WO2014030663A1 - 鋼材 - Google Patents
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- WO2014030663A1 WO2014030663A1 PCT/JP2013/072262 JP2013072262W WO2014030663A1 WO 2014030663 A1 WO2014030663 A1 WO 2014030663A1 JP 2013072262 W JP2013072262 W JP 2013072262W WO 2014030663 A1 WO2014030663 A1 WO 2014030663A1
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
- C21D1/20—Isothermal quenching, e.g. bainitic hardening
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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
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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
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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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
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0273—Final recrystallisation annealing
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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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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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
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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
- C22C38/04—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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
- H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
- H01F1/16—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of sheets
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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
- C21D2211/002—Bainite
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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
- C21D2211/005—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 steel material, and more specifically, to a steel material that is suitable as a material for an impact-absorbing member, in which the occurrence of cracks during impact load application is suppressed and the effective flow stress is high.
- Such high-strength steel materials include high-strength composites such as low-alloy TRIP steel, which has a high static difference (difference between static strength and dynamic strength), and multi-phase structure steel having a second phase mainly composed of martensite. Phase structure steels are known.
- Patent Document 1 discloses a work-induced transformation type high strength steel plate (TRIP steel plate) for absorbing automobile collision energy having excellent dynamic deformation characteristics.
- the following invention is disclosed regarding the multiphase steel sheet having the second phase mainly composed of martensite.
- Patent Document 2 discloses an average grain size ds of nanocrystal grains made of fine ferrite grains and having a crystal grain size of 1.2 ⁇ m or less, and an average crystal grain size dL of microcrystal grains having a crystal grain size exceeding 1.2 ⁇ m.
- a high-strength steel sheet that satisfies the relationship of dL / ds ⁇ 3, is excellent in strength and ductility balance, and has a static difference of 170 MPa or more is disclosed.
- Patent Document 3 discloses a steel sheet having a high static ratio, which is composed of a two-phase structure of martensite having an average particle diameter of 3 ⁇ m or less and martensite having an average particle diameter of 5 ⁇ m or less.
- Patent Document 4 discloses a cold-rolled steel sheet containing 75% or more of a ferrite phase having an average particle size of 3.5 ⁇ m or less, and the balance being tempered martensite and having excellent impact absorption characteristics.
- Patent Document 5 discloses a cold rolling method in which a pre-strain is applied to form a two-phase structure composed of ferrite and martensite and a static difference at a strain rate of 5 ⁇ 10 2 to 5 ⁇ 10 3 / s satisfies 60 MPa or more.
- a steel sheet is disclosed.
- Patent Document 6 discloses a high-strength hot-rolled steel sheet having excellent impact resistance properties consisting of 85% or more of a hard phase such as bainite and martensite.
- the steel material that is the material of the conventional shock absorbing member has the following problems. That is, in order to improve the impact absorption energy of an impact absorbing member (hereinafter also simply referred to as “member”), the strength of a steel material (hereinafter also simply referred to as “steel material”) that is a material of the impact absorbing member is increased. It is essential.
- the average load (F ave ) that determines the impact absorption energy is F ave ⁇ ( ⁇ Y ⁇ t 2 ) / 4
- ⁇ Y effective flow stress t: given as a plate thickness
- the impact absorption energy largely depends on the plate thickness of the steel material. Therefore, there is a limit in achieving both a reduction in the thickness of the impact absorbing member and a high impact absorbing performance by simply increasing the strength of the steel material.
- the flow stress is a stress necessary to continue the plastic deformation at the start or after the start of the plastic deformation, and the effective flow stress is applied to the member at the time of steel plate thickness, shape, and impact. It means the plastic flow stress considering the strain rate.
- the impact absorbing energy of the impact absorbing member is It also depends greatly on the shape.
- the shock absorbing energy of the shock absorbing member can be dramatically reduced to a level that cannot be achieved simply by increasing the strength of the steel material. There is a possibility that can be increased.
- the shape of the shock absorbing member is optimized so as to increase the plastic deformation work, if the steel material does not have a deformability capable of withstanding the plastic deformation work, the assumed plastic deformation is completed. Before this, the impact absorbing member is cracked at an early stage. As a result, the amount of plastic deformation work cannot be increased, and the impact absorbing energy cannot be dramatically increased. Moreover, if a crack occurs in the impact absorbing member at an early stage, an unexpected situation such as damage to other members disposed adjacent to the impact absorbing member may occur.
- the optimization of the shape of the shock absorbing member is based on the deformability of the existing steel material from the beginning.
- studies have been made to improve the deformability of the steel material and optimize the shape of the shock absorbing member so as to increase the work of plastic deformation.
- the present invention provides a steel material suitable as a material for an impact-absorbing member, which has a high effective flow stress, and therefore has a high impact absorption energy, and at the same time, is suppressed from cracking when an impact load is applied. Let it be an issue.
- the work of plastic deformation can be increased, and the work of plastic deformation can be increased while suppressing the occurrence of cracks when impact load is applied so that the shape of the shock absorbing member can be optimized. It is important to increase the effective flow stress.
- impact cracking sensitivity the sensitivity (hereinafter also referred to as “impact cracking sensitivity”) to cracking (hereinafter also referred to as “impact cracking”) at the time of impact load application increases.
- ductility can be increased by refining bainite as a main phase.
- the second phase contains one or more selected from the group consisting of ferrite, martensite and austenite. Can be improved.
- the present invention has been made on the basis of the above new findings, and the gist thereof is as follows.
- the present invention it is possible to suppress or eliminate the occurrence of cracks in the impact absorbing member when an impact load is applied, and to obtain an impact absorbing member having a high effective flow stress. It is possible to dramatically increase the absorbed energy. By applying such a shock absorbing member, it is possible to further improve the collision safety of products such as automobiles, which is extremely useful in industry.
- C more than 0.05% to 0.18% C strengthens the steel by the action of promoting the formation of bainite as the main phase and austenite as the second phase, the action of improving the yield strength and tensile strength by increasing the strength of the second phase, and solid solution strengthening. , Has the effect of improving yield strength and tensile strength. Furthermore, it combines with Ti and V to precipitate MX type fine carbides, and has the effect of improving the yield stress and the work hardening coefficient in the low strain region. If the C content is 0.05% or less, it may be difficult to obtain the effect by the above-described action. Therefore, the C content is more than 0.05%.
- the C content is 0.18% or less. Preferably it is 0.15% or less, More preferably, it is 0.13% or less. In addition, this invention includes the case where C content is 0.18%.
- Mn 1% to 3% Mn has the effect of promoting the formation of bainite by enhancing the hardenability, and the effect of strengthening the steel by solid solution strengthening and improving the yield strength and tensile strength. If the Mn content is less than 1%, it may be difficult to obtain the effect of the above action. Therefore, the Mn content is 1% or more. Preferably it is 1.5% or more. On the other hand, if the Mn content exceeds 3%, excessive martensite and austenite may be generated, which may cause a significant decrease in local ductility. Therefore, the Mn content is 3% or less. Preferably it is 2.5% or less.
- the present invention includes cases where the Mn content is 1% and 3%.
- Si more than 0.5% to 1.8% Si suppresses the formation of carbides in bainite and martensite, thereby improving the uniform ductility and local ductility, and strengthening the steel by solid solution strengthening, thereby improving the yield strength and tensile strength.
- the Si content is more than 0.5%. Preferably it is 0.8% or more, More preferably, it is 1% or more.
- the Si content exceeds 1.8%, austenite may remain excessively and the impact cracking sensitivity may be remarkably increased. Therefore, the Si content is 1.8% or less. Preferably it is 1.5% or less, More preferably, it is 1.3% or less.
- this invention includes the case where Si content is 1.8%.
- Al 0.01% to 0.5%
- Al has the effect
- the present invention includes cases where the Al content is 0.01% and 0.5%.
- N 0.001% to 0.015%
- N has the effect of suppressing the impact cracking by suppressing the grain growth of austenite and ferrite by forming nitrides and by refining the structure.
- the N content is less than 0.001%, it is difficult to obtain the effect by the above action. Therefore, the N content is 0.001% or more.
- the N content exceeds 0.015%, the nitride becomes coarse, which promotes impact cracking. Therefore, the N content is set to 0.015% or less.
- this invention includes the case where N content is 0.001% and the case of 0.015%.
- V or Ti in total or both V and Ti generate carbides such as VC and TiC in steel, and suppress the impact cracking by suppressing the coarsening of crystal grains by the pinning effect on the ferrite grain growth. Furthermore, it has the effect
- the total content of V and Ti (hereinafter, also referred to as “(V + Ti) content”) is less than 0.01%, it is difficult to obtain the effect by the above-described action. Therefore, the (V + Ti) content is set to 0.01% or more.
- the (V + Ti) content is more than 0.3%, VC or TiC is excessively generated, and the impact cracking sensitivity is increased. Therefore, the (V + Ti) content is 0.3% or less.
- the present invention includes the case where the total content of V and Ti is 0.01% and 0.3%. When only 0.01% to 0.3% of V is contained, when only 0.01% to 0.3% of Ti is contained, both V and Ti are contained in total of 0.01% to 0.3%. If you want, you can either.
- Cr 0% to 0.25%
- Cr is an optionally contained element, it has the effect of promoting the formation of bainite by enhancing the hardenability and the effect of strengthening the steel by solid solution strengthening and improving the yield strength and tensile strength.
- Cr 0.05% or more is preferable.
- the Cr content is 0.25% or less.
- this invention includes the case where content of Cr is 0.25%.
- Mo 0% to 0.35%
- Mo is an optional element, but it enhances hardenability, promotes the formation of bainite and martensite, and strengthens steel by solid solution strengthening, and improves yield strength and tensile strength.
- Mo 0.1% or more is preferable.
- the Mo content exceeds 0.35%, the martensite phase is excessively generated and the impact cracking sensitivity is increased. Therefore, when it contains Mo, the content shall be 0.35% or less.
- this invention includes the case where content of Mo is 0.35%.
- the steel material of the present invention contains the above-described essential elements, and further contains optional elements as necessary, and the balance is Fe and impurities.
- impurities include those contained in raw materials such as ore and scrap, and those contained in the production process. However, it is allowed to contain other components as long as the properties of the steel material of the present invention are not impaired.
- P and S are contained as impurities in the steel, but P and S are preferably limited as follows.
- the upper limit of P is 0.02% or less.
- the upper limit of P is 0.02%. Desirably, it is 0.015% or less.
- the upper limit of P is set to 0.005% or less.
- the upper limit of S is 0.005% on the assumption that the S content is removed within the range of realistic manufacturing processes and manufacturing costs. Desirably, it is 0.002% or less.
- the steel structure according to the present invention increases the effective flow stress by obtaining high yield strength and a high work hardening coefficient in a low strain region, and has a fine block size in order to combine impact cracking resistance.
- the main phase is bainite, and the plastic flow stress is improved by fine precipitates.
- the area ratio of bainite 80% or more If the area ratio of bainite as the main phase is less than 80%, it is difficult to ensure high yield strength. Therefore, the area ratio of bainite as the main phase is 80% or more.
- the area ratio of bainite is preferably 85% or more, more preferably more than 90%.
- Average block size of bainite less than 2.0 ⁇ m
- Ductility can be increased by refining bainite as the main phase.
- the average block size of bainite is 2.0 ⁇ m or more, it is difficult to improve ductility. Therefore, the average block size of bainite is less than 2.0 ⁇ m. This block size is preferably 1.5 ⁇ m or less.
- a total of 5% or more of one or more selected from the group consisting of ferrite, martensite, and austenite, and the average particle size of the ferrite, martensite, and bainite is less than 1.0 ⁇ m.
- the second phase contains one or more selected from the group consisting of ferrite, martensite and austenite, and when these are refined, the local ductility can be further improved. it can.
- the total area ratio of ferrite, martensite and austenite is less than 5%, or the average particle size of the entire ferrite, martensite and austenite is 1.0 ⁇ m or more, it is difficult to further improve the local ductility. Therefore, the total content of one or more selected from the group consisting of ferrite, martensite and austenite is 5% or more, and the total average particle size of the ferrite, martensite and austenite is less than 1.0 ⁇ m.
- Average nanohardness of bainite 4.0 GPa or more and 5.0 GPa or less
- a steel material having a bainite area ratio of 80% or more ensures a tensile strength of 980 MPa or more. It becomes difficult. Therefore, the average nano hardness of bainite is 4.0 GPa or more.
- the average nanohardness of bainite exceeds 5.0 GPa, it becomes difficult to suppress the occurrence of cracks when an impact load is applied. Therefore, the average nano hardness of bainite is set to 5.0 GPa or less.
- the nano hardness is a value obtained by measuring the nano hardness in the bainite block using nano indentation.
- a cube corner indenter is used, and nano hardness obtained with an indentation load of 500 ⁇ N is adopted.
- MX type carbide is a carbide having a NaCl type crystal structure, and is composed of V and / or Ti and C.
- the size of the MX type carbide that exhibits the pinning effect is 10 nm or more in terms of equivalent circle diameter. If the size of the MX type carbide is less than 10 nm in the equivalent circle diameter, the pinning effect on the movement of the grain boundary cannot be expected. Therefore, although the microstructure is refined by the presence of MX type carbide having an equivalent circle diameter of 10 nm or more, it is difficult to obtain a sufficient pinning effect if the average particle spacing exceeds 300 nm. Accordingly, it is assumed that MX type carbides having an equivalent circle diameter of 10 nm or more are present at an average particle interval of 300 nm or less.
- the lower limit of the average particle interval is not particularly defined, but it is practically 50 nm or more.
- the upper limit of the size of the MX carbide is not particularly specified, but it is preferable that the upper limit of the MX carbide size (equivalent circle diameter) is 50 nm because it is excessively coarse and may adversely affect the ductility.
- the steel material according to the present invention is characterized in that the effective flow stress is high and the impact absorption energy is high, and at the same time, the occurrence of cracks when an impact load is applied is suppressed. This feature is demonstrated by a high 5% flow stress, a high average crush load, and a high stable buckling rate in a buckling test, as shown in the examples described later.
- the 5% flow stress is preferably 700 MPa or more.
- Other mechanical properties include tensile strength of 982 MPa or more, uniform elongation (total elongation) of 7% or more, and hole expansion ratio of Japan Iron and Steel Federation Standard JFS. It can be mentioned that the measurement method according to T 1001-1996 is 120% or more and has high strength and excellent ductility and hole expansibility.
- the steel material of the present invention can be obtained, for example, by the following production methods (1) to (3).
- Manufacturing method (1) Hot rolled material (no heat treatment)
- VC and TiC are appropriately precipitated in the hot rolling process, and the coarsening of crystal grains is suppressed by the pinning effect of VC and TiC, and the thermal history is controlled. Therefore, it is preferable to optimize the multiphase structure.
- multi-pass rolling with a slab having the above chemical composition at 1200 ° C. or higher and a total rolling reduction of 50% or higher is performed, and rolling is completed in a temperature range of 800 ° C. or higher and 950 ° C. or lower.
- the steel sheet is cooled to a temperature range of 500 ° C. or less at a cooling rate of 600 ° C./second or more, and is wound in a temperature range of 300 ° C. or more to 500 ° C. or less to obtain a hot-rolled steel sheet.
- the austenite coarsens and the precipitation density of MX type carbides decreases, so that the intended steel structure cannot be obtained, and ductility and strength may decrease. is there. Furthermore, if the above cooling conditions are not satisfied, the generation of ferrite in the cooling process becomes excessive, and the block size of bainite becomes excessive, and desired impact characteristics may not be obtained.
- rapid cooling is performed at a cooling rate of 600 ° C./second or more to a temperature range of 500 ° C. or less within 0.4 seconds.
- the substantial completion of hot rolling means the pass in which substantial rolling was performed at the end among the multiple-pass rolling performed in the finish rolling of hot rolling. For example, when substantial final reduction is performed in the upstream pass of the finish rolling mill and substantial rolling is not performed in the downstream pass of the finish rolling mill, the rolling in the upstream pass is finished. Thereafter, rapid cooling is performed to a temperature range of 500 ° C. or less within 0.4 seconds. Also, for example, when substantial rolling is performed up to the downstream pass of the finish rolling mill, rapid cooling to a temperature range of 500 ° C.
- the rapid cooling is basically performed by a cooling nozzle disposed on the run-out table, but can also be performed by an inter-stand cooling nozzle disposed between each pass of the finish rolling mill.
- the pre-cooling rate (600 ° C./second or more) is based on the sample surface temperature (steel plate surface temperature) measured by the thermotracer.
- the cooling rate (average cooling rate) of the entire steel sheet is estimated to be about 200 ° C./second or more when converted from the cooling rate based on the surface temperature (600 ° C./second or more).
- Production method (2) Hot rolling, heat treated material
- VC and TiC are appropriately precipitated in the temperature raising process of the hot rolling step and the heat treatment step, It is preferable to suppress the coarsening of crystal grains by the pinning effect by VC or TiC and to optimize the multiphase structure during the heat treatment.
- multi-pass rolling with a slab having the above chemical composition at 1200 ° C. or higher and a total rolling reduction of 50% or higher is performed, and rolling is completed in a temperature range of 800 ° C. or higher and 950 ° C. or lower.
- cooling is performed at a cooling rate of 600 ° C./second or more to a temperature range of 700 ° C. or less (this cooling is also referred to as primary cooling), and then a cooling rate of less than 100 ° C./second.
- a temperature range of 500 ° C. or lower this cooling is also referred to as secondary cooling
- the substantial completion of the hot rolling is the last of the multiple-pass rolling performed in the finish rolling of the hot rolling. It means a pass where substantial rolling has been performed.
- the rapid cooling is basically performed by a cooling nozzle disposed on the run-out table, but can also be performed by an inter-stand cooling nozzle disposed between each pass of the finish rolling mill.
- the pre-cooling rate (600 ° C./second or more) is based on the sample surface temperature (steel plate surface temperature) measured by the thermotracer.
- the cooling rate (average cooling rate) of the entire steel sheet is estimated to be about 200 ° C./second or more when converted from the cooling rate based on the surface temperature (600 ° C./second or more).
- the hot-rolled steel sheet obtained by the hot rolling step is a temperature range of 850 ° C. or more and 920 ° C. or less at an average temperature increase rate of 2 ° C./second or more and 50 ° C./second or less.
- the temperature is raised to 100 ° C. for 300 seconds or less (annealing in FIG. 1).
- the sample is cooled to a temperature range of 270 ° C. or more and 390 ° C. or less at an average cooling rate of 10 ° C./second or more and 50 ° C./second or less, and heat treatment is performed in the temperature range for 10 seconds or more and 300 seconds or less (see FIG. 1). Quenching).
- the average heating rate is less than 2 ° C./second, ferrite grain growth occurs during heating, and the crystal grains become coarse.
- the average heating rate is preferably as high as possible, but practically it is 50 ° C./second or less. If the temperature held after the temperature rise is less than 850 ° C. or if the holding time is less than 100 seconds, austenitization necessary for quenching becomes insufficient, and it is difficult to obtain a target multiphase structure. Become. On the other hand, if the temperature maintained after the temperature rise is over 920 ° C. or over 300 seconds, austenite is coarsened, making it difficult to obtain a target multiphase structure.
- the holding time in the temperature range of 270 ° C. or more and 390 ° C. or less is less than 10 seconds, the promotion of the bainite transformation may be insufficient.
- the holding time in the temperature range of 270 ° C. or higher and 390 ° C. or lower exceeds 300 seconds, productivity is remarkably impaired.
- the bainite hardness may be adjusted by performing a tempering treatment in which a temperature range of 400 ° C. or more and 550 ° C. or less is maintained for 10 seconds or more and 650 seconds or less as necessary (tempering 1 in FIG. 1). 2).
- This tempering may be performed in one stage or may be performed in a plurality of stages.
- FIG. 1 shows an example in which tempering is performed in two stages.
- the tempering temperature is less than 400 ° C. or the tempering time is less than 10 seconds, the effect of tempering cannot be sufficiently obtained.
- the tempering temperature is 550 ° C. or the tempering time exceeds 650 seconds, the target strength may not be obtained due to the strength reduction.
- This tempering can be performed by two or more stages of heating within the above temperature range. In that case, it is preferable that the first stage heating temperature is lower than the second stage heating temperature.
- Production method (3) Cold rolling, heat treated material
- a hot rolling step and a heat treatment step are performed as in the production method (2). It is preferable to properly precipitate VC and TiC in the temperature rising process, suppress the coarsening of crystal grains by the pinning effect of VC and TiC, and optimize the multiphase structure during the heat treatment. For that purpose, it is preferable to manufacture by the manufacturing method provided with the following process.
- multi-pass rolling with a slab having the above chemical composition at 1200 ° C. or higher and a total rolling reduction of 50% or higher is performed, and rolling is completed in a temperature range of 800 ° C. or higher and 950 ° C. or lower.
- cooling is performed at a cooling rate of 600 ° C./second or more to a temperature range of 700 ° C. or less (this cooling is also referred to as primary cooling), and then a cooling rate of less than 100 ° C./second.
- a temperature range of 500 ° C. or lower this cooling is also referred to as secondary cooling
- the substantial completion of hot rolling refers to a multi-pass rolling performed by hot rolling finish rolling. Of these, it means the path where the final rolling was performed.
- the rapid cooling is basically performed by a cooling nozzle disposed on the run-out table, but can also be performed by an inter-stand cooling nozzle disposed between each pass of the finish rolling mill.
- the pre-cooling rate (600 ° C./second or more) is based on the sample surface temperature (steel plate surface temperature) measured by the thermotracer.
- the cooling rate (average cooling rate) of the entire steel sheet is estimated to be about 200 ° C./second or more when converted from the cooling rate based on the surface temperature (600 ° C./second or more).
- the cold rolled steel sheet obtained by the cold rolling step is heated to a temperature range of 850 ° C. or more and 920 ° C. or less at an average temperature increase rate of 2 ° C./second or more and 50 ° C./second or less. For 100 seconds to 300 seconds (annealing in FIG. 1).
- heat treatment is performed by cooling to a temperature range of 270 ° C. or more and 390 ° C. or less at an average cooling rate of 10 ° C./second or more and 50 ° C./second or less and maintaining the temperature range for 10 seconds or more and 300 seconds or less (see FIG. 1). Get in).
- the average heating rate is less than 2 ° C./second, ferrite grain growth occurs during heating, and the crystal grains become coarse.
- the average heating rate is preferably as high as possible, but practically it is 50 ° C./second or less. If the temperature held after the temperature rise is less than 850 ° C. or if the holding time is less than 100 seconds, austenitization necessary for quenching becomes insufficient, and it is difficult to obtain a target multiphase structure. Become. On the other hand, if the temperature maintained after the temperature rise is over 920 ° C. or over 300 seconds, austenite is coarsened, making it difficult to obtain a target multiphase structure.
- the holding time in the temperature range of 270 ° C. or more and 390 ° C. or less is less than 10 seconds, the promotion of the bainite transformation may be insufficient.
- the holding time in the temperature range of 270 ° C. or higher and 390 ° C. or lower exceeds 300 seconds, productivity is remarkably impaired.
- the bainite hardness is maintained by maintaining a temperature range of 400 ° C. to 550 ° C. for 10 seconds to 650 seconds as necessary. May be adjusted.
- the tempering temperature is less than 400 ° C. or the tempering time is less than 10 seconds, the effect of tempering cannot be sufficiently obtained.
- the tempering temperature is 550 ° C. or the tempering time exceeds 650 seconds, the target strength may not be obtained due to the strength reduction.
- This tempering can be performed by two or more stages of heating within the above temperature range. In that case, it is preferable that the first stage heating temperature is lower than the second stage heating temperature.
- the steel material of the present invention may be a hot-rolled steel plate or a cold-rolled steel plate manufactured by the manufacturing methods (1) to (3) in this way, or may be cut from the steel plate and used as appropriate such as bending or pressing as required. It may be processed. Further, it may be a steel plate or may be plated after processing.
- the plating may be either electroplating or hot dipping, and the plating type is not limited, but is usually zinc or zinc alloy plating.
- the slab is reheated at 1250 ° C. within 1 hour, then subjected to 4 passes of rough hot rolling using a hot rolling tester, and further subjected to 3 passes of finish hot rolling, followed by primary cooling after the completion of rolling. And secondary cooling was implemented and it was set as the hot rolled sheet steel.
- Table 2 shows the hot rolling conditions. Primary cooling and secondary cooling immediately after completion of rolling were performed by water cooling. Secondary cooling was completed at the coiling temperature in the table.
- the steel plates with test numbers 1, 2, 6, 13, 15 to 17 were not hot-rolled and kept hot.
- the other test plates 3-5, 7-12, and 14 were cold-rolled.
- the thickness of the obtained hot-rolled steel sheet or cold-rolled steel sheet was 1.6 mm.
- the steel plates with test numbers 4, 5, 9-12 and 14 were heat-treated using a continuous annealing simulator under the heat pattern shown in FIG. 1 and the conditions shown in Table 3.
- the temperature rise in the heat treatment ⁇ temperature maintenance is annealing
- the cooling after annealing is quenching
- the subsequent heat treatment is tempering for the purpose of hardness adjustment (softening).
- tempering heat treatment in a temperature range of 400 ° C. or higher and 550 ° C. or lower was performed in two stages.
- the steel plates of test numbers 3, 7, 8, and 13 were only tempered and not tempered after annealing.
- JIS No. 5 tensile test specimens were taken from the test steel sheet in the direction perpendicular to the rolling direction, and a tensile test was conducted to obtain 5% flow stress, maximum tensile strength (TS), uniform elongation (u-El). Asked.
- the 5% flow stress is a stress at the time of plastic deformation at which the strain becomes 5% in the tensile test, and is proportional to the effective flow stress, and is an index thereof.
- EBSD analysis was performed at a 1/4 depth position of the plate thickness of the cross section parallel to the rolling direction of the steel sheet to obtain an average grain size for the main phase and the second phase, and a grain interface orientation difference map was prepared.
- block size of bainite an average block size was obtained by assuming that a structural unit surrounded by an interface having an orientation difference of 15 ° or more is a bainite block and averaging the equivalent circle diameter.
- the nanohardness of bainite was determined by the nanoindentation method. After the 1/4 depth position of the thickness of the cross-section specimen taken in parallel with the rolling direction is polished with emery paper, it is subjected to mechanochemical polishing with colloidal silica, and the processed layer is removed by electrolytic polishing for use in the test. did. Nanoindentation was performed using a cube corner indenter and an indentation load of 500 ⁇ N. The indentation size at this time is 0.5 ⁇ m or less in diameter. The bainite hardness of each sample was randomly measured at 20 points, and the average nano hardness of each sample was determined.
- the austenite phase was distinguished by crystal system analysis by EBSD.
- the pro-eutectoid ferrite phase and martensite phase were separated by hardness by nanoindentation. That is, a phase having a nano hardness of less than 4 GPa is a pro-eutectoid ferrite phase, while a phase having a nano hardness of 6 GPa or more is a martensite phase, and from a two-dimensional image by an atomic force microscope attached to the nano-indentation device, The total area ratio and average particle size of these ferrite phase, martensite phase and austenite phase were determined.
- MX type carbide was identified by TEM observation using an extracted replica sample, and the average particle spacing of MX type carbide having an average particle size of 10 nm or more was calculated from a two-dimensional image of a TEM bright field image.
- a rectangular tube member was produced using the steel plate, an axial crush test was performed at an axial collision speed of 64 km / h, and the impact absorption performance was evaluated.
- the shape of the cross section perpendicular to the axial direction of the rectangular tube member was a regular octagon, and the axial length of the rectangular tube member was 200 mm.
- the plate thickness was 1.6 mm, and the length of one side of the regular octagon (the length of the straight portion excluding the curved portion of the corner) (Wp) was 25.6 mm.
- Two such square tube members were prepared for each steel plate and subjected to an axial crush test.
- the evaluation was performed based on the average load (average value of two tests) at the time of axial crushing and the stable buckling rate.
- the stable buckling rate is a ratio with respect to the total number of test specimens in which no crack occurred in the axial crush test.
- the impact absorption energy increases, the possibility of cracking during crushing increases, and as a result, the plastic deformation work cannot be increased, and the impact absorption energy may not be increased. That is, no matter how high the average crushing load (impact absorbing performance) is, if the stable buckling rate is not good, high shock absorbing performance cannot be shown.
- the steel material according to the present invention has a high average load by axial crushing of 0.38 kN / mm 2 or more. Furthermore, the stable buckling rate is 2/2, indicating good axial crushing characteristics. Further, the tensile strength was as high as 980 MPa or higher, the hole expansion rate was 122% or higher, the 5% flow stress was high as 745 MPa or higher, and the ductility was a sufficient value. Therefore, the steel material according to the present invention is suitable for use as a material for the above-described crash box, side member, center pillar, locker, and the like.
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Abstract
Description
Fave∝(σY・t2)/4
σY:有効流動応力
t:板厚
として与えられることが開示されているように、衝撃吸収エネルギーは鋼材の板厚に大きく依存する。したがって、単に鋼材を高強度化することだけでは、衝撃吸収部材について薄肉化と高衝撃吸収性能とを両立させることには限界がある。
[衝撃吸収エネルギーの向上]
(1)鋼材の衝撃吸収エネルギーを高めるには、5%の真ひずみを付与した際の有効流動応力(以下、「5%流動応力」と記載する。)を高めることが有効である。
(5)衝撃吸収部材において、衝撃荷重負荷時に割れが発生すると、衝撃吸収エネルギーが低下する。また、当該部材に隣接する他の部材を損傷させる場合もある。
質量%で、
C:0.05%超~0.18%、
Mn:1%~3%、
Si:0.5%超~1.8%、
Al:0.01%~0.5%、
N:0.001%~0.015%、
V、Tiのいずれか一方または両方:合計で0.01%~0.3%、
Cr:0%~0.25%、
Mo:0%~0.35%、
であり、
残部:Feおよび不純物であり、
面積%で、ベイナイトを80%以上含有するとともに、フェライト、マルテンサイトおよびオーステナイトからなる群から選択される1種または2種以上を合計で5%以上含有し、
前記ベイナイトの平均ブロックサイズが2.0μm未満、前記フェライト、マルテンサイトおよびオーステナイトの全体の平均粒径が1.0μm未満であり、
前記ベイナイトの平均ナノ硬さが4.0GPa~5.0GPaであり、
円相当直径が10nm以上のMX型炭化物が300nm以下の平均粒子間隔で存在する、鋼材。
質量%で、
Cr:0.05%~0.25%、
Mo:0.1%~0.35%、
からなる群から選択された1種または2種を含有する、[1]に記載の鋼材。
なお、化学組成について以下に示す「%」は、特に説明がない限り、「質量%」を意味する。
Cは、主相であるベイナイト、第2相であるオーステナイトの生成を促進する作用、第2相の強度を高めることにより降伏強度および引張強度を向上させる作用、ならびに固溶強化により鋼を強化し、降伏強度および引張強度を向上させる作用を有する。さらには、TiやVと結合してMX型の微細炭化物を析出させ、降伏応力および低歪域の加工硬化係数を向上させる作用を有する。C含有量が0.05%以下では、上記作用による効果を得ることが困難な場合がある。したがって、C含有量は0.05%超とする。一方、C含有量が0.18%を超えると、マルテンサイトやオーステナイトが過剰に生成して、衝撃荷重負荷時における割れの発生を促進する場合がある。したがって、C含有量は0.18%以下とする。好ましくは0.15%以下、さらに好ましくは0.13%以下である。なお、本発明はC含有量が0.18%の場合を含む。
Mnは、焼入れ性を高めることによりベイナイトの生成を促進する作用、固溶強化により鋼を強化し降伏強度および引張強度を向上させる作用を有する。Mn含有量が1%未満では、上記作用による効果を得ることが困難な場合がある。したがって、Mn含有量は1%以上とする。好ましくは1.5%以上である。一方、Mn含有量が3%超では、マルテンサイトやオーステナイトが過剰に生成して、局部延性の著しい低下を招く場合がある。したがって、Mn含有量は3%以下とする。好ましくは2.5%以下である。なお、本発明はMn含有量が1%の場合と3%の場合を含む。
Siは、ベイナイトやマルテンサイト中の炭化物の生成を抑制することにより、均一延性や局部延性を向上させる作用、および固溶強化により鋼を強化し、降伏強度および引張強度を向上させる作用を有する。Siの含有量が0.5%以下では、上記作用による効果を得ることが困難な場合がある。したがって、Si量は0.5%超とする。好ましくは0.8%以上、さらに好ましくは1%以上である。一方、Si含有量が1.8%を超えると、オーステナイトが過剰に残留し、衝撃割れ感受性が著しく高くなる場合がある。したがって、Si含有量は1.8%以下とする。好ましくは1.5%以下、さらに好ましくは1.3%以下である。なお、本発明はSi含有量が1.8%の場合を含む。
Alは、脱酸により鋼中の介在物の生成を抑制し、衝撃割れを防止する作用がある。Al含有量が0.01%未満では上記作用による効果を得ることが困難である。したがって、Al含有量は0.01%以上とする。一方、Al含有量が0.5%超では、酸化物や窒化物が粗大化し、かえって衝撃割れを助長する。したがって、Al含有量は0.5%以下とする。なお、本発明はAl含有量が0.01%の場合と0.5%の場合を含む。
Nは、窒化物を生成することにより、オーステナイトやフェライトの粒成長を抑制し、組織を微細化することにより、衝撃割れを抑制する作用を有する。N含有量が0.001%未満では、上記作用による効果を得ることが困難である。したがって、N含有量は0.001%以上とする。一方、N含有量が0.015%超では、窒化物が粗大化してしまい、却って衝撃割れを助長する。したがって、N含有量は0.015%以下とする。なお、本発明はN含有量が0.001%の場合と0.015%の場合を含む。
VおよびTiは、VCやTiCなどの炭化物を鋼中に生成し、フェライトの粒成長に対するピンニング効果により結晶粒の粗大化を抑制して、衝撃割れを抑制する作用を有する。さらに、VCやTiCによる析出強化により鋼を強化し、降伏強度および引張強度を向上させる作用を有する。したがって、V、Tiのいずれか一方または両方を含有させる。VとTiの合計含有量(以下、「(V+Ti)含有量」ともいう。)が0.01%未満では、上記作用による効果を得ることが困難である。したがって、(V+Ti)含有量は0.01%以上とする。一方、(V+Ti)含有量が0.3%超では、VCまたはTiCが過剰に生成してしまい、かえって衝撃割れ感受性を高める。したがって、(V+Ti)含有量は0.3%以下とする。本発明はVとTiの合計の含有量が0.01%の場合と0.3%の場合を含む。Vのみを0.01%~0.3%含有する場合、Tiのみを0.01%~0.3%含有する場合、VとTiの両方を合計で0.01%~0.3%含有する場合、のいずれでも良い。
Crは任意含有元素であるが、焼き入れ性を高めることによりベイナイトの生成を促進する作用、および固溶強化により鋼を強化し、降伏強度および引張強度を向上させる作用を有する。これらの作用をより確実に得るにはCr:0.05%以上であることが好ましい。しかし、Cr含有量が0.25%を超えると、マルテンサイト相が過剰に生成し、衝撃割れ感受性を高める。したがって、Cr含有量は0.25%以下とする。なお、本発明はCrの含有量が0.25%の場合を含む。
Crと同様に、Moは任意含有元素であるが、焼き入れ性を高め、ベイナイトやマルテンサイトの生成を促進する作用、および固溶強化により鋼を強化し、降伏強度および引張強度を向上させる作用を有する。これらの作用をより確実に得るにはMo:0.1%以上であることが好ましい。しかし、Mo含有量が0.35%を超えると、マルテンサイト相が過剰に生成し、衝撃割れ感受性を高める。したがって、Moを含有する場合は、その含有量は0.35%以下とする。なお、本発明はMoの含有量が0.35%の場合を含む。
Pは、粒界を脆弱にし、熱間加工性の悪化を招く。そこで、Pの上限は0.02%以下とする。P含有量は少なければ少ないほど望ましいが、現実的な製造工程と製造コストの範囲内で脱Pすることを前提にすれば、Pの上限は0.02%である。望ましくは0.015%以下である。
Sは、粒界を脆弱にし、熱間加工性や延性の劣化を招く。そこで、Pの上限は0.005%以下とする。S含有量は少なければ少ないほど望ましいが、現実的な製造工程と製造コストの範囲内で脱Sすることを前提にすれば、Sの上限は0.005%である。望ましくは0.002%以下である。
本発明に係る鋼組織は、高い降伏強度と低ひずみ域での高い加工硬化係数とを得ることで有効流動応力を高め、且つ、耐衝撃割れ性を兼ね備えるために、ブロックサイズが微細なベイナイトを主相とし、さらに、微細析出物により塑性流動応力を向上させる。
主相であるベイナイトの面積率が80%未満では、高い降伏強度を確保することが困難でとなる。したがって、主相であるベイナイトの面積率は80%以上とする。ベイナイトの面積率は好ましくは85%以上であり、より好ましくは90%超である。
主相であるベイナイトを微細化することにより延性を高めることができる。ベイナイトの平均ブロックサイズが2.0μm以上では、延性を向上させることが困難である。したがって、ベイナイトの平均ブロックサイズは2.0μm未満とする。このブロックサイズは好ましくは1.5μm以下である。
ベイナイトを主相とする鋼材において、第2相をフェライト、マルテンサイトおよびオーステナイトからなる群から選択される1種または2種以上を含むものとし、これらの微細化を図ると局部延性をさらに向上させることができる。フェライト、マルテンサイトおよびオーステナイトの合計面積率が5%未満、もしくは、フェライト、マルテンサイトおよびオーステナイトの全体の平均粒径が1.0μm以上であると、局部延性をさらに向上させることが困難である。したがって、フェライト、マルテンサイトおよびオーステナイトからなる群から選択される1種または2種以上を合計で5%以上含有し、かつ、前記フェライト、マルテンサイトおよびオーステナイトの全体の平均粒径を1.0μm未満とする。
ベイナイトの平均ナノ硬さが4.0GPa未満では、ベイナイト面積率が80%以上である鋼材において980MPa以上の引張強度を確保することが困難となる。したがって、ベイナイトの平均ナノ硬さは4.0GPa以上とする。一方、ベイナイトの平均ナノ硬さが5.0GPa超では、衝撃荷重負荷時における割れの発生を抑制することが困難となる。したがって、ベイナイトの平均ナノ硬さは5.0GPa以下とする。
ベイナイトを主相とする鋼材において、第2相の析出サイトは旧オーステナイト粒界であり、第2相の微細化のためには、オーステナイト粒の微細化が必要である。オーステナイト粒微細化の方法を種々検討した結果、後述するように、好適な熱間圧延条件や熱処理条件を採用して、MX型炭化物によるピンニング効果を図ることにより、結晶粒の粗大化が大幅に抑制されることが明らかとなった。
本発明に係る鋼材は、有効流動応力が高く、衝撃吸収エネルギーが高いと同時に、衝撃荷重負荷時における割れの発生が抑制されている点に特徴を有する。この特徴は、後述する実施例に示すように、5%流動応力が高いこと、平均圧潰荷重が高いこと、及び座屈試験における安定座屈率が高いことにより実証される。5%流動応力は700MPa以上であることが好ましい。
T 1001-1996に準じた測定法で120%以上と、高強度で延性及び穴広げ性に優れていることが挙げられる。
本発明の鋼材は、例えば以下の製造方法(1)~(3)によって得ることができる。
熱間圧延ままで本発明の鋼材を得るには、熱間圧延工程においてVCやTiCを適正に析出させ、VCやTiCによるピンニング効果により結晶粒の粗大化を抑制するとともに、熱履歴を制御することにより複相組織の最適化を図ることが好ましい。
熱間圧延後に熱処理を施して本発明の鋼材を得るには、熱間圧延工程および熱処理工程の昇温過程においてVCやTiCを適正に析出させ、VCやTiCによるピンニング効果により結晶粒の粗大化を抑制するとともに、熱処理中に複相組織の最適化を図ることが好ましい。
熱間圧延と冷間圧延の後に熱処理を施して本発明の鋼材を得るには、製造方法(2)と同様に、熱間圧延工程および熱処理工程の昇温過程においてVCやTiCを適正に析出させ、VCやTiCによるピンニング効果により結晶粒の粗大化を抑制するとともに、熱処理中に複相組織の最適化を図ることが好ましい。そのためには下記工程を備える製造方法により製造することが好ましい。
まず、供試鋼板から、圧延方向と垂直方向にJIS5号引張試験片を採取し、引張試験を行うことにより、5%流動応力、最大引張強さ(TS)、一様伸び(u-El)を求めた。5%流動応力とは、引張試験において歪みが5%となる塑性変形時の応力であり、有効流動応力と比例関係にあり、その指標となる。
T 1001-1996に準じて穴拡げ試験を行い、穴拡げ率を求めた。
Claims (2)
- 質量%で、
C:0.05%超~0.18%、
Mn:1%~3%、
Si:0.5%超~1.8%、
Al:0.01%~0.5%、
N:0.001%~0.015%、
V、Tiのいずれか一方または両方:合計で0.01%~0.3%、
Cr:0%~0.25%、
Mo:0%~0.35%、
であり、
残部:Feおよび不純物であり、
面積%で、ベイナイトを80%以上含有するとともに、フェライト、マルテンサイトおよびオーステナイトからなる群から選択される1種または2種以上を合計で5%以上含有し、
前記ベイナイトの平均ブロックサイズが2.0μm未満、前記フェライト、マルテンサイトおよびオーステナイトの全体の平均粒径が1.0μm未満であり、
前記ベイナイトの平均ナノ硬さが4.0GPa~5.0GPaであり、
円相当直径が10nm以上のMX型炭化物が300nm以下の平均粒子間隔で存在する、鋼材。 - 質量%で、
Cr:0.05%~0.25%、
Mo:0.1%~0.35%、
からなる群から選択された1種または2種を含有する、請求項1に記載の鋼材。
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JP2014510327A JP5610102B2 (ja) | 2012-08-21 | 2013-08-21 | 鋼材 |
PL13831018T PL2889395T3 (pl) | 2012-08-21 | 2013-08-21 | Materiał stalowy |
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CN201380043201.3A CN104583444B (zh) | 2012-08-21 | 2013-08-21 | 钢材 |
KR1020157001858A KR101657017B1 (ko) | 2012-08-21 | 2013-08-21 | 강재 |
CA2880617A CA2880617C (en) | 2012-08-21 | 2013-08-21 | Steel material |
EP13831018.0A EP2889395B1 (en) | 2012-08-21 | 2013-08-21 | Steel material |
ES13831018.0T ES2650487T3 (es) | 2012-08-21 | 2013-08-21 | Material de acero |
BR112015002778A BR112015002778B1 (pt) | 2012-08-21 | 2013-08-21 | material de aço |
US14/400,301 US9994942B2 (en) | 2012-08-21 | 2013-08-21 | Steel material |
MX2015001911A MX369196B (es) | 2012-08-21 | 2013-08-21 | Material de acero. |
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EP (1) | EP2889395B1 (ja) |
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WO2020179387A1 (ja) * | 2019-03-07 | 2020-09-10 | 日本製鉄株式会社 | 熱延鋼板およびその製造方法 |
JP2021031703A (ja) * | 2019-08-20 | 2021-03-01 | 日本製鉄株式会社 | 薄鋼板及びその製造方法 |
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Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
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WO2020179387A1 (ja) * | 2019-03-07 | 2020-09-10 | 日本製鉄株式会社 | 熱延鋼板およびその製造方法 |
JPWO2020179387A1 (ja) * | 2019-03-07 | 2021-03-11 | 日本製鉄株式会社 | 熱延鋼板およびその製造方法 |
JP2021031703A (ja) * | 2019-08-20 | 2021-03-01 | 日本製鉄株式会社 | 薄鋼板及びその製造方法 |
JP7389322B2 (ja) | 2019-08-20 | 2023-11-30 | 日本製鉄株式会社 | 薄鋼板及びその製造方法 |
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IN2014DN09672A (ja) | 2015-07-31 |
US9994942B2 (en) | 2018-06-12 |
JP5610102B2 (ja) | 2014-10-22 |
ES2650487T3 (es) | 2018-01-18 |
KR20150029718A (ko) | 2015-03-18 |
TWI486460B (zh) | 2015-06-01 |
CA2880617A1 (en) | 2014-02-27 |
MX2015001911A (es) | 2015-06-05 |
US20150098857A1 (en) | 2015-04-09 |
JPWO2014030663A1 (ja) | 2016-07-28 |
EP2889395B1 (en) | 2017-10-04 |
RU2599317C1 (ru) | 2016-10-10 |
MX369196B (es) | 2019-10-31 |
EP2889395A4 (en) | 2016-05-11 |
BR112015002778A2 (pt) | 2017-07-04 |
TW201418482A (zh) | 2014-05-16 |
CA2880617C (en) | 2017-04-04 |
CN104583444A (zh) | 2015-04-29 |
ZA201409300B (en) | 2015-12-23 |
KR101657017B1 (ko) | 2016-09-12 |
PL2889395T3 (pl) | 2018-03-30 |
EP2889395A1 (en) | 2015-07-01 |
BR112015002778B1 (pt) | 2020-04-22 |
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