WO2013160938A1 - Tôle d'acier laminé à froid à haute résistance présentant une excellente ductilité et son procédé de fabrication - Google Patents

Tôle d'acier laminé à froid à haute résistance présentant une excellente ductilité et son procédé de fabrication Download PDF

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Publication number
WO2013160938A1
WO2013160938A1 PCT/JP2012/002807 JP2012002807W WO2013160938A1 WO 2013160938 A1 WO2013160938 A1 WO 2013160938A1 JP 2012002807 W JP2012002807 W JP 2012002807W WO 2013160938 A1 WO2013160938 A1 WO 2013160938A1
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Prior art keywords
phase
annealing
martensite
strength
volume fraction
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PCT/JP2012/002807
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English (en)
Japanese (ja)
Inventor
英尚 川邉
横田　毅
瀬戸　一洋
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Ｊｆｅスチール株式会社
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Priority to PCT/JP2012/002807 priority Critical patent/WO2013160938A1/fr
Publication of WO2013160938A1 publication Critical patent/WO2013160938A1/fr

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Classifications

    • 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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—Final recrystallisation annealing
    • 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
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • 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
    • C21D1/26—Methods of annealing
    • 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
    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—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
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • 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

Definitions

  • the present invention relates to a high-strength cold-rolled steel sheet suitable for use in automobile parts and the like that are required to be press-formed into a strict shape, and a method for producing the same, and in particular, actively uses expensive elements such as Cu, Ni, Cr, and Mo.
  • TS tensile strength
  • high-strength steel sheets of TS: 1180 MPa class or higher were often applied to light-worked parts, but recently, application to press parts with complex shapes has been studied.
  • steel sheets tend to have lower workability as the strength increases. Further, when the strength is increased to TS: 1180 MPa class or higher, the amount of additive elements such as C and Mn increases, and the weldability may be significantly reduced. This tendency is particularly strong in C. On the other hand, if it is difficult to contain a large amount of C, Si, or Mn from the viewpoints of weldability and chemical conversion properties, extremely expensive rare elements such as Nb, Cu, Ni, Cr, and Mo are required from the viewpoint of securing strength. May be positively added. Therefore, it is required to achieve both strength and formability with an alloy component that is low in content from the viewpoint of weldability and inexpensive from the economical aspect.
  • Patent Documents 1 to 4 disclose that high-strength cold-rolled steel is utilized by utilizing retained austenite by limiting steel components and structures, optimizing hot-rolling conditions, and annealing conditions. A technique for obtaining a rolled steel sheet is disclosed.
  • Patent Document 1 is mainly composed of tempered martensite obtained by performing tempering treatment after cooling to room temperature once in the annealing process, so that the volume fraction of retained austenite is small and sufficient ductility is achieved. Therefore, there is a problem that it cannot be applied to strict molding.
  • the base metal structure is mainly tempered martensite or bainite in which many carbides and dislocations exist in grains that are disadvantageous for ductility, the volume fraction of retained austenite is low. Since there are many, the component from which the outstanding ductility is obtained is disclosed. However, the content of C which is disadvantageous to weldability is large, and there remains a problem in that it is necessary to contain a large amount of expensive Cu and Ni.
  • Patent Document 3 has a problem in chemical conversion treatment property and post-coating corrosion resistance because the Cr content is essential, and there is a low volume fraction of retained austenite, which is a high dislocation density disadvantageous for ductility. There was a problem that excellent ductility could not be obtained due to the large volume fraction of nittic ferrite and martensite.
  • the technique described in Patent Document 4 needs to contain a large amount of C, which is disadvantageous for weldability, and has a high volume fraction of bainitic ferrite and martensite, which is disadvantageous for ductility. Therefore, excellent ductility is obtained. There was no problem.
  • the present invention advantageously solves the above-mentioned problems, reduces the content of C and Al, which are undesirable for weldability, and positively adds expensive elements such as Nb, Cu, Ni, Cr, and Mo.
  • the object is to provide a cold-rolled steel sheet together with its advantageous production method.
  • the gist configuration of the present invention is as follows. (1) In mass%, C: 0.16-0.20% Si: 1.0-2.0% Mn: 2.5-3.5% P: 0.030% or less, S: 0.0050% or less, Al: 0.005-0.1%, N: 0.01% or less, Ti: 0.001 to 0.050% and B: 0.0001 to 0.0050% And the balance has a component composition consisting of Fe and inevitable impurities, with a volume fraction, Ferrite phase: 40-65%, Martensite phase: 30-55% and residual austenite phase: 5-15% With a structure satisfying 0.5 to 5.0 martensite phases per unit area: 1 ⁇ m 2 in the cross section in the rolling direction, and having a tensile strength of 1180 MPa or more, high strength with excellent ductility Cold rolled steel sheet.
  • a high-strength cold-rolled steel sheet having excellent ductility and a tensile strength of 1180 MPa or more can be obtained without containing an expensive alloy element.
  • the high-strength cold-rolled steel sheet obtained by the present invention is suitable as an automobile part that is press-formed into a particularly severe shape.
  • the present invention will be specifically described below.
  • the inventors have obtained a volume fraction in a component system that is low C and does not contain Nb, Cu, Ni, Cr, or Mo. It has been found that the ductility is remarkably improved by forming a structure containing 40 to 65% ferrite phase, 30 to 55% martensite phase and 5 to 15% residual austenite phase.
  • the unit of the element content in the steel sheet is “mass%”, but hereinafter, it is simply indicated by “%” unless otherwise specified.
  • C 0.16-0.20%
  • C is an element indispensable for forming a low-temperature transformation phase that contributes to securing the strength. If the amount of C is less than 0.16%, it is difficult to secure a desired steel sheet, and a desired amount of retained austenite cannot be obtained.
  • the C content exceeds 0.20%, not only the spot weldability is remarkably deteriorated, but also the low temperature transformation phase is excessively hardened, resulting in a decrease in formability. Therefore, the C content is in the range of 0.16 to 0.20%.
  • Si 1.0-2.0%
  • Si is an element that can be increased in strength without deteriorating elongation. Moreover, it has the effect
  • the Si content exceeds 2.0%, austenite formation is inhibited. Therefore, the Si content is in the range of 1.0 to 2.0%. The range is preferably 1.1 to 1.8%, more preferably 1.2 to 1.6%.
  • Mn 2.5-3.5%
  • Mn is an austenite stabilizing element and an essential element for obtaining a predetermined amount of retained austenite.
  • the content of 2.5% or more is necessary, but if it exceeds 3.5%, slab cracking occurs. Therefore, the Mn content is in the range of 2.5 to 3.5%. Preferably it is 2.6 to 3.0% of range.
  • P 0.030% or less P is preferably reduced as much as possible because P promotes grain boundary fracture by grain boundary segregation and adversely affects spot weldability, but 0.030% is acceptable. However, excessively reducing the amount of P lowers the production efficiency in the steel making process and increases the cost, so the lower limit of the amount of P is preferably about 0.001%.
  • S 0.0050% or less
  • S is a sulfide-based inclusion such as MnS in steel and is a starting point of cracking during stretch flange forming, which deteriorates formability. Therefore, it is preferable to reduce S as much as possible. Up to 0.0050% is acceptable. Preferably it is 0.0030% or less. However, excessive reduction of the amount of S is industrially difficult, and increases the desulfurization cost in the steel making process, so the lower limit of the amount of S is preferably about 0.0001%.
  • Al 0.005-0.1%
  • Al is used as a deoxidizer.
  • the Al amount needs to be 0.005% or more.
  • the Al amount exceeds 0.1%, the formability deteriorates due to an increase in inclusions such as alumina. Therefore, the Al content is in the range of 0.005 to 0.1%. Preferably it is 0.02 to 0.06% of range.
  • N 0.01% or less N combines with B to form BN, consumes B, and lowers the hardenability of solute B. Moreover, since it exists as an impurity element in ferrite and lowers the ductility by strain aging, it is preferable that the content is small, but an N content of up to 0.01% is acceptable. However, excessive reduction of the amount of N causes an increase in denitrification costs in the steelmaking process, so the lower limit of the amount of N is preferably about 0.0001%. More preferably, it is in the range of 0.0010 to 0.0050%.
  • Ti 0.001 to 0.050%
  • Ti is an element necessary for suppressing the formation of BN and expressing the hardenability by B by strongly fixing N as TiN.
  • Ti combines with C and N in steel to form fine carbides and nitrides, thereby suppressing the coarsening of crystal grains during heating, and the hot rolled sheet structure and the steel sheet structure after annealing Contributes effectively to uniform fine grains.
  • 0.001% or more of Ti is required.
  • the Ti content exceeds 0.050%, these effects tend to saturate. Ti precipitates are generated excessively, reducing the ductility of the ferrite phase, further hardening the hot-rolled sheet, and increasing the rolling load during hot rolling and cold rolling. Therefore, the Ti content is in the range of 0.001 to 0.050%. Preferably it is 0.005 to 0.025% of range.
  • B 0.0001-0.0050%
  • B is an element effective for enhancing hardenability, securing martensite, and achieving high strength.
  • the B amount needs to be 0.0001% or more.
  • the amount of B exceeds 0.0050%, the above effect is saturated. Therefore, the B amount is in the range of 0.0001 to 0.0050%. Preferably it is 0.0005 to 0.0020% of range.
  • components other than those described above are Fe and inevitable impurities. However, as long as the effects of the present invention are not impaired, the inclusion of components other than those described above is not rejected.
  • Ferrite phase volume fraction 40-65%
  • the ferrite phase is softer and more ductile than the hard martensite phase with high dislocation density, which is a low-temperature transformation phase from austenite, the bainite phase with carbides precipitated in the grains, and the bainitic ferrite with high dislocation density. It contributes to the improvement. In order to obtain this effect, it is necessary to contain 40% or more of a ferrite phase. On the other hand, if the ferrite phase is present in a volume fraction exceeding 65%, it is difficult to ensure a tensile strength of 1180 MPa or more.
  • the ferrite phase is in the range of 40 to 65% in volume fraction.
  • Martensite volume fraction 30-55%
  • the martensite phase contributes to the improvement of strength.
  • the volume fraction of the martensite phase exceeds 55%, it is preferable from the viewpoint of securing the strength, but it is difficult to secure a desired amount of ferrite phase and residual austenite phase that contribute to ductility. Therefore, the volume fraction of the martensite phase is in the range of 30 to 55%.
  • volume fraction of retained austenite phase 5-15%
  • the retained austenite phase is a structure that contributes to improvement of ductility by strain-induced transformation.
  • it is necessary to contain a residual austenite phase with a volume fraction of 5% or more.
  • the volume fraction of the retained austenite phase is 5 to 15%.
  • the number of martensite phases is less than 0.5 / ⁇ m 2 , there are few martensite phases and the tensile strength (TS) is insufficient, or coarse martensite phases are connected and present in high TS. The El will be lowered.
  • the martensite phase exists in the vicinity and the martensite phase surrounds the ferrite phase, so that the ferrite phase deforms and contributes to ductility. It becomes difficult. Accordingly, the number of martensite phases is in the range of 0.5 to 5.0 / ⁇ m 2 .
  • a steel slab having the above composition is annealed at 800 to 950 ° C, cooled to a cooling stop temperature of 200 to 500 ° C, then reheated to 750 to 850 ° C, and then an average cooling rate of 5 to 50 ° C / sec. Then, cool to the cooling stop temperature range of 350-450 ° C and let it stay in this temperature range for 100-1000 seconds.
  • the high-strength cold-rolled steel sheet which is the object of the present invention is obtained by such a production method, the obtained steel sheet may be subjected to skin pass rolling.
  • the process before hot finish rolling may be performed according to a conventional method.
  • a steel slab obtained by melting and casting steel prepared in the above component composition range can be used.
  • a steel slab obtained by melting and casting steel prepared in the above component composition range can be used.
  • not only continuous casting slabs and ingot-bundling slabs, but also thin slabs with a thickness of about 50 to 100 mm can be used.
  • direct heating without reheating is possible. It can use for a hot rolling process.
  • Hot rolling and cold rolling are not particularly limited, and may be performed according to a conventionally known method.
  • hot rolling may be performed at a hot rolling temperature of 850 to 950 ° C., wound at 450 to 650 ° C., and then cold rolled at a rolling reduction of 30 to 60%.
  • annealing is performed.
  • this annealing step is important, and the annealing is performed in two stages.
  • Annealing temperature 800-950 ° C
  • the annealing temperature in the first annealing is lower than 800 ° C.
  • the volume fraction of the ferrite phase increases during annealing, and the structure obtained after the first annealing becomes a structure mainly composed of a soft ferrite phase.
  • the enrichment of C in the austenite is not promoted, and a predetermined martensite phase and residual austenite cannot be obtained. As a result, it becomes difficult to secure a tensile strength of 1180 MPa or more.
  • the annealing temperature in the first annealing is in the range of 800 to 950 ° C. More preferably, it is in the range of 820 to 900 ° C.
  • Cooling stop temperature 200-500 ° C
  • the structure obtained after the first annealing becomes a structure containing mainly a bainite phase and a small amount of ferrite phase, and the formation of the ferrite phase is suppressed during the second annealing.
  • the volume fraction of the site phase becomes excessive and the TS increases, the ductility (El) decreases.
  • the cooling stop temperature after the first annealing is lower than 200 ° C.
  • the structure obtained after the first annealing is a structure mainly composed of martensite phase, and the formation of the ferrite phase is also suppressed during the second annealing.
  • the cooling stop temperature of the first annealing is set to 200 to 500 ° C. Also, if there is a lot of retained austenite after the first annealing, the second annealing will further promote the concentration of C in the austenite and promote the formation of retained austenite, so the cooling of the first annealing is stopped.
  • the temperature is preferably 350 to 450 ° C. at which the formation of retained austenite is promoted.
  • the cooling rate to the cooling stop temperature is not particularly limited, but is preferably about 10 to 50 ° C./second. Further, after the cooling is stopped, reheating may be continued, or after cooling to room temperature by cooling (air cooling), reheating may be performed.
  • Re-annealing temperature 750-850 ° C
  • the annealing temperature in the second annealing is set in the range of 750 to 850 ° C. More preferably, it is in the range of 770 to 830 ° C.
  • Average cooling rate 5 to 50 ° C./second
  • the cooling rate after the second annealing is important for obtaining a low temperature transformation phase having a desired volume fraction, and if the average cooling rate is lower than 5 ° C./second, The volume fraction of the ferrite phase generated in the process becomes too large, and it becomes difficult to secure a tensile strength of 1180 MPa or more.
  • the average cooling rate exceeds 50 ° C./second, the formation of the ferrite phase during cooling is suppressed, and the volume fraction of the martensite phase, which is a low-temperature transformation phase, increases from the austenite phase during annealing. It is easy to secure the 1180 MPa class, but the ductility decreases.
  • the average cooling rate after the second annealing is in the range of 5 to 50 ° C./second. More preferably, it is in the range of 10 to 35 ° C./second.
  • the cooling in this case is preferably gas cooling, but other methods such as furnace cooling, mist cooling, roll cooling, and water cooling can be used, or a combination thereof can also be used. .
  • Cooling stop temperature 350-450 ° C Since the low temperature transformation phase from austenite becomes harder as the transformation temperature is lower, the steel plate residence temperature after cooling is stopped is important for controlling the strength of the low temperature transformation phase.
  • the cooling stop temperature after the second annealing is lower than 350 ° C, it is cooled to a low temperature, so the low-temperature transformation phase is mainly a hard martensite phase, and it is easy to secure TS: 1180 MPa class, but the ductility is descend.
  • the cooling stop temperature after the second annealing is higher than 450 ° C., although the retained austenite phase is generated, the formation of the ferrite phase does not proceed, so that it becomes difficult to obtain excellent ductility.
  • the volume fraction of the martensite phase and the ferrite phase is controlled to ensure a tensile strength of 1180 MPa or more, while ensuring the desired volume fraction of the retained austenite phase and excellent ductility.
  • the cooling stop temperature after the second annealing must be in the range of 350 to 450 ° C.
  • Residence time at 350 to 450 ° C 100 to 1000 seconds Cooling stop temperature after the second annealing: If the residence time at 350 to 450 ° C is less than 100 seconds, it is difficult to obtain the desired retained austenite volume fraction In the cooling process to room temperature after residence, the untransformed austenite phase becomes the martensite phase, and the volume fraction of the martensite phase becomes excessive. As a result, the strength is increased, but the ductility is lowered. On the other hand, when retained for more than 1000 seconds, the formation of a retained austenite phase proceeds, so that ductility is improved, but it becomes difficult to obtain a tensile strength of 1180 MPa or more. Therefore, in order to secure a tensile strength of 1180 MPa or more and to obtain excellent ductility, the residence time at 350 to 450 ° C. needs to be in the range of 100 to 1000 seconds. The range is preferably 200 to 800 seconds.
  • Examples of the means for holding the steel sheet after stopping the cooling in the residence temperature range include a means for adjusting the temperature of the steel sheet to the residence temperature by providing a heat retaining device or the like in the downstream process of the cooling equipment after annealing. .
  • the steel plate after a residence is cooled to desired temperature by the conventionally well-known arbitrary methods.
  • the cold-rolled steel sheet finally obtained may be subjected to temper rolling (skin pass rolling) for the purpose of shape correction or surface roughness adjustment. Therefore, the crystal grains are expanded to form a rolled structure, and the ductility may be reduced. Therefore, the rolling reduction of skin pass rolling is preferably about 0.05% to 0.5%.
  • the volume fraction of the ferrite phase is the occupation of the phase existing in a square area of 10 ⁇ m ⁇ 10 ⁇ m square arbitrarily set by image analysis using a cross-sectional structure photograph of 1000 times magnification and cross-sectional SEM photographs of 1000 times and 3000 times The area was determined and used as the volume fraction of the ferrite phase.
  • the amount of retained austenite was determined by X-ray diffraction using Mo K ⁇ rays.
  • the volume fraction of the retained austenite phase was calculated.
  • the volume fraction of each phase is first distinguished from the ferrite phase and the low temperature transformation phase, first the volume fraction of the ferrite phase is determined, then the volume fraction of the residual austenite phase is determined by X-rays, and the remaining volume The fraction was judged as the martensite phase.
  • the number of martensite phases was determined by using a cross-sectional SEM photograph of 3000 times the number of martensite phases present in an arbitrarily set 10 ⁇ m ⁇ 10 ⁇ m square area, and this was taken as the number of martensite phases. .
  • the volume of each of the ferrite phase, martensite phase and residual austenite phase is reduced without reducing the amount of C in the steel sheet and actively including expensive elements such as Nb, Cu, Ni, Cr, Mo and V.
  • the fraction it is possible to obtain a high-strength cold-rolled steel sheet that is inexpensive and has excellent ductility and has a tensile strength (TS) of 1180 MPa or more.
  • TS tensile strength
  • the high-strength cold-rolled steel sheet of the present invention is also suitable for applications that require strict dimensional accuracy and workability, such as in the field of architecture and home appliances, in addition to automobile parts.

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  • Physics & Mathematics (AREA)
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Abstract

L'invention porte sur une tôle d'acier laminé à froid à haute résistance présentant une résistance à la traction supérieure ou égale à 1180 MPa et une excellente ductilité, du fait que la tôle d'acier a une composition contenant, en % en masse, 0,16-0,20 % de C, 1,0-2,0 % de Si, 2,5-3,5 % de Mn, 0,030 % ou moins de P, 0,0050 % ou moins de S, 0,005-0,1 % d'Al, 0,01 % ou moins de N, 0,001-0,050 % de Ti et 0,0001-0,0050 % de B, le reste étant obtenu à partir de Fe et d'impuretés inévitables, comprenant, en pourcentage en volume, 40-65 % de phase de type ferrite, 30-55 % de phase de type martensite et 5-15 % de phase de type austénite résiduelle et ayant une structure dans laquelle le nombre de phases de type martensite pour une unité de surface de 1 µm2 dans une section transversale dans la direction du laminage est de 0,5-5,0.
PCT/JP2012/002807 2012-04-24 2012-04-24 Tôle d'acier laminé à froid à haute résistance présentant une excellente ductilité et son procédé de fabrication WO2013160938A1 (fr)

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PCT/JP2012/002807 WO2013160938A1 (fr) 2012-04-24 2012-04-24 Tôle d'acier laminé à froid à haute résistance présentant une excellente ductilité et son procédé de fabrication

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008169475A (ja) * 2006-12-11 2008-07-24 Kobe Steel Ltd 高強度薄鋼板
JP2011047042A (ja) * 2009-07-29 2011-03-10 Jfe Steel Corp 化成処理性に優れた高強度冷延鋼板の製造方法

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008169475A (ja) * 2006-12-11 2008-07-24 Kobe Steel Ltd 高強度薄鋼板
JP2011047042A (ja) * 2009-07-29 2011-03-10 Jfe Steel Corp 化成処理性に優れた高強度冷延鋼板の製造方法

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