WO2013179497A1 - Tôle en acier laminée à froid haute résistance à faible rapport de limite d'élasticité présentant un excellent allongement et une excellente formabilité de bord tombé, et son procédé de fabrication - Google Patents

Tôle en acier laminée à froid haute résistance à faible rapport de limite d'élasticité présentant un excellent allongement et une excellente formabilité de bord tombé, et son procédé de fabrication Download PDF

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WO2013179497A1
WO2013179497A1 PCT/JP2012/064735 JP2012064735W WO2013179497A1 WO 2013179497 A1 WO2013179497 A1 WO 2013179497A1 JP 2012064735 W JP2012064735 W JP 2012064735W WO 2013179497 A1 WO2013179497 A1 WO 2013179497A1
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steel sheet
martensite
yield ratio
strength
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PCT/JP2012/064735
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English (en)
Japanese (ja)
Inventor
克利 ▲高▼島
勇樹 田路
長谷川　浩平
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Ｊｆｅスチール株式会社
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Application filed by Ｊｆｅスチール株式会社 filed Critical Ｊｆｅスチール株式会社
Priority to CN201280073571.7A priority Critical patent/CN104350170B/zh
Priority to PCT/JP2012/064735 priority patent/WO2013179497A1/fr
Priority to KR1020147034518A priority patent/KR101674283B1/ko
Publication of WO2013179497A1 publication Critical patent/WO2013179497A1/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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies

Definitions

  • the present invention relates to a high-strength cold-rolled steel sheet having a low yield ratio and excellent elongation and stretch flangeability, which is suitable as a member for automobile undercarriage parts and structural parts used by being pressed.
  • the steel sheet having a TS of 590 MPa or more is required to have excellent elongation and stretch flangeability (hole expanding property) from the viewpoint of formability. Furthermore, since it is assembled by arc welding, spot welding or the like after press working and modularized, high dimensional accuracy is required at the time of assembly. For this reason, it is necessary to make it difficult for a springback or the like to occur after processing, and a low yield ratio is required before processing.
  • Patent Document 1 discloses a high-strength steel sheet for automobiles that achieves both collision safety and formability by controlling the space factor and the average crystal grain size of the entire structure of ferrite and martensite.
  • Patent Document 2 discloses a high-strength steel sheet having improved elongation and stretch flangeability by controlling the space factor of the fine ferrite having an average grain size of 3 ⁇ m or less and the martensite having an average grain size of 6 ⁇ m or less with respect to the entire structure. It is disclosed.
  • Patent Document 3 discloses a DP steel sheet in which fine inclusions are dispersed in the steel sheet by containing Ce or La in the steel sheet component to improve stretch flangeability.
  • Patent Document 4 a composite structure composed of ferrite, residual austenite, the balance being bainite and martensite, the aspect ratio and average particle size of martensite and residual austenite are defined, and martensite and residual per unit area By defining the number of austenite, a composite structure cold-rolled steel sheet having excellent elongation and stretch flangeability is disclosed.
  • Non-Patent Document 1 will be described in an example.
  • Patent Document 1 defines the average crystal grain size of ferrite and martensite, it does not ensure sufficient hole expansion property for press molding.
  • Patent Document 2 since the volume fraction of martensite is remarkably large, the elongation is insufficient.
  • Patent Document 3 is low in production cost because Ce and La are added, and the manufacturing cost is high, and the material variation is large in order to control the size of inclusions.
  • Patent Document 4 a steel sheet containing bainite or retained austenite requires a high cooling rate using special equipment to obtain its structure, so that the manufacturing cost is high and the material variation is large. Furthermore, as a characteristic, a high strength steel plate having a steel structure having retained austenite and bainite has a higher YR than DP steel, so it is difficult to stably set the YR to 70% or less.
  • an object of the present invention is to provide a high-strength cold-rolled steel sheet that has solved the above-mentioned problems of the prior art, has excellent elongation and stretch flangeability, and has a low yield ratio and a method for manufacturing the same.
  • the inventors have added a suitable amount of Si and controlled the volume fraction of ferrite, martensite and pearlite, and are excellent in elongation and stretch flangeability that ensure high strength at low YR. It was found that a cold-rolled steel sheet can be obtained.
  • Si is added in an amount of 0.6 to 1.2%
  • the main phase ferrite is 80% or more in terms of volume fraction
  • martensite is 3 to 15%
  • pearlite is 0.5 to 10%.
  • the present invention provides the following (1) and (2).
  • the chemical composition of the steel sheet is mass%, C: 0.05 to 0.13%, Si: 0.6 to 1.2%, Mn: 1.6 to 2.4%, P: 0.00. 10% or less, S: 0.0050% or less, Al: 0.01 to 0.10%, N: less than 0.0050%, the balance is made of Fe and inevitable impurities, and the microstructure of the steel sheet is It has a composite structure containing 80% or more of ferrite, 3 to 15% of martensite, and 0.5 to 10% of pearlite in volume fraction, yield ratio is 70% or less, and tensile strength is 590 MPa or more. Low yield ratio high strength cold-rolled steel sheet with excellent elongation and stretch flangeability.
  • the volume fraction includes ferrite of 80% or more, martensite of 3 to 15%, and pearlite of 0.5 to 10%.
  • High-strength cold-rolled steel sheet with a low yield ratio that has a composite structure has a tensile strength of 590 MPa or more, a yield ratio of 70% or less, an elongation of 29.0% or more, and an elongation and stretch flangeability of 65% or more. Can be obtained.
  • C 0.05 to 0.13% C is an element effective for increasing the strength of a steel sheet, and contributes to increasing the strength by forming a second phase of pearlite and martensite.
  • 0.05% or more must be added.
  • it is 0.08% or more.
  • the upper limit is made 0.13%.
  • Si 0.6-1.2%
  • Si is an element that contributes to high strength, and since it has a high work-hardening ability, it has a relatively small decrease in elongation with respect to an increase in strength, and is an element that also contributes to an improvement in strength-elongation balance. Furthermore, the solid solution strengthening of the ferrite phase reduces the hardness difference from the hard second phase, thereby contributing to the improvement of stretch flangeability.
  • the addition of an appropriate amount of Si can suppress the generation of voids from the interface between the ferrite phase and the pearlite phase, but in order to obtain the effect, it is necessary to contain 0.6% or more.
  • the upper limit is not particularly defined from the viewpoint of elongation and stretch flangeability, but if it exceeds 1.2%, the chemical conversion treatment property is lowered, so the content is made 1.2% or less. Preferably it is 1.0% or less.
  • Mn 1.6 to 2.4% Mn is an element that contributes to strengthening by forming solid solution strengthening and martensite. To obtain this effect, it is necessary to contain 1.6% or more. On the other hand, when the content is excessive, the moldability is significantly lowered. Therefore, the content is set to 2.4% or less. Preferably it is 2.2% or less.
  • P 0.10% or less P contributes to high strength by solid solution strengthening, but when excessively added, segregation to the grain boundary becomes remarkable and the grain boundary becomes brittle, and weldability. Therefore, the content is made 0.10% or less. Preferably it is 0.05% or less.
  • S 0.0050% or less
  • the content of S is large, a large amount of sulfides such as MnS are generated, and the local elongation represented by stretch flangeability is reduced, so the upper limit of the content is 0.0050%. To do. Preferably, it is 0.0030% or less. Although a minimum is not specifically limited, Since ultra-low S raises steelmaking cost, it is preferable to contain 0.0005% or more.
  • Al 0.01 to 0.10%
  • Al is an element necessary for deoxidation. In order to obtain this effect, it is necessary to contain 0.01% or more, but even if it exceeds 0.10%, the effect is saturated.
  • the content is 0.10% or less. Preferably it is 0.05% or less.
  • N Less than 0.0050% Since N forms coarse nitrides and deteriorates stretch flangeability, it is necessary to suppress the content. When N is 0.0050% or more, this tendency becomes remarkable, so the N content is less than 0.0050%.
  • V 0.10% or less
  • V can contribute to an increase in strength by forming fine carbonitrides. In order to exhibit such an effect, it is preferable to contain the addition amount of V 0.01% or more. On the other hand, even if added over 0.10%, the effect of increasing the strength is small, and on the contrary, the cost of the alloy is increased, so the content is preferably 0.10% or less.
  • Ti 0.10% or less Ti, like V, can contribute to an increase in strength by forming fine carbonitride, and can be added as necessary. In order to exert such an effect, the Ti content is preferably 0.005% or more. On the other hand, when a large amount of Ti is added, YR increases remarkably, so the content is preferably 0.10% or less.
  • Nb 0.10% or less
  • Nb can contribute to an increase in strength by forming fine carbonitrides, and can be added as necessary.
  • the Nb content is preferably 0.005% or more.
  • the content is preferably 0.10% or less.
  • Cr 0.50% or less Cr is an element that contributes to increasing the strength by improving the hardenability and generating the second phase, and can be added as necessary. In order to exhibit this effect, it is preferable to make it contain 0.10% or more. On the other hand, since the effect is saturated even if the content exceeds 0.50%, the content is preferably 0.50% or less.
  • Mo 0.50% or less Mo is an element that improves hardenability and contributes to high strength by generating the second phase, and further contributes to high strength by generating some carbides. Can be added accordingly. In order to exhibit these effects, it is preferable to make it contain 0.05% or more. Since the effect is saturated even if the content exceeds 0.50%, the content is preferably 0.50% or less.
  • Cu 0.50% or less
  • Cu is an element that contributes to high strength by solid solution strengthening, improves hardenability, and contributes to high strength by generating a second phase. Can be added. In order to exhibit these effects, it is preferable to make it contain 0.05% or more. On the other hand, even if the content exceeds 0.50%, the effect is saturated and surface defects due to Cu are likely to occur. Therefore, the content is preferably 0.50% or less.
  • Ni 0.50% or less
  • Ni is an element that contributes to strengthening by solid solution strengthening, improves hardenability, and generates a second phase to contribute to strengthening. It can be added as necessary. In order to exhibit these effects, it is preferable to make it contain 0.05% or more. Moreover, since it has the effect of suppressing the surface defect resulting from Cu when it adds simultaneously with Cu, it is effective at the time of Cu addition. On the other hand, since the effect is saturated even if the content exceeds 0.50%, the content is preferably 0.50% or less.
  • Inevitable impurities include, for example, Sb, Sn, Zn, Co, etc.
  • the allowable ranges of these contents are Sb: 0.01% or less, Sn: 0.1% or less, Zn: 0. 01% or less, Co: 0.1% or less.
  • this invention even if it contains Ta, Mg, Ca, Zr, and REM within the range of a normal steel composition, the effect is not impaired.
  • the microstructure of the high-strength cold-rolled steel sheet has a main phase of ferrite with a volume fraction of 80% or more, martensite with a volume fraction of 3-15%, and pearlite with a volume fraction of 0.5-10%.
  • the volume fraction is the volume fraction with respect to the entire steel sheet.
  • the volume fraction of the ferrite phase is 80% or more. Preferably, it is 83% or more.
  • the volume fraction of martensite is less than 3%, the effect of increasing the strength is small, sufficient elongation cannot be obtained, and YR exceeds 70%. Therefore, the volume fraction of martensite is 3% or more.
  • the volume fraction of martensite exceeds 15%, the stretch flangeability is remarkably lowered. Therefore, the volume fraction of martensite is made 15% or less. Preferably it is 12% or less.
  • the pearlite volume fraction When the pearlite volume fraction is less than 0.5%, the effect of increasing the strength is small. Therefore, in order to achieve a good balance between strength and formability, the pearlite volume fraction needs to be 0.5% or more. On the other hand, when the pearlite volume fraction exceeds 10%, YR becomes remarkably high, so the pearlite volume fraction is 10% or less. Preferably it is 8% or less.
  • the remaining structure other than ferrite, martensite and pearlite may be a structure containing one or more of bainite, residual ⁇ , spherical cementite, etc., but from the viewpoint of stretch flangeability, other than ferrite, martensite and pearlite.
  • the volume fraction of the remaining tissue is preferably 5% or less.
  • the average crystal grain size of martensite and pearlite is not particularly limited, but if the average crystal grain size is fine, the connection of the generated voids is suppressed and the stretch flangeability is improved. Therefore, the average crystal grain size of martensite is preferably 10 ⁇ m or less, and the average crystal grain size of pearlite is preferably 5 ⁇ m or less.
  • the steel slab having the above component composition (chemical component) is hot-rolled and pickled, then cold-rolled, and then annealed. This will be described in detail below.
  • the steel slab is preferably manufactured by a continuous casting method in order to prevent macro segregation of components, but can also be manufactured by an ingot forming method or a thin slab casting method.
  • the steel slab is subjected to rough rolling and finish rolling to obtain hot rolled sheets. It is preferable to heat the slab before rolling.
  • the slab heating temperature is preferably 1100 to 1300 ° C.
  • the slab once cooled to room temperature may be reheated in a heating furnace, or the steel slab may be charged into the heating furnace as it is without being cooled to room temperature and reheated.
  • energy saving processes such as direct feed rolling and direct rolling which carry out hot rolling immediately after heat-retaining steel slab, or hot-rolling as it is after casting, without performing slab heating.
  • the finish rolling end temperature is preferably 830 ° C. or higher.
  • the finish rolling finish temperature is preferably 830 to 950 ° C.
  • the subsequent cooling method is not particularly limited.
  • the coiling temperature is not limited, but when the coiling temperature exceeds 700 ° C., coarse pearlite is remarkably formed, which affects the formability of the steel sheet after annealing. preferable. More preferably, it is 650 degrees C or less.
  • the lower limit of the coiling temperature is not particularly limited, but if the coiling temperature becomes too low, hard bainite and martensite are excessively generated and the cold rolling load increases, so 400 ° C or higher is preferable.
  • the pickling process After the hot rolling step, it is preferable to carry out an acidic step and remove the scale of the hot rolled sheet surface layer.
  • the pickling step is not particularly limited, and may be performed according to a conventional method.
  • Cold rolling process The hot-rolled sheet after pickling is subjected to a cold rolling process for rolling into a cold-rolled sheet having a predetermined thickness.
  • a cold rolling process is not specifically limited, What is necessary is just to implement by a conventional method.
  • the annealing process is carried out in order to advance recrystallization and to form a second phase structure of martensite and pearlite for high strength.
  • the annealing step is performed by heating to a temperature range of Ac 1 to Ac 3 points (also referred to as a soaking temperature or holding temperature) and then holding the temperature from the soaking temperature to a temperature of 500 to 550 ° C. at 1 ° C./s. Cool at an average cooling rate of ⁇ 25 ° C./s, and then cool at an average cooling rate of 5 ° C./s or less.
  • Soaking temperature (holding temperature): Ac 1 to Ac 3 points Since austenite is not generated when the soaking temperature is less than Ac 1 point, then martensite cannot be obtained, and if it exceeds Ac 3 points, coarse austenite is obtained. Therefore, the predetermined martensite and pearlite volume fraction cannot be obtained thereafter. Therefore, the soaking temperature is in the range of Ac 1 to Ac 3 points. Ac 3 points-100 ° C. to Ac 3 points are preferred. If the heating rate up to the soaking temperature is too high, recrystallization will not proceed easily. If the heating rate is too low, the ferrite grains will become coarse and the strength will decrease, so the average heating rate up to the soaking temperature will be 3-30 ° C. / S is preferable. Further, the soaking time is preferably set to 30 s to 300 s (seconds) in order to sufficiently advance the recrystallization and partially austenite transformation.
  • Cooling from a soaking temperature to a temperature of 500 to 550 ° C at an average cooling rate of 1 ° C / s to 25 ° C / s (primary cooling)
  • the microstructure of the steel sheet finally obtained after the annealing process is controlled so that the volume fraction of ferrite is 80% or more, the volume fraction of martensite is 3 to 15%, and the volume fraction of pearlite is 0.5 to 10%. Therefore, primary cooling is performed by cooling from the soaking temperature to a temperature of 500 to 550 ° C. as a primary cooling temperature at an average cooling rate of 1 ° C./s to 25 ° C./s.
  • the primary cooling temperature exceeds 550 ° C, martensite is not sufficiently formed, and when it is less than 500 ° C, pearlite is not sufficiently formed.
  • both martensite and pearlite can be formed and the volume fraction thereof can be adjusted.
  • the average cooling rate to the temperature range of 500 to 550 ° C is less than 1 ° C / s, martensite does not form 3% or more in volume fraction, and when the average cooling rate exceeds 25 ° C / s, pearlite has volume fraction. And not 0.5% or more. Therefore, the average cooling rate from the soaking temperature to the temperature range of 500 to 550 ° C. needs to be 1 ° C./s to 25 ° C./s.
  • a preferable average cooling rate is 15 ° C./s or less.
  • Cool from the primary cooling temperature at an average cooling rate of 5 ° C / s or less (secondary cooling) After cooling to the primary cooling temperature (500 to 550 ° C.), secondary cooling is performed at an average cooling rate of 5 ° C./s or less.
  • the average cooling rate of the secondary cooling exceeds 5 ° C./s, the volume fraction of martensite increases and the predetermined martensite and pearlite volume fraction cannot be obtained, so the average cooling rate from the primary cooling temperature Is 5 ° C./s or less.
  • it is 3 degrees C / s or less.
  • temper rolling may be performed after annealing.
  • a preferable range of the elongation rate is 0.3% to 2.0%.
  • hot dip galvanization may be performed after the primary cooling to obtain a hot dip galvanized steel sheet. It may be a steel plate.
  • the present invention is not originally limited by the following examples, and can be implemented with appropriate modifications within a range that can be adapted to the gist of the present invention. Included in the scope.
  • the cooling rate 1 in Table 2 indicates the average cooling rate from the soaking temperature during annealing to the primary cooling temperature, and the cooling rate 2 indicates the average cooling rate from the primary cooling temperature to room temperature.
  • the average heating rate up to the soaking temperature was 10 ° C./s.
  • a JIS No. 5 tensile test piece was sampled so that the direction perpendicular to the rolling direction was the longitudinal direction (tensile direction), and was subjected to a tensile test (JIS Z2241 (1998)) to yield strength (YS), tensile strength (TS), total elongation (EL), and yield ratio (YR) were measured.
  • Yield strength (YS) yield strength
  • TS tensile strength
  • EL total elongation
  • YR yield ratio
  • Stretch flangeability is based on the Japan Iron and Steel Federation standard (JFS T1001 (1996)), after punching a hole with a diameter of 10mm ⁇ at a clearance of 12.5%, and setting the burr on the die side after setting
  • JFS T1001 Japan Iron and Steel Federation standard
  • the hole expansion rate ( ⁇ ) was measured by conducting a hole expansion test with a 60 ° conical punch. ⁇ (%) was 65% or more to make a steel sheet having good stretch flangeability.
  • volume fractions of ferrite, martensite and pearlite were determined by the following method.
  • the microstructure of the steel sheet corrodes the cross section in the rolling direction of the steel sheet (depth position at 1/4 of the plate thickness) using 3% Nital reagent (3% nitric acid + ethanol), and is observed with an optical microscope at 500 to 1000 times.
  • the volume fraction of ferrite, the volume fraction of martensite, and the volume fraction of pearlite were quantified using tissue photographs observed and photographed with an electron microscope (scanning type and transmission type) of 1000 to 100,000 times.
  • ferrite is a region with a slightly black contrast, and martensite has a white contrast.
  • Pearlite is a layered structure in which plate-like ferrite and cementite are alternately arranged.
  • bainite is a plate-like bainite having a higher dislocation density than polygonal ferrite in the observation using the above-described optical microscope or electron microscope (scanning type and transmission type). It is a structure containing tick ferrite and cementite, and spherical cementite is cementite having a spheroidized shape.
  • the surface polished to 1/4 thickness from the surface layer was used, and the K ⁇ ray of Mo was used as the radiation source at an acceleration voltage of 50 keV by an X-ray diffraction method (apparatus: RINT2200 manufactured by Rigaku).
  • Measure the integrated intensity of the X-ray diffraction lines of the ⁇ 200 ⁇ , ⁇ 211 ⁇ , ⁇ 220 ⁇ , and ⁇ 200 ⁇ , ⁇ 220 ⁇ , and ⁇ 311 ⁇ planes of austenite. was used to determine the volume fraction of retained austenite from the calculation formula described in Non-Patent Document 1, and the presence or absence of retained austenite was determined.
  • Table 2 shows the measurement results of tensile properties, stretch flangeability, and steel sheet structure.
  • all of the examples of the present invention have a steel sheet structure in which the volume fraction of ferrite is 80% or more, the volume fraction of martensite is 3 to 15%, and the volume fraction of pearlite is 0.5 to 10%.
  • good formability with a tensile strength of 590 MPa or more and a yield ratio of 70% or less, and an elongation of 29.0% or more and a hole expansion ratio of 65% or more can be obtained.
  • the steel sheet structure does not satisfy the scope of the present invention, and as a result, at least one characteristic of tensile strength, yield ratio, elongation, and hole expansion ratio is inferior.
  • the volume fraction has a composite structure including ferrite of 80% or more, martensite of 3 to 15%, and pearlite of 0.5 to 10%, a tensile strength of 590 MPa or more, and a yield ratio of 70% or less. Further, a high strength cold-rolled steel sheet having a low yield ratio and excellent elongation and stretch flangeability having an elongation of 29.0% or more and a hole expansion ratio of 65% or more can be obtained.

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  • Engineering & Computer Science (AREA)
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  • Crystallography & Structural Chemistry (AREA)
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Abstract

L'invention concerne une tôle d'acier laminée à froid haute résistance présentant un faible rapport de la limite d'élasticité ainsi qu'un excellent allongement et une excellente formabilité de bord tombé, et son procédé de fabrication. Cette tôle d'acier laminée à froid haute résistance ayant un faible rapport de la limite d'élasticité ainsi qu'un excellent allongement et une excellente formabilité de bord tombé est caractérisée en ce que les composants chimiques de la tôle d'acier comprennent, en % en masse, C : 0,05 à 0,13 %, Si : 0,6 à 1,2 %, Mn : 1,6 à 2,4 %, P : 0,10 % ou moins, S : 0,0050 % ou moins, Al : 0,01 à 0,10 % et N : moins de 0,0050 %, et le reste consiste en Fe et des impuretés inévitables, et en ce que la tôle d'acier a une microstructure composite contenant, en pourcentage en volume, 80 % ou plus de ferrite, 3 à 15 % de martensite et 0,5 à 10 % de perlite, le rapport de limite d'élasticité étant de 70 % ou moins, et la résistance à la traction étant de 590 Mpa ou plus.
PCT/JP2012/064735 2012-06-01 2012-06-01 Tôle en acier laminée à froid haute résistance à faible rapport de limite d'élasticité présentant un excellent allongement et une excellente formabilité de bord tombé, et son procédé de fabrication WO2013179497A1 (fr)

Priority Applications (3)

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CN201280073571.7A CN104350170B (zh) 2012-06-01 2012-06-01 伸长率和延伸凸缘性优良的低屈服比高强度冷轧钢板及其制造方法
PCT/JP2012/064735 WO2013179497A1 (fr) 2012-06-01 2012-06-01 Tôle en acier laminée à froid haute résistance à faible rapport de limite d'élasticité présentant un excellent allongement et une excellente formabilité de bord tombé, et son procédé de fabrication
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