WO2014156140A1 - 高強度溶融亜鉛めっき鋼板およびその製造方法 - Google Patents
高強度溶融亜鉛めっき鋼板およびその製造方法 Download PDFInfo
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- WO2014156140A1 WO2014156140A1 PCT/JP2014/001728 JP2014001728W WO2014156140A1 WO 2014156140 A1 WO2014156140 A1 WO 2014156140A1 JP 2014001728 W JP2014001728 W JP 2014001728W WO 2014156140 A1 WO2014156140 A1 WO 2014156140A1
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- 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
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- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B15/00—Layered products comprising a layer of metal
- B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
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- C23C2/0224—Two or more thermal pretreatments
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
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- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
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- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
Definitions
- the present invention relates to a high-strength steel sheet suitable for use in automobile parts and the like, and a method for producing the same, and without tensile addition of expensive elements such as Ti, Nb, V, Cu, Ni, Cr, and Mo.
- Automotive parts often have complex shapes, and materials that are excellent in elongation (El) and stretch flangeability (also referred to as hole expandability), which are one index of workability, are required. Further, when the strength is increased to the TS900 MPa class or higher, extremely expensive rare elements such as Ti, Nb, V, Cu, Ni, Cr, and Mo may be positively added from the viewpoint of securing the strength.
- Patent Document 1 C: 0.12 to 0.3% by mass, Si: 0.1% or less (excluding 0%), Mn: 2.0 to 3.5%, P: 0 0.05% or less (not including 0%), S: 0.05% or less (not including 0%), Al: 0.005 to 0.1%, and N: 0.015% or less (0% And the balance is iron and inevitable impurities, the metal structure is bainite as the parent phase structure, and the ferrite area ratio is 3 to 20% in proportion to the total structure: A high yield ratio high strength hot dip galvanized steel sheet excellent in workability having a tensile strength of 980 MPa or more, characterized by satisfying a site area ratio of 10 to 35% is disclosed.
- Patent Document 2 C%: 0.03 to 0.20%, Si: 1.0% or less, Mn: 0.01 to 3%, P: 0.0010 to 0.1%, S : 0.0010 to 0.05%, Al: 0.3 to 2.0%, Mo: 0.01 to 5.0%, Ti: 0.001 to 0.5%, Nb: Containing one or more of 0.001 to 0.5%, B: 0.0001 to 0.0050%, Cr: 0.01 to 5%, the balance consisting of Fe and unavoidable impurities, microstructure
- a hot-dip galvanized high-strength steel sheet excellent in hole expansibility and ductility, characterized by containing ferrite with an area ratio of 30% or more and a tensile strength of 850 MPa or more is disclosed.
- Patent Document 3 by mass%, C: 0.10 to 0.50%, Mn: 1.0 to 3.0%, Si: 0.005 to 2.5%, Al: 0.005 to 2.5%, P: 0.05% or less, S: 0.02% or less, N: 0.006% or less, and the sum of Si and Al is Si + Al ⁇ 0.8%
- the ductility is characterized in that the microstructure contains 10 to 75% ferrite in area ratio, 2 to 30% retained austenite, and the C content in the retained austenite is 0.8 to 1.0%.
- an alloyed hot-dip galvanized steel sheet excellent in corrosion resistance is disclosed.
- the steel sheet disclosed in Patent Document 1 has a structure including a ferrite phase and a martensite phase and a bainite phase as a parent phase, and the elongation was not sufficient.
- the steel sheet disclosed in Patent Document 2 contains an expensive element such as Mo, and the structure contains ferrite having an area ratio of 30% or more, but the elongation is not sufficient.
- the present invention solves the above problems in a component system that does not actively contain expensive alloy elements such as Ti, Nb, V, Cu, Ni, Cr, and Mo, and has excellent elongation and stretch flangeability. It is an object of the present invention to provide a high-strength hot-dip galvanized steel sheet having excellent workability and a tensile strength (TS) of 900 MPa or more and a method for producing the same.
- TS tensile strength
- the present inventors have intensively studied to solve the above problems.
- the hot dip galvanized steel sheet having a tensile strength of 900 MPa or more that is extremely excellent in elongation and excellent in stretch flangeability even when the content of the above-mentioned expensive rare metal is small. It was found that can be obtained.
- the C content should be 0.24% or less.
- the metal structure is a ferrite phase, a bainite phase, a tempered martensite phase, a retained austenite phase, and a martensite phase, and the area ratio of these phases is controlled within a predetermined range.
- the present invention has been made on the basis of such knowledge, and the gist thereof is as follows.
- the high-strength hot-dip galvanized steel sheet of the present invention is, for example, a steel slab having the above component composition is hot-rolled, pickled, cold-rolled, and then in a temperature range of 800 to 950 ° C. Then, the substrate is heated to a temperature range of 700 to 850 ° C. and then cooled to a temperature range of 100 to 300 ° C. at a cooling rate of 5 to 50 ° C./second. It can be manufactured by a method in which a heat treatment is performed by heating in a temperature range of 600 ° C. and holding for 10 to 500 seconds, followed by hot dip galvanization.
- a high-strength hot-dip galvanized steel sheet having a tensile strength of 900 MPa or more that is excellent in elongation and excellent in stretch flangeability can be obtained without positively adding expensive elements as described above.
- the high-strength hot-dip galvanized steel sheet obtained by the present invention is suitable as an automobile part that is press-formed into a strict shape.
- the present inventors diligently studied on improving the elongation of the high-strength hot-dip galvanized steel sheet. As a result, it has been found that even if the component composition does not contain expensive elements such as Ti, Nb, V, Cu, Ni, Cr, and Mo, the improvement in elongation becomes remarkable by using a predetermined structure. That is, in the present invention, the total area ratio of the ferrite phase and the bainite phase is 30 to 70%, the area ratio of the tempered martensite phase to the entire structure is 20 to 40%, and the residual austenite phase is based on the entire structure. The structure has an area ratio of 10 to 20% and an area ratio of 2 to 20% of the entire structure of the martensite phase. Details of the present invention will be described below.
- C 0.16 to 0.24%
- C is an austenite stabilizing element that affects the formation of retained austenite phase and contributes to the improvement of uniform elongation, and also affects the area ratio and hardness of the tempered martensite phase and martensite phase and contributes to strength. Element. If the amount of C is less than 0.16%, the ferrite phase is excessively generated, and it is difficult to ensure the tensile strength, the desired retained austenite amount cannot be obtained, and it is difficult to ensure excellent elongation. Therefore, the C amount is 0.16% or more. Preferably, the amount of C is 0.18% or more.
- the C amount is 0.24% or less.
- the amount of C is 0.23% or less, more preferably 0.22% or less.
- the C content is in the range of 0.16% to 0.24%. From the viewpoint of weldability, the range is preferably from 0.18% to 0.23%. A more preferable range is 0.18% or more and 0.22% or less.
- Si 0.8-1.8% Si is an element effective for strengthening steel by solid solution strengthening, affects the formation of retained austenite phase, contributes to improvement of uniform elongation, and improves the balance between strength and elongation (TS-El balance). If the Si amount is less than 0.8%, such an effect cannot be obtained. Therefore, the Si amount is 0.8% or more. Preferably, the amount of Si is 1.2% or more. On the other hand, when the amount of Si exceeds 1.8%, the amount of Si concentrated on the surface increases and non-plating occurs. Therefore, the Si amount is 1.8% or less. Preferably, the amount of Si is 1.6% or less. Therefore, the Si amount is set in the range of 0.8% to 1.8%. The range is preferably 1.2% or more and 1.8% or less, more preferably 1.2% or more and 1.6% or less.
- Mn 1.0 to 3.0%
- Mn is an austenite stabilizing element, and is an element that contributes to strength by generating a desired amount of tempered martensite phase and martensite phase finally obtained.
- the amount of Mn needs to be 1.0% or more.
- the amount of Mn is 1.5% or more, and more preferably 1.7% or more.
- the Mn content is 3.0% or less.
- the amount of Mn is 2.5% or less, more preferably 2.3% or less. Therefore, the Mn content is in the range of 1.0% to 3.0%. Preferably it is 1.5% or more and 2.5% or less, More preferably, it is 1.7% or more and 2.3% or less.
- P 0.020% or less
- P is an element that adversely affects weldability
- the amount of P is preferably smaller.
- the range of the P amount is 0.020% or less.
- the amount of P is less than 0.010%.
- the P content is preferably 0.001% or more. Therefore, the range of the P amount is preferably 0.001% or more and 0.020%. In consideration of weldability, the range is more preferably 0.001% or more and less than 0.010%.
- the amount of S is preferably small.
- the amount of S is 0.0020% or less.
- the S content is preferably 0.0001% or more. Therefore, the range of the amount of S is preferably 0.0001% or more and 0.0040% or less. More preferably, it is 0.0001% or more and 0.0020% or less of range.
- Al 0.01 to 0.1% Al is added as a deoxidizer for steel, and it is necessary to add 0.01% or more.
- the Al content is 0.02% or more.
- the Al content is 0.1% or less.
- the Al content is 0.08% or less, more preferably 0.06% or less. Therefore, the Al content is set to 0.01% or more and 0.1% or less.
- it is 0.02% or more and 0.08% or less, More preferably, it is 0.02% or more and 0.06% or less of range.
- N is an element that affects aging, and the N content is preferably low.
- the N amount is 0.0060% or less.
- the N content is preferably 0.0001% or more. Therefore, a preferable range of the N amount is 0.0001% or more and 0.01% or less. A more preferable range is 0.0001% or more and 0.0060% or less.
- Ca 0.0001 to 0.0020%
- Ca has the effect of reducing the shape of the sulfide, which is the starting point of cracking during deformation, from a plate shape to a spherical shape and suppressing a decrease in local deformability.
- the Ca content needs to be 0.0001% or more.
- the Ca content is 0.0020% or less.
- the Ca content is 0.0010% or less. Therefore, the Ca content is in the range of 0.0001% to 0.0020%.
- it is 0.0001% or more and 0.0010% or less of range.
- components other than the above are Fe and inevitable impurities. However, components other than those described above are not rejected as long as the effects of the present invention are not impaired. From the object of the present invention not to actively contain expensive alloy elements, it is preferable not to contain Ti, Nb, V, Cu, Ni, Cr, and Mo.
- Area ratio of the total of the ferrite phase and bainite phase to the entire structure 30 to 70%
- the bainite phase and ferrite phase composed of cementite and ferrite phase are softer than the martensite phase and contribute to elongation.
- the area ratio of the total of the ferrite phase and the bainite phase to the entire structure needs to be 30% or more.
- the area ratio of the hard martensite phase increases, the strength becomes excessively high, and only low elongation can be obtained.
- the area ratio of the total of the ferrite phase and the bainite phase to the entire structure is 45% or more.
- the total area ratio of the ferrite phase and the bainite phase needs to be 70% or less.
- the total area ratio of the ferrite phase and the bainite phase is 68% or less, and more preferably 65% or less. Therefore, the total area ratio of the ferrite phase and the bainite phase is in the range of 30% to 70%. A preferable range is 30% or more and 68% or less, and a more preferable range is 45% or more and 65% or less.
- the tempered martensite phase contributes to strength and has less adverse effect on elongation than the hard martensite phase before tempering.
- the tempered martensite phase is effective for securing a high elongation and achieving a high TS-El balance, specifically, TS ⁇ El ⁇ 26000 MPa ⁇ %.
- the area ratio of the tempered martensite phase to the entire structure needs to be 20% or more.
- the area ratio of the tempered martensite phase to the whole structure is 25% or more.
- the area ratio of a tempered martensite phase shall be 40% or less.
- the area ratio of the tempered martensite phase is 35% or less. Therefore, the area ratio of the tempered martensite phase is in the range of 20% to 40%. A more preferable range is 25% or more and 35% or less.
- the residual austenite phase is strain induced transformation, that is, when the material is deformed, the deformed part is transformed into the martensite phase, the deformed part becomes hard, and the uniform elongation is prevented by preventing strain concentration. There is an effect to improve.
- tissue of a retained austenite phase shall be 10% or more.
- the residual austenite phase has a high C concentration and is hard.
- tissue of a retained austenite phase shall be 20% or less.
- the area ratio of the retained austenite phase to the entire structure is 15% or less. Therefore, the area ratio of the retained austenite phase is 10% or more and 20% or less. Preferably, it is in the range of 10% to 15%.
- a hard martensite phase with a high dislocation density is clearly distinguished from a tempered soft martensite phase with a low dislocation density. That is, the martensite phase referred to in the present invention does not include a tempered martensite phase.
- the hard martensite phase greatly contributes to the tensile strength, and the area ratio of the martensite phase needs to be 2% or more in order to secure TS of 900 MPa or more.
- the area ratio of the martensite phase is 5% or more.
- the area ratio of the martensite phase needs to be 20% or less because the strength is excessively increased and the elongation is lowered.
- the area ratio of the martensite phase is 18% or less, more preferably the area ratio of the martensite phase is 15% or less.
- the area ratio of the martensite phase is in the range of 2% to 15%, more preferably 5% to 15%.
- the steel sheet of the present invention is a high-strength hot-dip galvanized steel sheet, and has a hot-dip galvanized film on the surface of the high-strength steel sheet having the above-described component composition and structure.
- the hot dip galvanized steel sheet of the present invention is a non-alloy hot dip galvanized steel sheet (GI) which is manufactured by dipping in a hot dip galvanizing bath as described later.
- the coating weight of galvanizing is not particularly limited, it is preferable that the two-sided plating or one side plating per side 30g / m 2 ⁇ 120g / m 2.
- the steel slab having the above composition is hot-rolled, pickled, cold-rolled, then heated to a temperature range of 800-950 ° C. and then cooled, and then at a temperature of 700-850 ° C.
- Heat treatment cooling to a temperature range of 100 to 300 ° C. at a cooling rate of 5 to 50 ° C./second, stopping the cooling, and subsequently heating to a temperature range of 350 to 600 ° C. and holding for 10 to 500 seconds
- hot dip galvanizing is performed to obtain the high-strength galvanized steel sheet of the present invention.
- skin pass rolling may be applied to the steel sheet after hot dip galvanization.
- the production of the steel slab is not particularly limited, and it may be produced by thin slab casting or ingot forming. In particular, in order to reduce segregation, it is preferable to manufacture by a continuous casting method.
- the hot rolling is not particularly limited, and may be performed according to a conventional method.
- the heating temperature at the time of hot rolling shall be 1100 degreeC or more, and it is preferable that an upper limit shall be about 1300 degreeC from a viewpoint of reduction of a scale production
- the hot rolling finishing temperature (finishing rolling exit temperature) is preferably 850 ° C. or higher so as to avoid the formation of a layered structure of ferrite and pearlite.
- the upper limit of the hot rolling finishing temperature is preferably about 950 ° C.
- the coiling temperature after completion of hot rolling is preferably 400 ° C. or higher, and preferably 600 ° C. or lower, from the viewpoints of cold rollability and surface properties. Therefore, the winding temperature is preferably 400 to 600 ° C.
- the steel sheet after winding is pickled according to a conventional method, and then cold-rolled to a desired thickness.
- the conditions for pickling are not particularly limited, and may be performed according to a conventionally known method such as pickling with hydrochloric acid.
- limiting in particular also about cold rolling What is necessary is just to carry out according to a conventionally well-known method and to set it as desired plate thickness.
- the rolling reduction of cold rolling is not particularly limited, but is preferably 30% or more, and preferably 60% or less. Therefore, the rolling rate of cold rolling is preferably about 30 to 60%.
- the cold-rolled steel sheet is heated to a temperature range of 800 to 950 ° C. and then cooled, then heated to a temperature range of 700 to 850 ° C. and heated to a temperature range of 100 to 300 ° C. at a cooling rate of 5 to 50 ° C./second. After cooling to a temperature range and stopping the cooling, a heat treatment is continued by heating to a temperature range of 350 to 600 ° C. and holding for 10 to 500 seconds, followed by hot dip galvanization.
- Cold-rolled steel sheet After cold rolling, heating to 800 to 950 ° C. and cooling after cooling Cold-rolled steel sheet (cold rolled sheet) is subjected to heat treatment (annealing).
- the temperature of this heat treatment is less than 800 ° C., the austenite fraction during heat treatment is small, the distribution of C and Mn into the austenite proceeds, and austenite having a high C and Mn concentration is finely dispersed.
- the area ratio of the martensite phase is increased since the region with a high C concentration originally becomes the martensite phase preferentially after the final heat treatment described later, and The martensite phase becomes a non-uniform structure in a band shape again.
- the temperature of the heat treatment (annealing) applied to the steel sheet after cold rolling is set to 800 ° C. or higher.
- the temperature is 840 ° C or higher.
- the heat treatment temperature exceeds 950 ° C. and is heated to the temperature range of the austenite single phase, the austenite grain size is excessively coarsened, so that the finally obtained crystal grains are excessively coarsened, and the nucleation site of the ferrite phase The grain boundary which is is reduced.
- the temperature of the heat treatment (annealing) applied to the steel sheet after cold rolling is set to 950 ° C. or less.
- the temperature is 900 ° C. or lower.
- the heat treatment temperature (annealing temperature) is 800 ° C. or higher and 950 ° C. or lower.
- it is the range of 840 degreeC or more and 900 degrees C or less.
- the cooling after annealing is not particularly specified, and may be appropriately cooled to room temperature.
- the cooling stop temperature of cooling after annealing is preferably 300 ° C. or higher. More preferably, it is 350 ° C. or higher. Moreover, it is preferable that this cooling stop temperature shall be 500 degrees C or less, More preferably, it is 450 degrees C or less. Therefore, the cooling stop temperature is preferably in the range of 300 to 500 ° C., more preferably in the range of 350 to 450 ° C.
- the holding time in the cooling stop temperature range is preferably 1000 seconds or less, more preferably 600 seconds or less. Therefore, it is preferable to maintain the range of 100 to 1000 seconds, and more preferably 200 to 600 seconds, in the cooling stop temperature range.
- the final heat treatment is performed after the heat treatment (annealing) after the cold rolling described above.
- heating was performed in a temperature range of 700 to 850 ° C., and cooling was stopped at a cooling rate of 5 to 50 ° C./second to a temperature range of 100 to 300 ° C. Thereafter, the heat treatment is continued in the temperature range of 350 to 600 ° C. and held for 10 to 500 seconds.
- Heat treatment temperature for final heat treatment 700 to 850 ° C
- the heat treatment temperature of the final heat treatment is set to 700 ° C. or higher.
- the heat treatment temperature is 750 ° C. or higher.
- the heat treatment temperature of the final heat treatment exceeds 850 ° C.
- the area ratio of the austenite phase during the heat treatment increases, the area ratio of the ferrite phase of the steel sheet after the hot dip galvanizing treatment is small, and the area ratio other than the ferrite phase increases.
- the heat treatment temperature of the final heat treatment is set to 850 ° C. or lower.
- the heat treatment temperature is 830 ° C. or lower. Therefore, the heat treatment temperature of the final heat treatment is set to 700 ° C. or higher and 850 ° C. or lower.
- a more preferable heat treatment temperature is 750 ° C. or higher and 830 ° C. or lower.
- Cooling rate 5 to 50 ° C./second
- the cooling rate from the above-mentioned final heat treatment temperature is important for obtaining the desired phase area ratio.
- the cooling rate is an average cooling rate from the heat treatment temperature of the final heat treatment to the cooling stop temperature.
- the cooling rate is 5 ° C./second or more.
- the cooling rate is 10 ° C./second or more.
- the cooling rate is set to 50 ° C./second or less.
- the cooling rate is 40 ° C./second or less, more preferably 30 ° C./second or less. Therefore, the cooling rate is in the range of 5 ° C./second to 50 ° C./second. The range is preferably 10 ° C./second or more and 40 ° C./second or less, more preferably 10 ° C./second or more and 30 ° C./second or less.
- This cooling is preferably gas cooling, but there is no particular need to define it, and it is possible to combine furnace cooling, mist cooling, roll cooling, water cooling, and the like.
- Cooling stop temperature 100-300 ° C
- the martensite phase is excessively generated when the cooling is stopped.
- the martensite phase is tempered by subsequent heating to a temperature range of 350 to 600 ° C. (re-heating), the area ratio of the finally obtained tempered martensite phase increases, and the residual austenite phase Is suppressed, and it is difficult to secure excellent elongation. Therefore, the cooling stop temperature is set to 100 ° C. or higher.
- the cooling stop temperature is 150 ° C. or higher.
- the cooling stop temperature exceeds 300 ° C.
- the martensite phase generated at the time of cooling stop is small, and the martensite phase is baked by heating to a temperature range of 350 to 600 ° C. (re-heating).
- the area ratio of the tempered martensite phase finally obtained is reduced too much.
- the amount of austenite increases after holding in the temperature range of 350 to 600 ° C., and a hard martensite phase is excessively generated in the cooling process to room temperature after holding, and the strength is increased too much to ensure excellent elongation. It becomes difficult. Therefore, the cooling stop temperature is set to 300 ° C. or lower.
- the cooling stop temperature is 275 ° C.
- the cooling stop temperature is 250 ° C. or lower. Therefore, in order to control the area ratio of the ferrite phase, bainite phase, martensite phase and residual austenite phase to a desired range, to secure a tensile strength of TS 900 MPa or more and to obtain excellent elongation, the cooling stop temperature is 100 ° C. or more.
- the range is 300 ° C. or lower. Preferably it is 100 degreeC or more and 275 degrees C or less, More preferably, it is the range of 150 degreeC or more and 250 degrees C or less.
- the heating temperature also referred to as re-heating temperature
- the holding time is less than 10 seconds
- tempered martensite is not obtained, and finally a hard martensite phase is excessively generated in the steel sheet, The steel sheet becomes stronger and it becomes difficult to ensure excellent elongation. Therefore, the re-heating temperature is set to 350 ° C. or higher.
- the holding time is 10 seconds or longer.
- the re-heating temperature is 370 ° C. or higher.
- the holding time is 20 seconds or longer.
- the re-heating temperature is set to 600 ° C. or less.
- the holding time is 500 seconds or less.
- the re-heating temperature is 500 ° C. or less.
- the holding time is 180 seconds or less. For this reason, after the cooling is stopped, it is heated to a temperature range of 350 to 600 ° C. and held for 10 to 500 seconds.
- Hot dip galvanizing treatment After holding at the above re-heating temperature, hot dip galvanizing treatment is performed.
- Zinc plating may be performed according to a conventional method. For example, after immersing a steel sheet in a 440 to 500 ° C. galvanizing bath containing Al in an amount of 0.05 to 0.25% by mass, the amount of adhesion is reduced by gas wiping or the like. Adjust and implement. Although it does not specifically limit after hot dip galvanization, what is necessary is just to cool to normal temperature by air cooling or gas cooling. Further, although not particularly limited, the hot dip galvanizing treatment is preferably performed following the final heat treatment in a continuous hot dip galvanizing facility having a continuous annealing furnace for productivity. Note that the steel sheet after the hot dip galvanizing treatment can be subjected to temper rolling and various coating treatments such as oil coating and coating for the purpose of adjusting the surface roughness and correcting the shape.
- the heat treatment performed after hot rolling and pickling and before cold rolling eliminates uneven distribution of elements such as C and Mn resulting from the hot rolled structure, and has a uniform structure in which cementite is finely dispersed with the ferrite phase as the parent phase, This is effective for controlling the area ratio of the martensite phase generated excessively under the influence of uneven distribution of elements such as C and Mn after the final heat treatment to an appropriate range.
- it is effective in eliminating a heterogeneous structure in which the martensite phase exists in a band shape and obtaining a higher TS-El balance.
- the heat treatment temperature after hot rolling and pickling needs to be 400 ° C. or higher.
- the heat treatment temperature is 450 ° C. or higher.
- a non-uniform structure in which elements such as C and Mn are unevenly distributed is formed after the heat treatment.
- the martensite phase is preferentially generated from the location where C and Mn are unevenly distributed, there are many martensite phases after the final heat treatment, making it difficult to obtain a desired structure.
- the heat treatment temperature is preferably 750 ° C. or lower. More preferably, it is 700 degrees C or less, More preferably, it is 650 degrees C or less. Therefore, there is an optimum temperature range to obtain a very uniform structure before cold rolling, and the heat treatment temperature after hot rolling and pickling is set to a range of 400 ° C. or higher and 750 ° C. or lower. Preferably it is the range of 450 degreeC or more and 700 degrees C or less, More preferably, it is the range of 450 degreeC or more and 650 degrees C or less.
- the black region observed in the structure observation is a ferrite phase (polygonal ferrite phase) or a bainite phase
- the total area ratio of the ferrite phase and the bainite phase was determined.
- the remaining region other than the black region is a tempered martensite phase, a martensite phase and a retained austenite phase
- the total area ratio of the tempered martensite phase, the martensite phase and the retained austenite phase is determined, and the steel sheet structure was divided into two regions.
- the amount of retained austenite was obtained by X-ray diffraction, and the obtained amount of retained austenite was defined as the area ratio of the retained austenite phase.
- the amount of retained austenite was determined by an X-ray diffraction method using Mo K ⁇ rays. That is, using a test piece having a surface near a thickness of 1 ⁇ 4 of the steel sheet as a measurement surface, from the peak intensity of the (211) and (220) surfaces of the austenite phase and the (200) and (220) surfaces of the ferrite phase The amount (volume ratio) of the retained austenite phase was calculated and used as the area ratio.
- SEM scanning electron microscope
- Tensile properties (tensile strength, elongation) Using the No. 5 test piece described in JISZ2201 with the rolling direction and the 90 ° direction as the longitudinal direction (tensile direction), a tensile test based on JISZ2241 was performed to yield strength (YP), tensile strength (TS) and total elongation ( El) was investigated. The results are shown in Table 3. The elongation was evaluated based on the TS-El balance, and the evaluation standard was TS ⁇ E1 ⁇ 26000 MPa ⁇ %.
- hole expansion rate (%) ((d ⁇ d 0 ) / d 0 ) ⁇ 100.
- Three tests were performed on the same number of steel plates, and the average value ( ⁇ ) of the hole expansion rate was obtained.
- the stretch flangeability was evaluated by the TS- ⁇ balance, and the evaluation standard was TS ⁇ ⁇ ⁇ 30000 MPa ⁇ %.
- No. with a high Mn content and component composition outside the scope of the present invention No. 6 has a large area ratio of martensite phase and low elongation.
- the heat treatment temperature after cold rolling is low.
- No. 8 has a large area ratio of the martensite phase and low elongation.
- the heat treatment temperature in the final heat treatment is low. 9.
- No. 11 has a large total area ratio of ferrite phase (polygonal ferrite phase) and bainite phase, and has a small area ratio with respect to the entire structure of the tempered martensite phase, and TS is less than 900 MPa.
- No. with high heat treatment temperature in the final heat treatment No. with high heat treatment temperature in the final heat treatment.
- No. 10 with a fast cooling rate in the final heat treatment No. 12, which has a high cooling stop temperature in the final heat treatment.
- No. 17 has a large area ratio with respect to the entire structure of the martensite phase and has a low elongation.
- No. with low cooling stop temperature after the final heat treatment No. 13 with a long holding time in re-heating.
- No. 18 has a small area ratio of residual austenite phase and low elongation.
- No. 16 produces pearlite, has a small area ratio of residual austenite phase, and has low elongation.
- a tensile strength (TS) that is inexpensive and has excellent elongation without actively containing expensive elements such as Nb, V, Cu, Ni, Cr, and Mo in the steel sheet: 900 MPa or more
- a high-strength hot-dip galvanized steel sheet can be obtained.
- the high-strength hot-dip galvanized steel sheet according to 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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Abstract
Description
a)溶接性、成形性の観点からC含有量を0.24%以下とすること。
b)金属組織をフェライト相とベイナイト相、焼戻マルテンサイト相、残留オーステナイト相およびマルテンサイト相とし、これらの相の面積比率を所定の範囲に制御すること。
Cはオーステナイト安定化元素であり、残留オーステナイト相の生成に影響し、均一伸びの向上に寄与し、また、焼戻マルテンサイト相、マルテンサイト相の面積比率、硬さに影響し、強度に寄与する元素である。C量が0.16%未満ではフェライト相が過度に生成し、引張強度の確保が困難となり、また所望の残留オーステナイト量が得られず、優れた伸びの確保が困難となる。よって、C量は0.16%以上とする。好ましくは、C量は0.18%以上である。一方、C量が0.24%を超えると溶接性が著しく劣化し、またマルテンサイト相が過度に硬質化して引張強度が高くなりすぎ、優れた伸びの確保が困難となる。よって、C量は0.24%以下とする。好ましくは、C量は0.23%以下であり、より好ましくは0.22%以下である。したがってC量は0.16%以上0.24%以下の範囲とする。溶接性の観点から好ましくは0.18%以上0.23%以下の範囲である。より好ましい範囲は0.18%以上0.22%以下の範囲である。
Siは固溶強化による鋼の強化に有効であり、また残留オーステナイト相の生成に影響し、均一伸びの向上に寄与し、強度と伸びのバランス(TS-Elバランス)を向上させる元素である。Si量が0.8%未満では、このような効果が得られない。よって、Si量は0.8%以上とする。好ましくは、Si量は1.2%以上である。一方、Si量が1.8%を超えると表面に濃化するSi量が増加し、不めっきが発生する。よって、Si量は1.8%以下とする。好ましくは、Si量は1.6%以下である。したがってSi量は0.8%以上1.8%以下の範囲とする。好ましくは1.2%以上1.8%以下、より好ましくは1.2%以上1.6%以下の範囲である。
Mnはオーステナイト安定化元素であり、最終的に得られる焼戻マルテンサイト相およびマルテンサイト相を所望量生成させ強度に寄与する元素である。上記作用を得るにはMn量は1.0%以上とする必要がある。好ましくは、Mn量は1.5%以上であり、より好ましくは、1.7%以上である。一方、Mn量が3.0%を超えると焼入性が過度に向上し、所望のフェライト相とベイナイト相が得られず、焼戻マルテンサイト相およびマルテンサイト相の面積比率が増加し、過度に硬質化して優れた伸びを確保することが困難となる。よって、Mn量は3.0%以下とする。好ましくは、Mn量は2.5%以下であり、より好ましくは2.3%以下である。したがってMn量は1.0%以上3.0%以下の範囲とする。好ましくは1.5%以上2.5%以下、より好ましくは1.7%以上2.3%以下の範囲である。
Pは溶接性に悪影響をおよぼす元素であり、P量は少ないほうが好ましい。特にP量は0.020%を超えると溶接性の劣化が顕著となるが、0.020%までは許容できる。したがってP量の範囲は0.020%以下とする。好ましくは、P量は0.010%未満である。一方、過度に低減すると製鋼工程での生産能率が低下し、高コストとなるため、P量は0.001%以上とすることが好ましい。したがって、P量の範囲は0.001%以上0.020%とすることが好ましい。溶接性を考慮すると、より好ましくは0.001%以上0.010%未満の範囲である。
Sは介在物として鋼中に存在し、介在物割れの起点となるため、S量は少ないほうが好ましい。特にS量が0.0040%を超えると伸びフランジ性の低下が顕著となるが、0.0040%までは許容できる。したがってS量の範囲は0.0040%以下とする。好ましくは、S量は0.0020%以下である。一方、過度の低減は工業的に困難であり、製鋼工程における脱硫コストの増加、生産性の低下を伴うため、S量は0.0001%以上とすることが好ましい。したがって、S量の範囲は0.0001%以上0.0040%以下とすることが好ましい。より好ましくは0.0001%以上0.0020%以下の範囲である。
Alは、鋼の脱酸剤として添加され、0.01%以上の添加が必要である。好ましくは、Al量は0.02%以上である。一方、0.1%を超えてAlを添加すると、アルミナなどの鋼板表層部における介在物が増加し、伸びや曲げ性が低下する。よって、Al量は0.1%以下とする。好ましくは、Al量は0.08%以下であり、より好ましくは0.06%以下である。したがって、Al量は0.01%以上0.1%以下とする。好ましくは0.02%以上0.08%以下、より好ましくは0.02%以上0.06%以下の範囲である。
Nは時効性に影響をおよぼす元素であり、N量は低いほうが好ましい。特にN量が0.01%を超えると歪時効が顕著になるため、N量の範囲は0.01%以下とする。好ましくは、N量は0.0060%以下である。一方、過度の低減は製鋼工程における脱窒コストの増加を伴い、生産性の低下を伴うため、N量は0.0001%以上とすることが好ましい。したがって、N量の好ましい範囲は0.0001%以上0.01%以下である。より好ましい範囲は、0.0001%以上0.0060%以下である。
Caは変形時の割れの起点となる硫化物の形状を板状から球状化し、局部変形能の低下を抑制する効果がある。この効果を得るためには、Ca量は0.0001%以上とする必要がある。一方、0.0020%を超えて添加すると、Ca介在物が過度に増加し、介在物割れの起点となり伸びや曲げ性が低下する。よって、Ca量は0.0020%以下とする。好ましくは、Ca量は0.0010%以下である。したがって、Ca量は0.0001%以上0.0020%以下の範囲とする。好ましくは0.0001%以上0.0010%以下の範囲である。
高価な合金元素を積極的に含有しないという本発明の目的からは、Ti、Nb、V、Cu、Ni、Cr、Moは含有しないことが好ましい。
セメンタイトとフェライト相から構成されるベイナイト相とフェライト相はマルテンサイト相よりも軟質であり、伸びに寄与する。所望の伸びを得るにはフェライト相とベイナイト相の合計の組織全体に対する面積比率を30%以上にする必要がある。フェライト相とベイナイト相の合計の面積比率が30%に満たない場合、硬質なマルテンサイト相の面積比率が増加し、過度に高強度化し、低い伸びしか得られない。好ましくは、フェライト相とベイナイト相の合計の組織全体に対する面積比率は、45%以上である。一方で、フェライト相とベイナイト相の合計の面積比率が70%を超えると、引張強度900MPa以上の確保が困難となる。また伸びに寄与する残留オーステナイト相を所定量確保することが困難となる。このため、フェライト相とベイナイト相の合計の面積比率は70%以下にする必要がある。好ましくは、フェライト相とベイナイト相の合計の面積比率は68%以下であり、より好ましくは、65%以下である。よって、フェライト相とベイナイト相の合計の面積比率は30%以上70%以下の範囲とする。好ましい範囲は30%以上68%以下であり、より好ましい範囲は45%以上65%以下である。
焼戻マルテンサイト相は、強度に寄与すると同時に、焼戻前の硬質なマルテンサイト相に比べ、伸びへの悪影響が少ない。焼戻マルテンサイト相は、高強度化に際して優れた伸びを確保して高いTS-Elバランス、具体的には、TS×El≧26000MPa・%を得るのに有効である。上記作用を得るには、焼戻マルテンサイト相の組織全体に対する面積比率を20%以上にする必要がある。好ましくは、焼戻マルテンサイト相の組織全体に対する面積比率は、25%以上である。しかしながら、焼戻マルテンサイト相の面積比率が40%を超えると、伸びに寄与する残留オーステナイト相を所定量確保することが困難となり、TS×El≧26000MPa・%を確保することができない。このため、焼戻マルテンサイト相の面積比率は40%以下とする。好ましくは、焼戻マルテンサイト相の面積比率は35%以下である。よって焼戻マルテンサイト相の面積比率は20%以上40%以下の範囲とする。より好ましい範囲は25%以上35%以下である。
残留オーステナイト相は歪誘起変態(strain induced transformation)、すなわち材料が変形する場合に歪を受けた部分がマルテンサイト相に変態することで変形部が硬質化し、歪の集中を防ぐことにより均一伸びを向上させる効果がある。高い均一伸びを得て、所望の優れた伸び(全伸び)を得るには10%以上の残留オーステナイト相を含有させることが必要である。このため、残留オーステナイト相の組織全体に対する面積比率は10%以上とする。しかしながら残留オーステナイト相はC濃度が高く、硬質である。残留オーステナイト相が鋼板中に20%を超えて過度に存在すると、局所的に硬質な部分が存在するため、局部伸びを阻害する要因となり、優れた伸び(全伸び)や曲げ性を確保することが困難となる。よって、残留オーステナイト相の組織全体に対する面積比率は20%以下とする。好ましくは、残留オーステナイト相の組織全体に対する面積比率は15%以下である。したがって、残留オーステナイト相の面積比率は10%以上20%以下とする。好ましくは10%以上15%以下の範囲である。
転位密度が高く硬質なマルテンサイト相は、転位密度の低い焼き戻された軟質なマルテンサイト相とは明確に区別される。すなわち、本発明で言うマルテンサイト相には、焼戻マルテンサイト相は含まれない。硬質なマルテンサイト相は引張強度に大きく寄与し、900MPa以上のTSを確保するためにマルテンサイト相の面積比率は2%以上にする必要がある。好ましくは、マルテンサイト相の面積比率は5%以上である。しかしながら、マルテンサイト相の面積比率が過度に多い場合には過度に高強度化し、伸びが低下するため、マルテンサイト相の面積比率は20%以下にする必要がある。好ましくはマルテンサイト相の面積比率は18%以下であり、より好ましくはマルテンサイト相の面積比率は15%以下である。マルテンサイト相の面積比率を2%以上20%以下とすることで、良好な伸びが得られる。好ましくは、マルテンサイト相の面積比率は2%以上15%以下、さらに好ましくは5%以上15%以下の範囲である。
冷間圧延後の鋼板(冷延板)には、熱処理(焼鈍)を施す。この熱処理の温度が800℃未満では、熱処理中のオーステナイト分率が少なく、オーステナイト中へのC、Mnの分配が進行し、CおよびMn濃度の高いオーステナイトが微細分散した状態となる。この結果、C、Mnなどの元素の偏在に起因して、後述する最終熱処理後に、元々C濃度の高い領域が優先的にマルテンサイト相となるため、マルテンサイト相の面積比率が多くなり、かつマルテンサイト相がバンド状に存在する不均一な組織に再びなる。このため、伸びの低下を招き、TS×El≧26000MPa・%が得られない。よって、冷間圧延後の鋼板に施す熱処理(焼鈍)の温度は800℃以上とする。好ましくは、該温度は840℃以上である。一方、熱処理温度が950℃を超えてオーステナイト単相の温度域まで加熱すると、オーステナイト粒径が過度に粗大化するため、最終的に得られる結晶粒も過度に粗大化し、フェライト相の核生成サイトである粒界が減少する。その結果、その後の最終熱処理においてフェライト相の生成が抑制され、焼戻マルテンサイト相およびマルテンサイト相の面積比率が増加し、伸びの低下を招く。よって、冷間圧延後の鋼板に施す熱処理(焼鈍)の温度は950℃以下とする。好ましくは、該温度は900℃以下である。したがって、熱処理温度(焼鈍温度)は800℃以上950℃以下とする。好ましくは840℃以上900℃以下の範囲である。
最終熱処理の熱処理温度が700℃より低い場合は、熱処理中のフェライト相の面積比率が過度に多くなり、900MPa以上のTSの確保が困難となる。よって、最終熱処理の熱処理温度は700℃以上とする。好ましくは、該熱処理温度は750℃以上である。一方、最終熱処理の熱処理温度が850℃を超えると熱処理中のオーステナイト相の面積比率が増加し、溶融亜鉛めっき処理後の鋼板のフェライト相の面積比率が少なく、フェライト相以外の面積比率が多くなり、伸びの確保が困難となる。よって、最終熱処理の熱処理温度は850℃以下とする。好ましくは、該熱処理温度は830℃以下である。したがって、最終熱処理の熱処理温度は700℃以上850℃以下とする。より好ましい熱処理温度は750℃以上830℃以下である。
上記した最終熱処理温度からの冷却速度は所望の相の面積比率を得るために重要である。なお本発明において、該冷却速度は最終熱処理の熱処理温度から冷却停止温度までの平均冷却速度である。該冷却速度が5℃/秒未満の場合、過度にフェライト相が生成し、過度に軟質化するため、900MPa以上のTSの確保が困難となる。よって、該冷却速度は5℃/秒以上とする。好ましくは、該冷却速度は10℃/秒以上である。一方で、該冷却速度が50℃/秒を超えると、フェライト相以外の面積比率が多くなり、過度に硬質化するため、伸びが低下する。よって、該冷却速度は50℃/秒以下とする。好ましくは、該冷却速度は40℃/秒以下、より好ましくは、30℃/秒以下である。したがって該冷却速度は5℃/秒以上50℃/秒以下の範囲とする。好ましくは10℃/秒以上40℃/秒以下、より好ましくは10℃/秒以上30℃/秒以下の範囲である。なお、この冷却は、ガス冷却とすることが好ましいが、特に規定する必要は無く、炉冷、ミスト冷却、ロール冷却、水冷などを組み合わせて行うことが可能である。
冷却停止温度が100℃未満の場合、冷却停止時に過度にマルテンサイト相が生成する。次いで、その後に行う350~600℃の温度域への加熱(再昇温加熱)によってマルテンサイト相が焼戻され、最終的に得られる焼戻マルテンサイト相の面積比率が増大し、残留オーステナイト相の生成が抑制され、優れた伸びの確保が困難となる。よって、冷却停止温度は100℃以上とする。好ましくは、冷却停止温度は150℃以上である。一方、冷却停止温度が300℃を超える場合、冷却停止時に生成しているマルテンサイト相が少なく、その後に行う350~600℃の温度域への加熱(再昇温加熱)によってマルテンサイト相が焼戻され、最終的に得られる焼戻マルテンサイト相の面積比率が少なくなりすぎる。さらに該350~600℃の温度域での保持後にオーステナイト量が多くなり、保持後の室温までの冷却過程において硬質なマルテンサイト相が過度に生成し、高強度化し過ぎて優れた伸びの確保が困難となる。よって、冷却停止温度は300℃以下とする。好ましくは、冷却停止温度は275℃以下であり、より好ましくは、冷却停止温度は250℃以下である。したがって、フェライト相、ベイナイト相、マルテンサイト相および残留オーステナイト相の面積比率を所望の範囲に制御し、TS900MPa以上の引張強度を確保するとともに優れた伸びを得るには、冷却停止温度は100℃以上300℃以下の範囲とする。好ましくは100℃以上275℃以下、さらに好ましくは150℃以上250℃以下の範囲とする。
上記冷却停止に引き続き、350~600℃の温度域に加熱(再昇温加熱)する。該加熱温度(再昇温加熱温度ともいう)が350℃未満、あるいは保持時間が10秒未満では焼戻マルテンサイトが得られず、最終的に鋼板に硬質なマルテンサイト相が過度に生成し、鋼板が高強度化し、優れた伸びの確保が困難となる。よって、再昇温加熱温度は350℃以上とする。また、該保持時間は10秒以上とする。好ましくは、再昇温加熱温度は370℃以上である。好ましくは、該保持時間は20秒以上である。一方、再昇温加熱温度が600℃を超える、または保持時間が500秒を超える場合、パーライト相が生成、または過度にベイナイト変態が進行してベイナイト相が増加する。このため、最終的に得られる残留オーステナイト相の面積比率が少なく伸びの確保が困難となり、またはマルテンサイト相の生成が抑制され、900MPa以上の引張強度の確保が困難となる。よって、再昇温加熱温度は600℃以下とする。また、該保持時間は500秒以下とする。好ましくは、再昇温加熱温度は500℃以下である。好ましくは、該保持時間は180秒以下である。このため、上記冷却停止後、350~600℃の温度域に加熱して10~500秒保持することとする。
上記再昇温加熱温度での保持後、溶融亜鉛めっき処理を施す。亜鉛めっきは常法にしたがって行えばよく、例えば質量%でAl量:0.05~0.25%を含む440~500℃の亜鉛めっき浴中に鋼板を浸漬後、ガスワイピングなどにより付着量を調整して実施すればよい。溶融亜鉛めっき後は、特に限定するものではないが、空冷あるいはガス冷却などの常法により常温まで冷却すればよい。また、特に限定するものではないが、溶融亜鉛めっき処理は、生産性のため、連続焼鈍炉を有する連続溶融亜鉛めっき設備にて、上記最終熱処理に引き続き行うことが好ましい。なお、溶融亜鉛めっき処理後の鋼板には、表面粗度の調整、形状矯正などを目的とし、調質圧延を行ったり、塗油、コーティングなど各種塗装処理を施すことも可能である。
組織全体に占める各相の面積比率は、圧延方向断面かつ板厚1/4面位置を光学顕微鏡で観察することにより求めた。倍率1000倍の断面組織写真を用いて、画像解析により任意に設定した100μm×100μm四方の正方形領域内に存在する占有面積を求めた。なお、観察はN=5(観察視野5箇所)で実施した。また、組織観察に際しては、3vol.%ピクラールと3vol.%ピロ亜硫酸ソーダの混合液でエッチングした。そして、該組織観察において観察される黒色領域が、フェライト相(ポリゴナルフェライト相)あるいはベイナイト相であるとして、フェライト相とベイナイト相の合計の面積比率を求めた。また、該黒色領域以外の残部領域が焼戻マルテンサイト相、マルテンサイト相および残留オーステナイト相であるとして、焼戻マルテンサイト相、マルテンサイト相および残留オーステナイト相の合計の面積比率を求め、鋼板組織を2領域に区別した。
圧延方向と90°の方向を長手方向(引張方向)とするJISZ2201に記載の5号試験片を用い、JISZ2241に準拠した引張試験を行い降伏強度(YP)、引張強度(TS)および全伸び(El)を調査した。結果を表3に示す。なお、伸びはTS-Elバランスで評価し、評価基準はTS×El≧26000MPa・%を伸びが良好であるとした。
日本鉄鋼連盟規格JFST1001に基づき、穴拡げ率の測定をおこなった。すなわち、初期直径d0=10mmの穴を打抜き、60°の円錐ポンチを上昇させ穴を拡げた際に、亀裂が板厚方向に貫通したところでポンチ上昇を止め、亀裂貫通後の打抜き穴径dを測定し、穴拡げ率(%)=((d-d0)/d0)×100として算出した。同一番号の鋼板について3回試験を実施し、穴拡げ率の平均値(λ)を求めた。なお、伸びフランジ性はTS-λバランスで評価し、評価基準はTS×λ≧30000MPa・%を伸びフランジ性が良好であるとした。
Claims (3)
- 質量%で、
C:0.16~0.24%、
Si:0.8~1.8%、
Mn:1.0~3.0%、
P:0.020%以下、
S:0.0040%以下、
Al:0.01~0.1%、
N:0.01%以下、
Ca:0.0001~0.0020%
を含有し、残部がFeおよび不可避不純物からなる成分組成を有し、フェライト相とベイナイト相の合計の組織全体に対する面積比率が30~70%、焼戻マルテンサイト相の組織全体に対する面積比率が20~40%、残留オーステナイト相の組織全体に対する面積比率が10~20%、マルテンサイト相の組織全体に対する面積比率が2~20%であることを特徴とする高強度溶融亜鉛めっき鋼板。 - 請求項1に記載の成分組成からなる鋼スラブを、熱間圧延し、酸洗した後、冷間圧延を行い、次いで800~950℃の温度域に加熱後冷却する熱処理を行い、次いで700~850℃の温度域に加熱し、冷却速度5~50℃/秒で100~300℃の温度域に冷却し、該冷却を停止後、引き続き350~600℃の温度域に加熱して10~500秒保持する熱処理を行い、次いで溶融亜鉛めっきを施すことを行うことを特徴とする高強度溶融亜鉛めっき鋼板の製造方法。
- さらに、前記酸洗後、前記冷間圧延前に400~750℃の温度域に加熱する熱処理を施すことを特徴とする請求項2に記載の高強度溶融亜鉛めっき鋼板の製造方法。
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EP2980239A1 (en) | 2016-02-03 |
KR101747584B1 (ko) | 2017-06-14 |
JP2014189869A (ja) | 2014-10-06 |
US10266906B2 (en) | 2019-04-23 |
MX2015013646A (es) | 2016-02-18 |
JP5867435B2 (ja) | 2016-02-24 |
CN105074037A (zh) | 2015-11-18 |
CN105074037B (zh) | 2017-10-24 |
EP2980239A4 (en) | 2016-03-02 |
US20160047011A1 (en) | 2016-02-18 |
EP2980239B1 (en) | 2020-04-29 |
KR20150123903A (ko) | 2015-11-04 |
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