WO2005095663A1 - 高剛性高強度薄鋼板およびその製造方法 - Google Patents
高剛性高強度薄鋼板およびその製造方法 Download PDFInfo
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- WO2005095663A1 WO2005095663A1 PCT/JP2005/006288 JP2005006288W WO2005095663A1 WO 2005095663 A1 WO2005095663 A1 WO 2005095663A1 JP 2005006288 W JP2005006288 W JP 2005006288W WO 2005095663 A1 WO2005095663 A1 WO 2005095663A1
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- 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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- 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
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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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
-
- 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
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- 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 high-rigidity, high-strength thin steel sheet suitable mainly for an automobile body and a method for producing the same.
- the high-rigidity, high-strength thin steel sheet of the present invention is a column-shaped structural member having a rigidity sensitivity index close to 1 such as an automobile center villa, rocker, side frame, cross member, etc. It is suitable for a wide range of applications. Background art
- the stiffness of a part having the same part shape or welding condition is represented by the product of the Young's modulus of the member and the second moment of area of the part. It can be expressed as approximately proportional to ⁇ .
- ⁇ is the thickness sensitivity index and the shape of the part It takes a value of 1 to 3 depending on the condition. For example, ⁇ takes a value close to 3 when the shape is a single plate such as an automobile panel component, and ⁇ takes a value close to 1 when the shape is a column such as a structural component.
- the Young's modulus is largely controlled by the texture and increases in the direction of the closest density of atoms. Therefore, in the steel process of rolling by rolls and heat treatment, it is effective to develop ⁇ 112 ⁇ ⁇ 110> in order to develop the orientation that is advantageous for the Young's modulus of the steel, which is a body-centered cubic lattice, Thereby, the Young's modulus in the direction perpendicular to the rolling direction can be increased.
- the aggregate structure of ferrite at the hot-rolled sheet stage was changed to ⁇ 311 ⁇ 011> and ⁇ 332 ⁇ 113>, and the initial orientation was used for cold rolling and recrystallization annealing.
- a technique for increasing the Young's modulus in a direction perpendicular to the rolling direction by setting ⁇ 211 ⁇ 011> as the main orientation by performing the rolling process is disclosed.
- Patent Document 2 low-carbon steel having a C content of 0.02 to 0.15% is added with Nb, Mo, and B, and Ar is added.
- a method for producing a hot-rolled steel sheet in which the rolling reduction at -950 ° C is made 50% or more to develop ⁇ 211 ⁇ 011> and increase the Young's modulus is disclosed.
- Nb is added to low-carbon steel having a C content of 0.05% or less, the finish rolling start temperature is 950 ° C or less, and the finish rolling end temperature is (Ar-50 ° C) or less. (Ar + 100 ° C) and Young
- Patent Document 4 Si and A1 are added to a low-carbon steel having a C content of 0.05% or less to add Ar and
- Patent Document 1 Japanese Patent Application Laid-Open No. 5-255804
- Patent Document 2 JP-A-8-311541
- Patent Document 3 JP-A-5-247530
- Patent document 4 JP-A-953118
- Patent Document 1 controls the texture by using ultra-low carbon steel with a C content of 0.01% or less and increases the Young's modulus of the steel sheet.
- Patent Document 2 Although the C content is as high as 0.02 to 0.15%, it is possible to increase the strength, but since the target steel sheet is a hot-rolled steel sheet, It is not possible to utilize the texture control by processing, and it is difficult to further increase the Young's modulus.In addition, stable production of high-strength steel sheets with a thickness of less than 2.0 mm by low-temperature finish rolling is required. There was a problem that it was difficult.
- Patent Document 3 is also a technology for manufacturing a hot-rolled steel sheet, and has the same problem.
- the high Young's modulus of a steel sheet in the prior art is intended for a sheet having a large thickness, a hot-rolled steel sheet, or a soft steel sheet. It was difficult to achieve a high Young's modulus of a high-strength steel sheet as thin as 2.0 mm or less.
- a strengthening mechanism for increasing the tensile strength of a steel sheet to 590 MPa or more there are mainly a precipitation strengthening mechanism and a transformation structure strengthening mechanism.
- a precipitation strengthening mechanism is used as the strengthening mechanism, it is possible to increase the strength while suppressing the decrease in the Young's modulus of the steel sheet as much as possible, but it involves the following difficulties. That is, for example, if a precipitation strengthening mechanism is used to finely precipitate carbonitrides such as Ti and Nb, the strength of hot-rolled steel sheets can be increased by fine precipitation during winding after hot rolling. On the other hand, in cold-rolled steel sheets, coarsening of precipitates in the recrystallization annealing process after cold rolling was inevitable, and it was difficult to increase the strength by precipitation strengthening.
- the Young's modulus of the steel sheet decreases due to the strain contained in the low-temperature transformation phase such as the bainite phase or the martensite phase. There was a problem.
- An object of the present invention is to solve the above-mentioned problems, to provide a high tensile strength of 59 knits or more, more preferably 700 MPa or more, and a Young's modulus of 225 GPa or more, more preferably 230 GPa or more, and further preferably 240 GPa.
- An object of the present invention is to provide a thin steel sheet having a thickness of 2.0 mm or less, which has both the above and high rigidity, together with an advantageous manufacturing method thereof.
- the gist configuration of the present invention is as follows.
- It has a composition of iron and unavoidable impurities qualitatively, and has a microstructure composed of a fryte phase as the main phase, a martensite phase with an area ratio of 1% or more, and a tensile strength of 590 MPa or more and Young A high-rigidity, high-strength thin steel sheet having a modulus of 225 GPa or more.
- N * N— (14 / 47.9) XTi, N— (14 / 47.9) XTi when N— (14 / 47.9) XTi> 0
- Ti * 0.
- a method for producing high-rigidity, high-strength thin steel sheets characterized by performing annealing for cooling at a cooling rate of 5 ° C / s or higher.
- V 0.01 to 0.50%, containing one or two selected from the above and (1)
- N * N— (14 / 47.9) XTi, N— (14 / 47.9) XTi when N— (14 / 47.9) XTi> 0
- Ti * 0.
- a thin steel sheet having a high tensile strength of at least 590 MPa, more preferably at least 700 MPa, and a Young's modulus of at least 225 GPa, more preferably at least 230 GPa, and still more preferably at least 240 GPa. Becomes possible.
- a low-carbon steel material added with Mn and Nb is subjected to hot rolling at a temperature of 950 ° C or lower, more preferably 900 ° C or lower (strictly above the Ar point). Perform rolling and unrecrystallized aus
- the combination of promotion of the fly transformation from tenite and subsequent cold rolling develops a crystal orientation that is advantageous for improving the Young's modulus, control of the heating rate in the subsequent annealing process, and equalization in the two-phase region.
- a low-temperature transformation phase that suppresses a decrease in Young's modulus is generated by heat, and a large amount of ferrite phase that is advantageous for improving the Young's modulus is retained, thereby increasing strength and increasing Young's modulus. It is possible to manufacture a thin steel plate satisfying both, and this has an industrially effective effect.
- the low-carbon steel material to which Mn and Nb are added is reduced in the hot rolling immediately above the Ar transformation point to reduce the crystal orientation force of ⁇ 112 ⁇ ⁇ 111>.
- the ferrite orientation of ⁇ 113 ⁇ * 110> can be developed by increasing the austenite structure of the crystal and promoting ferrite transformation from unrecrystallized austenite of ⁇ 112 ⁇ * 111> in the subsequent cooling process. .
- the crystal orientation of ⁇ 113 ⁇ ⁇ 110> is advantageous for improving the Young's modulus ⁇ 112 ⁇ .
- the ⁇ 112 ⁇ In addition to promoting the recrystallization of ferrites with, the non-recrystallized grains of ⁇ 112 ⁇ 110 110 ⁇ Austenite transformation can be promoted.
- the austenite phase is transformed into the fly phase during cooling after soaking, the ferrite grains having the orientation of ⁇ 112 ⁇ ⁇ 110> grow to increase the Young's modulus and increase the Mn addition.
- a low-temperature transformation phase is formed, and high strength can be achieved.
- the austenite phase transformed from ferrite having the orientation of ⁇ 112 ⁇ ⁇ 110> is formed by retransformation during cooling, the low-temperature transformation phase has a small crystal orientation of the low-temperature transformation phase. Can also develop ⁇ 112 ⁇ ⁇ 110>.
- the Young's modulus is increased by developing the ⁇ 112 ⁇ -110> of the ferrite phase, and the orientation of the low-temperature transformation phase, which has a great effect on the decrease of the Young's modulus, is particularly increased.
- the strength can be increased by the formation of the low-temperature transformation phase, and the decrease in the Young's modulus due to the formation of the low-temperature transformation phase can be greatly suppressed.
- FIG. 1 is a diagram showing the influence of the total draft at 950 ° C. or less and 900 ° C. or less on the Young's modulus.
- FIG. 2 is a graph showing the influence of the final temperature of hot finish rolling on the Young's modulus.
- FIG. 3 is a diagram showing the influence of the winding temperature on the Young's modulus.
- FIG. 4 is a graph showing the effect of the rolling reduction in cold rolling on the Young's modulus.
- FIG. 5 is a graph showing the influence of the average heating rate from 500 ° C. to the soaking temperature during annealing on the Young's modulus.
- the high-rigidity high-strength thin steel sheet of the present invention has a tensile strength of at least 59 Pa, more preferably
- the steel sheet has a modulus of 700 MPa or more, a Young's modulus of 225 GPa or more, more preferably 230 GPa or more, and still more preferably 240 GPa or more, and a sheet thickness of 2.0 mm or less.
- the steel sheets targeted by the present invention include not only cold-rolled steel sheets but also steel sheets which have been subjected to surface treatment such as hot-dip galvanized material including alloying and electrogalvanized materials.
- the unit of the content of each element in the component composition of the steel sheet is a force of “% by mass” or less, and is simply indicated by “%” unless otherwise specified.
- C is an element that stabilizes austenite, and greatly contributes to high strength by enhancing hardenability and greatly promoting the formation of a low-temperature transformation phase in a cooling process during annealing after cold rolling. be able to. Furthermore, during hot rolling, Ar
- the C content needs to be 0.02% or more, more preferably 0.05% or more, and still more preferably 0.06% or more.
- the C content is more than 0.15%, the fraction of the hard low-temperature transformation phase increases, and the workability deteriorates not only by extremely increasing the strength of the steel but also.
- the presence of a large amount of C suppresses recrystallization in an orientation advantageous for high Young's modulus in the annealing step after cold rolling.
- large amounts also cause deterioration of weldability.
- the C content needs to be 0.15% or less, and more preferably 0.10% or less.
- Si is an element that stabilizes ferrite, promotes ferrite transformation in the cooling process after soaking in the two-phase region in the annealing process after cold rolling, and enriches C in austenite. By doing so, it is possible to stabilize austenite and promote the formation of a low-temperature transformation phase. Therefore, the strength of the steel can be increased as necessary, and in order to obtain such an effect, it is desirable that the Si content be 0.2% or more.
- ⁇ is one of the important elements of the present invention. ⁇ is an element that suppresses recrystallization of worked austenite during hot rolling and stabilizes austenite.
- Mn which is an austenite stabilizing element, lowers the Ac transformation point during the temperature rise process in the annealing step after cold rolling, and changes the austenite transformation from unrecrystallized ferrite.
- Mn greatly contributes to high strength by enhancing hardenability and greatly promoting the formation of a low-temperature transformation phase. You can also. And, by acting as a solid solution strengthening element, it can also contribute to increasing the strength of steel. In order to obtain such effects, the Mn content needs to be 1.5% or more.
- the Mn content is set to 4.0% or less, more preferably 3.5% or less.
- ⁇ segregates at the grain boundaries, if the ⁇ content exceeds 0.05%, not only the ductility and toughness of the steel sheet will decrease, but also the weldability will deteriorate. In addition, when used as an alloyed hot-dip galvanized steel sheet, the alloying speed is slowed by ⁇ . Therefore, the content must be 0.05% or less.
- ⁇ is an element effective for increasing the strength as a solid solution strengthening element, and also has an effect of promoting C concentration in austenite as an element for stabilizing ferrite.
- the steel to which Si is added also has the effect of suppressing the generation of red scale. In order to obtain such an effect, the P content is preferably set to 0.01% or more.
- S remarkably reduces the ductility in hot, causing hot cracking and significantly deteriorating the surface properties. Furthermore, S not only contributes little to the strength, but also reduces ductility and hole-expandability by forming coarse MnS as an impurity element. These problems become significant when the S content exceeds 0.01%, so it is desirable to reduce them as much as possible. Therefore, the S content is set to 0.01% or less. Further, from the viewpoint of particularly improving the hole expanding property, the content is preferably 0.005% or less.
- Al is a ferrite-stabilizing element and can significantly increase the Ar transformation point of steel.
- the A1 content needs to be 1.5% or less, and from this viewpoint, it is more preferable to limit A1 to 0.1% or less, which is more preferable.
- A1 which is a ferrite-forming element, promotes ferrite formation in the cooling process after soaking in the two-phase region in the annealing process after cold rolling, and stabilizes austenite by enriching C in austenite. And promote the formation of a low-temperature transformation phase. Therefore, the strength of the steel can be increased as necessary, and in order to obtain such an effect, the A1 content is desirably 0.2% or more.
- ⁇ is a harmful element that causes slab cracks during hot rolling and generates surface flaws. ⁇ When the content exceeds 0.01%, slab cracks and surface flaws become noticeable. Therefore, the content must be 0.01% or less.
- Nb is the most important element in the present invention.
- Nb promotes ferrite transformation from unrecrystallized austenite by suppressing recrystallization of processed austenite in the finish rolling step in hot rolling, and develops ⁇ 113 ⁇ ku110>
- the Young's modulus can be improved in the subsequent cold rolling and annealing steps.
- the austenite transformation from unrecrystallized ferrite is promoted, and the cooling process after soaking is performed.
- the orientation of the low-temperature transformation phase generated by V it is possible to develop an orientation advantageous for improving the Young's modulus, and to suppress a decrease in the Young's modulus due to the generation of the low-temperature transformation phase.
- fine carbonitrides of Nb can also contribute to increased strength.
- the Nb content needs to be 0.02% or more, and more preferably 0.05% or more.
- the Nb content is set to 0.02 to 0.40%, more preferably 0.05 to 0.40%.
- the amount of C not fixed as carbonitride calculated by (C + (12/14) XN-(12 / 92.9) X Nb), must be 0.06% or less. And more preferably 0.05% or less.
- N is fixed preferentially over C by Nb and precipitates. Therefore, the amount of C not fixed as carbonitride by (C + (12/14) XN— (12 / 92.9) X Nb) Can be calculated.
- the amount of C not fixed as carbonitride is less than 0.01%, the amount of C in austenite decreases during annealing in the two-phase region after cold rolling, and the formation of a martensite phase after cooling is suppressed. This makes it difficult to increase the strength of the steel. Therefore, the amount of ( ⁇ + (12/14)? ⁇ (12 / 92.9)) which is fixed as carbonitride is 0.01 to 0.06%, more preferably 0.01 to 0.05%. I do. Also, N coarsely precipitates Nb nitride at a high temperature, so that the effect of suppressing recrystallization of Nb is reduced.
- N content In order to suppress this effect, it is necessary to limit the N content to N ⁇ (14 / 92.9) X (Nb-0.01) in relation to the Nb content. More preferably, it is limited to N ⁇ (14 / 92.9) X (Nb-0.02).
- the balance is substantially iron and unavoidable impurities means that those containing other trace elements are within the scope of the present invention, as long as the action and effect of the present invention are not impaired. Means to be included. In order to further improve the strength, In addition to the component specifications, if necessary, one or more of Ti and V, and one or more components that also select the neutrality of Cr, Ni, Mo, Cu and B! / ,.
- the content of Ti is preferably set to 0.01% or more.
- the Ti content is preferably 0.50% or less, more preferably 0.20% or less.
- V 0.01 to 0.50%
- V is an element that contributes to an increase in strength by forming fine carbonitrides.
- the content of V is preferably set to 0.01% or more.
- the addition amount of V is 0.50% or less, more preferably 0.20% or less.
- N * ⁇ (14 / 92.9) X (Nb-O.Ol) (4)
- Ti * 0.
- N coarsely precipitates Nb nitride at a high temperature, so that the effect of suppressing recrystallization of Nb is reduced.
- N is preferentially fixed as a nitride of Ti, so N *, which is the amount of N not fixed as a nitride of Ti, is changed to N * ⁇ (14 / 92.9) X (Nb — Must be limited to 0.01). More preferably, it is limited to N * ⁇ (14 / 92.9) X (Nb 0.02).
- Ti and V form carbonitrides, which are not fixed as carbonitrides but reduce the amount of C. Furthermore, since is fixed by the formation of sulfur nitride, the amount of C not fixed as carbonitride is set to 0.01 to 0.06%. + (12/14) XN * — (12 / 92.9) X Nb— (12 / 47.9) X Ti * — (12 / 50.9) It is necessary to make the value of XV 0.01 to 0.06%, which is more preferable. Should be 0.01-0.05%.
- Cr is an element that enhances hardenability by suppressing the formation of cementite, and greatly enhances the formation of a low-temperature transformation phase during the cooling process after soaking in the annealing process, thereby increasing the strength. Can be greatly contributed to. Furthermore, in the hot rolling process, by suppressing the recrystallization of the worked austenite, the ferrite transformation from unrecrystallized austenite is promoted, and ⁇ 113 ⁇ ⁇ 110> is developed, followed by cold rolling and annealing. The Young's modulus can be improved in the process. In order to obtain such an effect, it is preferable to contain Cr in an amount of 0.1% or more.
- the thin steel sheet of the present invention is used as a hot-dip galvanized steel sheet, it is preferable to contain Cr at 0.5% or less because Cr oxide generated on the surface induces non-plating. .
- Ni is an element that enhances hardenability by stabilizing austenite, and is used in the annealing process. In the cooling process after soaking, the formation of a low-temperature transformation phase is greatly promoted, which can greatly contribute to strengthening. Furthermore, Ni, which is an austenite stabilizing element, lowers the Ac transformation point during the heating process in the annealing process after cold rolling, and
- Austenite transformation from crystalline ferrite is promoted, and in the cooling process after soaking, the orientation of the low-temperature transformation phase generated in the cooling process develops in a direction that is advantageous for improving the Young's modulus.
- the rate can be prevented from lowering.
- Ni suppresses the recrystallization of worked austenite during hot rolling and lowers the Ar transformation point because it is an element that stabilizes austenite.
- the presence of a large amount of Ni exceeding 1.0% causes the Ac transformation point to be excessively lowered during the heating process in the annealing step after cold rolling, thereby causing the formation of the fly phase in the two-phase region.
- Mo is an element that enhances hardenability by reducing the mobility of the interface.In the cooling process in the annealing process after cold rolling, the formation of a low-temperature transformation phase is greatly promoted to increase the strength. Can be greatly contributed to. Further, recrystallization of the processed austenite can be suppressed, and by promoting ferrite transformation from unrecrystallized austenite, ⁇ 113 ⁇ ⁇ 110> is developed, and the Young's modulus is reduced in the subsequent cold rolling and annealing processes. Can be improved. In order to obtain such an effect, it is preferable to contain Mo in an amount of 0.1% or more. On the other hand, even if Mo is contained in a large amount exceeding 1.0%, the above effect is only saturated Mo is preferably contained at 1.0% or less because of an increase in cost.
- ⁇ is an element that enhances the hardenability by suppressing the transformation from the austenite phase to the ferrite phase, and greatly promotes the formation of the low-temperature transformation phase in the cooling process in the annealing process after cold rolling. , Can greatly contribute to high strength. Furthermore, recrystallization of worked austenite can be suppressed, and by promoting ferrite transformation from unrecrystallized austenite, ⁇ 113 ⁇ ⁇ 110> can be developed, and it can be used in the subsequent cold rolling and annealing processes. Rate can be improved. In order to obtain this effect, it is preferable to contain 0.0005% or more. On the other hand, even if an excessive amount of ⁇ exceeding 0.0030% is contained, the above effect is saturated. Therefore, it is preferable that ⁇ ⁇ ⁇ is contained at 0.0030% or less.
- Cu is an element that enhances hardenability, and in the cooling process in the annealing process after cold rolling, it can greatly contribute to high strength by greatly promoting the formation of a low-temperature transformation phase. In order to obtain this effect, it is preferable to contain Cu in an amount of 0.1% or more. On the other hand, an excessive Cu content exceeding 2.0% lowers hot ductility, induces surface defects due to cracking during hot rolling, and saturates the quenching effect of Cu. U is preferably contained at 2.0% or less.
- the thin steel sheet of the present invention it is necessary to have a structure having a ferrite phase as a main phase and a martensite phase at an area ratio of 1% or more.
- the term “ferrite phase as the main phase” means that the area ratio of the ferrite phase is 50% or more.
- the ferrite phase has little distortion, is advantageous for high Young's modulus, is excellent in ductility, and has good workability. Therefore, it is necessary that the structure be mainly composed of the ferrite phase.
- the composite phase is formed by forming the low-temperature transformation phase, which is a hard phase, in the V, the so-called second phase, which is a part other than the ferrite phase, which is the main phase. I need to do it.
- having a particularly hard martensite phase in the structure among the low-temperature transformation phases reduces the fraction of the second phase for obtaining the target tensile strength level, and reduces the fraction. This is advantageous because a high Young's modulus can be achieved by increasing the fraction of the ellitic phase, and the workability can be improved.
- the area ratio of the martensite phase to the entire structure must be 1% or more. is there.
- the area ratio of the martensite phase is preferably set to 16% or more.
- the structure of the steel sheet of the present invention is preferably a structure composed of the ferrite phase and the martensite phase, but U is a bainite phase or a retained austenite phase, or is a ferrite phase such as a pearlite phase or a cementite phase. There is no problem even if it has a phase other than the phase and the martensite phase in an area ratio of 10% or less, more preferably 5% or less. That is, the total area ratio of the ferrite phase and the martensite phase is preferably set to 90% or more, more preferably 95% or more.
- composition of the steel material used in the production method of the present invention is the same as the composition of the steel plate described above, the description of the reason for limiting the steel material composition is omitted.
- the thin steel sheet of the present invention is obtained by subjecting a steel material having the same composition as the above-described steel sheet to hot rolling to form a hot rolled sheet, and pickling and cooling the hot rolled sheet. It can be manufactured by sequentially passing through a cold rolling step of performing cold rolling to form a cold rolled sheet, and an annealing step of achieving recrystallization and composite structure of the cold rolled sheet.
- the unrecrystallized austenite structure with the crystal orientation force of ⁇ 112 ⁇ ⁇ 111> develops, and in the subsequent cooling process, the ⁇ 113 ⁇ ⁇ 111> unrecrystallized austenite undergoes ferrite transformation to produce ⁇ 113 ⁇ ⁇ 111>.
- 110> ferrite orientation can be developed. This orientation is advantageous in improving the Young's modulus in the formation of texture in the subsequent cold rolling and annealing processes.
- the total reduction at 950 ° C or lower should be 30% or more, and more preferably, the total reduction at 900 ° C or lower should be 30% or more.
- the winding temperature after finish rolling exceeds 650 ° C, the carbonitride of Nb becomes coarse, and the effect of suppressing the recrystallization of ferrite during the heating process in the annealing process after cold rolling is reduced. It becomes difficult to transform unrecrystallized ferrite into austenite. As a result, the orientation of the low-temperature transformation phase that transforms in the cooling process after soaking cannot be controlled, and the Young's modulus is greatly reduced by the low-temperature transformation phase having this distortion. Therefore, the winding temperature after finish rolling must be 650 ° C or less.
- the temperature is preferably set to 400 ° C. or more.
- pickling is performed to remove scale generated on the surface of the steel sheet.
- the pickling may be performed according to a conventional method.
- cold rolling is performed.
- the ⁇ 113 ⁇ ⁇ 110> orientation developed in the hot-rolled steel sheet can be rotated to the ⁇ 112 ⁇ ⁇ 110> orientation effective for improving the Young's modulus. it can.
- the structure after the subsequent annealing step also increases the ⁇ 112 ⁇ ⁇ 110> orientation in ferrite, and furthermore, during the low-temperature transformation phase
- the Young's modulus can be increased. To obtain such an effect, it is necessary to reduce the rolling reduction during cold rolling to 50% or more.
- the heating rate in the annealing step is an important process condition in the present invention.
- the annealing process during the process of raising the temperature to the soaking temperature in the two-phase region, that is, to the soaking temperature of 780 to 900 ° C, it promotes the recrystallization of ferrite having the ⁇ 112 ⁇ ⁇ 110> orientation and ⁇ A part of the ferrite grains having the ⁇ 112 ⁇ ⁇ 110> orientation reaches the two-phase region in an unrecrystallized state, and the austenite transformation from the unrecrystallized ferrite having the ⁇ 112 ⁇ ⁇ 110> orientation Can be promoted.
- the Young's modulus can be increased by promoting the grain growth of ferrite having the ⁇ 112 ⁇ ⁇ 110> orientation. Furthermore, when the low-temperature transformation phase is generated and the strength is increased, the austenite phase transformed from the ferrite including the ⁇ 112 ⁇ ⁇ 110> orientation is re-transformed upon cooling. ⁇ 112 ⁇ ⁇ 110> can be developed. As described above, the Young's modulus is increased by developing the ⁇ 112 ⁇ ⁇ 110> of the ferrite phase, and ⁇ 112 ⁇ ⁇ 110> is increased in the orientation of the low-temperature transformation phase, which has a great effect on the decrease of the Young's modulus.
- the soaking temperature from 500 ° C which greatly affects recrystallization behavior, is 780 to 780 ° C.
- the average heating rate up to 900 ° C needs to be 1 to 40 ° C / s, more preferably 1 to 30 ° C / s.
- the soaking temperature is set to 780 to 900 ° C because recrystallization is not completed below 780 ° C, and when it exceeds 900 ° C, the austenite fraction increases, and ⁇ 112 This is because the lights in the ⁇ 110> direction decrease or disappear.
- the soaking time is not particularly limited, but is preferably set to about 30 seconds or more in order to generate austenite.On the other hand, if it is too long, the production efficiency deteriorates. Is preferred.
- the average cooling rate up to 500 ° C after soaking must be 5 ° C / s or more.
- steel having a chemical composition corresponding to the intended strength level is melted.
- the smelting method can be appropriately applied, such as a normal converter method or an electric furnace method.
- the molten steel is formed into a slab and then hot-rolled as it is or after being cooled and heated.
- hot rolling after finishing under the above-mentioned finishing conditions, winding is performed at the above-described winding temperature, and then normal pickling and cold rolling are performed.
- the annealing the temperature is raised under the above-described conditions, and the cooling after soaking can increase the cooling rate within a range in which a desired low-temperature transformation phase is obtained. Then, in the case of a cold-rolled steel sheet, it may be overaged!
- hot-dip galvanized steel sheet If it is to be manufactured as a hot-dip galvanized steel sheet, it can be plated by passing it through hot-dip zinc, and furthermore, it can be alloyed Chemical solution When manufactured as a hot-dip galvanized steel sheet, it can be reheated to a temperature of 500 ° C or higher for alloying treatment.
- steel A having the components shown in Table 1 was melted in a laboratory vacuum melting furnace, and once cooled to room temperature to produce a steel ingot (steel material).
- hot rolling, pickling, cold rolling and annealing were sequentially performed in a laboratory.
- the basic manufacturing conditions are as follows. After heating the ingot for 1 hour at 1250 ° C, Hot rolling is started, and the total rolling reduction of 900 ° C or less, that is, the total rolling reduction of 900 ° C or less is set to 40%, and the final rolling temperature (corresponding to the finish rolling finish temperature) is 830 ° C. Thickness: A hot-rolled sheet of 4.0 mm was used. Thereafter, after the temperature reached 600 ° C., it was placed in a furnace at 600 ° C., held for 1 hour, and then cooled in the furnace to simulate winding conditions (equivalent to a winding temperature of 600 ° C.).
- the hot-rolled sheet thus obtained was pickled, cold-rolled at a rolling reduction of 60% to a sheet thickness of 1.6 mm, and heated to 500 ° C at an average of 10 ° C / s. Then, the temperature was raised from 500 ° C to a soaking temperature of 820 ° C at an average of 5 ° C / s. Next, after soaking at 820 ° C for 180 seconds, cool to 500 ° C at an average cooling rate of 10 ° C / s, hold at 500 ° C for 80 seconds, and then cool to room temperature. Air cooled.
- the Ar transformation point for this steel type and production conditions is 730 ° C.
- the total reduction rate at 950 ° C or less or the total reduction rate at 900 ° C or less is 20-65%
- the final temperature of hot finish rolling is 710-920 ° C
- the winding temperature is 500-670 ° C.
- the rolling reduction of cold rolling is 40-75% (sheet thickness 2.4-1.0mm)
- the average heating rate from 500 ° C to soaking temperature (820 ° C) during annealing is 0.5-45 ° C / s.
- the experiment was performed under basic conditions except for the individual conditions that were changed.
- the annealed sample had a longitudinal direction perpendicular to the rolling direction of 10 mm X
- a 120 mm test piece was cut out, and the thickness was reduced to 0.8 mm by mechanical grinding and chemical polishing to remove distortion.
- the resonance frequency of the sample was measured using a lateral vibration type internal friction measurement device.
- the Young's modulus was calculated therefrom.
- a JIS No. 5 tensile test piece was cut out in a direction perpendicular to the rolling direction with respect to the sheet subjected to the temper rolling of 0.5%, and subjected to a tensile test.
- the cross-sectional structure was observed with a scanning electron microscope (SEM) to observe the type of the structure and to take three photographs in a 30 mx 30 m field of view.
- SEM scanning electron microscope
- the mechanical property values under the basic conditions in this experiment according to the manufacturing method of the present invention were as follows: Young's modulus E: 245 GPa, TS: 800 MPa, El: 20%, ferrite phase fraction: 70%, Tensite phase fraction was 25%, and the steel sheet had excellent strength-ductility balance and high Young's modulus.
- Young's modulus E 245 GPa
- TS 800 MPa
- El 20%
- ferrite phase fraction 70%
- Tensite phase fraction was 25%
- the steel sheet had excellent strength-ductility balance and high Young's modulus.
- the ferrite phase and the martensite phase The remainder was either a bainite phase, a retained austenite phase, a pearlite phase or a cementite phase.
- the relationship between the manufacturing conditions and the Young's modulus will be described with reference to the drawings based on the results of the test investigation.
- the tensile strength was 750 to 850 MPa
- the ferrite phase fraction was 80 to 60%
- the martensite phase fraction was 17 to 40%
- the structure of the second phase was The remainder other than the martensite phase was the difference between the bainite phase, retained austenite phase, perlite phase and cementite phase.
- Fig. 1 shows the effects of the total draft below 950 ° C and the total draft below 900 ° C on the Young's modulus.
- the Young's modulus shows an excellent value of 225 GPa or more, and the total draft at 900 ° C or lower is 30% or more. In this case, the Young's modulus was more excellent at 240 GPa or more.
- FIG. 2 shows the effect of the final temperature of hot finish rolling on the Young's modulus.
- this final temperature is in the range claimed in the present invention, Ar to 900 ° C, the Young's modulus is an excellent value of 225 GPa or more.
- FIG. 3 shows the effect of the winding temperature on the Young's modulus.
- the winding temperature was 650 ° C. or lower as claimed in the present invention
- the Young's modulus showed an excellent value of 225 GPa or higher.
- FIG. 4 shows the effect of the rolling reduction in cold rolling on the Young's modulus.
- the rolling reduction was 50% or more as claimed in the present invention
- the Young's modulus showed an excellent value of 225 GPa or more.
- Fig. 5 shows the effect of the average heating rate from 500 ° C during annealing to 820 ° C, which is the soaking temperature, on the Young's modulus.
- the heating rate is l to 40 ° C / s, which is the claimed range of the present invention
- the Young's modulus shows an excellent value of 225 GPa or more, and when the heating rate is l to 30 ° C / s, However, the Young's modulus was more excellent at 240 GPa or more.
- steels B to Z and AA to BF having the components shown in Tables 2 and 3 were melted in a laboratory vacuum melting furnace, and hot-rolled, pickled, cold-rolled under the above basic conditions. Annealing was performed sequentially. Tables 4 and 5 summarize the characteristics obtained from the test survey.
- the Ar transformation point of the steels B to Z and AA to BF under the above production conditions was 650 to 760 ° C. Ma
- the remaining structure other than the ferrite phase and the martensite phase in the table was shifted from the bainite phase, the remaining austenite phase, the pearlite phase, and the cementite phase.
- N * N- (14 / 47.9) x Ti
- N * 0,
- Ti * (47.9 / 14) xN— (47.9 / 32.1)
- Ti * Ti— (47.9 / 14> xN— (47.9 / 32.1)
- N * N— (14 / 47.9) xTi, N- (14 / 47.9)
- N * N— (14 / 47.9) xTi, N- (14 / 47.9)
- Steel type AY has a Mn capacity of 0.2%, which is a large Young's modulus smaller than the claimed range of the present invention. Since the steel type AZ does not contain Nb, and the steel type BA has a small Nb content of 0.01%, the Young's modulus is smaller than the claims of the present invention.
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Abstract
Description
Claims
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AU2005227556A AU2005227556B2 (en) | 2004-03-31 | 2005-03-31 | High-rigidity high-strength thin steel sheet and method for producing same |
CA002546003A CA2546003A1 (en) | 2004-03-31 | 2005-03-31 | High-rigidity high-strength thin steel sheet and method for producing same |
US10/578,525 US20080118390A1 (en) | 2004-03-31 | 2005-03-31 | High-Stiffness High-Strength Thin Steel Sheet and Method For Producing the Same |
EP05727349.2A EP1731626B1 (en) | 2004-03-31 | 2005-03-31 | High-rigidity high-strength thin steel sheet and method for producing same |
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EP (1) | EP1731626B1 (ja) |
KR (1) | KR100881048B1 (ja) |
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2005
- 2005-03-31 AU AU2005227556A patent/AU2005227556B2/en not_active Ceased
- 2005-03-31 WO PCT/JP2005/006288 patent/WO2005095663A1/ja not_active Application Discontinuation
- 2005-03-31 EP EP05727349.2A patent/EP1731626B1/en not_active Expired - Fee Related
- 2005-03-31 CA CA002546003A patent/CA2546003A1/en not_active Abandoned
- 2005-03-31 US US10/578,525 patent/US20080118390A1/en not_active Abandoned
- 2005-03-31 TW TW094110204A patent/TW200604347A/zh not_active IP Right Cessation
- 2005-03-31 KR KR1020067014873A patent/KR100881048B1/ko active IP Right Grant
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JPH04235253A (ja) * | 1990-12-28 | 1992-08-24 | Kawasaki Steel Corp | 曲げ加工性、衝撃特性の良好な超強度冷延鋼板及びその製造方法 |
JPH11343535A (ja) * | 1998-05-29 | 1999-12-14 | Kawasaki Steel Corp | 塗装焼付硬化型高張力鋼板およびその製造方法 |
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Cited By (11)
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JP2008106352A (ja) * | 2006-09-27 | 2008-05-08 | Nippon Steel Corp | 局部延性に優れた高ヤング率高強度冷延鋼板及びその製造方法 |
JP2016141857A (ja) * | 2015-02-03 | 2016-08-08 | Jfeスチール株式会社 | 高強度鋼板、高強度めっき鋼板、高強度溶融亜鉛めっき鋼板および高強度合金化溶融亜鉛めっき鋼板、並びにそれらの製造方法 |
JP2016141858A (ja) * | 2015-02-03 | 2016-08-08 | Jfeスチール株式会社 | 高強度鋼板、高強度めっき鋼板、高強度溶融亜鉛めっき鋼板および高強度合金化溶融亜鉛めっき鋼板、並びにそれらの製造方法 |
JP2016141859A (ja) * | 2015-02-03 | 2016-08-08 | Jfeスチール株式会社 | 高強度鋼板、高強度めっき鋼板、高強度溶融亜鉛めっき鋼板および高強度合金化溶融亜鉛めっき鋼板、並びにそれらの製造方法 |
WO2016125463A1 (ja) * | 2015-02-03 | 2016-08-11 | Jfeスチール株式会社 | 高強度鋼板およびその製造方法 |
WO2016125462A1 (ja) * | 2015-02-03 | 2016-08-11 | Jfeスチール株式会社 | 高強度鋼板およびその製造方法 |
WO2016125461A1 (ja) * | 2015-02-03 | 2016-08-11 | Jfeスチール株式会社 | 高強度鋼板およびその製造方法 |
US10472697B2 (en) | 2015-02-03 | 2019-11-12 | Jfe Steel Corporation | High-strength steel sheet and production method therefor |
US10934600B2 (en) | 2015-02-03 | 2021-03-02 | Jfe Steel Corporation | High-strength steel sheet and production method therefor |
US11035019B2 (en) | 2015-02-03 | 2021-06-15 | Jfe Steel Corporation | High-strength steel sheet and production method therefor |
Also Published As
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AU2005227556A1 (en) | 2005-10-13 |
AU2005227556B2 (en) | 2008-02-14 |
KR20060134030A (ko) | 2006-12-27 |
CA2546003A1 (en) | 2005-10-13 |
EP1731626A1 (en) | 2006-12-13 |
TW200604347A (en) | 2006-02-01 |
EP1731626A4 (en) | 2007-10-31 |
EP1731626B1 (en) | 2017-07-19 |
TWI307721B (ja) | 2009-03-21 |
US20080118390A1 (en) | 2008-05-22 |
KR100881048B1 (ko) | 2009-01-30 |
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