deformation of more than 0% to 10% or less at equivalent strain, 5 X 10 " 4 to 5 X 10 — 3 (s — ') The difference (σ) between the shape strength s and the dynamic deformation strength σ d when deformed in the strain rate range of 5 × 10 2 to 5 × 10 3 (s ″ ′) after the pre-deformation is applied. (3-σ s) satisfies 6 OMPa or more, and a work hardening index at a strain of 5 to 10% satisfies 0.13 or more. High-strength steel sheet,
② 最終的に得られる鋼板の ミ ク ロ組織において、 主相がフ ェ ラ イ トで第 2相が前記鋼板の相当歪で 5 %成形加工後にマルテンサイ トを体積分率で 3〜 5 0 %を含むその他の低温生成相との複合組織 であり、 相当歪にて 0 %超〜 1 0 %以下の予変形を加えた後、 5 X (2) In the microstructure of the finally obtained steel sheet, the main phase is ferrite and the second phase is 5% with the equivalent strain of the steel sheet. After forming, the martensite is converted to a volume fraction of 3 to 50%. This is a composite structure with other low-temperature generation phases containing 5% after applying a predeformation of more than 0% to 10% or less at equivalent strain.
1 0 2 - 5 X 1 0 3 ( s の歪速度範囲で変形した時の 3 ~ 1 0 %の相当歪範囲における変形応力の平均値 σ d y n (M P a ) が予 変形を与える前の 5 X 1 0 — 4〜 5 X 1 0 —3 ( s — ') の歪速度範囲で 測定された静的な引張試験における最大応力 ： T S (M P a ) によ つて表現される式 ： ひ d y n≥ 0. 7 6 6 x T S + 2 5 0 を満足し 、 かつ歪 5〜 1 0 %の加工硬化指数が 0. 1 3以上を満足すること を特徴とする動的変形特性に優れたデュアルフ ェーズ型高強度鋼板 1 0 2 - 5 X 1 0 3 (5 X before the average value of the deformation stress in the equivalent strain range of 3 to 1 0% when deformed in a strain rate range of s σ dyn (MP a) gives pre deformation 1 0 — 4 to 5 X 1 0 — 3 (s — ') Maximum stress in a static tensile test measured in the strain rate range: TS (MP a) Expression: d dyn≥ 0 Dual phase type with excellent dynamic deformation characteristics, characterized by satisfying 706 x TS + 250 and a work hardening index of 0.13 or more at a strain of 5 to 10%. Strength steel plate
③ 前記①または②において、 降伏強度 Y S ( 0 ) と、 相当歪に て 5 %の予変形を加え、 或いは更に焼き付け硬化処理 （ B H処理） を行った後の引張試験における最大強度 T S ' ( 5 ) との比 ： Y S(3) In (1) or (2) above, the maximum strength TS '(5) in the tensile test after the yield strength YS (0) and the pre-deformation of 5% to the equivalent strain, or after further baking hardening treatment (BH treatment). ) And ratio: YS
( 0 ) /T S ' ( 5 ) 0. 7 を満足し、 更に前記降伏強度 Y S ( 0 ) X加工硬化指数≥ 7 0 を満足するこ とを特徴とする動的変形特 性に優れたデュアルフ ェーズ型高強度鋼板、 (0) / TS '(5) Dual phase excellent in dynamic deformation characteristics characterized by satisfying 0.7 and further satisfying the yield strength YS (0) X work hardening index ≥ 70. High strength steel sheet,
④ 前記①、 ②または③の何れかにおいて、 前記マルテ ンサイ 卜 の平均結晶粒径が 5 m以下、 および前記フ ラ イ トの平均結晶粒 径が 1 0 m以下を満足することを特徴とする動的変形特性に優れ たデュアルフ ヱ一ズ型高強度鋼板、 ⑤ 前記①、 ②、 ③または④の何れかにおいて、 引張強度 （M P a ) X全伸び （％) ≥ 1 8， 0 0 0 を満足し、 かつ穴拡げ比 （ d / d o ) ≥ 1 . 2 を満足することを特徴とする動的変形特性に優れた デュアルフ ェーズ型高強度鋼板、 (4) In any one of (1), (2) and (3), the average crystal grain size of the martensite satisfies 5 m or less and the average crystal grain size of the fly satisfies 10 m or less. Dual-pipe high-strength steel sheet with excellent dynamic deformation characteristics, に お い て In any of ①, ②, ③ or ② above, tensile strength (MPa) X total elongation (%) ≥18,000 and hole expansion ratio (d / do) ≥1.2 A dual-phase high-strength steel sheet with excellent dynamic deformation characteristics characterized by satisfying
⑥ 前記①、 ②、 ③、 ④または⑤の何れかにおいて、 調質圧延と テ ンシ ョ ンレべラーの一方または双方による予変形時の、 塑性変形 量 （T) が下記式 ：  に お い て In any of the above ①, ②, ③, ⑤ or が, the amount of plastic deformation (T) at the time of pre-deformation by either or both of the temper rolling and the tension leveler is expressed by the following formula:
2.5 {YS(0)/TS' (5) - 0.5) + 15 ≥ Ύ≥ 2.5 {YS(0)/TS' (5) - 0.5} + 0.5  2.5 {YS (0) / TS '(5)-0.5) + 15 ≥ Ύ≥ 2.5 {YS (0) / TS' (5)-0.5} + 0.5
を満足することを特徴とする動的変形特性に優れたデュアルフ エ一 ズ型高強度鋼板、 である。 A dual-phase high-strength steel sheet having excellent dynamic deformation characteristics, characterized by satisfying the following requirements.
⑦ また、 本発明による動的変形特性に優れたデュアルフ ェーズ 型高強度鋼板は、 前記①〜⑥において、 素材成分と して、 重量％で 、 C : 0. 0 2 〜 0. 2 5 %、 M n と C rの 1 種または 2種以上を 合計で 0. 1 5〜 3. 5 %、 S i 、 A l 、 Pの 1 種または 2種以上 を合計で 0. 0 2 ~ 4. 0 %を含み、 更に必要に応じて N i 、 C u 、 M oの 1 種または 2種以上を合計で 3. 5 %以下、 N b、 T i 、 Vの 1 種または 2種以上を合計で 0. 3 0 %以下、 C a、 R E Mの 1 種または 2種以上を、 C aについては 0. 0 0 0 5〜 0. 0 1 % 、 R E Mについては 0. 0 0 5 〜 0. 0 5 %を含有し、 残部 F eを 主成分とすることを特徴とする動的変形特性に優れたデュアルフ エ 一ズ型高強度鋼板である。  デ ュ ア ル Further, the dual-phase high-strength steel sheet having excellent dynamic deformation characteristics according to the present invention is characterized in that, in the above-mentioned ① to ⑥, C: 0.02 to 0.25% by weight as a material component, 0.15 to 3.5% in total of one or more of Mn and Cr, 0.02 to 4.0 in total of one or more of Si, Al, P %, And if necessary, one or more of Ni, Cu and Mo in a total of 3.5% or less, and one or more of Nb, Ti and V in total 0.3% or less, one or more of Ca and REM, 0.05 to 0.01% for Ca, and 0.05 to 0.05 for REM %, With the balance being Fe as the main component.
⑧ また、 本発明による動的変形特性に優れたデュアルフ ェーズ 型高強度鋼板は、 前記①〜⑦における素材成分に、 更に B≤ 0. 0 I %, S≤ 0. 0 1 N≤ 0. 0 2 %の 1 種または 2種以上を必 要に応じて添加することを特徴とする動的変形特性に優れたデュア ルフ ェーズ型高強度鋼板である。 ⑨ 本発明における動的変形特性に優れたデュアルフ エ一ズ型高 強度熱延鋼板の製造方法と しては、 連続铸造スラブを、 铸造ままで 熱延工程へ直送し、 も しく は一旦冷却後に再度加熱した後、 熱延仕 上温度 A r 3 — 5 0 °C〜 A r 3 + 1 2 0 °Cで熱間圧延を行い、 次い で、 ラ ンアウ トテーブルにおける平均冷却速度 5 °CZ秒以上で冷却 を行い、 更に、 3 5 0 °C以下の温度で巻取ることを特徴とする前記 ①〜⑧の動的変形特性に優れたデュアルフ 一ズ型高強度熱延鋼板 の製造方法である。 デ ュ ア ル In addition, the dual-phase high-strength steel sheet having excellent dynamic deformation characteristics according to the present invention further comprises B≤0.0I%, S≤0.01 N≤0.0 A dual-phase high-strength steel sheet with excellent dynamic deformation characteristics characterized by the addition of one or more of 2% or more as required. デ ュ ア ル As a method for producing a dual-phase high-strength hot-rolled steel sheet having excellent dynamic deformation characteristics in the present invention, a continuous forged slab is directly sent to a hot-rolling process as it is, or after being cooled once. After heating again, hot rolling was performed at a hot rolling finish temperature of Ar 3 — 50 ° C to Ar 3 + 120 ° C, and then an average cooling rate of the run-out table of 5 ° CZ Cooling in seconds or more, and winding at a temperature of 350 ° C or less. The method for producing a dual-fused high-strength hot-rolled steel sheet having excellent dynamic deformation characteristics described in (1) to (4) above. is there.
⑩ 前記⑨において、 熱延仕上温度 A r - 5 0 °C〜A r 3 + 1⑨ In the above ⑨, the hot rolling finish temperature A r-50 ° C ~ A r 3 + 1
2 0 °Cの温度範囲内において、 メ タラ ジ一パラメ 一ター ： A力く ( 1 ) 式および （ 2 ) 式を満たすような熱間圧延を行い、 その後のラ ン ァゥ トテ一ブルにおける平均冷却速度を 5 °C/秒以上と し、 更に前 記メ タラ ジーパラメ ータ一 ： Aと巻取り温度 （ C T) との関係が （Within the temperature range of 20 ° C, the metallurgical parameters: A force The hot rolling that satisfies the formulas (1) and (2) is performed, and in the subsequent runtable The average cooling rate was set to 5 ° C / sec or more, and the relationship between the above-mentioned metal parameter: A and the winding temperature (CT) was (
3 ) 式を満たすような条件で巻取ることを特徴とする動的変形特性 に優れたデュアルフェーズ型高強度熱延鋼板の製造方法である。 3) This is a method for manufacturing a dual-phase high-strength hot-rolled steel sheet with excellent dynamic deformation characteristics, characterized by winding under conditions that satisfy equation (3).
9 ≤ 1 0 g A≤ 1 8 ( 1 )  9 ≤ 1 0 g A ≤ 1 8 (1)
AT≤ 2 l x l o g A - 6 1 ( 2 )  AT≤ 2 l x l o g A-6 1 (2)
C T≤ 6 x l o g A + 2 4 2 ( 3 )  C T≤ 6 x l o g A + 2 4 2 (3)
⑪ また、 本発明における動的変形特性に優れたデュアルフ エ一 ズ型高強度冷延鋼板の製造方法と しては、 連続铸造スラ ブを、 铸造 ままで熱延工程へ直送し、 も し く は一旦冷却後に再度加熱した後、 熱延し、 熱延後卷取った熱延鋼板を酸洗後冷延し、 連続焼鈍工程で 焼鈍して最終的な製品とする際に、 A c , 〜A c 3 の温度に加熱し 、 この温度範囲内で 1 0秒以上保持する焼鈍を施した後、 冷却速度 5 °C/秒以上の条件で冷却するこ とを特徴とする、 前記①〜⑧の動 的変形特性に優れたデュアルフェーズ型高強度冷延鋼板の製造方法 である。 ⑫ 前記⑪において、 前記連続焼鈍工程において、 冷延後の鋼板 を A c , 〜A c 3 の温度 （T o ) に加熱し、 この温度範囲内で 1 0 秒以上保持する焼鈍を施した後、 冷却するに際し、 1 〜 1 0 °C/秒 の一次冷却速度で 5 5 0〜 T 0の範囲の二次冷却開始温度 （T q ) まで冷却し、 引き続いて 1 0〜 2 0 0 °CZ秒の二次冷却速度で、 成 分と焼鈍温度 （T o ) で決まる T e m以下の二次冷却終了温度 （T e ) まで冷却することを特徴とする、 前記①〜⑧の動的変形特性に 優れたデュアルフ ェーズ型高強度冷延鋼板の製造方法である。 図面の簡単な説明 デ ュ ア ル Further, as a method for producing a dual-phase high-strength cold-rolled steel sheet having excellent dynamic deformation characteristics according to the present invention, a continuous production slab is directly sent to a hot-rolling process as it is produced. After cooling and heating again, hot-rolled, hot-rolled and rolled hot-rolled steel sheet is pickled, cold-rolled, and annealed in a continuous annealing process to obtain a final product, A c, ~ After heating to the temperature of A c 3 and performing annealing for maintaining the temperature within this temperature range for 10 seconds or more, cooling is performed at a cooling rate of 5 ° C./second or more. This is a method for manufacturing a dual-phase high-strength cold-rolled steel sheet with excellent dynamic deformation characteristics. ⑪ In the above ⑪, in the continuous annealing step, the cold-rolled steel sheet is heated to a temperature of A c, to A c 3 (T o), and annealed for more than 10 seconds within this temperature range. When cooling, cool to a secondary cooling start temperature (Tq) in the range of 550 to T0 at a primary cooling rate of 1 to 10 ° C / sec, and then cool to 10 to 200 ° CZ The dynamic deformation characteristics of (1) to (4), characterized by cooling to a secondary cooling end temperature (T e) of less than T em determined by the component and the annealing temperature (T o) at a secondary cooling rate of seconds. This is a method for producing a dual-phase high-strength cold-rolled steel sheet with excellent heat resistance. BRIEF DESCRIPTION OF THE FIGURES
図 1 …本発明における衝突時の成形部材の吸収エネルギー （ E a b ) と素材強度 （ S ) との関係を示す図。  FIG. 1 is a view showing the relationship between the absorbed energy (E ab) of the molded member and the material strength (S) at the time of collision in the present invention.
図 2 …図 1 における衝撃吸収エネルギー測定用の成形部材を示す 斜視図  Fig. 2 ... Perspective view showing the molded member for measuring the shock absorption energy in Fig. 1.
図 3 鋼板の加工硬化指数と動的エネルギー吸収量との関係を示 す図。  Fig. 3 Diagram showing the relationship between the work hardening index of steel sheets and the amount of dynamic energy absorption.
図 4 鋼板の降伏強さ X加工硬化指数と動的エネルギー吸収量と の関係を示す図。  Fig. 4 A graph showing the relationship between the yield strength of a steel sheet X work hardening index and the amount of dynamic energy absorption.
図 5 …図 3 、 図 4 に関わる衝撃圧壊試験方法に用いられる （ハツ トモデル） の概観図。  Fig. 5 ... Schematic view of the (hat model) used in the impact crush test method related to Figs.
図 6 …図 5 の試験片形状の断面図。  Fig. 6 ... Sectional view of the test piece shape of Fig. 5.
図 7 …図 3 〜図 6 に関わる衝撃圧壊試験方法の模式図。  Fig. 7 ... Schematic diagram of the impact crush test method related to Figs.
図 8 …本発明における衝突時の衝撃エネルギー吸収能の指標であ る、 5 X 1 0 2 〜 5 X 1 0 3 ( 1 Z S ) の歪速度で変形した時の 3 〜 1 0 %の相当歪範囲における変形応力の平均値ひ d y n— T S と T S との関係を示す図。 Fig. 8… Equivalent strain of 3 to 10% when deformed at a strain rate of 5 × 10 2 to 5 × 10 3 (1ZS), which is an index of the impact energy absorption capacity at the time of collision in the present invention. The figure which shows the relationship between the average value of deformation stress dyn-TS and TS in the range.
図 9 …本発明例および比較例の調質圧延による静動比の変化を示 すグラ フ。 Fig. 9… Shows the change in static-dynamic ratio due to temper rolling in the present invention example and the comparative example. Graph.
図 1 0 …本発明による熱延工程における Δ Τとメ タラ ジーパラメ 一ター ： Aとの関係を示す図。  FIG. 10 is a view showing the relationship between Δ に お け る and metal parameter: A in the hot rolling process according to the present invention.
図 1 1 …本発明による熱延工程における巻取り温度とメ タラ ジー パラメ ーター ： Aとの関係を示す図。  FIG. 11 is a view showing the relationship between the winding temperature and the metallurgical parameter: A in the hot rolling process according to the present invention.
図 1 2 …本発明による連続焼鈍の焼鈍サイ クルを示す模式図。 発明を実施するための最良の実施形態  FIG. 12 is a schematic view showing an annealing cycle of continuous annealing according to the present invention. BEST MODE FOR CARRYING OUT THE INVENTION
自動車のフ ロ ン トサイ ドメ ンバ等の衝撃吸収用部材は、 鋼板に曲 げ加工やプレス加工などを施して製造される。 自動車衝突時の衝撃 は、 これら成形加工された部材に対して加えられるため、 このよう な成形加工に相当する予変形後の状態で高い衝撃吸収能を有してい るこ とが必要である。 しかし、 現在までのところ、 成形による変形 応力の上昇と歪速度上昇による変形応力の上昇とを同時に考慮して 、 実部材と しての衝撃吸収特性に優れた高強度鋼板を得る試みはな されていないことは前述した通りである。  Shock absorbing members such as front side members of automobiles are manufactured by bending and pressing steel plates. Since the impact at the time of vehicle collision is applied to these formed members, it is necessary to have a high shock absorbing capacity in a state after pre-deformation corresponding to such forming. However, up to now, attempts have been made to obtain a high-strength steel sheet having excellent shock absorption properties as a real member by simultaneously considering the increase in deformation stress due to forming and the increase in deformation stress due to increase in strain rate. That is not described above.
本発明者らは、 前記目的を達成するために種々の実験と研究を重 ねた結果、 前述の成形加工された実部材において優れた衝撃吸収特 性を有する高強度鋼板と して、 デュアルフ ェーズ （D P ) 組織を有 する鋼板が最適であることを知見した。 このデュアルフ ヱ一ズ組織 を有する鋼板は、 変形速度上昇による変形抵抗増加を担うフ ェ ラ イ ト相を主相と し、 硬質なマルテ ンサイ ト相を含む第 2 相との複合組 織であり、 動的変形特性に優れていることが判明した。 すなわち、 最終的に得られる鋼板の ミ ク ロ組織は、 フ ェ ライ ト相を主相と し、 硬質のマルテ ンサイ ト相を前記鋼板の相当歪で 5 %の成形加工後に 体積分率で 3 ~ 5 0 %含むその他の低温生成相との複合組織である 場合に高い動的変形抵抗を示すことを見いだした。 こ こで、 前記硬質のマルテンサイ ト相の体積分率 ： 3〜 5 0 %に ついて述べると、 前記マルテンサイ ト相が 3 %未満では高強度鋼板 を得ることができず、 また動的変形強度の高い鋼板も得られないこ とからマルテ ンサイ ト相は体積分率で 3 %以上が必要である。 また 、 このマルテンサイ ト相が 5 0 %を超えると変形速度上昇による変 形抵抗増加を担うべきフ ェ ラ イ ト相の体積分率は低下し、 静的変形 強度に比して動的変形強度の優れた鋼板を得ることができなく なり 、 しかも成形性が阻害されるため、 マルテ ンサイ ト相の体積分率は 3 〜 5 0 %とする必要性も見いだした。 The present inventors have conducted various experiments and studies in order to achieve the above object, and as a result, as a high-strength steel sheet having excellent shock absorption characteristics in the above-formed real member, a dual phase steel plate (DP) We found that a steel sheet with a structure was optimal. The steel sheet having this dual-phase structure is a composite structure with the ferrite phase, which plays a role in increasing the deformation resistance due to the increase in deformation speed, as the main phase, and the second phase including a hard martensite phase. It was found to be excellent in dynamic deformation characteristics. In other words, the microstructure of the finally obtained steel sheet has a ferrite phase as a main phase and a hard martensite phase with a volumetric equivalent of the above steel sheet of 3% by volume after forming by 5%. It was found that the composite showed high dynamic deformation resistance when it had a composite structure with other low-temperature generation phases containing up to 50%. Here, regarding the volume fraction of the hard martensite phase: 3 to 50%, if the martensite phase is less than 3%, a high-strength steel sheet cannot be obtained, and the dynamic deformation strength cannot be increased. Since a high steel sheet cannot be obtained, the volume fraction of the martensite phase must be 3% or more. Further, when the martensite phase exceeds 50%, the volume fraction of the ferrite phase, which should be responsible for the increase in deformation resistance due to the increase in deformation speed, decreases, and the dynamic deformation strength becomes smaller than the static deformation strength. It has also been found that it is not possible to obtain a steel sheet excellent in quality and the formability is impaired, so that the volume fraction of the martensite phase must be 3 to 50%.
次に、 本発明者らは、 上記知見に基づき更に実験 · 研究を進めた 結果、 フ ロ ン トサイ ドメ ンバ等の衝撃吸収用部材の成形加工に相当 する予変形量は、 部位によっては最大 2 0 %以上に達する場合もあ る力く、 相当歪と して 0 %~ 1 0 %の部位が大半であること も見いだ し、 この範囲の予変形の効果を把握することで、 部材全体と しての 予変形後の挙動を推定することが可能であるこ と も見いだした。 従 つて、 本発明においては、 部材への加工時に与えられる予変形量と して相当歪にして 0 %~ 1 0 %の変形を選択した。  Next, as a result of further experiments and researches based on the above findings, the present inventors found that the amount of pre-deformation corresponding to the forming process of a shock absorbing member such as a front side member was up to 2 parts depending on the part. The force can reach 0% or more, and it is also found that the equivalent strain is mostly in the range of 0% to 10%, and by grasping the effect of pre-deformation in this range, We also found that it was possible to estimate the behavior after pre-deformation as a whole. Therefore, in the present invention, a deformation of 0% to 10% was selected as an equivalent strain as an amount of pre-deformation to be given to the member during processing.
図 1 は、 後述の実施例における表 5 の各鋼種について、 衝突時に おける成形部材の吸収エネルギー （ E a b ) と素材強度 （ S ) の関 係を示したものである。 素材強度 Sは、 通常の引張試験による引張 強度 （ T S ) である。 部材吸収エネルギー （ E a b ) は、 図 2 に示 すような成形部材の長さ方向 （矢印方向） に、 質量 4 0 0 k gの重 錘を速度 1 5 m/秒で衝突させ、 その時の圧潰量 1 0 0 mmまでの 吸収エネルギーである。 なお、 図 2の成形部材は、 厚さ 2. 0 mm の鋼板をハッ ト型部 1 に、 同じ厚さ、 同じ鋼種の鋼板 2 をスポッ ト 溶接により接合したものであり、 ハツ ト型部 1 のコーナー半径は 2 mmで、 3 はスポッ ト溶接部である。 図 1 から、 部材吸収エネルギー （ E a b ) は、 通常の引張試験に で得られる素材強度の高いものほど高く なる傾向が見られるが、 バ ラツキの大きいこ とが分かる。 そこで、 図 1 に示す各素材について 、 相当歪にして 0 %超〜 1 0 %以下の予変形を加えた後、 5 X 1 0 -4〜 5 X 1 0 —3 ( s— ') の歪速度範囲で変形した時の準静的変形強 度 σ s と、 前記予変形を加えた後、 5 X 1 0 2 〜 5 X 1 0 3 ( s — ' ) の歪速度範囲で変形した時の動的変形強度 σ dを測定した。 その 結果、 （ CT d— CT S ) によって層別することができた。 図 1 の各プ ロ ッ 卜の記号で、 FIG. 1 shows the relationship between the absorbed energy (E ab) of the formed member and the material strength (S) at the time of collision for each of the steel types in Table 5 in the examples described later. The material strength S is the tensile strength (TS) from a normal tensile test. The material absorption energy (E ab) is calculated by colliding a weight of 400 kg with a velocity of 15 m / s in the length direction (the direction of the arrow) of the molded member as shown in Fig. 2 and crushing it. Absorbed energy up to 100 mm. The formed member shown in Fig. 2 is made by joining a steel plate with a thickness of 2.0 mm to the hat-shaped part 1 and a steel sheet 2 of the same thickness and the same steel type by spot welding. Has a corner radius of 2 mm and 3 is a spot weld. From Fig. 1, it can be seen that the component absorbed energy (E ab) tends to increase as the material strength obtained by a normal tensile test increases, but the variability is large. Therefore, for each material shown in FIG. 1, after the addition of equivalent strain to 0% Super-1 0% or less pre-deformation, 5 X 1 0 - 4 ~ 5 X 1 0 - strain 3 (s- ') The quasi-static deformation strength σ s when deformed in the speed range and the deformation speed in the range of 5 X 10 2 to 5 X 10 3 (s — ') after the pre-deformation The dynamic deformation strength σ d was measured. As a result, stratification was possible by (CT d—CTS). The symbols for each plot in Fig. 1
〇 ： 0 %超〜 1 0 %以下の何れの予変形量で （ σ ά— CT S ) < 6 〇: (σ ά—CT S) <6 at any pre-deformation amount from more than 0% to 10% or less
O M P a となる もの、 O M P a
秦 ： 前記範囲全ての予変形量で 6 0 M P a ≤ ( CT d— び s ) であ り、 かつ予変形量が 5 %の時、 6 0 M P a ≤ ( σ d - σ s ) < 8 O M P aであるもの、  Hata: 60 MPa a ≤ (CT d— and s) for all the pre-deformation amounts in the above range, and when the pre-deformation amount is 5%, 60 MPa a ≤ (σ d-σ s) <8 What is OMP a,
疆 ： 前記範囲全ての予変形量で 6 0 M P a ≤ ( σ d - σ s ) であ り、 かつ予変形量が 5 %の時、 8 0 M P a ≤ ( σ d - σ s ) く 1 0 O M P aである もの、  Jiang: 60 MPa a ≤ (σ d-σ s) for all the pre-deformation amounts in the above range, and when the pre-deformation amount is 5%, 80 MP a ≤ (σ d-σ s) 1 0 OMP a
▲ : 前記範囲全ての予変形量で 6 0 M P a ≤ ( σ d - σ s ) であ り、 かつ予変形量が 5 %の時、 1 0 0 M P a ≤ ( σ d - σ s ) である もの、  ▲: 60 MPa a ≤ (σ d-σ s) for all pre-deformation amounts in the above range, and when the pre-deformation amount is 5%, 100 MPa a ≤ (σ d-σ s) some stuff,
である。 It is.
そ して、 相当歪にして 0 %超〜 1 0 %以下の範囲の全ての予変形 量において 6 0 M P a ≤ ( σ d - σ s ) である ものは衝突時の部材 吸収エネルギー （ E a b ) が、 素材強度 Sから予測される値以上で あり、 衝突時の衝撃吸収用部材と して優れた動的変形特性を有する 鋼板であった。 前述の予測される値は、 図 1 の曲線で示す値であり 、 E a b = 0. 0 6 2 S ° 8 で示される。 従って、 （ σ (1— ひ s ) は 6 0 M P a以上が必要である。 For all the pre-deformations in the range of more than 0% to 10% or less in terms of the equivalent strain, those for which 60 MPa a ≤ (σ d-σ s) are the member absorbed energy (E ab ) Is higher than the value predicted from the material strength S, and was a steel sheet having excellent dynamic deformation characteristics as a shock absorbing member in the event of a collision. The predicted value described above is the value shown by the curve in FIG. 1 and is expressed by E ab = 0.062 S ° 8 . Therefore, (σ (1—his) Requires 60 MPa or more.
次に、 耐衝突安全性の向上には鋼の加工硬化指数を高めること、 具体的には 0 . 1 3以上、 好ま し く は 0 . 1 6以上が基本的に重要 であり、 降伏強さ と加工硬化指数を特定範囲に制御することにより 、 優れた耐衝突安全性を達成できること、 成形性の向上にはマルテ ンサイ 卜の体積分率と粒径を特定範囲に造り込むこ と等の効果があ る。  Second, to improve the crashworthiness, it is essential to raise the work hardening index of the steel, specifically, 0.13 or more, preferably 0.16 or more. By controlling the work hardening index and the work hardening index to a specific range, it is possible to achieve excellent collision safety, and to improve the formability, effects such as incorporating the volume fraction and the particle size of the martensite in a specific range. There is.
図 3 は、 部材の耐衝突安全性の指標となる動的エネルギー吸収量 と、 鋼板の加工硬化指数の関係を同一降伏強さ ク ラスのものについ て示すものである。 鋼板の加工硬化指数の増大により部材の衝突安 全性 （動的エネルギー吸収量） が向上しており、 部材の耐衝突安全 性の指標と して同一降伏強さ クラスであれば鋼板の加工硬化指数が 妥当であることを示している。 更に、 降伏強さが異なる場合には、 図 4 に示すように、 降伏強さ X加工硬化指数を部材の耐衝突安全性 の指標とすることができる。 ただし、 部材が成形加工時に歪を受け ることを考慮して、 加工硬化指数は歪 5 %〜 1 0 %の n値で表現し たが、 動的エネルギー吸収量向上の観点からは、 歪 5 %以下の加工 硬化指数、 歪 1 0 %以上の加工硬化指数も高いこ とが好ま しい。  Figure 3 shows the relationship between the dynamic energy absorption, which is an index of the collision safety of the member, and the work hardening index of the steel sheet, for the same yield strength class. The collision safety (dynamic energy absorption) of the members is improved due to the increase in the work hardening index of the steel sheet, and the work hardening of the steel sheet with the same yield strength class is used as an index of the collision safety of the member. This indicates that the index is valid. Furthermore, when the yield strength is different, as shown in Fig. 4, the yield strength X work hardening index can be used as an index of the collision safety of the member. However, the work hardening index is represented by an n value of 5% to 10% in consideration of the fact that the member is subjected to distortion during molding. From the viewpoint of improving the dynamic energy absorption, the work hardening index is expressed as 5%. It is preferable that the work hardening index is less than 10% and the work hardening index is more than 10%.
なお、 図 3、 図 4 における部材の動的エネルギー吸収量は次のよ うにして求めた。 すなわち、 鋼板を図 5、 図 6 に示す部品形状 （コ ーナー R = 5 m m ) に成形し、 先端 5 . 5 m mの電極によりチリ発 生電流の 0 . 9倍の電流で 3 5 m mピッチでスポ ッ ト溶接し、 1 7 0 °C X 2 0分の焼付塗装処理を行つた後、 約 1 5 0 k gの落錘を約 1 0 mの高さから落下させ、 部材を長手方向に圧壊し、 その際の荷 重変位線図の面積から変位 = 0 〜 1 5 0 m mの変位仕事を算出 して 動的エネルギー吸収量と した。 試験方法の模式図を図 7 に示す。 図 5 において、 4 は天板、 5 は試験片、 6 はスポッ ト溶接部である。 図 6 において、 7 はハッ ト型の試験片、 8 はスポッ ト溶接部である 。 図 7 において、 9 は天板、 1 0 は試験片、 1 1 は落錘 （ 1 5 0 k g ) 、 1 2 は架台、 1 3 はショ ッ ク /アブゾ一バ一である。 また、 鋼板の加工硬化指数、 降伏強さは次のようにして求めた。 鋼板を J I S — 5号試験片 （標点距離 5 0 mm, 平行部幅 2 5 mm) に加工 し、 歪速度 0. 0 0 1 ( s -') で引張試験し、 降伏強さ と加工硬化 指数 （歪 5 %〜 1 0 %の！1値） を求めた。 使用 した鋼板は、 板厚 1 . 2 mmで、 鋼板組成は C : 0. 0 2〜 0. 2 5重量％、 1^ 1 、 〇 rの 1 種または 2種以上の合計が 0. 1 5〜 3. 5重量％、 S i 、 A l 、 Pの 1 種または 2種の合計量が 0. 0 2 ~ 4. 0重量％を含 み、 残部 F eを主成分とする ものである。 The dynamic energy absorption of the members in Figs. 3 and 4 was obtained as follows. That is, the steel sheet is formed into the part shape (corner R = 5 mm) shown in Fig. 5 and Fig. 6, and the current at the tip of 5.5 mm is 0.9 times the dust generation current at a pitch of 35 mm. After spot welding and baking coating at 170 ° C for 20 minutes, a falling weight of about 150 kg was dropped from a height of about 10 m to crush the member in the longitudinal direction. Then, the displacement work of displacement = 0 to 150 mm was calculated from the area of the load displacement diagram at that time, and it was determined as the dynamic energy absorption. Figure 7 shows a schematic diagram of the test method. In Fig. 5, 4 is a top plate, 5 is a test piece, and 6 is a spot weld. In FIG. 6, 7 is a hat-shaped test piece, and 8 is a spot weld. In FIG. 7, 9 is a top plate, 10 is a test piece, 11 is a drop weight (150 kg), 12 is a gantry, and 13 is a shock / absolute bar. The work hardening index and yield strength of the steel sheet were obtained as follows. Steel sheet is processed into JIS-5 test piece (gauge length 50 mm, parallel part width 25 mm), tensile test at strain rate 0.0001 (s-'), yield strength and work hardening Exponents (5% to 10%! 1 values) were determined. The steel sheet used was 1.2 mm in thickness, and the composition of the steel sheet was C: 0.02 to 0.25% by weight, and the total of one or more of 1 ^ 1 and 〇r was 0.15%. To 3.5% by weight, the total amount of one or two of Si, Al, and P is from 0.02 to 4.0% by weight, and the balance is Fe.
図 8 は、 本発明における衝突時の衝撃エネルギー吸収能の指標で ある、 5 X 1 0 2 〜 5 X 1 0 3 ( s — 1) の歪速度範囲で変形した時 の 3 ~ 1 0 %相当歪範囲における変形応力の平均値 σ d y n と静的 な素材強度 （T S ) 、 すなわち、 この静的な素材強度 （T S ) は、 5 X 1 0 ―4〜 5 X 1 0 — 3 ( s — 1 ) の歪速度範囲で測定された静的な 引張試験における最大応力 （T S ： M P a ) をいう、 との関係を示 したものである。 FIG. 8 is an index of the impact energy absorbing ability at the time of collision according to the present invention, which is equivalent to 3 to 10% when deformed in a strain rate range of 5 × 10 2 to 5 × 10 3 (s- 1 ). mean value sigma dyn and static material strength of deformation stress in the distortion range (TS), i.e., the static material strength (TS) is, 5 X 1 0 - 4 ~ 5 X 1 0 - 3 (s - 1 ) Means the maximum stress (TS: MPa) in the static tensile test measured in the strain rate range of, and shows the relationship with.
フロ ン トサイ ドメ ンバ等の衝撃吸収部材は、 前述したよう にハツ ト型の断面形状を有しており、 このような部材の高速での衝突圧潰 時の変形を本発明者らが解析した結果、 最大では 4 0 %以上の高い 歪まで変形が進んでいる ものの、 吸収エネルギー全体の 7 0 %以上 が高速の応力一歪線図の 1 0 %以下の歪範囲で吸収されているこ と を見いだした。 従って、 高速での衝突エネルギーの吸収能の指標と して 1 0 %以下での高速変形時の動的変形抵抗を採用 した。 特に、 歪量と して 3〜 1 0 %の範囲が最も重要であることから、 高速引張 り変形、 5 X 1 0 2 ~ 5 X 1 0 3 ( s —') の歪速度範囲で変形した 時の相当歪で 3〜 1 0 %の範囲の平均応力 ： d y nを以て衝撃ェ ネルギー吸収能の指標と した。 As described above, the shock absorbing member such as the front side member has a hat-shaped cross-sectional shape, and the present inventors have analyzed the deformation of such a member during high-speed collision crushing. However, although deformation is progressing up to a high strain of 40% or more at the maximum, 70% or more of the total absorbed energy is absorbed in the strain range of 10% or less in the high-speed stress-strain diagram. I found it. Therefore, the dynamic deformation resistance at the time of high-speed deformation of 10% or less was adopted as an index of the absorption capacity of the collision energy at high speed. In particular, since the range of 3 to 10% is the most important as the amount of strain, high-speed tensile deformation and deformation in the strain rate range of 5 X 10 2 to 5 X 10 3 (s- ') The equivalent strain at the time was in the range of 3 to 10% and the average stress: dyn was used as an index of the impact energy absorption capacity.
この高速変形時の 3 ~ 1 0 %の平均応力 ： CT d y nは、 予変形や 焼き付け処理が行われる前の鋼板の静的な引張強度 （ 5 X 1 0 "4~ 5 X 1 0 — 3 ( s ') の歪速度範囲で測定された静的な引張試験にお ける最大応力 （ T S ： M P a ) } の上昇に伴って大き く なること力く 一般的である。 従って、 鋼板の静的な引張強度 （これは静的な素材 強度と同義的である。 ） を増加させるこ とは部材の衝撃エネルギー 吸収能の向上に直接寄与する。 しかしながら、 鋼板の強度が上昇す ると部材への成形性が劣化し、 必要な部材形状を得ることが困難に なる。 従って、 同一の引張強度 ： T Sで、 高い CT d y nを持つ鋼板 が望ま しい。 この関係から、 0 %超、 1 0 %以下の予変形を与えた 後、 5 X 1 0 2 〜 5 X 1 0 3 ( s の歪速度範囲で変形した時の 3〜 1 0 %の相当歪範囲における変形応力の平均値 ： CT d y n (M P a ) 力く、 予変形を与える前の 5 X I 0 — 4〜 5 X 1 0 —3 ( s — ') の 歪速度範囲で測定された静的な引張試験における最大応力 （T S ： M P a ) によって表現される式 ： ひ d y n 0. 7 6 6 x T S + 2 5 0 (M P a ) を満足する鋼板は、 実部材と しての衝撃吸収エネル ギー吸収能が他の鋼板に比べて高く 、 部材の総重量を増加させるこ となく衝撃吸収エネルギー吸収能を向上させ、 高い動的変形抵抗を 有する高強度鋼板を提供できることを見いだした。 The high-speed deformation at 3 to 1 0% of the average stress: CT dyn are the static tensile strength of the steel sheet before pre-deformation and baking treatment is carried out (5 X 1 0 "4 ~ 5 X 1 0 - 3 ( s'), which generally increases with an increase in the maximum stress (TS: MPa)} in the static tensile test measured in the strain rate range of Increasing the tensile strength (which is synonymous with the static material strength) directly contributes to the improvement of the impact energy absorption capacity of the member. Deterioration of the formability makes it difficult to obtain the required member shape, therefore, it is desirable to use a steel plate with the same tensile strength: TS and a high CT dyn. After applying a pre-deformation of 5 × 10 2 to 5 × 10 3 (with an equivalent strain range of 3 to 10% when deformed at a strain rate range of s) Average value of deformation stress applied: CT dyn (MP a) Powerful, static strain measured in the strain rate range of 5 XI 0 — 4 to 5 X 10 — 3 (s — ') before pre-deformation The steel sheet that satisfies the formula expressed by the maximum stress (TS: MPa) in the tensile test: dyn 0.76 x TS + 250 (MPa) is a shock absorbing energy as a real member. It has been found that the absorption capacity is higher than other steel sheets, the impact absorption energy absorption capacity is improved without increasing the total weight of the members, and a high-strength steel sheet having high dynamic deformation resistance can be provided.
また、 詳細は未だ解明されていないが、 初期転位密度、 マルテン サイ ト相以外の低温生成相、 主相であるフェライ 卜相中の固溶元素 量および炭化物、 窒化物、 炭窒化物の析出状態に依存する量である Y S ( 0 ) /T S ' ( 5 ) が図 9 に示すように、 0. 7以下である 場合に、 優れた動的変形特性を有する鋼板が得られるこ とが判明し た。 ここで、 Y S ( 0 ) は降伏強度、 T S ' ( 5 ) は相当歪にて 5 %の予変形を加え、 或いは更に焼付け硬化処理 （ B H処理） を行つ た後の静的な引張試験における最大強度 （T S ' ) である。 更に、 前記降伏強度 ： Y S ( 0 ) X加工硬化指数が 7 0以上を満足する場 合に更に優れた動的変形特性を有する鋼板が得られることが判明し た。 Although details have not been elucidated yet, it depends on the initial dislocation density, the low-temperature formed phase other than the martensite phase, the amount of solid-solution elements in the ferrite phase, which is the main phase, and the precipitation state of carbides, nitrides, and carbonitrides. As shown in FIG. 9, it was found that a steel sheet having excellent dynamic deformation characteristics could be obtained when the amount of YS (0) / TS '(5), as shown in FIG. Here, YS (0) is the yield strength and TS '(5) is the equivalent strain of 5 This is the maximum strength (TS ') in a static tensile test after pre-deformation or bake hardening (BH). Further, it was found that when the yield strength: YS (0) X work hardening index satisfies 70 or more, a steel sheet having more excellent dynamic deformation characteristics can be obtained.
また、 通常、 動的変形強度は静的変形強度の累乗の形で表される ことが知られており、 静的変形強度が高く なるにつれて、 動的変形 強度と静的変形強度の差は小さ く なる。 しかし、 材料の高強度化に よる軽量化を考えた場合、 動的変形強度と静的変形強度の差が小さ く なると材料置換による衝撃吸収能の向上が大き く なるこ とは期待 できず、 軽量化の達成が困難になる。 この点に関しては、 （ ひ d — CT S ) 値が、 （ d — CT S ) ≥ 4 . 1 X CT S 。' 8 — s を満足する 範囲であるこ とが好ま しい。 It is also known that the dynamic deformation strength is usually expressed as a power of the static deformation strength. As the static deformation strength increases, the difference between the dynamic deformation strength and the static deformation strength decreases. It becomes bad. However, when considering the weight reduction by increasing the strength of the material, it is not expected that if the difference between the dynamic deformation strength and the static deformation strength becomes smaller, the improvement in the shock absorption capacity by replacing the material will not increase. It is difficult to achieve weight reduction. In this regard, the (d — CTS) value is (d — CTS) ≥ 4.1 X CT S. ' 8 — It is preferable that the range satisfy s.
次に、 本発明における鋼板の ミ ク ロ組織について詳細に説明する 。 マルテ ンサイ トは、 前述したように、 その体積分率を 3 〜 5 0 % と し、 好ま し く は 3 〜 3 0 %とする。 マルテ ンサイ 卜の平均結晶粒 径は 5 m以下とすることが好ま しく 、 フ ェ ラ イ 卜の平均結晶粒径 は 1 0 z m以下とすることが好ま しい。 すなわち、 マルテンサイ ト は硬質であり、 主に周囲のフ ェ ライ 卜に可動転位を発生させるこ と により降伏比の低減や加工硬化指数の向上に寄与するが、 上記規制 を満たすことにより鋼中に微細マルテンサイ トを分散させること力く でき、 その特性向上作用が鋼板全体に及ぶようになる。 更に、 鋼中 に前述の微細マルテンサイ トが分散することにより硬いマルテ ンサ ィ 卜の悪影響である穴拡げ比の劣化や引張強さ X全伸びの劣化を回 避することができる。 また、 加工硬化指数≥ 0 . 1 3 0 、 かつ引張 強さ X全伸び^ 1 8 , 0 0 0 、 穴拡げ比 1 . 2 を確実に達成する ことができるため耐衝突安全性および成形性を向上させることがで きる o Next, the microstructure of the steel sheet according to the present invention will be described in detail. As described above, the martensite has a volume fraction of 3 to 50%, preferably 3 to 30%. The average crystal grain size of the martensite is preferably 5 m or less, and the average crystal grain size of the ferrite is preferably 10 zm or less. In other words, martensite is hard and contributes to the reduction of the yield ratio and the improvement of the work hardening index by generating mobile dislocations mainly in the surrounding ferrite. It is possible to disperse fine martensite, and the effect of improving its properties extends to the entire steel sheet. Further, by dispersing the aforementioned fine martensite in the steel, it is possible to avoid the deterioration of the hole expansion ratio and the deterioration of the tensile strength X total elongation, which are the adverse effects of the hard martensite. In addition, a work hardening index of ≥ 0.130, tensile strength X total elongation of ^ 18, 000, and hole expansion ratio of 1.2 can be reliably achieved. Can be improved Cut o
マルテ ンサイ 卜の体積分率が 3 %未満では、 降伏比が高く なると 共に、 成形後の部材が衝突変形を受けた際に優れた加工硬化能 （加 ェ硬化指数≥ 0 . 1 3 0 ) を発揮することができず、 変形抵抗 （荷 重） が低いレベルに留ま り変形仕事量が小さ く なるため動的エネル ギ一吸収量が低く 、 耐衝撃安全性の向上が達成できない。 一方、 マ ルテンサイ 卜の体積分率が 5 0 %超では、 降伏比が高く なると共に 加工硬化指数が低下し、 更に引張強さ X全伸びや穴拡げ比の劣化が 起こる。 成形性の観点からはマルテ ンサイ 卜の体積分率を 3 0 %以 下とすることが好ま しい。  When the volume fraction of the martensite is less than 3%, the yield ratio is increased and the work hardening ability (the work hardening index ≥ 0.130) when the molded member is subjected to collision deformation is increased. It is not possible to exert it, the deformation resistance (load) remains at a low level, and the deformation work becomes small, so that the dynamic energy absorption is low and the improvement in impact safety cannot be achieved. On the other hand, when the volume fraction of the martensite exceeds 50%, the yield ratio increases and the work hardening index decreases, and further, the tensile strength X total elongation and the hole expansion ratio deteriorate. From the viewpoint of moldability, it is preferable that the volume fraction of the martensite be 30% or less.
更に、 フ ェ ラ イ トを体積分率で好ま し く は 5 0 %以上、 より好ま し く は 7 0 %以上含有させ、 その平均結晶粒径 （平均円相当径） を 好ま しく は 1 0 2 m以下、 より好ま しく は 5 m以下と し、 マルテ ンサイ トをフェライ トに隣接させることが好ま しい。 これにより、 マルテ ンサイ 卜がフ ライ ト地中に微細分散するこ とを助長すると 共に、 上記特性向上効果が局所的な影響に留ま らず鋼板全体に及ぶ よう有効に作用 し、 マルテ ンサイ トの悪影響を抑制するよう好ま し く作用する。 また、 マルテンサイ トゃフ ヱライ ト以外の残部組織は パーライ ト、 ベイナイ ト、 残留ァ等の 1 種あるいは 2種以上を組み 合わせた混合組織と してもよいが、 穴拡げ特性が要求される場合に はべイナィ ト主体とすることが好ま しいが、 残留 ァ は成形加工によ りマルテンサイ 卜へ加工誘起変態するため、 成形加工前に残留ォ一 ステナイ トを含むことは好ま しく少量 （ 5 %以下） でも効果を有す ることが実験の結果判明している。  Further, ferrite is contained in a volume fraction of preferably 50% or more, more preferably 70% or more, and its average crystal grain size (average equivalent circle diameter) is preferably 10% or more. It is preferred that the length be less than 2 m, more preferably less than 5 m, and that the martensite be adjacent to the ferrite. This not only promotes the fine dispersion of the martensite in the ground, but also works effectively so that the above-mentioned effect of improving the properties extends not only to the local influence but also to the entire steel sheet. Works favorably to reduce the adverse effects of In addition, the remaining structure other than martensite-filled light may be one or a combination of two or more of perlite, bainite, residual iron, etc., but when hole-expanding properties are required Although it is preferable to mainly use bainite, it is preferable that a small amount (5% However, experiments have shown that this is effective.
また、 衝突安全性と成形性の観点からは、 マルテ ンサイ トとフ エ ライ トの粒径の比を 0 . 6以下、 硬さの比を 1 . 5以上とすること が好ま しい。 次に、 本発明による動的変形特性に優れたデュアルフヱ一ズ型高 強度鋼板を得るための鋼板の化学成分の規制値とその制限理由を説 明する。 Further, from the viewpoints of collision safety and formability, it is preferable that the ratio of the particle size of the martensite to the ferrite be 0.6 or less and the hardness ratio be 1.5 or more. Next, the regulated values of the chemical components of the steel sheet to obtain a dual-fused high-strength steel sheet having excellent dynamic deformation characteristics according to the present invention and the reasons for the limitation will be described.
本発明で使用される動的変形特性に優れたデュアルフ ェーズ型高 強度鋼板は、 素材成分と して、 重量％で、 C ： 0. 0 2〜 0. 2 5 %、 M n と C rの 1 種または 2種以上を合計で 0. 1 5〜 3. 5 % 、 S i 、 A 1 、 Pの 1 種または 2種以上を合計で 0. 0 2〜 4. 0 %を含み更に必要に応じて N i 、 C u、 M oの 1 種または 2種以上 を合計で 3. 5 %以下、 N b、 T i 、 Vの 1 種または 2種以上を合 計で 0. 3 0 %以下、 C a、 R E Mの 1 種または 2種以上を、 C a については 0. 0 0 0 5〜 0. 0 1 %、 尺 £ ?^にっぃては 0. 0 0 5 ~ 0. 0 5 %を含有し、 残部 F eを主成分とする鋼板である。 ま た、 更に必要に応じて B≤ 0. 0 1 % S ≤ 0. 0 1 %、 N≤ 0. 0 2 %の 1 種または 2種以上を含む動的変形特性に優れたデュアル フェーズ型高強度鋼板である。 これらの化学成分とその含有量 （重 量 について詳述する。  The dual-phase high-strength steel sheet having excellent dynamic deformation characteristics used in the present invention has a C: 0.02 to 0.25% by weight as a material component, and a content of Mn and Cr. 0.15 to 3.5% in total of 1 or 2 or more, 0.02 to 4.0% in total of 1 or 2 or more of Si, A1, P Depending on the type, one or more of Ni, Cu, and Mo are 3.5% or less in total, and one or more of Nb, Ti, and V are 0.30% or less in total , C a, REM, one or more of them, C a is 0.0 0 0 5 to 0 .01%, and the length is 0.05 to 0.05. %, With the balance being Fe. In addition, if necessary, one or more of B≤0.01% S ≤0.01% and N≤0.02% dual phase type with excellent dynamic deformation characteristics It is a high strength steel plate. These chemical components and their contents (weight) will be described in detail.
C ： Cは鋼板の組織に強く 影響を与える元素であり、 その含有量 が少なく なると目的とする量および強度のマルテンサイ ト相を得る のが困難になる。 添加量が多く なると不必要な炭化物の析出を招き 、 歪速度上昇による変形抵抗増加を阻害したり、 強度が高く なり過 ぎたり、 更に成形性および溶接性を劣化させるこ とから 0. 0 2 ~ 0. 2 5重量％とする。  C: C is an element that strongly affects the structure of the steel sheet, and when its content is low, it becomes difficult to obtain the desired amount and strength of the martensite phase. If the amount of addition increases, unnecessary precipitation of carbides is caused, which hinders an increase in deformation resistance due to an increase in strain rate, increases the strength too much, and further deteriorates formability and weldability. ~ 0.25% by weight.
M n、 C r ： M n と C r はオーステナイ トを安定化してマルテン サイ トを確保する作用があると共に強化元素でもあるため、 その下 限添加量は 0. 1 5重量％必要であり、 一方、 過度の添加は上記効 果を飽和し、 逆にフ ェライ ト変態抑制等の悪影響を生じるため上限 添加量を 3. 5重量％とする。 S i 、 A l 、 P : S i 、 A l はマルテ ンサイ トを生成させるため に有用な元素であり、 フ ェ ライ トの生成を促進し、 炭化物の生成を 抑制することによりマルテ ンサイ トを確保する作用があると共に固 溶強化作用と脱酸作用を有する。 また、 P も A l 、 S i と同様にマ ルテ ンサイ 卜生成促進と固溶強化の能力を有する。 この観点から S i + A 1 + Pの下限添加量は 0. 0 2重量％以上とする必要がある 。 一方、 過度の添加は上記効果を飽和し、 逆に鋼を脆化させるため 上限添加量は 4. 0重量％以下とする。 特に、 優れた表面性状が要 求される場合には、 S i添加量を 0. 1重量％以下とすることによ り S i スケールを回避する力く、 逆に 1. 0重量％以上とすることに より S i スケールを全面に発生させて目立たなく することが望ま し い。 また、 優れた 2次加工性、 靱性、 スポッ ト溶接性、 リサイ クル 性が要求される場合には、 Pの含有量を 0. 0 5 %以下、 好ま し く は 0. 0 2 %以下とする。 Mn, Cr: Since Mn and Cr act to stabilize austenite and secure martensite and are also strengthening elements, the lower additive amount is 0.15% by weight. On the other hand, excessive addition saturates the above effects and adversely affects ferrite transformation, etc., so the upper limit is 3.5% by weight. S i, A l, P: S i, A l are useful elements for forming martensite, and promote martensite formation by promoting ferrite formation and suppressing carbide formation. It has the effect of securing and has the effect of strengthening the solid solution and the effect of deoxidation. P, like Al and Si, also has the ability to promote martensite formation and strengthen solid solution. From this viewpoint, the lower limit of the addition of Si + A1 + P needs to be 0.02% by weight or more. On the other hand, excessive addition saturates the above effects and conversely embrittles the steel, so the upper limit of the addition is set to 4.0% by weight or less. In particular, when excellent surface properties are required, the Si content is reduced to 0.1% by weight or less to avoid the Si scale, and conversely to 1.0% by weight or more. Therefore, it is desirable that the Si scale be generated over the entire surface to make it inconspicuous. When excellent secondary workability, toughness, spot weldability, and recyclability are required, the P content should be 0.05% or less, preferably 0.02% or less. I do.
N i 、 C u、 M o ： これらの元素は必要に応じて添加される力 M nと同様にオーステナイ ト安定化元素でもあり、 鋼の焼き入れ性 を高め、 マルテンサイ 卜の生成を容易にし、 強度調整のために有効 な元素でもある。 溶接性や化成処理の観点からは、 C、 S i 、 A 1 、 M n量に制限がある場合に使用することができるが、 これらの元 素の添加量が合計で 3. 5重量％を超えると母相であるフ ェライ 卜 相の硬質化を招き、 歪速度上昇による変形抵抗増加を阻害し、 母相 が硬化する他、 鋼板コス 卜の上昇を招く ためこれら元素の添加量は 3. 5 0重量％以下とする。  Ni, Cu, Mo: These elements are austenite stabilizing elements as well as the force Mn that is added as needed, enhance the hardenability of steel, facilitate the formation of martensite, It is also an effective element for adjusting the strength. From the viewpoint of weldability and chemical conversion treatment, it can be used when there are restrictions on the amounts of C, S i, A 1, and M n, but the total amount of these elements added is 3.5% by weight. Exceeding this causes the ferrite phase, which is the parent phase, to be hardened, hinders the increase in deformation resistance due to the increase in strain rate, hardens the parent phase, and also increases the cost of steel sheets. 50% by weight or less.
N b、 T i 、 V ： これらの元素は必要に応じて添加されるが、 炭 化物、 窒化物、 炭窒化物を形成し、 鋼板の高強度化に有効な元素で ある。 しかし、 0. 3重量％を超えて添加すると母相であるフ ェ ラ ィ ト相中または粒界に多量の炭化物、 窒化物も しく は炭窒化物と し て析出し、 高速変形時に可動転位の放出源となり、 歪速度上昇によ る変形抵抗増加を阻害する。 また、 母相の変形抵抗が必要以上に増 加し、 更に不必要に Cを浪費し、 コス トの上昇を招く ことから上限 添加量を 0 . 3重量％とする。 Nb, Ti, V: These elements are added as necessary, but form carbides, nitrides, and carbonitrides, and are effective elements for increasing the strength of steel sheets. However, if added in excess of 0.3% by weight, a large amount of carbides, nitrides or carbonitrides is formed in the ferrite phase, which is the parent phase, or in the grain boundaries. It precipitates and becomes a source of mobile dislocations during high-speed deformation, hindering an increase in deformation resistance due to an increase in strain rate. In addition, since the deformation resistance of the mother phase is increased more than necessary, C is unnecessarily wasted, and the cost is increased. Therefore, the upper limit of the addition amount is set to 0.3% by weight.
B ： Bはフ ライ 卜の生成を抑制することで鋼の焼入れ性を向上 させることから高強度化に有効な元素であるが、 その添加量が 0 . 0 1 重量％超では効果が飽和することから、 B添加量の上限を 0 . 0 1 重量％とする。  B: B is an element that is effective for increasing the strength because it improves the hardenability of steel by suppressing the formation of frit, but the effect is saturated when the added amount exceeds 0.01% by weight. Therefore, the upper limit of the amount of B added is set to 0.01% by weight.
C a、 R E M : C aは硫化物系介在物の形状制御 （球状化） によ り成形性 （特に穴拡げ比） をより向上させるために 0 . 0 0 0 5重 量％以上添加するが、 効果の飽和、 介在物の増加による逆効果 （穴 拡げ比の劣化） の点からその上限添加量を 0 . 0 1 重量％とする。 また、 R E Mも同様の理由からその添加量を 0 . 0 0 5 ~ 0 . 0 5 重量％とする。  Ca, REM: Ca is added in an amount of 0.0005% by weight or more in order to further improve the formability (particularly the hole expansion ratio) by controlling the shape (spheroidization) of sulfide-based inclusions. The upper limit of the addition amount is set to 0.01% by weight from the viewpoint of saturation of the effect and adverse effects (deterioration of the hole expansion ratio) due to the increase of inclusions. For the same reason, the addition amount of REM is set to 0.005 to 0.05% by weight.
S ： Sは硫化物系介在物による成形性 （特に穴拡げ比） 、 スポッ ト溶接性の劣化の観点から 0 . 0 1 重量％以下、 好ま し く は 0 . 0 0 3重量％以下とする。  S: S should be 0.01% by weight or less, preferably 0.03% by weight or less, from the viewpoint of deterioration of formability (particularly hole expansion ratio) by sulfide-based inclusions and deterioration of spot weldability. .
次に、 本発明における予変形の付与方法について説明する。 予変 形は、 部材成形のための成形加工であってもよ く 、 また成形加工以 前の鋼板素材に与えられる調質圧延やテ ンシ ョ ン レベラ一による加 ェであってもよい。 この場合、 調質圧延、 テンシ ョ ンレべラーの一 方または双方とすることもできる。 すなわち、 調質圧延、 テンショ ン レベラ一、 調質圧延およびテンショ ンレベラ一のいずれの手段で もよい。 更に、 調質圧延やテンショ ンレベラ一により加工された鋼 板素材に成形加工を加えてもよい。 前記調質圧延および Zまたはテ ンシ ヨ ンレべラーで付与される予変形量、 すなわち塑性変形量 （T Next, a method for imparting a pre-deformation according to the present invention will be described. The pre-deformation may be a forming process for forming a member, or may be a temper rolling applied to a steel sheet material before the forming process or a process performed by a tension leveler. In this case, one or both of the temper rolling and the tension leveler can be used. That is, any of the means of the temper rolling, the tension leveler, the temper rolling and the tension leveler may be used. Further, a forming process may be added to the steel sheet material processed by the temper rolling or the tension leveler. The amount of pre-deformation imparted by the temper rolling and the Z or tension leveler, ie, the amount of plastic deformation (T
) は、 初期転位密度により異なるが初期転位密度が大であれば前記 Tの量が小さ くてよい。 また、 固溶元素が少ない場合には導入され た転位を固着できず、 高い動的変形特性を確保できない。 従って、 前記塑性変形量 （Τ) は、 降伏強度 ： Y S ( 0 ) と、 相当歪にて 5 %の予変形を加え、 或いは更に焼き付け硬化処理 （ Β Η処理） を行 つた後の静的な引張試験における最大強度 T S ' ( 5 ) との比、 Υ S ( 0 ) /T S ' ( 5 ) に応じて規定されること も分かった。 すな わち、 Y S ( 0 ) ZT S ' ( 5 ) は、 初期転位密度と 5 %の変形に より導入された転位密度の和、 および固溶元素量を示す指標となり 、 Y S ( 0 ) ZT S ' ( 5 ) が小さいほど初期転位密度が高く 、 固 溶元素が多いといえる。 従って、 Y S ( 0 ) / T S ' ( 5 ) を 0. 7以下と し、 下記式 ： ) Depends on the initial dislocation density, but if the initial dislocation density is large, The amount of T may be small. When the amount of solid solution elements is small, the introduced dislocations cannot be fixed and high dynamic deformation characteristics cannot be secured. Therefore, the amount of plastic deformation (は) is the yield strength: YS (0) and the static deformation after the pre-deformation of 5% at the equivalent strain or after further baking hardening treatment (Β Η treatment). It was also found that the maximum strength in the tensile test was determined according to the ratio to TS ′ (5), ΔS (0) / TS ′ (5). That is, YS (0) ZT S ′ (5) is an index indicating the sum of the initial dislocation density and the dislocation density introduced by the 5% deformation, and the amount of solid-solution elements. It can be said that the smaller the value of S ′ (5), the higher the initial dislocation density and the more solid solution elements. Therefore, YS (0) / TS '(5) is set to 0.7 or less, and the following equation:
2.5 {YS(0)/TS' (5) - 0.5) + 15 ≥ T≥ 2.5 {YS(0)/TS' (5) - 2.5 (YS (0) / TS '(5)-0.5) + 15 ≥ T≥ 2.5 {YS (0) / TS' (5)-
0.5 } + 0.5 0.5} + 0.5
に従って付与されるこ とが好ま しく 、 前記 Tの上限は衝撃吸収能、 曲げ性などの成形性の観点から決定されたものである。 The upper limit of T is determined from the viewpoint of formability such as impact absorption capacity and bendability.
次に、 本発明による動的変形特性に優れたデュアルフ エ ーズ型高 強度熱延鋼板および冷延鋼板のそれぞれの製造方法について説明す る。 この製造方法と しては、 铸造ままで熱間圧延工程へ直送し、 も しく は一旦冷却した後再度加熱した後、 熱間圧延を行う。 この熱間 圧延においては、 通常の連続铸造に加え、 薄肉連続铸造および熱延 連続化技術 （エン ドレス圧延） の適用も可能であるが、 フ ライ ト 体積分率の低下、 薄鋼板ミ ク 口組織の平均結晶粒径の粗大化を考慮 すると仕上げ熱延入側における鋼片 （铸片） 厚 （初期鋼片厚） は 2 5 mm以上とすることが好ま しい。 2 5 mm未満ではフ ヱライ 卜占 積率の低下や鋼板ミ ク ロ組織の平均円相当径の粗大化が起こるとと もに、 所望のマルテ ンサイ 卜を得るには不利となる。 この熱間圧延 においては、 最終パス圧延速度は上記問題から 5 0 0 m p m以上、 好ま し く は 6 0 0 m p m以上で熱間圧延を行う こ とが好ま しい。 5 0 O m p m未満ではフ ライ 卜占積率の低下や鋼板ミ ク ロ組織の平 均円相当径の粗大化が起こるとと もに、 所望のマルテ ンサイ トを得 るには不利となる。 Next, a method of manufacturing a dual-phase high-strength hot-rolled steel sheet and a cold-rolled steel sheet having excellent dynamic deformation characteristics according to the present invention will be described. In this production method, the as-fabricated product is directly sent to a hot rolling step, or is cooled once and then heated again, and then hot-rolled. In this hot rolling, in addition to normal continuous forming, thin-wall continuous forming and hot-rolling continuous forming technology (end rolling) can be applied, but the volume fraction of the light is reduced, and Considering the coarsening of the average crystal grain size of the structure, it is preferable that the slab (铸) thickness (initial slab thickness) on the hot-rolled side of the finish be 25 mm or more. If the thickness is less than 25 mm, the space factor of the steel sheet decreases and the average equivalent circle diameter of the microstructure of the steel sheet becomes coarse, and it is disadvantageous to obtain a desired martensite. In this hot rolling, the final pass rolling speed was 500 mpm or more due to the above problem. Preferably, hot rolling is performed at 600 mpm or more. If it is less than 50 O mpm, a decrease in the space factor of the light and an increase in the average equivalent circle diameter of the microstructure of the steel sheet occur, and it is disadvantageous to obtain a desired martensite.
熱間圧延における仕上温度は A r 3 — 5 0 °C〜 A r 3 + 1 2 0 DC とする。 A r 3 — 5 0 °C未満では加エフヱライ トが生成し、 加工硬 化能や成形性を劣化させる。 A r 3 + 1 2 0 °C超ではフ ヱライ ト占 積率の低下や鋼板ミ ク ロ組織の平均円相当径の粗大化が起こるとと もに、 所望のマルテンサイ トを得ることが困難となる。 Temperature finishing in hot rolling A r 3 - and 5 0 ° C~ A r 3 + 1 2 0 D C. A r 3 — When the temperature is lower than 50 ° C, effluent is generated, and the work hardening ability and formability are deteriorated. Above Ar 3 + 120 ° C, it is difficult to obtain the desired martensite as well as a decrease in the space factor of the steel and a coarsening of the equivalent circle diameter of the microstructure of the steel sheet. Become.
ホッ 卜ラ ンテープルにおける冷却は平均冷却速度を 5 °C Z秒以上 とする。 5 °C Z秒未満では所望のマルテ ンサイ トを得ることが困難 となる。  The average cooling rate of hot run staples should be 5 ° C Z seconds or more. If it is less than 5 ° C Z seconds, it is difficult to obtain a desired martensite.
巻取温度は 3 5 0 °C以下とする。 3 5 0 °C超では所望のマルテ ン サイ トを得るこ とが困難となる。  The winding temperature shall be 350 ° C or less. Above 350 ° C, it is difficult to obtain the desired martensite.
特に、 本発明においては熱延工程における仕上げ温度、 仕上げ入 側温度と巻き取り温度との間には相関関係があるこ とを見いだした 。 すなわち、 図 1 0 および図 1 1 に示すように前記仕上げ温度、 仕 上げ入側温度と巻き取り温度との間には一義的に決まる特定の条件 がある。 すなわち、 熱延の仕上げ温度が A r 3 — 5 0 °C〜 A r 3 + 1 2 0 °Cの温度範囲において、 メ タラジーパラメ 一ター ： A力く、 ( 1 ) 式および （ 2 ) 式を満たすような熱間圧延を行う。 ただし、 前 記メ タラ ジーパラメ ータ一 ： Aとは以下のよう に表わすことができ る。 In particular, in the present invention, it has been found that there is a correlation between the finishing temperature in the hot rolling process, the finishing inlet temperature and the winding temperature. That is, as shown in FIGS. 10 and 11, there are specific conditions uniquely determined between the finishing temperature, the finishing inlet temperature, and the winding temperature. In other words, when the finishing temperature of hot rolling is in the temperature range of Ar 3 — 50 ° C to Ar 3 + 120 ° C, the metallurgical parameter: A is strong, and the equations (1) and (2) are Hot rolling is performed to satisfy the condition. However, the above-mentioned meta-parameter: A can be expressed as follows.
A = ε * x e χ ρ { (75282- 42745 x CeJ Z [1.978 x (FT + 273)] ) A = ε * xe χ ρ {(75282- 42745 x C e JZ [1.978 x (FT + 273)])
ただし、 F T ： 仕上げ温度 （°C)  However, F T: Finishing temperature (° C)
C e q ： 炭素当量 = C + M n e q/ 6 (%) M n e q : マ ンガン当量 = M n + (N i + C r + C u + M o )C eq: carbon equivalent = C + M n eq / 6 (%) M n eq : Mangan equivalent = M n + (N i + C r + Cu + Mo)
/ 2 (%) / 2 (%)
ε * ： 最終パス歪み速度 （ s — ' )  ε *: Final path strain rate (s— ')
£ * = ( V / R X h , ) ( 1 / V ) X 1 n { 1 / ( 1 - r  £ * = (V / R X h,) (1 / V) X 1 n {1 / (1-r
) }  )}
h , ： 最終パス入側板厚 h 2 ： 最終パス出側板厚 r ： ( h i - h ) / h , R ： ロール径 h,: Thickness of the final pass entrance side h 2 : Thickness of the final pass exit side r: (hi-h) / h, R: Roll diameter
V ： 最終パス出側速度  V: Final pass exit speed
Δ Τ ： 仕上げ温度 （仕上最終パス出側温度） 一仕上げ入側温度  Δ Τ: Finishing temperature (finish final pass outlet temperature) One finishing inlet temperature
(仕上げ第一パス入側温度）  (Finish first pass inlet temperature)
A r ： 9 0 1 - 3 2 5 C % + 3 3 S i % - 9 2 M n e q その後、 ラ ンアウ トテーブルにおける平均冷却速度を 5 °C /秒以 上と し、 更に前記メ タラ ジーパラメ 一ター ： Aと巻き取り温度 （ C T) との関係が （ 3 ) 式を満たすような条件で巻き取ることが好ま しい。 A r: 90 1-32 5 C% + 33 S i%-92 M n eq Then, set the average cooling rate in the run-out table to 5 ° C / sec or more, and furthermore, One: It is preferable to wind under the condition that the relationship between A and the winding temperature (CT) satisfies the expression (3).
9 ≤ 1 0 g A ≤ 1 8 ( 1 )  9 ≤ 10 g A ≤ 1 8 (1)
A T≤ 2 l x l o g A - 6 1 ( 2 )  A T≤ 2 l x l o g A-6 1 (2)
C T ≤ 6 x l o g A + 2 4 2 ( 3 )  C T ≤ 6 x l og A + 2 4 2 (3)
前記 （ 1 ) 式において、 1 o g Aが 9未満ではマルテ ンサイ 卜の 生成、 ミ ク ロ組織微細化の観点から不十分となり、 動的変形抵抗 σ d y n、 5〜 1 0 %の加工硬化能等を劣化させる。 また、 1 o g A が 1 8超ではそれを達成するための設備が過大となる。 また、 （ 2 ) 式において、 （ 2 ) 式の条件を満たさない場合には所望のマルテ ンサイ トを得ることができず、 動的変形抵抗 σ d y η、 5〜 1 0 % の加工硬化能等を劣化させる。 なお、 （ 2 ) 式に示したように Δ Τ の下限は 1 o g Aの低下により緩和される。 更に、 巻き取り温度が ( 3 ) 式の関係を満たさないと、 マルテンサイ ト量確保に悪影響が 出たり、 残留 7が得られた場合にも残留ァが過度に安定となり、 変 形途中での所望のマルテンサイ トを得ることができず動的変形抵抗 ひ d y n、 5〜 1 0 %の加工硬化能等を劣化させる。 なお、 巻き取 り温度の限界は 1 0 g Aの増大により緩和される。 In the above equation (1), if 1 og A is less than 9, the formation of martensite and the microstructural refinement become insufficient, and the dynamic deformation resistance σ dyn, work hardening ability of 5 to 10%, etc. Deteriorates. If 1 og A is more than 18, the facilities for achieving it will be excessive. In addition, in the equation (2), if the condition of the equation (2) is not satisfied, a desired martensite cannot be obtained, a dynamic deformation resistance σ dy η, a work hardening ability of 5 to 10%, etc. Deteriorates. Note that, as shown in equation (2), the lower limit of Δ Δ is relaxed by a decrease of 1 ogA. Furthermore, if the winding temperature does not satisfy the relationship of the formula (3), there is an adverse effect on securing the amount of martensite. Even when a residual 7 is obtained, the residual resistance becomes excessively stable, the desired martensite during the deformation cannot be obtained, and the dynamic deformation resistance dyn, 5 to 10% work hardening Deterioration of performance. The limit of the winding temperature is relaxed by increasing 10 gA.
次に、 本発明による冷延鋼板は、 熱延、 巻き取り後の各工程を経 た鋼板を、 冷間圧延し、 焼鈍に付される。 この焼鈍は、 図 1 2 に示 すよ うな焼鈍サイ クルを有する連続焼鈍が最適であり、 この連続焼 鈍工程で焼鈍して最終的な製品とする際に、 A c , 〜A c 3 の温度 範囲において、 1 0秒以上保持することが必要である。 A c , 未満 ではオーステナィ 卜が生成しないため、 その後、 マルテンサイ トを 得る事ができず、 A c 3 超では粗大なオーステナイ 卜の単相組織と なるため、 その後、 所望のマルテ ンサイ 卜の占積率とその平均粒径 を得る事ができない。 また、 1 0秒未満ではオーステナイ 卜の生成 量が不足するため、 その後、 所望のマルテンサイ 卜を得る事ができ ない。 なお、 滞在時間の上限は設備の長大化、 ミ ク ロ組織の粗大化 を避ける観点から、 2 0 0秒以下が好ま しい。 上記焼鈍後の冷却に ついては、 平均冷却速度を 5 °C/秒以上とすることが必要である。 5 °C /秒未満では所望のマルテ ンサイ 卜占積率が得られない。 その 上限は特に設ける ものではないが、 冷却時の温度制御性から、 3 0 0 °C /秒が好ま しい。 Next, the cold-rolled steel sheet according to the present invention is subjected to cold rolling and annealing of the steel sheet that has undergone each step of hot rolling and winding. For this annealing, continuous annealing having an annealing cycle as shown in Fig. 12 is optimal.When annealing in this continuous annealing process to obtain a final product, A c, ~ A c 3 It is necessary to hold for 10 seconds or more in the temperature range. Since A c, the Osutenai I below does not generate, then it is impossible to obtain martensite, since the single phase structure of coarse austenite Bok in A c 3 greater, then the desired Marte Nsai Bok of occupying Ratio and its average particle size cannot be obtained. If the time is less than 10 seconds, the amount of austenite generated is insufficient, so that a desired martensite cannot be obtained thereafter. The upper limit of the staying time is preferably 200 seconds or less from the viewpoint of avoiding lengthening of equipment and coarsening of microstructure. For cooling after the above annealing, the average cooling rate must be 5 ° C / sec or more. If it is less than 5 ° C / sec, the desired martensite space factor cannot be obtained. The upper limit is not particularly set, but is preferably 300 ° C./sec from the viewpoint of temperature controllability during cooling.
特に、 本発明においては、 図 1 2 に示す連続焼鈍サイ クルで、 冷 延後の鋼板を A c , 〜A c 3 の温度 T oに加熱し、 冷却するに際し 、 冷却条件と しては、 1 〜 1 0 °CZ秒の一次冷却速度で 5 5 0〜T 0の範囲の二次冷却開始温度 T qまで冷却し、 引き続いて 1 0〜 2 0 0 °C/秒の二次冷却速度で、 鋼材成分と焼鈍温度 T 0で決まる温 度 ： T e m以下の二次冷却終了温度 T e まで冷却する方法である。 これは、 図 1 2 に示す連続焼鈍サイ クルにおける急冷終点温度 T e を成分と焼鈍温度 T o との関数と して表し、 ある限界値以下とする 方法である。 T eまで冷却した後、 T e— 5 0。C以上 4 0 0 °C以下 の温度範囲で 2 0分以下の時間保持し、 室温まで冷却することが好 ま しい。 In particular, in the present invention, in the continuous annealing cycle shown in FIG. 12, the steel sheet after cold rolling is heated to a temperature To of A c, to A c 3 , and the cooling conditions are as follows. Cool at the primary cooling rate of 1 to 10 ° CZ seconds to the secondary cooling start temperature Tq in the range of 550 to T0, and then at the secondary cooling rate of 10 to 200 ° C / sec. Temperature determined by steel material composition and annealing temperature T 0: This is a method of cooling to the secondary cooling end temperature Te below T em. This is due to the quenching end point temperature T e in the continuous annealing cycle shown in Fig. 12. Is expressed as a function of the components and the annealing temperature T o, and is a method to keep the temperature below a certain limit value. After cooling to Te, Te-50. It is preferable to maintain the temperature in a temperature range of not less than C and not more than 400 ° C. for not more than 20 minutes and cool to room temperature.
ここで、 T e mとは、 急冷開始時点 T qで残留 しているオーステ ナイ 卜のマルテンサイ ト変態開始温度である。 すなわち、 T e mは 、 オーステナイ ト中の C濃度の影響を除外した値 （T 1 ) と C濃度 の影響を示す値 （T 2 ) の差 ： T e m = T l — T 2である。 ここで 、 T 1 とは、 C以外の固溶元素濃度によって計算される温度であり 、 また、 T 2 は鋼板の成分で決まる A c , と A c 3 および焼鈍温度 T oによって決まる T Qでの残留オーステナイ 卜中の C濃度から計 算される温度である。 また、 C e q * は、 前記焼鈍温度 T oで残留 しているオーステナイ ト中の炭素当量である。 従って、 T 1 は、Here, T em is the martensitic transformation start temperature of the austenite remaining at the quenching start time T q. That is, T em is the difference between the value excluding the effect of the C concentration in austenite (T 1) and the value indicating the effect of the C concentration (T 2): T em = T 1 —T 2. Here, T 1 is a temperature calculated by the concentration of a solid solution element other than C, and T 2 is a temperature determined by A c, and A c 3 determined by the composition of the steel sheet, and a TQ determined by the annealing temperature T o. This is the temperature calculated from the C concentration in the residual austenite. C eq * is the carbon equivalent in the austenite remaining at the annealing temperature To. Therefore, T 1 is
T 1 = 5 6 1 — 3 3 X {M n % + (N i + C r + C u +M o ) / 2 } 、 T 1 = 5 6 1 — 3 3 X {M n% + (N i + C r + C u + M o) / 2},
また、 T 2 は、  T 2 is
A c , = 7 2 3 - 0. 7 X M n % - 1 6. 9 x N i % + 2 9. 1 x S i % + 1 6. 9 x C r %、 および、  A c, = 7 2 3-0.7 X M n%-1 6.9 x N i% + 2 9.1 x S i% + 1 6.9 x C r%, and
A c 3 = 9 1 0 - 2 0 3 x (C %) , 2 - 1 5. 2 x N i % + 4 A c 3 = 9 1 0-2 0 3 x (C%) , 2-1 5.2 x N i% + 4
4. 7 x S i %+ 1 0 4 x V %+ 3 1. 5 x M o % - 3 0 x M n % - 1 1 C r % ~ 2 0 x C u % + 7 0 x P % + 4 0 X A l %+ 4 0 0 x T i %,  4.7 x S i% + 10 4 x V% + 3 1.5 x Mo%-30 x M n%-11 Cr% ~ 20 x Cu% + 70 x P% + 4 0 XA l% + 4 0 0 x T i%,
と焼鈍温度 T oにより表現され、 And the annealing temperature To
C e q * = ( A c - A c , ) x C / (T o - A c , ) + (M n  C e q * = (A c-A c,) x C / (T o-A c,) + (M n
+ S i Z 4 + N i / 7 + C r + C u + l . 5 M o ) Z 6が、  + S i Z 4 + N i / 7 + C r + C u + l .5 Mo) Z 6
0. 6超の場合には、 T 2 = 4 7 4 x ( A c - A c , ) x C / ( T o - A c . ) 、 If it exceeds 0.6, T 2 = 4 7 4 x (A c-A c,) x C / (T o-A c.),
0. 6以下の場合には、  0.6 or less,
T 2 二 4 7 4 x ( A c 3 - A c , ) x C / { 3 x (A c 3 - A c , ) x C 4- C (M n + S i / 4 + N i / 7 + C r + C u + l . 5 M o ) / 2 - 0. 8 5 ) 〕 x (T o - A c , ) 、 によ り表現される。 T 2 2 4 7 4 x (A c 3-A c,) x C / (3 x (A c 3 -A c,) x C 4- C (M n + S i / 4 + N i / 7 + 5 M o) / 2-0.85)] x (T o -A c,).
すなわち、 T eが T e m以上の場合には所望のマルテ ンサイ ト力く 得られない。 また、 T 0 aが 4 0 0 °C以上では冷却によ って得られ たマルテンサイ 卜が分解し、 良好な動的特性と成形性が得られなく なる。 一方、 T 0 aが T e — 5 0 °C未満の場合には、 付加的な冷却 設備が必要であつたり、 連続焼鈍炉の炉温と鋼板の温度差に起因し た材質のバラツキが大き く なることから、 この温度を下限と した。 また、 保持時間が 2 0分を超える場合には設備が長大となることか ら、 その上限を 2 0分と した。  That is, when Te is equal to or greater than Tem, a desired martensite force cannot be obtained. On the other hand, when T 0a is 400 ° C. or higher, the martensite obtained by cooling is decomposed, and good dynamic characteristics and moldability cannot be obtained. On the other hand, when T 0a is less than T e — 50 ° C, additional cooling equipment is required, and there is large material variation due to the difference between the furnace temperature of the continuous annealing furnace and the temperature of the steel sheet. Therefore, this temperature was set as the lower limit. If the holding time exceeds 20 minutes, the equipment becomes longer, so the upper limit was set to 20 minutes.
以上述べたような鋼板組成と製造方法を採用する こ とにより、 鋼 板の ミ クロ組織が、 主相をフ ェライ 卜 と し、 相当歪で 5 %の成形加 ェ後に体積分率で 3〜 5 0 %のマルテ ンサイ トを含むその他の低温 生成相との複合組織であり、 かつ相当歪みで 0 %超 1 0 %以下の予 変形を与えた後、 5 X 1 0 〜 5 X 1 0 —3 ( 1 / s ) の歪み速度範 囲で変形した時の準静的変形強度 （ σ s ) と、 前記予変形を与えた 後の 5 X 1 0 2 〜 5 X 1 0 3 ( 1 / s ) の歪み速度範囲で測定され た動的変形強度 （ CT d ) との差 （ d— CT S ) が 6 0 MPa 以上を満 足し、 かつ歪み 5〜 1 0 %の加工硬化指数が 0. 1 3以上を満足す る高い動的変形特性に優れたデュアルフニ—ズ型高強度鋼板を得る ことが可能になる。 なお、 本発明による鋼板は、 焼鈍、 調質圧延、 電気めつき等を施して目的とする製品とするこ と も可能である。 実施例 By adopting the steel sheet composition and manufacturing method as described above, the microstructure of the steel sheet has a main phase of ferrite, and a volumetric fraction of 3% after forming with 5% with equivalent strain. It is a composite structure with other low-temperature generation phases containing 50% martensite, and after giving a predeformation of more than 0% and 10% or less with equivalent strain, 5X10 to 5X10 — Quasi-static deformation strength (σ s) when deformed within the strain rate range of 3 (1 / s) and 5 X 10 2 to 5 X 10 3 (1 / s) ) With the dynamic deformation strength (CT d) measured in the strain rate range (d – CTS) of 60 MPa or more, and a work hardening index of 0.1% at a strain of 5 to 10%. It is possible to obtain a dual-fused high-strength steel sheet excellent in dynamic deformation characteristics satisfying 3 or more. In addition, the steel sheet according to the present invention can be subjected to annealing, temper rolling, electric plating, etc. to obtain a target product. Example
次に本発明を実施例に基づいて説明する。  Next, the present invention will be described based on examples.
く実施例 1 〉 Example 1>
表 1 に示す 2 6種類 （鋼番 1 〜 2 6 ) の鋼材を 1 0 5 0〜 1 2 5 0 °Cに加熱し、 表 2 に示す製造条件にて、 熱間圧延、 冷却、 巻取り を行い、 熱延鋼板を製造した。 本発明による成分条件と製造条件を 満足する鋼板は、 表 3 に示すようにマルテンサイ 卜体積分率で 3 % 以上 5 0 %以下含有するデュアルフ ヱ一ズ組織を有していると共に 、 これら熱延鋼板の機械的性質は、 表 4 に示すように歪 5 〜 1 0 % の加工硬化指数が 0 . 1 3以上、 CT d — CT S力く 6 O M P a以上、 σ d y η ≥ 0 . 7 6 6 x T S + 2 5 0 という優れた耐衝撃安全性を示 すと共に、 成形性および溶接性をも兼ね備えていることが明らかで ある。 The 26 types (steel numbers 1-26) shown in Table 1 were heated to 150-125 ° C and hot rolled, cooled, and wound under the manufacturing conditions shown in Table 2. To produce a hot-rolled steel sheet. As shown in Table 3, the steel sheet satisfying the component conditions and the production conditions according to the present invention has a dual-phase structure containing a martensite volume fraction of 3% or more and 50% or less. As shown in Table 4, the mechanical properties of the steel sheet are such that the work hardening index at a strain of 5 to 10% is 0.13 or more, CT d — CT S force is 6 OMPa or more, σ dy η ≥ 0.76 It is clear that it has excellent impact resistance of 6 x TS + 250 and also has both formability and weldability.
表 1 (続き） 鋼の化学成分 変態温度 鋼番 "C 種類 Table 1 (continued) Chemical composition of steel Transformation temperature Steel number "C type"
Ac 1 Ac J Ar3 Ac 1 Ac J Ar3
ob 本発明鋼 ob Invention steel
/yd 本発明鋼 本発明鋼 本発明鋼 本発明鋼 本発明鋼 本発明鋼 本発明鋼 本発明鋼 本発明鋼 本発明鋼 oo3 793 本発明鋼/ yd invention steel invention invention steel invention invention steel invention invention steel invention invention steel invention invention steel invention invention steel invention invention steel oo3 793 invention invention steel
/ /0 比較例/ / 0 Comparative example
/41 /yj 比較例/ 41 / yj Comparative example
/ l 1 oOo 比較例 本発明鋼/ l 1 oOo Comparative example Steel of the present invention
/4U oo i 本発明鋼 本発明鋼 本発明鋼 本発明鋼 本発明鋼 本発明鋼 本発明鋼 本発明鋼 本発明鋼 比較例 / 4U oo i Invented steel Invented steel Invented steel Invented steel Invented steel Invented steel Invented steel Invented steel Invented steel Comparative Example
Figure imgf000030_0001
Figure imgf000030_0001
表 3 鋼のミクロ組織 Table 3 Microstructure of steel
主相 フェライ卜 マルテンサイト 鋼番 円相当径 体積率 円相当径 5%加工後の体積率 名称 μ m % μ m %  Main phase Ferrite Martensite Steel number Circle equivalent diameter Volume ratio Circle equivalent diameter 5% Volume ratio after machining Name μ m% μ m%
1 フェライ卜 5.5 80 2.5 15 1 Ferrite 5.5 80 2.5 15
2 フェライ卜 4.0 90 1.8 82 Ferrite 4.0 90 1.8 8
3 フェライ卜 5.0 85 2.2 103 Ferrite 5.0 85 2.2 10
4 フェライ卜 4.0 80 1 .8 44 Ferrite 4.0 80 1.8 4
5 フェライ卜 4.5 80 2.0 205 Ferrite 4.5 80 2.0 20
6 フェライ卜 5.0 85 2.2 156 Ferrite 5.0 85 2.2 15
7 フェライ卜 4.5 90 2 107 Ferrite 4.5 90 2 10
8 フェライ卜 4.5 90 2 108 Ferrite 4.5 90 2 10
9 フェライ卜 5.0 90 2.2 109 Ferrite 5.0 90 2.2 10
10 フェライ卜 5.0 90 2.2 1010 Ferrite 5.0 90 2.2 10
1 1 フェライ卜 4.0 80 1.7 201 1 Ferrite 4.0 80 1.7 20
12 フェライ卜 5.0 90 2.2 1012 Ferrite 5.0 90 2.2 10
13 フェライ卜 1 1.0 50 二 013 Ferrite 1 1.0 50 Two 0
14 フェライ卜加工組織 90 二 014 Ferrite processing organization 90 2 0
15 フェライ卜 10.0 95 二 015 Ferrite 10.0 95 Two 0
16 フェライ卜 4.4 90 1.9 1016 Ferrite 4.4 90 1.9 10
17 フェライ卜 4.5 91 2 917 Ferrite 4.5 91 2 9
18 フェライ卜 3.4 78 1.4 2218 Ferrite 3.4 78 1.4 22
19 フェライ卜 4.4 91 1.9 919 Ferrite 4.4 91 1.9 9
20 フェライ卜 4.3 88 1.8 1220 Ferrite 4.3 88 1.8 12
21 フェライ卜 4.5 85 2 1321 Ferrite 4.5 85 2 13
22 フェライ卜 4.4 84 1.9 1 122 Ferrite 4.4 84 1.9 1 1
23 フェライ卜 4.4 85 1.9 823 Ferrite 4.4 85 1.9 8
24 フェライ卜 4.4 85 1.8 1224 Ferrite 4.4 85 1.8 12
25 フェライ卜 2.4 80 1 1025 Ferrite 2.4 80 1 10
26 ペイナイト 10.5 30 0 26 Pay Night 10.5 30 0
下線は本発明の範囲外であることを示す。 The underline indicates that it is outside the scope of the present invention.
表 4 の 械的性質 Table 4 Mechanical properties
Figure imgf000032_0001
Figure imgf000032_0001
下線は本発明の 囲 で る と 示 。  The underline indicates that it is within the scope of the present invention.
*3: adyn-(0.766 XTS + 250)  * 3: adyn- (0.766 XTS + 250)
*4:2.5(YS/TS'(5) 性変形量丁≥ 2.5 ( YS/TS ' (5)-0.5) +0.5 * 4: 2.5 (YS / TS '(5) 変 形 deformation amount ≥ 2.5 (YS / TS' (5) -0.5) +0.5
表 4(镜き） 鍋の機械的性質 Table 4 Mechanical properties of pot
Figure imgf000033_0001
Figure imgf000033_0001
*3: adyn— (0.766 XTS + 250)  * 3: adyn— (0.766 XTS + 250)
*4:2.5(YS/TS'(5)- 0.5卜 15≥塑性変形量 T; ;2.5(YS/TS'(5)-0.5]+0.5 * 4: 2.5 (YS / TS '(5) -0.5] 15≥Plastic deformation T;; 2.5 (YS / TS' (5) -0.5] +0.5
く実施例 2 > Example 2>
表 5 に示す 2 2種類 （鋼番 2 7〜 4 8 ) の鋼材を 1 0 5 0〜 1 2 5 0 °Cに加熱し、 熱延後、 冷却、 巻取りを行い、 更に酸洗後、 表 6 に示した条件で冷延して冷延鋼板を製造した。 その後、 各鋼の成分 から A c , 、 A c 3 の各温度を求め、 表 6 に示すような焼鈍条件で 加熱、 冷却、 保持を行い、 その後室温まで冷却した。 本発明による 成分条件と製造条件を満足する鋼板は、 表 7 に示すようにマルテ ン サイ ト体積分率で 3 %以上 5 0 %以下含有するデュアルフ ヱーズ組 織を有していると共に、 これら冷延鋼板の機械的性質は、 表 8 に示 すように、 歪 5 〜 1 0 %の加工硬化指数が 0 . 1 3以上、 （7 d — σ s力く 6 0 M P a以上、 ひ d y n ≥ 0 . 7 6 6 X T S + 2 5 0 という 優れた耐衝撃安全性を示すと共に、 成形性および溶接性をも兼ね備 えていることが明らかである。 The 22 types (steel numbers 27-48) shown in Table 5 were heated to 105-125 ° C, hot-rolled, cooled, rolled up, and pickled. Cold rolled steel sheets were produced by cold rolling under the conditions shown in Table 6. After that, the temperatures of A c, A c 3 were determined from the components of each steel, and heating, cooling, and holding were performed under the annealing conditions shown in Table 6, and then cooled to room temperature. The steel sheet satisfying the component conditions and the production conditions according to the present invention has a dual-phase structure containing 3% to 50% by martensite volume fraction as shown in Table 7, As shown in Table 8, the mechanical properties of the rolled steel sheet are such that the work hardening index at a strain of 5 to 10% is 0.13 or more, (7 d — σs force is more than 60 MPa, and dyn ≥ It is clear that it has excellent impact resistance of 0.766 XTS + 250 and also has both formability and weldability.
Figure imgf000035_0001
Figure imgf000035_0001
表 6 製造条件 Table 6 Manufacturing conditions
冷間圧延条件 焼鈍条件  Cold rolling conditions Annealing conditions
鋼番 圧下率板厚 焼鈍温度焼鈍時間 1 '久, TiJ¾急冷開始 乂' 1Ϊ速急冷終了計算 十昇 Ceq*計算 T2 s†算 Tera 保持/ m/ 保持時間Steel number Reduction rate Thickness Annealing temperature Annealing time 1 'Hi, TiJ ¾Quench start AGE' 1 ΪQuick quenching end calculation Toho Ceq * calculation T2 s calculation Tera retention / m / retention time
% m m To °C 秒 。C/秒 Tq °C °C/秒 Te 。C °C 。C で To 。C 秒% mm To ° C seconds. C / sec Tq ° C ° C / sec Te. C ° C. To in C. C seconds
27 80 0. 8 780 90 5 680 100 350 558 0. 12 -62 619 350 18027 80 0.8 780 90 5 680 100 350 558 0.12 -62 619 350 180
28 80 0. 8 780 90 5 680 100 230 521 0. 39 224 297 230 27028 80 0.8 0.8 780 90 5 680 100 230 521 0.39 224 297 230 270
29 80 0. 8 780 90 5 680 100 320 52 ) 0. 39 224 297 320 27029 80 0.8 780 90 5 680 100 320 52) 0.39 224 297 320 270
30 80 0. 8 780 90 5 500 100 230 521 0. 39 224 297 230 27030 80 0.8 0.8 780 90 5 500 100 230 521 0.39 224 297 230 270
31 80 0. 8 780 90 5 700 100 270 521 0. 47 182 339 270 30031 80 0.8 780 90 5 700 100 270 521 0.47 182 339 270 300
32 80 0. 8 780 90 5 680 80 270 521 0. 49 190 331 270 25032 80 0.8 780 90 5 680 80 270 521 0.49 190 331 270 250
33 80 0. 8 750 1 20 8 680 100 200 538 0. 46 297 241 ZOO 30033 80 0.8 750 1 20 8 680 100 200 538 0.46 297 241 ZOO 300
34 80 0. 8 750 120 8 680 100 270 492 0. 52 1 14 378 270 30034 80 0.8 750 120 8 680 100 270 492 0.52 1 14 378 270 300
35 80 0. 8 800 90 5 680 100 270 528 0. 41 259 269 270 30035 80 0.8 0.8 90 5 680 100 270 528 0.41 41 259 269 270 300
36 80 0. 8 750 90 5 650 130 200 528 0. 54 217 31 1 250 30036 80 0.8 750 90 5 650 130 200 528 0.55 54 217 31 1 250 300
37 80 0. 8 750 90 5 650 1 30 250 51 3 0. 53 192 321 240 30037 80 0.8 750 90 5 650 1 30 250 51 3 0.53 192 321 240 300
38 80 0. 8 800 90 5 650 100 270 512 0. 48 83 428 270 30038 80 0.8 0.8 90 5 650 100 270 512 0.48 83 428 270 300
39 80 0. 8 780 90 5 650 100 250 526 0. 42 216 310 250 30039 80 0.8 780 90 5 650 100 250 526 0.42 216 310 250 300
40 80 0. 8 780 90 5 680 100 270 495 0. 65 90 405 270 30040 80 0.8 780 90 5 680 100 270 495 0.65 90 405 270 300
41 80 0. 8 780 90 8 680 100 250 512 0. 58 1 54 358 250 30041 80 0.8 780 90 8 680 100 250 512 0.58 1 54 358 250 300
42 68 1. 2 780 90 8 680 100 250 512 0. 58 154 358 270 30042 68 1.2 780 90 8 680 100 250 512 0.58 154 358 270 300
43 68 1. 2 780 90 5 630 1 50 250 512 0. 58 1 54 358 250 30043 68 1.2 780 90 5 630 1 50 250 512 0.58 1 54 358 250 300
44 68 I . 2 780 90 5 680 100 250 512 0. 55 153 359 250 30044 68 I. 2 780 90 5 680 100 250 512 0.55 153 359 250 300
45 80 0. 8 750 90 5 680 100 250 51 2 0. 47 186 326 250 30045 80 0.8 750 90 5 680 100 250 51 2 0.47 186 326 250 300
46 80 0. 8 780 90 5 680 100 200 521 0. 77 252 269 200 30046 80 0.8 780 90 5 680 100 200 521 0.77 252 269 200 300
47 80 0. 8 770 90 5 680 100 270 446 0. 94 74 371 270 30047 80 0.8 770 90 5 680 100 270 446 0.94 74 371 270 300
48 80 0. 8 850 90 5 680 100 250 512 0. 79 188 323 250 300 下線は本発明の範囲外であることを示す。 48 80 0.8 850 90 5 680 100 250 512 0.79 188 323 250 300 Underlines indicate that they are outside the scope of the present invention.
Figure imgf000037_0001
Figure imgf000037_0001
ί¾的引張 （歪速度 =0. 00 Λ) 予変形及び B H処理 予変形 · BH処理後の静的. 動的引張り（歪速度 =100 塑性変形 鋼番 TS YS T. Ε 5-10¾ |YS X n YS/ TS X T. E 予変形の形態 - 相当歪 BH 5XWH t ] △YS *2 σ s a d σ ά- a s cr dyn条件式 T M式の溶接性 MPa MPa % の η値 TS' (S MPa · % % 処理 MPa MPa MPa MPa MPa MPa *3 % 判定Dynamic tension (strain rate = 0.000Λ) Pre-deformation and BH treatment Pre-deformation · Static after BH treatment. Dynamic tension (strain rate = 100 plastic deformation Steel No. TS YS T. Ε 5-10¾ | YS X n YS / TS X T.E Pre-deformation form-equivalent strain BH 5XWH t] △ YS * 2 σ sad σ ά- as cr dyn Conditional formula TM weldability MPa MPa% η value TS '(S MPa %% Treatment MPa MPa MPa MPa MPa MPa * 3% judgment
27 357 243 48 357 0. 28 68 0. 68 17136 C方向単軸引張 5有り 90 ! 16 390 438 48 412 - 1 1 1. 5 1. 0 o 適27 357 243 48 357 0.28 68 0.68 17136 Uniaxial tension 5 in C-direction 5 90! 16 390 438 48 412-1 1 1.5.
28 592 349 34 630 0. 24 84 0. 55 20128 C方向単铀引張 5無し 182 260 630 734 104 721 17. 5 1. 0 o 適28 592 349 34 630 0.24 84 0.55 20128 C-direction single tension 5 None 182 260 630 734 104 721 17.5 1.0 o Suitable
29 B03 457 32 612 0. 20 91 0. 75 19296 C方向単 ¾引張 5無し 102 127 620 ES2 42 645 -66. 9 1. 5 o 適29 B03 457 32 612 0.20 91 0.75 19296 C direction single ¾ Tensile 5 102 127 620 ES2 42 645 -66.9 1.5 o Suitable
30 583 472 2S： 591 0. 15 71 0. 80 15158 C方向単 i由引張 5無し 97 1 15 593 626 33 599 -97. 6 1. 5 〇 適30 583 472 2S: 591 0.15 71 0.80 15158 C direction single i free tension 5 None 97 1 15 593 626 33 599 -97. 6 1.5 〇 Suitable
31 599 341 33 621 0. 23 7¾ 0. 55 19767 し方向単軸引張 10有り 240 297 740 846 106 798 89. 2 I. 0 o 適31 599 341 33 621 0.23 7¾ 0.55 19767 Tensile uniaxial tension 10 Available 240 297 740 846 106 798 89.2 I. 0 o Suitable
32 641 359 34 690 0. 23 83 0. 52 21794 C方向単 ίώ引張 5有り 212 294 757 818 61 786 45. 0 1. 0 o is32 641 359 34 690 0.23 83 0.52 21794 C direction single ίώ tensile 5 with 212 294 757 818 61 786 45.0 1.0 ois
33 558 340 36 597 0. 26 88 0. 57 20088 C方向単铀引長 5有り 143 212 607 686 79 680 2. 6 1. 0 o 適33 558 340 36 597 0.26 88 0.57 20088 C direction single length 5 Available 143 212 607 686 79 680 2.6.1.0 o Suitable
34 640 397 33 650 0. 22 87 0. 61 21 120 C方向平面歪引 3有リ 191 229 660 748 88 745 4. 8 1. 0 o34 640 397 33 650 0.22 87 0.61 21 120 Plane strain in C direction 3 Yes 191 229 660 748 88 745 4.81.00
35 61 1 354 35 633 0. 23 82 0. 56 21385 C方向単軸引掁 5有り 201 275 658 756 98 742 . 24. 0 1. 0 o 適35 61 1 354 35 633 0.23 82 0.56 21385 C-axis single axis with 5 201 275 658 756 98 742 .24.0 1.0 o Suitable
36 589 324 36 600 0. 24 78 0. 54 21204 C方向単铀引張 5有り 212 289 612 733 121 722 20. 8 1. 0 〇 適36 589 324 36 600 0.24 78 0.54 21204 C direction single tension 5 With 212 289 612 733 121 722 20.8 1.0 適 Suitable
37 634 361 33 657 0. 21 76 0. 55 20922 等 2軸引張 10有り 257 318 703 790 87 776 40. 4 1. 0 〇 適37 634 361 33 657 0.21 76 0.55 20922 etc.Two-axis tension 10 with 257 318 703 790 87 776 40.4 1.0 適 Suitable
38 625 388 31 668 0. 19 74 0. 58 19375 C方向単釉引張 5有り 182 244 678 762 84 748 19. 3 1. 0 〇 連38 625 388 31 668 0.19 74 0.58 19375 C direction single glaze tension 5 with 182 244 678 762 84 748 19.3 1.10 連
39 689 434 29 712 0. 18 78 0. 61 19981 し方向単軸引張 1 無し 199 239 712 798 86 789 1 1. 2 4. 0 o 適39 689 434 29 712 0.18 78 0.61 19981 Uniaxial tension 1 direction None 199 239 712 798 86 789 1 1.2 4.0 o Suitable
40 623 368 32 623 0. 20 74 0. 59 】993S C方向単軸引張 1 有り 201 181 625 748 123 740 12. 8 1. 0 〇40 623 368 32 623 0.20 74 0.59】 993S Uniaxial tension in C direction 1 Yes 201 181 625 748 123 740 12.8 1. 0 〇
41 709 425 26 721 0. 17 72 0. 59 18434 C方向単軸引張 5有り 209 280 729 824 95 819 25. 9 1. 0 〇 適41 709 425 26 721 0.17 72 0.59 18434 Uniaxial tension 5 in C direction 5 209 280 729 824 95 819 25.9 1.0 〇 Suitable
42 722 448 25 734 0. 17 76 0. 61 18050 C方向単铀引張 5無し 201 260 734 833 99 818 14. 9 1. 0 〇 適42 722 448 25 734 0.17 76 0.61 18050 C direction single tension 5 None 201 260 734 833 99 818 14.9 1.0 適 Suitable
43 731 468 25 755 0. 16 75 0. 62 18275 等 2轴引張 5有リ 182 246 767 829 62 820 10. 1 1. 0 〇 適43 731 468 25 755 0.16 75 0.62 18275 etc.2 轴 tensile 5 with 182 246 767 829 62 820 10.1 1.0 0 suitable
44 715 465 26 726 0. 16 74 0. 64 18590 C方向単铀引張 5有リ ) 77 253 739 835 96 824 26. 3 1. 0 〇 適44 715 465 26 726 0.16 74 0.64 18590 C direction single tension 5 Yes) 77 253 739 835 96 824 26.3 1.0
45 648 531 25 681 0. 12 64 0. 78 16200 C方向単铀引張 5有リ 58 92 696 744 48 712 -34. 4 1. 0 X45 648 531 25 681 0.12 64 0.78 16200 C direction single tension 5 Yes 58 92 696 744 48 712 -34.4 1.0 X
46 1075 742 10 107S 0. 08 59 0. 69 10750 C方向単軸引張 5有リ 299 341 1076 1088 1 Z 1052 -21. 5 1. 0 〇 个 ia46 1075 742 10 107S 0.008 59 0.69 10750 Uniaxial tension in C direction 5 Yes 299 341 1076 1088 1 Z 1052 -21.5 1.0 0 piece ia
47 712 484 21 712 0. 1 1 53 0. 68 14952 C方向単铀引張 5有り 181 229 7 I S 757 42 740 -55. 4 1. 0 o 不適47 712 484 21 712 0.1 1 1 53 0.68 14952 C direction single tension 5 With 181 229 7 I S 757 42 740 -55.
48 792 475 22 792 0. 14 67 0. 60 17424 C方向単釉引張 5有り 2G5 332 80S 856 50 832 -24. 7 1. 0 o 適 下棕は本発明の範囲外であることを示す， 48 792 475 22 792 0.14 67 0.60 17424 C direction single glaze tension 5 with 2G5 332 80S 856 50 832 -24. 71.0 o Suitable lower palm is outside the scope of the present invention,
t l ： WHは表中の相当歪みで 5Xの予変形を与えることによる YSの上昇 Sを示す.  t l: WH indicates the rise S of YS by giving 5X pre-deformation with the equivalent strain in the table.
*2： AYSは表中の予変形を与え、 1 7 0 °C X 2 0分の塗装焼き付け処理相当の熱処理を行った際の YSの上昇量を示す ·  * 2: AYS gives the pre-deformation shown in the table and indicates the amount of increase in YS when heat treatment equivalent to paint baking is performed at 170 ° C for 20 minutes.
*3： cr dyn— (0. 76S X TS + 250)  * 3: cr dyn— (0.76S X TS + 250)
*4： 2. 5 X {YS/TS' (5) -0. 5} +15≥塑性変形量 >2. 5 X {YS/TS' (5) -0. 5} +0. 5 * 4: 2.5 X {YS / TS '(5) -0.5} + 15≥Plastic deformation> 2.5 X {YS / TS' (5) -0.5} +0.5
ミ ク ロ組織は以下の方法で評価した。 The microstructure was evaluated by the following method.
フェライ ト、 ベイナイ ト、 マルテンサイ ト及び残部組織の同定、 存在位置の観察、 及び平均結晶粒径 （平均円相当径） と占積率の測 定はナイタール試薬及び特開昭 59— 219473に開示された試薬により 鋼板圧延方向断面を腐食した倍率 1000倍の光学顕微鏡写真により行 つた o  The identification of ferrite, bainite, martensite and the rest of the structure, observation of the location, and measurement of the average crystal grain size (average circle equivalent diameter) and the space factor are disclosed in Nital Reagent and JP-A-59-219473. O Corrosion of the cross section in the rolling direction of the steel sheet by the reagent
特性評価は以下の方法で実施した。  The characteristic evaluation was performed by the following method.
引張試験は JIS 5号 （標点距離 50mm、 平行部幅 25mm) を用い歪速 度 0 . 0 0 1 Z s で実施し、 引張強さ （TS) 、 降伏強さ （YS) 、 全 伸び （T. El)、 加工硬化指数 （歪 1 %〜 5 %の n値） を求め、 YSX 加工硬化指数、 TSX T. E1 を計算した。  Tensile tests were conducted using JIS No. 5 (gauge length 50 mm, parallel part width 25 mm) at a strain rate of 0.001 Zs. Tensile strength (TS), yield strength (YS), total elongation ( T. El) and work hardening index (n value of strain 1% to 5%) were calculated, and YSX work hardening index, TSX T. E1 was calculated.
伸びフ ラ ンジ性は 2 0 nunの打ち抜き穴をバリのない面から 30度円 錐ポンチで押し拡げ、 クラ ッ クが板厚を貫通した時点での穴径 （ d ) と初期穴径 （ d。 ， 2 0 mm) との穴拡げ比 （ d / d。 ） を求めた スポッ ト溶接性は鋼板板厚の平方根の 5倍の先端径を有する電極 によりチリ発生電流の 0 . 9倍の電流で接合したスポッ ト溶接試験 片をたがねで破断させた時にいわゆる剥離破断を生じたら不適と し  Stretch flangeability is obtained by pushing a 20-nun punched hole out of a burr-free surface with a 30-degree circular cone punch, and when the crack penetrates the plate thickness (d) and initial hole diameter (d) , 20 mm) and the spot weldability was found to be 0.9 times the current generated by dust with an electrode having a tip diameter 5 times the square root of the steel sheet thickness. If so-called peel rupture occurs when the spot welding test piece joined by
産業上の利用可能性 Industrial applicability
上述したように、 本発明は従来にない優れた耐衝突安全性および 成形性を兼ね備えた自動車用高強度熱延鋼板および冷延鋼板を低コ ス トで、 しかも安定的に提供することが可能になり、 高強度鋼板の 使用用途および使用条件が格段に拡大される ものである。  As described above, the present invention makes it possible to provide high-strength hot-rolled steel sheets and cold-rolled steel sheets for automobiles, which have both unprecedented excellent collision safety and formability, at low cost and stably. As a result, the uses and conditions of use of high-strength steel sheets will be greatly expanded.

Claims

請 求 の 範 囲 The scope of the claims
1 . 最終的に得られる鋼板のミ ク ロ組織において、 主相がフ ヱラ ィ 卜で第 2相が前記鋼板の相当歪で 5 %成形加工後にマルテンサイ トを体積分率で 3〜 5 0 %を含むその他の低温生成相との複合組織 であり、 相当歪にて 0 %超〜 1 0 %以下の予変形を加えた後、 5 X 1 0 〜 5 X l 0 — 3 ( s —つ の歪速度範囲で変形した時の準静的変 形強度び s と、 前記予変形を加えた後、 5 X 1 0 2 ~ 5 X 1 0 3 ( s -') の歪速度範囲で変形した時の動的変形強度び d との差 （ひ （1 - a s ) が 6 O M P a以上を満足し、 かつ歪 5〜 1 0 %の加工硬化 指数が 0. 1 3以上を満足することを特徴とする動的変形特性に優 れたデュアルフ ェーズ型高強度鋼板。 1. In the microstructure of the finally obtained steel sheet, the main phase is flat and the second phase is 5% with the equivalent strain of the steel sheet and after forming, the martensite is 3 to 50% by volume fraction. % And other low-temperature formed phases, and after pre-deformation of more than 0% to 10% or less at equivalent strain, 5 X 10 to 5 X l 0 — 3 (s The quasi-static deformation strength when deformed in the strain rate range of s and the pre-deformation were applied, and then the strain was deformed in the strain rate range of 5 X 10 2 to 5 X 10 3 (s-'). The difference between the dynamic deformation strength at d and the d (h (1-as)) satisfies 6 OMPa or more, and the work hardening index of strain 5 to 10% satisfies 0.13 or more. Dual-phase high-strength steel sheet with excellent dynamic deformation characteristics.
2. 最終的に得られる鋼板の ミ ク ロ組織において、 主相がフ ヱラ ィ 卜で第 2相が前記鋼板の相当歪で 5 %成形加工後にマルテンサイ トを体積分率で 3〜 5 0 %を含むその他の低温生成相との複合組織 であり、 相当歪にて 0 %超〜 1 0 %以下の予変形を加えた後、 5 X 2. In the microstructure of the finally obtained steel sheet, the main phase is flat and the second phase is equivalent to the strain of the steel sheet. % And other low-temperature-generated phases.After applying a pre-deformation of more than 0% to 10% or less at equivalent strain, 5X
1 0 2 〜 5 X 1 0 3 ( s -') の歪速度範囲で変形した時の 3〜 1 0 %の相当歪範囲における変形応力の平均値ひ d y n (M P a ) が予 変形を与える前の 5 X 1 0 — 4〜 5 X 1 (J —3 ( s の歪速度範囲で 測定された静的な引張試験における最大応力 ： T S (M P a ) によ つて表現される式 ： ff d y n≥ 0. 7 6 6 x T S + 2 5 0 を満足し 、 かつ歪 5〜 1 0 %の加工硬化指数が 0. 1 3以上を満足すること を特徴とする動的変形特性に優れたデュアルフ ェーズ型高強度鋼板 o The average value of the deformation stress dyn (MPa) in the equivalent strain range of 3 to 10% when deformed in the strain rate range of 10 2 to 5 X 10 3 (s- ') before the pre-deformation 5 X 10 — 4 to 5 X 1 (J — 3 (s) Maximum stress in a static tensile test measured in the strain rate range: TS (MP a) Expression: ff dyn≥ Dual phase type with excellent dynamic deformation characteristics characterized by satisfying 0.766 x TS + 250 and a work hardening index of 0.13 or more at a strain of 5 to 10%. High strength steel sheet o
3. 前記請求項 1 または 2 において、 降伏強度 Y S ( 0 ) と、 相 当歪にて 5 %の予変形を加え、 或いは更に焼き付け硬化処理 （ B H 処理） を行った後の静的な引張試験における最大強度 T S ' ( 5 ) との比 ： Y S ( 0 ) /T S ' ( 5 ) ≤ 0. 7 を満足し、 更に前記降 伏強度 Y S ( 0 ) X加工硬化指数≥ 7 0 を満足することを特徴とす る動的変形特性に優れたデュアルフ ェーズ型高強度鋼板。 3. A static tensile test according to claim 1 or 2, wherein a yield strength YS (0) and a pre-deformation of 5% with equivalent strain are applied, or further a bake hardening treatment (BH treatment) is performed. Maximum strength TS 'at (5) Dynamic deformation characterized by satisfying YS (0) / TS '(5) ≤ 0.7 and further satisfying the yield strength YS (0) X work hardening index ≥ 70. Dual-phase high strength steel sheet with excellent properties.
4. 前記請求項 1、 2 または 3 の何れかにおいて、 前記マルテン サイ トの平均結晶粒径が 5 m以下、 および前記フ ェ ライ トの平均 結晶粒径が 1 以下を満足することを特徴とする動的変形特性 に優れたデュアルフ ヱ一ズ型高強度鋼板。  4. The method according to any one of claims 1, 2 and 3, wherein the average crystal grain size of the martensite satisfies 5 m or less and the average crystal grain size of the ferrite satisfies 1 or less. Dual-fused high-strength steel sheet with excellent dynamic deformation characteristics.
5. 前記請求項 1 〜 4の何れかにおいて、 引張強度 （M P a ) x 全伸び （％) ≥ 1 8， 0 0 0 を満足し、 かつ穴拡げ比 （ d / d o ) ≥ 1 . 2を満足することを特徴とする動的変形特性に優れたデュア ルフ ェーズ型高強度鋼板。  5. In any one of claims 1 to 4, the tensile strength (MPa) x the total elongation (%) ≥ 18 and 0000, and the hole expansion ratio (d / do) ≥ 1.2 is satisfied. A dual-phase high-strength steel sheet with excellent dynamic deformation characteristics characterized by satisfaction.
6. 前記請求項 1 〜 5 の何れかにおいて、 調質圧延とテ ンシ ョ ン レべラーの一方または双方による予変形を、 塑性変形量 （T) を下 ヒ式 ：  6. In any one of claims 1 to 5, the pre-deformation by one or both of the temper rolling and the tension leveler is performed, and the plastic deformation (T) is reduced by the following equation.
2.5 {YS(0)/TS' (5) - 0.5} + 15 ≥ Ύ≥ 2.5 ί YS (0) /TS，（5) - 0.5} + 0.5  2.5 {YS (0) / TS '(5)-0.5} + 15 ≥ Ύ ≥ 2.5 YS YS (0) / TS, (5)-0.5} + 0.5
を満足するこ とを特徴とする動的変形特性に優れたデュアルフ エ一 ズ型高強度鋼板。 Dual-phase high-strength steel sheet with excellent dynamic deformation characteristics, characterized by satisfying the following requirements.
7. 前記請求項 1 〜 6 の何れかにおける動的変形特性に優れたデ ユアルフ ヱ一ズ型高強度鋼板が、 素材成分と して、 重量％で、 C ： 0. 0 2〜 0. 2 5 %、 M n と C rの 1 種または 2種以上を合計で 0. 1 5〜 3. 5 %、 S i、 A l 、 Pの 1 種または 2種以上を合計 で 0. 0 2〜 4. 0 %、 を含み、 更に必要に応じて N i 、 C u、 M oの 1 種または 2種以上を合計で 3. 5 %以下、 N b、 T i、 Vの 1 種または 2種以上を合計で 0. 3 0 %以下、 C a、 R E Mの 1 種 または 2種以上を、 C aについては 0. 0 0 0 5〜 0. 0 1 %、 R E Mについては 0. 0 0 5〜 0. 0 5 %を含有し、 残部 F eを主成 分とすることを特徴とする動的変形特性に優れたデュアルフ 一ズ 型高強度鋼板。 7. The dual-type high-strength steel sheet having excellent dynamic deformation characteristics according to any one of claims 1 to 6, wherein C: 0.02 to 0.2 in weight% as a material component. 5%, 0.15 to 3.5% in total of one or more of Mn and Cr, 0.02 to in total of one or more of Si, Al, P 4.0%, and if necessary, one or more of Ni, Cu, Mo at least 3.5% in total, and one or two of Nb, Ti, V 0.30% or less in total, one or two or more of Ca and REM, 0.05 to 0.01% for Ca, and 0.05 to 0.05% for REM 0.05%, with the balance being Fe A dual-fused high-strength steel sheet with excellent dynamic deformation characteristics.
8. 前記請求項 1 〜 7の何れかにおける動的変形特性に優れたデ ユアルフ ヱ一ズ型高強度鋼板が、 前記素材成分に、 更に 0 1 % S≤ 0. 0 1 N≤ 0. 0 2 %の 1種または 2種以上を必 要に応じて添加する動的変形特性に優れたデュアルフ エーズ型高強 度鋼板。  8. The dual-type high-strength steel sheet having excellent dynamic deformation characteristics according to any one of claims 1 to 7, further comprising: 0 1% S ≤ 0.01 N ≤ 0.0 Dual phase type high-strength steel sheet with excellent dynamic deformation characteristics by adding 2% or more of 1% or more as needed.
9. 連続铸造スラブを、 铸造ままで熱延工程へ直送し、 も しく は 一旦冷却後に再度加熱した後、 熱延仕上温度 A r 3 — 5 0 °C〜A r 3 + 1 2 0 °Cで熱間圧延を行い、 次いで、 ラ ンアウ トテーブルにお ける平均冷却速度が 5 °C/秒以上で冷却を行い、 更に、 3 5 0 °C以 下の温度で巻取ることを特徴とする前記請求項 1 〜 8の何れかに記 載の動的変形特性に優れたデュアルフェーズ型高強度鋼板の製造方 法。 9. The continuous production slab is directly sent to the hot rolling process as it is, or once cooled and heated again, the hot rolling finish temperature A r 3 — 50 ° C to Ar 3 + 120 ° C Hot rolling, then cooling at an average cooling rate of 5 ° C / sec or more in a run-out table, and winding at a temperature of 350 ° C or less. A method for producing a dual-phase high-strength steel sheet having excellent dynamic deformation characteristics according to any one of claims 1 to 8.
1 0. 前記熱延仕上温度 A r 3 — 5 0 °C〜 A r 3 + 1 2 0 °Cの温 度範囲内において、 メ タラジーパラメ ーター ： A力く ( 1 ) 式および ( 2 ) 式を満たすような熱間圧延を行い、 その後のラ ンアウ トテ一 ブルにおける平均冷却速度を 2 5 °CZ秒以上と し、 更に前記メ タラ ジ一パラメ ーター ： Aと巻取り温度 （ C T) との関係が （ 3 ) 式を 満たすような条件で巻取ることを特徴とする前記請求項 9記載の動 的変形特性に優れたデュアルフエ一ズ型高強度熱延鋼板の製造方法 10. Within the temperature range of the hot-rolling finishing temperature A r 3 — 50 ° C to A r 3 + 120 ° C, the metallurgical parameter: A force (1) and (2) Hot rolling is performed to satisfy the condition, the average cooling rate in the subsequent runout table is set to 25 ° CZ seconds or more, and the relationship between the above-mentioned metal parameter: A and the winding temperature (CT) 10. The method for producing a dual-phase high-strength hot-rolled steel sheet having excellent dynamic deformation characteristics according to claim 9, wherein the coil is wound under a condition satisfying the expression (3).
9 ≤ 1 0 g A≤ 1 8 ( 1 ) 9 ≤ 1 0 g A ≤ 1 8 (1)
AT≤ 2 l x l o g A - 6 1 ( 2 )  AT≤ 2 l x l o g A-6 1 (2)
C T≤ 6 x l o g A + 2 4 2 ( 3 )  C T≤ 6 x l o g A + 2 4 2 (3)
1 1. 連続铸造スラブを、 铸造ままで熱延工程へ直送し、 も しく は一旦冷却後に再度加熱した後、 熱延し、 熱延後巻取った熱延鋼板 を酸洗後冷延し、 連続焼鈍工程で焼鈍して最終的な製品とする際に1 1. Continuously cast steel slab is sent directly to the hot rolling process as it is, or once cooled and heated again, hot rolled, and rolled after hot rolling When pickling is cold rolled and then annealed in a continuous annealing process to obtain the final product
、 A c , 〜A c 3 の温度に加熱し、 この温度範囲内で 1 0秒以上保 持する焼鈍を施した後、 冷却速度を 5 °CZ秒以上の条件で冷却する ことを特徵とする前記請求項 1〜 8 の何れかに記載の動的変形特性 に優れたデュアルフ エ一ズ型高強度熱延鋼板の製造方法。 , A c, to A c 3 , annealing at a temperature within this temperature range for 10 seconds or more, and then cooling at a cooling rate of 5 ° CZ seconds or more. The method for producing a dual-phase high-strength hot-rolled steel sheet having excellent dynamic deformation characteristics according to any one of claims 1 to 8.
1 2. 前記連続焼鈍工程において、 冷延後の鋼板を A c , 〜A c 3 の温度に加熱し、 この温度範囲内で 1 0秒以上保持する焼鈍を施 した後、 冷却するに際し、 1〜 1 0 °CZ秒の一次冷却速度で 5 5 0 〜 7 2 0 °Cの範囲の二次冷却開始温度 （T q ) まで冷却し、 引き続 いて 1 0〜 2 0 0 °C/秒の二次冷却速度で、 成分と焼鈍温度 （T o ) で決まる T e m以下の二次冷却終了温度 （T e ) まで冷却するこ とを特徴とする前記請求項 1〜 8の何れかに記載の動的変形特性に 優れたデュアルフ X—ズ型高強度冷延鋼板の製造方法。  1 2. In the continuous annealing step, the cold-rolled steel sheet is heated to a temperature of A c, to A c 3, annealed for more than 10 seconds within this temperature range, and then cooled. Cool to the secondary cooling start temperature (Tq) in the range of 550 to 720 ° C at the primary cooling rate of ~ 10 ° CZ seconds, and then continue cooling at the rate of 10 to 200 ° C / sec. 9. The method according to claim 1, wherein cooling is performed at a secondary cooling rate to a secondary cooling end temperature (T e) equal to or lower than T em determined by a component and an annealing temperature (T o). A method for manufacturing dual-fed X-shaped high-strength cold-rolled steel sheets with excellent dynamic deformation characteristics.
PCT/JP1998/001101 1997-03-17 1998-03-16 Dual-phase high-strength steel sheet having excellent dynamic deformation properties and process for preparing the same WO1998041664A1 (en)

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