WO2017141953A1 - 高強度冷延鋼板 - Google Patents
高強度冷延鋼板 Download PDFInfo
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
Definitions
- the present invention relates to a high-strength cold-rolled steel sheet excellent in delayed fracture resistance and chemical conversion property, characterized by having a tensile strength of 1180 MPa or more.
- automotive steel sheets are used after being coated, and chemical conversion treatment such as phosphate treatment is performed as a pretreatment for the coating. Since the chemical conversion treatment of this steel plate is one of the important treatments for ensuring the corrosion resistance after coating, the automotive steel plate is also required to have excellent chemical conversion treatment properties.
- Si is an element that improves the ductility of steel with the same strength by strengthening ferrite in solid solution and refining the carbide in martensite or bainite. Moreover, since Si suppresses the formation of carbides, it also facilitates securing retained austenite that contributes to improving ductility. Furthermore, it is known that Si refines grain boundary carbides in martensite or bainite, thereby reducing stress / strain concentration near the grain boundary and improving delayed fracture resistance. For this reason, many techniques for producing high-strength thin steel sheets using Si have been disclosed so far.
- Patent Document 1 describes a steel sheet having a structure composed of ferrite and tempered martensite and having excellent delayed fracture resistance with a structure of ferrite and tempered martensite added with 1 to 3% by mass of Si.
- Patent Document 2 One element that improves delayed fracture resistance is Cu.
- the corrosion resistance of steel is improved by adding Cu, and the delayed fracture resistance is remarkably improved.
- the Si content is 0.05 to 0.5% by mass.
- Patent Document 3 describes a steel sheet excellent in chemical conversion treatment, to which Si is added by mass%, 0.5 to 3%, and Cu is added to 2% or less.
- the surface of a continuously annealed steel sheet is pickled, and the Si-containing oxide layer formed on the surface of the steel sheet during annealing is removed, so that an excellent chemical conversion treatment can be achieved even with 0.5% or more of Si addition. The sex is secured.
- JP 2012-12642 A Japanese Patent No. 3545980 Japanese Patent No. 5729211
- Patent Document 1 a Si-containing oxide is formed on the surface of a steel plate in a continuous annealing line, and it cannot be said that the chemical conversion treatment property is sufficient. Moreover, even if the Si addition amount is further increased, the effect is not saturated but manufacturing problems such as an increase in hot rolling load occur.
- the present invention has been made in view of such circumstances, and an object of the present invention is to provide a high-strength cold-rolled steel sheet excellent in delayed fracture resistance and chemical conversion property, characterized by having a tensile strength of 1180 MPa or more.
- pickling the surface of the steel sheet that has been continuously annealed removes the Si-containing oxide on the surface of the steel sheet, but Cu reprecipitates on the surface of the steel sheet, so that good chemical conversion properties cannot be obtained.
- the inventors have conducted extensive research to solve the above problems, and as a result, the Si-containing oxide layer on the steel sheet surface layer is removed by pickling after the continuous annealing, and Cu S / Cu B is 4.0 or less. It was found that by controlling (Cu S is the Cu concentration in the surface layer of the steel sheet and Cu B is the Cu concentration in the base material), deterioration of chemical conversion property due to Si and Cu can be prevented and delayed fracture resistance can be improved.
- the present invention is based on the above findings. That is, the gist configuration of the present invention is as follows.
- Component composition is mass%, C: 0.10% to 0.6%, Si: 1.0% to 3.0%, Mn: more than 2.5% to 10.0%, P: 0.05% or less, S: 0.02% or less, Al: 0.01% or more and 1.5% or less, N: 0.005% or less, Cu: 0.05% or more and 0.50% or less And the balance consists of iron and inevitable impurities, the steel sheet surface coverage of the oxide mainly composed of Si is 1% or less, the steel sheet surface coverage of the iron-based oxide is 40% or less, Cu 2 S 2 / Cu B is a high-strength cold-rolled steel sheet that satisfies 4.0 or less (Cu S is Cu concentration in the steel sheet surface layer, Cu B is Cu concentration in the base material) and has a tensile strength of 1180 MPa or more.
- the steel structure has tempered martensite and / or bainite in a total volume ratio of 40% to 100%, ferrite in a volume ratio of 0% to 60%, and residual austenite in a range of 2% to 30%.
- the component composition further includes, in mass%, Nb: 0.2% or less, Ti: 0.2% or less, V: 0.5% or less, Mo: 0.3% or less, Cr: 1.
- Nb 0.2% or less
- Ti 0.2% or less
- V 0.5% or less
- Mo 0.3% or less
- Cr 1.
- the component composition further includes, by mass%, Sn: 0.1% or less, Sb: 0.1% or less, W: 0.1% or less, Co: 0.1% or less, Ca: 0.0.
- the high-strength cold-rolled steel sheet of the present invention is excellent in delayed fracture resistance and chemical conversion properties while having a high tensile strength of 1180 MPa or more.
- FIG. 1 is a diagram schematically showing a test piece used for evaluation of delayed fracture resistance.
- FIG. 2 is an example of a histogram of the number of pixels with respect to the gray value of a reflection electron image photograph.
- the component composition of the high-strength steel sheet of the present invention (sometimes referred to as the steel sheet of the present invention) will be described.
- the component composition of the steel sheet of the present invention is mass%, C: 0.10% to 0.6%, Si: 1.0% to 3.0%, Mn: more than 2.5% and 10.0%.
- the above component composition is further in mass%, Nb: 0.2% or less, Ti: 0.2% or less, V: 0.5% or less, Mo: 0.3% or less, Cr: 1.0 %, B: 0.005% or less may be contained.
- the above-mentioned component composition is further mass%, Sn: 0.1% or less, Sb: 0.1% or less, W: 0.1% or less, Co: 0.1% or less, Ca: 0.005 % Or less, REM: Any one or more of 0.005% or less may be contained.
- % representing the content of a component means “mass%”.
- C 0.10% to 0.6%
- C is an element effective for improving the strength-ductility balance of the steel sheet. If the C content is less than 0.10%, it is difficult to ensure a tensile strength of 1180 MPa or more. On the other hand, when the C content exceeds 0.6%, coarse cementite precipitates, and hydrogen cracking occurs starting from the coarse cementite. Therefore, the C content is in the range of 0.10% to 0.6%.
- the lower limit is preferably 0.15% or more.
- the upper limit is preferably 0.4% or less.
- Si 1.0 or more and 3.0% or less Si is an effective element for ensuring strength without significantly reducing the ductility of the steel sheet.
- Si content is less than 1.0%, not only high strength and high workability (excellent workability) can be achieved, but also the cementite coarsening cannot be suppressed and the delayed fracture resistance is deteriorated.
- Si content exceeds 3.0%, not only the rolling load load at the time of hot rolling will increase, but an oxidation scale will be produced on the steel plate surface, and chemical conversion property will be deteriorated. Therefore, the Si content is in the range of 1.0% to 3.0%.
- the lower limit is preferably 1.2% or more.
- the upper limit is preferably 2.0% or less.
- Mn more than 2.5% and 10.0% or less Mn is an element effective for strengthening steel and stabilizing austenite.
- Mn content is more than 2.5% and not more than 10.0%.
- the lower limit is preferably 2.7% or more.
- the upper limit is preferably 4.5% or less.
- P 0.05% or less
- P is an impurity element, and if its content exceeds 0.05%, after forming through deterioration of local ductility due to grain boundary embrittlement accompanying P segregation to austenite grain boundaries during casting. Deteriorates the delayed fracture resistance of steel sheets. Therefore, the content is preferably 0.05% or less, more preferably 0.02% or less. In consideration of the manufacturing cost, the P content is preferably 0.001% or more.
- S 0.02% or less S is present as MnS in the steel sheet, and causes a reduction in impact resistance, strength, and delayed fracture resistance. For this reason, it is preferable to reduce S content as much as possible. Therefore, the upper limit of the S content is 0.02%. Preferably it is 0.002% or less. More preferably, it is 0.001% or less. In consideration of the manufacturing cost, the S content is preferably 0.0001% or more.
- Al 0.01% or more and 1.5% or less Since Al reduces the amount of oxides such as Si by itself forming an oxide, it has the effect of improving delayed fracture resistance. However, if the Al content is less than 0.01%, a significant effect cannot be obtained. On the other hand, when the Al content exceeds 1.5%, Al and N are combined to form a nitride. Nitride precipitates on the austenite grain boundary during casting and causes the grain boundary to become brittle, which degrades the delayed fracture resistance. For this reason, Al content shall be 1.5% or less. Preferably it is less than 0.08%, more preferably 0.07% or less.
- N 0.005% or less N, as described above, combines with Al to form a nitride and deteriorate the delayed fracture resistance. For this reason, it is preferable to reduce N content as much as possible. Therefore, the N content is set to 0.005% or less. More preferably, it is 0.003% or less. In consideration of the manufacturing cost, the N content is preferably 0.0001% or more.
- Cu 0.05% or more and 0.50% or less Cu, when exposed to a corrosive environment, has an effect of reducing the amount of hydrogen entering the steel sheet by suppressing dissolution of the steel sheet. If the Cu content is less than 0.05%, the effect is small. If the Cu content exceeds 0.50%, it becomes difficult to control the pickling conditions for obtaining a predetermined surface Cu concentration distribution. For this reason, Cu content shall be 0.05% or more and 0.50% or less. The lower limit is preferably 0.08% or more. The upper limit is preferably 0.3% or less.
- Nb, Ti, V, Mo, Cr, and B may be contained. Each reason for limitation will be described.
- Nb 0.2% or less Nb forms fine Nb carbonitride, refines the structure and improves delayed fracture resistance by the hydrogen trap effect, and may be added as necessary.
- the Nb content exceeds 0.2%, the effect of refining the structure is saturated, and in the presence of Ti, coarse composite carbides are formed with Ti and Nb to deteriorate the strength-ductility balance and delayed fracture resistance.
- the content shall be 0.2% or less.
- it is 0.1% or less. More preferably, it is made 0.05% or less.
- the lower limit is not particularly defined, but in order to obtain the above effect, the content is preferably at least 0.004% or more.
- Ti 0.2% or less Ti has the effect of generating carbides to refine the structure and the hydrogen trapping effect, so it may be added as necessary.
- the Ti content exceeds 0.2%, not only the effect of refining the structure is saturated, but also coarse TiN is formed, and in the presence of Nb, a Ti—Nb composite carbide is formed, resulting in a strength-ductility balance and resistance. Deteriorating delayed fracture characteristics. For this reason, when Ti is contained, the content is made 0.2% or less. Moreover, Preferably it is 0.1% or less. More preferably, it is made 0.05% or less.
- the lower limit is not particularly defined, but in order to obtain the above effect, the content is preferably at least 0.004% or more.
- V 0.5% or less Fine carbide formed by the combination of V and C acts as a precipitation strengthening of the steel sheet and acts as a hydrogen trap site, so it is effective in improving delayed fracture resistance. May be. If the V content exceeds 0.5%, carbides precipitate excessively and the strength-ductility balance deteriorates. For this reason, when it contains V, the content shall be 0.5% or less. Moreover, Preferably it is 0.1% or less. More preferably, it is made 0.05% or less. In the present invention, the lower limit is not particularly defined, but in order to obtain the above effect, the content is preferably at least 0.004% or more.
- Mo 0.3% or less Mo is effective in improving the hardenability of the steel sheet and has a hydrogen trap effect due to fine precipitates, so it may be added as necessary.
- Mo content exceeds 0.3%, not only the effect is saturated, but also the formation of Mo oxides on the steel sheet surface is promoted during continuous annealing, and the chemical conversion property of the steel sheet is significantly reduced.
- the content shall be 0.3% or less.
- the content is 0.1% or less. More preferably, it is made 0.05% or less.
- the lower limit is not particularly defined, but in order to obtain the above effect, the content is preferably at least 0.005% or more.
- Cr 1.0% or less Cr, like Mo, is effective in improving the hardenability of the steel sheet, and may be added as necessary.
- the content exceeds 1.0%, even if the pickling treatment is performed after the continuous annealing, the Cr oxide on the surface of the steel sheet cannot be completely removed, so that the chemical conversion property of the steel sheet is remarkably lowered.
- the content shall be 1.0% or less.
- it is 0.5% or less. More preferably, the content is 0.1% or less.
- the lower limit is not particularly defined, but in order to obtain the above effect, the content is preferably at least 0.04% or more.
- B 0.005% or less B segregates at austenite grain boundaries during heating in continuous annealing, suppresses ferrite transformation and bainite transformation from austenite during cooling, and facilitates the formation of tempered martensite. Effective for strengthening. Further, B may be added as necessary in order to improve the delayed fracture resistance by grain boundary strengthening. If the B content exceeds 0.005%, borocarbide Fe 23 (C, B) 6 is generated, resulting in deterioration of workability and strength. For this reason, when it contains B, the content shall be 0.005% or less. Moreover, Preferably it is 0.003% or less. In the present invention, the lower limit is not particularly defined, but in order to obtain the above effect, the content is preferably at least 0.0002% or more.
- any one or more of Sn, Sb, W, Co, Ca, or REM may be contained within a range that does not adversely affect the characteristics. The reason for this limitation will be described.
- Sn, Sb 0.1% or less Since both Sn and Sb have the effect of suppressing surface oxidation, decarburization, and nitriding, they may be added as necessary. However, even if the content exceeds 0.1%, the effect is saturated. For this reason, when it contains Sn and Sb, these content shall be 0.1% or less, respectively. Moreover, Preferably it is 0.05% or less. In the present invention, a lower limit value is not particularly defined, but in order to obtain the above effect, each content is preferably at least 0.001%.
- W, Co 0.1% or less Since W and Co have the effect of improving the properties of the steel sheet through the form control of sulfide, grain boundary strengthening, and solid solution strengthening, they may be added as necessary. However, if W or Co is contained excessively, ductility deteriorates due to grain boundary segregation or the like. For this reason, the content of these elements is preferably 0.1% or less. Moreover, Preferably it is 0.05% or less. In the present invention, the lower limit value is not particularly defined, but in order to obtain the above effect, the content is preferably at least 0.01%.
- Ca and REM both have the effect of improving ductility and delayed fracture resistance through sulfide morphology control, and may be added as necessary. However, if Ca or REM is excessively contained, ductility deteriorates due to grain boundary segregation or the like. Therefore, the content of these components is preferably 0.005% or less. More preferably, it is 0.002% or less. In the present invention, the lower limit is not particularly defined, but in order to obtain the above effect, the content is preferably at least 0.0002% or more.
- the remainder other than the above is Fe and inevitable impurities.
- the steel sheet surface coverage of an oxide mainly composed of Si is 1% or less.
- the steel sheet surface coverage of the oxide mainly composed of Si is set to 1% or less.
- it is 0%.
- the oxide mainly composed of Si is, for example, SiO 2 .
- the oxide mainly composed of Si can be measured by the method of Examples described later.
- “mainly Si” means that the atomic concentration ratio of Si among elements other than oxygen constituting the oxide is 70% or more.
- Iron-based oxide steel sheet surface coverage is 40% or less If iron-based oxide steel sheet surface coverage exceeds 85%, the dissolution reaction of iron in chemical conversion treatment is inhibited, and growth of chemical crystals such as zinc phosphate occurs. Is suppressed.
- the chemical conversion treatment liquid has been lowered in temperature, and the chemical conversion treatment conditions are stricter than before. Therefore, a surface coverage of 85% or less is insufficient, and preferably 40% or less. More preferably, it is 35% or less.
- the lower limit is not particularly limited, but the steel sheet surface coverage is often 20% or more.
- the steel plate surface coverage of an iron-type oxide can be measured by the method of the Example mentioned later.
- the iron-based oxide means an iron-based oxide having an atomic concentration ratio of iron of 30% or more among elements other than oxygen constituting the oxide.
- Cu S / Cu B 4.0 or less
- the Cu content is 0.05% or more and 0.50% or less
- Cu S / Cu B is 4.0 or less
- Cu S is the Cu concentration in the steel sheet surface layer
- Cu B is the Cu concentration in the base material
- the lower limit is not particularly limited, from the viewpoint of improving the chemical conversion treatability, Cu S / Cu B is 2.0 or more.
- the steel sheet surface layer means a region within 20 nm in the thickness direction from the surface.
- [Cu%] Cu content in steel
- the above Cu concentration distribution is also achieved by removing Cu re-precipitated on the surface of the steel sheet by grinding or the like, but an excellent chemical conversion property cannot be obtained because the grinding iron remains.
- Cu S / Cu B was measured by the method described in the examples.
- tempered martensite and / or bainite be 40% or more and 100% or less in total volume ratio. Tempered martensite and / or bainite is a structure indispensable for increasing the strength of steel. When the volume ratio is less than 40%, a tensile strength of 1180 MPa or more may not be obtained.
- ferrite is 0% to 60% by volume. Ferrite may be combined as necessary to contribute to improvement of ductility and to improve the workability of steel. This effect is obtained at over 0%.
- volume ratio exceeds 60%, in order to obtain a tensile strength of 1180 MPa or more, it is necessary to extremely increase the hardness of tempered martensite or bainite. As a result, at the interface due to the hardness difference between the structures. Delayed fracture is promoted by stress and strain concentration.
- the retained austenite is 2% to 30% by volume. Residual austenite improves the strength-ductility balance of the steel. This effect is obtained at 2% or more.
- the lower limit value of the volume fraction of retained austenite is not particularly specified, but it is preferable to include 5% or more in order to stably ensure that the tensile strength ⁇ total elongation is 16500 MPa ⁇ % or more.
- the upper limit of the volume ratio is 30%.
- the average aspect ratio of retained austenite is more than 2.0.
- the present invention may include other phases other than the tempered martensite, bainite, ferrite, and retained austenite as the steel sheet structure.
- other phases other than the tempered martensite, bainite, ferrite, and retained austenite as the steel sheet structure.
- pearlite, as-quenched martensite, or the like may be included.
- the other phase is preferably 5% or less by volume ratio.
- strength cold-rolled steel plate of this invention is demonstrated.
- the slab obtained by continuous casting is used as a steel material, hot-rolled, and after finishing rolling, cooled and wound into a coil, then pickled, cold-rolled, and then subjected to continuous annealing. Then, after the overaging treatment, pickling and re- pickling to obtain a cold-rolled steel sheet.
- the steps from the steel making process to the cold rolling may be performed according to a conventional method.
- the high-strength cold-rolled steel sheet of the present invention can be manufactured by setting the following conditions for continuous annealing, overaging treatment and pickling treatment.
- the annealing temperature is less than 1 Ac, austenite (transformation into martensite after quenching) necessary for securing a predetermined strength is not generated during annealing, and tensile strength of 1180 MPa or more is achieved even after quenching is performed. Cannot be obtained. Therefore, the annealing temperature is preferably Ac 1 point or higher. In this temperature range, the annealing temperature is preferably set to 800 ° C. or higher from the viewpoint of stably securing an equilibrium area ratio of austenite of 40% or higher.
- the residence (holding) time at the annealing temperature is too short, the steel structure is not sufficiently annealed and becomes a non-uniform structure in which a cold-rolled processed structure exists, and ductility is lowered.
- the residence time is preferably 30 to 1200 seconds.
- a particularly preferred residence time is in the range of 250 to 600 seconds.
- Ac1 point (degreeC) is calculated
- [X%] is mass% of the component element X of the steel sheet, and 0 is not included for the components not included.
- Ac1 723-10.7 ⁇ [Mn%] + 29.1 ⁇ [Si%] + 16.9 ⁇ [Cr%] + 6.38 ⁇ [W%]
- the annealed cold-rolled steel sheet is cooled by controlling the average cooling rate to 3 ° C./s or higher to the primary cooling stop temperature range of Ms-100 ° C. or higher and lower than the Ms point. In this cooling, a part of austenite is martensitic transformed by cooling to below the Ms point.
- the primary cooling stop temperature range is set to Ms-100 ° C. or higher and lower than the Ms point. It is preferably Ms-80 ° C. or higher and lower than Ms point, more preferably Ms ⁇ 50 ° C. or higher and lower than Ms point.
- the average cooling rate from the annealing temperature to the primary cooling stop temperature region is set to 3 ° C./s or more. Preferably it is 5 degrees C / s or more, More preferably, it is 8 degrees C / s or more.
- the upper limit of the average cooling rate is not particularly limited as long as the cooling stop temperature does not vary.
- the Ms point described above can be obtained by an approximate expression as shown in the following expression. Ms is an approximate value obtained empirically.
- Overaging conditions The steel sheet cooled to the primary cooling stop temperature range is heated to an overaging temperature range of 300 ° C to Bs-50 ° C and 450 ° C and stays in the overaging temperature range for 15 seconds to 1000 seconds. (Held).
- Bs indicates a bainite transformation start temperature and can be obtained by an approximate expression as shown in the following expression.
- Bs is an approximate value obtained empirically.
- Bs (° C.) 830 ⁇ 270 ⁇ [C%] ⁇ 90 ⁇ [Mn%] ⁇ 70 ⁇ [Cr%] ⁇ 83 ⁇ [Mo%]
- [X%] is mass% of the component element X of the steel sheet, and 0 is not included for elements not included.
- the overaging temperature range tempering martensite generated by cooling from the annealing temperature to the primary cooling stop temperature range, transforming untransformed austenite to lower bainite, concentrating solid solution C in austenite, etc. Promote stabilization.
- the upper limit of the overaging temperature range exceeds Bs-50 ° C or 450 ° C, the bainite transformation itself is suppressed.
- the lower limit of the overaging temperature range is less than 300 ° C., tempering of martensite becomes insufficient, and a predetermined tensile strength ⁇ total elongation cannot be obtained. Therefore, the range of the overaging temperature range is 300 ° C. or higher and Bs ⁇ 50 ° C. or lower and 450 ° C. or lower. Preferably, it is in the range of 320 ° C. or higher and Bs ⁇ 50 ° C. or lower and 420 ° C. or lower.
- the residence time in this overaging temperature range needs to be 15 seconds or longer.
- the residence time in the overaging temperature region is 1000 seconds due to the bainite transformation promoting effect by martensite generated in the primary cooling stop temperature region.
- the bainite transformation is delayed, but when martensite and untransformed austenite coexist as in the present invention, the bainite transformation rate is remarkably increased.
- the residence time in the overaging temperature region exceeds 1000 seconds, stable residual austenite in which C is concentrated by precipitation of carbides from untransformed austenite, which becomes residual austenite as the final structure of the steel sheet, cannot be obtained. As a result, the desired strength and / or ductility may not be obtained. Therefore, the residence time is 15 seconds or more and 1000 seconds or less. Preferably, it is 100 seconds or more and 700 seconds or less.
- the temperature does not have to be constant as long as it is within the predetermined temperature range described above, and even if it fluctuates within the predetermined temperature range, the gist of the present invention is not impaired.
- the cooling rate As long as the thermal history is satisfied, the steel sheet may be heat-treated with any equipment. Furthermore, it is included in the scope of the present invention to perform temper rolling on the surface of the steel sheet for shape correction after the heat treatment.
- the composition of the solution used for pickling is not particularly limited.
- any one of nitric acid, hydrochloric acid, hydrofluoric acid, sulfuric acid and an acid obtained by mixing two or more of them can be used.
- a strong oxidizing acid such as nitric acid
- a non-oxidizing acid is used as the pickling solution, unlike the pickling solution used in pickling. .
- the steel sheet after tempering treatment has a concentration: nitric acid concentration in the range of more than 50 g / L and not more than 200 g / L. / HNO 3 ) in the range of 0.01 to 1.0, or pickling solution mixed with hydrofluoric acid, the ratio of the hydrofluoric acid concentration to the nitric acid concentration (HF / HNO 3 ) is 0.01 to 1.
- pickling using a pickling solution mixed so as to be in the range of 0 it is possible to remove oxides mainly composed of Si and Si—Mn composite oxides on the steel sheet surface, which deteriorate the chemical conversion properties. is there.
- non-oxidizing acid examples include hydrochloric acid, sulfuric acid, phosphoric acid, pyrophosphoric acid, formic acid, acetic acid, citric acid, hydrofluoric acid, oxalic acid, and acids obtained by mixing two or more of these.
- hydrochloric acid having a concentration of 0.1 to 50 g / L, sulfuric acid of 0.1 to 150 g / L, an acid obtained by mixing 0.1 to 20 g / L hydrochloric acid and 0.1 to 60 g / L sulfuric acid, and the like are preferable.
- Sample steels having the composition shown in Table 1 were vacuum-melted into slabs, heated to 1250 ° C., and hot-rolled and rolled at 870 ° C. at 550 ° C., then hot rolled. After the steel plate was pickled, it was cold-rolled at a rolling rate (rolling rate) of 60% to obtain a cold-rolled steel plate having a thickness of 1.2 mm. The obtained cold-rolled steel sheet was subjected to continuous annealing and tempering treatment (overaging treatment) under the conditions described in Table 2, and pickling and re- pickling.
- Specimens were collected from the steel sheets obtained as described above, and observation of the metal structure (steel structure), analysis of surface Cu concentration distribution, tensile test, chemical conversion treatment evaluation and delayed fracture resistance evaluation were performed.
- the metal structure was observed with a scanning electron microscope (SEM) for a typical microstructure (steel structure) after a nital etching of a plate thickness section parallel to the rolling direction.
- SEM scanning electron microscope
- the area ratio of the ferrite region was obtained by image analysis of a SEM image at a magnification of 2000 times, and was used as the volume ratio of ferrite.
- the volume ratio was calculated
- Residual austenite was observed on the plate surface. After grinding to a thickness of 1 ⁇ 4 of the plate thickness, chemical polishing was performed, and the volume fraction of retained austenite was obtained by X-ray diffraction.
- the volume ratio of martensite and bainite was determined as the remainder of the volume ratio of ferrite, pearlite, and retained austenite. In the inventive examples, the average aspect ratio of retained austenite was more than 2.0.
- the evaluation of the Cu concentration distribution in the surface layer was performed by discharge emission spectroscopy (GDS).
- GDS discharge emission spectroscopy
- a 30 mm square was sheared from the target steel sheet, and GDS analysis was performed using a Rigaku GDA750, with an 8 mm ⁇ anode, DC 50 mA, and a discharge time of 2.9 hPa. I went there.
- the sputtering rate of the steel sheet under this discharge condition is about 20 nm / s.
- Fe: 371 nm, Si: 288 nm, Mn: 403 nm, and O: 130 nm were used for the measurement emission lines.
- the ratio of the average Cu intensity (corresponding to Cu S ) at a sputtering time of 0 to 1 s and the average Cu intensity (corresponding to Cu B ) at a sputtering time of 50 to 100 s was obtained.
- the steel sheet surface coverage of the oxide mainly composed of Si is to identify the oxide mainly composed of Si by observing 5 fields of view at 1000 times using SEM and analyzing the same field of view with EDX. The coverage was determined by the point counting method.
- the hot-rolled steel sheet was pickled, scale was removed, and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1.8 mm.
- the cold-rolled steel sheet was heated to a soaking temperature of 750 ° C. and held for 30 seconds, and then cooled from the soaking temperature to 400 ° C., which is a cooling stop temperature, at 20 ° C./sec.
- pickling and re- pickling under the conditions shown in Table 4 washing with water and drying, then subjected to temper rolling of 0.7%, the number of iron-based oxides on the steel sheet surface differing. Two types of cold-rolled steel sheets a and b were obtained. Then, the above No.
- the cold rolled steel sheet a is a standard sample with a lot of iron-based oxides, No.
- the cold rolled steel sheet b was a standard sample with a small amount of iron-based oxides, and a reflected electron image was obtained for each steel sheet under the conditions described above.
- FIG. 2 is a histogram of the number of pixels with respect to the gray value (parameter value indicating the intermediate tone of white to black) of the reflected electronic image photograph.
- the gray value (Y point) corresponding to the intersection (X point) of the histograms a and b is defined as a threshold value, and the area of the gray value (black tone) portion below the threshold value is defined as the surface coverage of the iron-based oxide. .
- using the above threshold No.
- the steel sheet of a is 85.3%
- No. As for the steel plate of b 25.8% was obtained.
- the tensile test was performed by cutting a JIS No. 5 test piece (distance between gauge points: 50 mm, width of parallel part: 25 mm) with the direction perpendicular to the rolling direction as the length on the plate surface, and a strain rate of 3.3 ⁇ 10 ⁇ 3 s ⁇ 1 . It was.
- the chemical conversion treatment evaluation was conducted using a degreasing agent: Surf Cleaner EC90, a surface conditioner: 5N-10, and a chemical conversion treatment agent: Surfdyne EC1000 manufactured by Nippon Paint Co., Ltd. under the following standard conditions. Chemical conversion treatment was performed so as to be 1.7 to 3.0 g / m 2 .
- the delayed fracture resistance evaluation was conducted by an immersion test. After cutting to 35 m ⁇ 105 mm with the direction perpendicular to the rolling direction as the long side, the end face was ground to prepare a 30 mm ⁇ 100 mm test piece. After bending the test piece 180 ° with a punch having a curvature radius of 10 mm at the tip so that the bending ridge line is parallel to the rolling direction, the inner distance between the test pieces 1 is reduced to 10 mm with bolts 2 as shown in FIG. Stress was applied. The test piece under stress was immersed in hydrochloric acid at 25 ° C. and pH 3, and the time until failure occurred was measured up to 100 hours.
- ⁇ Those with a destruction time of less than 40 hours are evaluated as “ ⁇ ”, those with a breakdown time of 40 hours or more and less than 100 hours are evaluated as “ ⁇ ”, and those without cracking for 100 hours are evaluated as “ ⁇ ”, and the breakdown time is 40 hours or more. It was decided to have excellent delayed fracture resistance.
- the examples conforming to the conditions of the present invention have a tensile strength of 1180 MPa or more, an excellent chemical conversion treatment property is obtained, and no fracture occurs for 100 hours in delayed fracture resistance. It was confirmed that it had excellent delayed fracture resistance.
- Nos. 11 to 18 are examples in which the component composition is outside the scope of the present invention. No. Since No. 11 has a low C content, a predetermined microstructure and tensile strength are not obtained. No. Since No. 12 has a high C content, the carbides are coarsened and the delayed fracture resistance is inferior. No. Since No. 13 has a low Si content, carbides are coarsened and delayed fracture resistance is inferior. No. Since No. 14 has a large Si content, the Si-containing oxide on the surface of the steel sheet cannot be sufficiently removed by pickling, so that the chemical conversion property is inferior. If the pickling weight loss is increased, the Cu concentration distribution in the surface layer exceeds the specified range, so the chemical conversion treatment performance is not improved. No. Since No. Since No. 11 has a low C content, a predetermined microstructure and tensile strength are not obtained. No. Since No. 12 has a high C content, the carbides are coarsened and the delayed fracture resistance is inferior. No. Since No. 13 has a low Si
- No. Reference numerals 17 to 21 are invention steels and comparative steels whose production methods are outside the recommended range of the present invention. No. Although Nos. 17 and 18 have excellent strength, chemical conversion properties, and delayed fracture resistance, the steel structure is not in a preferable range, so TS ⁇ El is less than 16,500.
- No. No. 19 is an example in which pickling was not performed after continuous annealing. Since Si-containing oxide remained on the steel sheet surface, the chemical conversion treatment property was inferior.
- No. No. 21 is an example in which re-acid pickling after pickling is omitted, and iron-based oxides remain on the surface of the steel sheet, so that the chemical conversion property is inferior.
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Abstract
Description
Cは鋼板の強度-延性バランスを改善するのに有効な元素である。C含有量が0.10%未満では、引張強さ1180MPa以上を確保するのが困難である。一方、C含有量が0.6%を超えると粗大なセメンタイトが析出し、粗大セメンタイトを起点として水素割れが発生する。そこで、C含有量は0.10%以上0.6%以下の範囲とする。下限について好ましくは0.15%以上である。上限について好ましくは0.4%以下である。
Siは鋼板の延性をさほど低下させることなく強度を確保するために有効な元素である。Si含有量が1.0%未満の場合、高強度かつ高加工性(優れた加工性)を達成できないばかりかセメンタイトの粗大化を抑制できず耐遅れ破壊特性が劣化する。また、Si含有量が3.0%を超えると、熱間圧延時の圧延負荷荷重が増大するばかりか、鋼板表面に酸化スケールを生じ、化成処理性を劣化させる。そこで、Si含有量は1.0%以上3.0%以下の範囲とする。下限について好ましくは1.2%以上である。上限について好ましくは2.0%以下である。
Mnは鋼の強化とオーステナイトの安定化に有効な元素である。一方、Mn含有量が多くなり過ぎると、鋳造時の偏析によりフェライトとマルテンサイトが帯状に分布した鋼組織を形成する。その結果、機械的特性に異方性が生じ、加工性が劣化する。更に粗大なMnSの生成による耐遅れ破壊特性の劣化も著しい。そこで、Mn含有量は2.5%超10.0%以下とする。下限について好ましくは2.7%以上である。上限について好ましくは4.5%以下の範囲である。
SiとMnのバランスにより、Si主体の酸化物とSi-Mn複合酸化物のそれぞれの生成量が決まる。各々の酸化物のどちらか一方が極端に多く生成した場合、酸洗後に再酸洗する工程を経たとしても鋼板表面の酸化物を除去しきれず、化成処理性が劣化する場合がある。そのため、SiとMnの含有量比を規定することが好ましい。Siに比べてMnが過剰に多い場合、つまり[Si]/[Mn]≦0.4のとき、Si-Mnを主体とする酸化物が過剰に生成する場合があり、本発明で意図する化成処理性が得られないことがある。よって、[Si]/[Mn]>0.4とすることが好ましい。また、Si含有量の最大値とMn含有量の最小値から[Si]/[Mn]は1.2未満となる。なお、[Si]はSi含有量、[Mn]はMn含有量を意味する。
Pは不純物元素であり、その含有量が0.05%を超えると、鋳造時のオーステナイト粒界へのP偏析に伴う粒界脆化により局部延性の劣化を通じて成形後の鋼板の耐遅れ破壊特性を劣化させる。そこで、その含有量は0.05%以下が好ましく、より好ましくは0.02%以下とする。なお、製造コストを考慮すればP含有量は、0.001%以上が好ましい。
Sは鋼板中にMnSとして存在し、耐衝撃特性や強度、耐遅れ破壊特性の低下を招く。このため、S含有量は極力低減することが好ましい。そのため、S含有量の上限は0.02%とする。好ましくは0.002%以下とする。より好ましくは0.001%以下とする。なお、製造コストを考慮すると、S含有量は、0.0001%以上が好ましい。
Alは自身が酸化物を形成することによってSiなどの酸化物の生成量を低減するため、耐遅れ破壊特性を改善する効果がある。しかしながら、Al含有量が0.01%未満では有意な効果は得られない。また、Al含有量が1.5%を超えるとAlとNとが結合して窒化物が生成する。窒化物は鋳造時にオーステナイト粒界上に析出して粒界脆化させるため、耐遅れ破壊特性を劣化させる。このため、Al含有量は1.5%以下とする。好ましくは0.08%未満、より好ましくは0.07%以下である。
Nは前述の通り、Alと結合して窒化物を生成し耐遅れ破壊特性を劣化させる。このためN含有量は、極力低減することが好ましい。そこで、N含有量は0.005%以下とする。より好ましくは0.003%以下とする。なお、製造コストを考慮すると、N含有量は0.0001%以上が好ましい。
Cuは腐食環境に晒された際、鋼板の溶解を抑制することで、鋼板に侵入する水素量を低減させる効果がある。Cu含有量が0.05%未満では、その効果は小さい。また、Cu含有量が0.50%を超えると、所定の表層Cu濃度分布を得るための酸洗条件の制御が困難となる。このため、Cu含有量は0.05%以上0.50%以下とする。下限について好ましくは0.08%以上とする。上限について好ましくは0.3%以下とする。
Nbは微細なNb炭窒化物を形成し、組織を微細化するとともに水素トラップ効果により耐遅れ破壊特性を向上させるため、必要に応じて添加してもよい。Nb含有量が0.2%を超えると、組織微細化の効果は飽和するばかりか、Ti存在下ではTiとNbで粗大な複合炭化物を形成して強度-延性バランスと耐遅れ破壊特性を劣化させる。このため、Nbを含有する場合には、その含有量を0.2%以下とする。また、好ましくは0.1%以下とする。より好ましくは0.05%以下とする。本発明では特に下限値を規定していないが、上記効果を得るためには少なくとも0.004%以上の含有が好ましい。
Tiは炭化物を生成して組織を微細化する効果と水素トラップ効果を有するため、必要に応じて添加してもよい。Ti含有量が0.2%を超えると、組織微細化の効果は飽和するばかりか、粗大なTiNを形成し、Nbの存在下ではTi-Nb複合炭化物を形成して強度-延性バランスと耐遅れ破壊特性を劣化させる。このため、Tiを含有する場合には、0.2%以下とする。また、好ましくは0.1%以下とする。より好ましくは0.05%以下とする。本発明では特に下限値を規定していないが、上記効果を得るためには少なくとも0.004%以上の含有が好ましい。
VとCとが結合して形成される微細炭化物は鋼板の析出強化および水素のトラップサイトとして作用するため耐遅れ破壊向上に有効であるため、必要に応じて添加してもよい。V含有量が0.5%を超えると、炭化物が過剰に析出して強度-延性バランスが劣化する。このため、Vを含有する場合にはその含有量を0.5%以下とする。また、好ましくは0.1%以下とする。より好ましくは0.05%以下とする。本発明では特に下限値を規定していないが、上記効果を得るためには少なくとも0.004%以上の含有が好ましい。
Moは鋼板の焼入性向上に有効であり、微細析出物による水素トラップ効果も有するので必要に応じて添加してもよい。Mo含有量が0.3%を超えると、効果が飽和するばかりか、連続焼鈍時に鋼板表面にMo酸化物の形成が促進され、鋼板の化成処理性が著しく低下する。このため、Moを含有する場合には、その含有量を0.3%以下とする。好ましくは0.1%以下とする。より好ましくは0.05%以下とする。本発明では特に下限値を規定していないが、上記効果を得るためには少なくとも0.005%以上の含有が好ましい。
CrはMoと同様、鋼板の焼入性向上に有効であり、必要に応じて添加してもよい。その含有量が1.0%を超えると、連続焼鈍後に酸洗処理を施しても鋼板表面のCr酸化物を除去しきれないため、鋼板の化成処理性が著しく低下する。このため、Crを含有する場合には、その含有量を1.0%以下とする。また、好ましくは0.5%以下とする。より好ましくは0.1%以下とする。本発明では特に下限値を規定していないが、上記効果を得るためには少なくとも0.04%以上の含有が好ましい。
Bは連続焼鈍における加熱時にオーステナイト粒界に偏析し、冷却時のオーステナイトからのフェライト変態およびベイナイト変態を抑制して、焼戻しマルテンサイトの形成を容易化するため、鋼板の強化に有効である。また、Bは、粒界強化により耐遅れ破壊特性を向上させるため、必要に応じて添加してもよい。B含有量が0.005%を超えると、ホウ炭化物Fe23(C,B)6が生じて加工性の劣化と強度の低下が起きる。このため、Bを含有する場合には、その含有量を0.005%以下とする。また、好ましくは0.003%以下とする。本発明では特に下限値を規定していないが、上記効果を得るためには少なくとも0.0002%以上の含有が好ましい。
Sn、Sbはいずれも表面酸化や脱炭、窒化を抑制する効果を有するため、必要に応じて添加してもよい。しかしながら、含有量がそれぞれ0.1%を超えてもその効果は飽和する。このため、Sn、Sbを含有する場合にはこれらの含有量をそれぞれ0.1%以下とする。また、好ましくは0.05%以下とする。本発明では特に下限値を規定していないが、上記効果を得るためには、それぞれ少なくとも0.001%以上の含有が好ましい。
W、Coはいずれも硫化物の形態制御や粒界強化、固溶強化を通じて鋼板の特性を向上させる効果を有するため、必要に応じて添加してもよい。しかしながら、WやCoを過度に含有すると粒界偏析などにより延性が劣化する。このため、これらの元素の含有量は0.1%以下とするのが好ましい。また、好ましくは0.05%以下とする。本発明では特に下限値を規定していないが、上記効果を得るためには少なくとも0.01%以上の含有が好ましい。
Ca、REMはいずれも硫化物の形態制御を通じて延性や耐遅れ破壊特性向上させる効果を有するため、必要に応じて添加してもよい。しかしながら、CaやREMを過度に含有すると粒界偏析などにより延性が劣化する。このためこれらの成分の含有量は0.005%以下とするのが好ましい。より好ましくは0.002%以下とする。本発明では特に下限値を規定していないが、上記効果を得るためには少なくとも0.0002%以上の含有が好ましい。
Siを主体とする酸化物が鋼板表面に存在すると、化成処理性が著しく低下する。そこで、Siを主体とする酸化物の鋼板表面被覆率は1%以下とする。好ましくは0%である。なお、Siを主体とする酸化物とは、例えばSiO2である。また、Siを主体とする酸化物は後述する実施例の方法にて測定することができる。なお、「Siを主体とする」とは酸化物を構成する酸素以外の元素のうちSiの原子濃度比が70%以上であることを意味する。
鉄系酸化物の鋼板表面被覆率が85%を超えると、化成処理における鉄の溶解反応が阻害されて、リン酸亜鉛等の化成結晶の成長が抑制される。近年では、製造コスト削減の観点から、化成処理液を低温化しており、化成処理条件としては従来よりも厳しい条件となっている。そのため、表面被覆率85%以下では不十分であり、好ましくは40%以下である。さらに好ましくは35%以下である。下限は特に限定されないが、鋼板表面被覆率は20%以上であることが多い。また、鉄系酸化物の鋼板表面被覆率は後述する実施例の方法にて測定することができる。なお、鉄系酸化物とは酸化物を構成する酸素以外の元素のうち鉄の原子濃度比が30%以上である鉄主体の酸化物のことを意味する。
本発明で所期した効果を得るには、Si含有量、Cu含有量を上記の範囲に調整するだけでは不十分で、Si含有酸化物を除去するための酸洗において、鋼板表層におけるCu濃度分布を制御する必要がある。すなわち、本発明では、Cu含有量を0.05%以上0.50%以下とし、CuS/CuBを4.0以下(CuSは鋼板表層におけるCu濃度、CuBは母材におけるCu濃度)とする必要がある。このCu濃度分布は、連続焼鈍後の酸洗処理において、酸洗減量を下記(1)式の範囲に制御することにより達成できる。下限は特に限定されないが、化成処理性を改善する観点から、CuS/CuBは2.0以上が好ましい。なお、鋼板表層とは表面から板厚方向に20nm以内の領域を意味する。
WR≦33.25×exp(-7.1×[Cu%]) (1)
(WR:酸洗減量(g/m2)、[Cu%]:鋼中のCu含有量)
鋼板表面に再析出したCuを研削等により除去することでも上記のCu濃度分布は達成されるが、研削疵が残るため優れた化成処理性が得られない。CuS/CuBは実施例に記載の方法で測定した。
焼鈍温度がAc1点未満になると、焼鈍中に所定の強度確保に必要なオーステナイト(焼入れ後にマルテンサイトに変態)が生成せず、焼鈍後焼入れを実施しても1180MPa以上の引張強さが得られない。そのため、焼鈍温度はAc1点以上が好ましい。この温度範囲において、オーステナイトの平衡面積率が40%以上を安定して確保する観点から、焼鈍温度は800℃以上とするのが好ましい。また、焼鈍温度での滞留(保持)時間が短すぎると鋼組織が十分に焼鈍されずに冷間圧延による加工組織が存在した不均一な組織となり延性が低下する。一方、滞留時間が長すぎると製造時間の増加を招き製造コスト上好ましくない。このため、滞留時間は30~1200秒が好ましい。特に好ましい滞留時間は250~600秒の範囲である。
Ac1=723-10.7×[Mn%]+29.1×[Si%]+16.9×[Cr%]+6.38×[W%]
焼鈍後の冷延鋼板は、Ms-100℃以上Ms点未満の一次冷却停止温度域まで、平均冷却速度を3℃/s以上に制御して冷却される。この冷却は、Ms点未満まで冷却することによりオーステナイトの一部をマルテンサイト変態させるものである。ここで、一次冷却停止温度域の下限がMs-100℃未満では、この時点で未変態オーステナイトがマルテンサイト化する量が過大となり、優れた強度と加工性の両立ができない。一方、一次冷却停止温度域の上限がMs以上になると、適正な焼戻しマルテンサイト量が確保できなくなる。従って、一次冷却停止温度域の範囲は、Ms-100℃以上Ms点未満とする。好ましくはMs-80℃以上Ms点未満、更に好ましくはMs-50℃以上Ms点未満である。また、平均冷却速度が3℃/s未満の場合、フェライトの過剰な生成、成長や、パーライト等の析出が生じ、所望の鋼組織を得られない。従って、焼鈍温度から一次冷却停止温度域までの平均冷却速度は、3℃/s以上とする。好ましくは5℃/s以上、さらに好ましくは8℃/s以上である。平均冷却速度の上限は、冷却停止温度にバラツキが生じない限り特に限定されない。なお、上述したMs点は、次式に示すような近似式によって求めることができる。Msは、経験的に求められる近似値である。
Ms(℃)=565-31×[Mn%]-13×[Si%]-10×[Cr%]-12×[Mo%]-600×(1-exp(-0.96×[C%]))
ただし、[X%]は鋼板の成分元素Xの質量%とし、含まない元素は0とする。
一次冷却停止温度域まで冷却された鋼板は、300℃以上Bs-50℃以下かつ450℃以下の過時効温度域まで昇温され、過時効温度域で15秒以上1000秒以下滞留(保持)される。
Bs(℃)=830-270×[C%]-90×[Mn%]-70×[Cr%]-83×[Mo%]
ただし、[X%]は鋼板の成分元素Xの質量%とし、含まない元素は0とする。
酸洗に用いる溶液の組成は特に限定されない。例えば、硝酸、塩酸、弗酸、硫酸およびそれらを2種以上混合した酸のいずれかを用いることができる。なお、酸洗では強酸化性の酸(硝酸等)を酸洗液として用い、再酸洗では、酸洗で用いる酸洗液とは異なり、かつ、非酸化性の酸を酸洗液として用いる。
<標準条件>
・脱脂工程:処理温度 45℃、処理時間120秒
・スプレー脱脂、表面調整工程:pH8.5、処理温度室温、処理時間 30秒
・化成処理工程:化成処理液の温度 40℃、処理時間 90秒
化成処理後の鋼板表面を、SEMを用いて倍率500倍で5視野観察し、5視野全てにおいて面積率95%以上で均一な化成結晶が生成している場合を化成処理性が良好「○」、1視野でも面積率5%超のスケが認められた場合を化成処理性が劣位「×」と評価した。
No.11はC含有量が少ないため、所定のミクロ組織と引張強さが得られていない。
No.12はC含有量が多いため、炭化物が粗大化し、耐遅れ破壊特性が劣位である。
No.13はSi含有量が少ないため、炭化物が粗大化し、耐遅れ破壊特性が劣位である。
No.14はSi含有量が多いため、鋼板表面のSi含有酸化物が酸洗によって十分に除去しきれないため、化成処理性が劣位である。酸洗減量を増すと、表層におけるCu濃度分布が規定の範囲を超えるため、化成処理性は改善しない。
No.15はCu含有量が少ないため、耐遅れ破壊特性が劣位である。
No.16はCu含有量が多いため、所定の表層Cu濃度分布を得るための酸洗条件の制御が困難となる。No.16では酸洗減量が小さくなるように制御したが、Si含有酸化物が十分に除去されなかったために化成処理性が劣位であった。
No.17、18は優れた強度、化成処理性、耐遅れ破壊特性を有するものの、鋼組織が好ましい範囲にないため、TS×Elが16500未満となっている。
2 ボルト
Claims (5)
- 成分組成が、質量%で、
C:0.10%以上0.6%以下、
Si:1.0%以上3.0%以下、
Mn:2.5%超え10.0%以下、
P:0.05%以下、
S:0.02%以下、
Al:0.01%以上1.5%以下、
N:0.005%以下、
Cu:0.05%以上0.50%以下
を含有し、残部は鉄及び不可避的不純物からなり、
Siを主体とする酸化物の鋼板表面被覆率が1%以下であり、
鉄系酸化物の鋼板表面被覆率が40%以下であり、
CuS/CuBが4.0以下(CuSは鋼板表層におけるCu濃度、CuBは母材におけるCu濃度)を満たし、
引張強さが1180MPa以上である高強度冷延鋼板。 - 鋼組織が、焼戻しマルテンサイト及び/又はベイナイトを合計体積率で40%以上100%以下、フェライトを体積率で0%以上60%以下、残留オーステナイトを体積率で2%以上30%以下であり、
引張強さ×全伸びが16500MPa・%以上である請求項1に記載の高強度冷延鋼板。 - [Si]/[Mn]が0.40超([Si]はSi含有量(質量%)、[Mn]はMn含有量(質量%))を満たす請求項1又は2に記載の高強度冷延鋼板。
- 前記成分組成が、さらに、質量%で、
Nb:0.2%以下、
Ti:0.2%以下、
V:0.5%以下、
Mo:0.3%以下、
Cr:1.0%以下、
B:0.005%以下の1種以上を含有する請求項1~3のいずれかに記載の高強度冷延鋼板。 - 前記成分組成は、さらに、質量%で、
Sn:0.1%以下、
Sb:0.1%以下、
W:0.1%以下、
Co:0.1%以下、
Ca:0.005%以下、
REM:0.005%以下のいずれか1種以上を含有する請求項1~4のいずれかに記載の高強度冷延鋼板。
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Also Published As
Publication number | Publication date |
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CN108699648A (zh) | 2018-10-23 |
KR20180102165A (ko) | 2018-09-14 |
MX2018009982A (es) | 2018-11-09 |
EP3418417B1 (en) | 2020-07-29 |
JP6308335B2 (ja) | 2018-04-11 |
KR102114741B1 (ko) | 2020-05-25 |
US20190040490A1 (en) | 2019-02-07 |
CN108699648B (zh) | 2020-11-03 |
US11008635B2 (en) | 2021-05-18 |
CA3009784A1 (en) | 2017-08-24 |
EP3418417A4 (en) | 2019-01-02 |
EP3418417A1 (en) | 2018-12-26 |
JPWO2017141953A1 (ja) | 2018-03-01 |
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