980-mpa-grade automotive galvanized steel sheet resistant to liquid metal embrittlement during spot welding, and manufacturing method therefor

Abstract

Disclosed in the present invention are a 980-MPa-grade automotive galvanized steel sheet resistant to liquid metal embrittlement during spot welding, and a manufacturing method therefor. The steel sheet is classified into a roll-formed steel sheet and a stamped steel sheet. The roll-formed steel sheet comprises the following chemical components in percentages by mass: C: 0.13%-0.16%, Mn: 1.60%-2.30%, Si: 0.80%-1.00%, Al: 0.035%-0.06%, P: 0.008%-0.015%, S≤0.003%, and the balance of Fe and inevitable impurities. The stamped steel sheet comprises the following chemical components in percentages by mass: C: 0.18%-0.25%, Mn: 1.80%-2.50%, Si: 0.80%-1.80%, Al: 0.05%-0.80%, P: 0.008%-0.015%, S≤0.003%, and the balance of Fe and inevitable impurities. The steel sheet is prepared by means of a process route consisting of continuous casting, hot rolling, cold rolling, and continuous annealing and galvanizing. The present invention has the advantage of involving a low-cost high-performance dual-carbon strategy, and produces roll-formed and stamped anti-LME QP 980-MPa products.

Description

980mpa grade zinc-coated steel sheet for automotive use resistant to liquid metal embrittlement in spot welding and method for manufacturing the same TECHNICAL FIELD

[0001] The present application relates to the technical field of cold-rolled hot-dip coated high-strength steel for automotive use, in particular, and more particularly, to a 980MPa grade zinc-coated steel sheet for automotive use resistant to liquid metal embrittlement in spot welding and a method for manufacturing the same. BACKGROUND

[0002] High-strength thinning is always a design goal for automotive materials, which can effectively improve fuel consumption, reduce carbon dioxide emissions, and ensure the safety of passengers. High-strengthening of automotive materials is also the general trend of automotive development. In recent years, with the gradual improvement of anti-corrosion regulations, Europe requires an increasing proportion of coatings. In order to fully ensure the corrosion resistance of the vehicle body and components, in addition to using high-strength hot-dip galvanized steel sheets, high-strength galvannealed steel sheets are also used. However, during the welding of components, cracks known as liquid metal embrittlement cracks (LME) sometimes occur at the spot welding site. LME is caused by the melting of zinc in the galvanized layer due to the resistance heat during spot welding, and the molten zinc invades the grain boundaries of the steel structure in the welding site, resulting in cracks under the action of tensile stress. It is worth noting that LME not only occurs during the spot welding of coated sheets, but also occurs when bare sheets are spot welded with coated sheets. Therefore, the application of high-strength coated sheets is limited.

[0003] The occurrence of LME is based on: ① the presence of liquid zinc, and liquid metal embrittlement only occurs in the plated state of hot-dip galvanized steel sheets or during the spot welding of bare sheets with hot-dip galvanized steel sheets; ② high-strength steel system, liquid metal embrittlement mostly occurs in 980MPa high-strength galvanized steel sheets, because high residual stress acts on the tensile stress state under spot welding conditions. Therefore, the research scope of LME mainly focuses on high-strength galvanized steel sheets above 980MPa, such as DP980, TRIP980, TWIP980 and QP980 hot-dip galvanized or galvannealed products. In addition, for the current 980MPa or higher automotive high-strength steel, the above-mentioned products are only the most widely used DP and QP. Therefore, it is crucial to study DP and QP anti-LME products above 980MPa for their application. In addition, it is also important to effectively suppress LME while meeting higher forming requirements.

[0004] Quenching and partitioning (Q&P) is a new process for preparing high-strength and high-ductility steel with a mixed structure of martensite and retained austenite, which was proposed by Speer et al. in 2003. The process is as follows: first, the steel is austenitized or partially austenitized, quenched to a temperature between the martensite start (Ms) and martensite finish (Mf) temperatures, and then held for a short time to obtain a certain amount of martensite and untransformed austenite; then, the steel is isothermally partitioned at the quenching temperature or a temperature higher than the quenching temperature to realize the diffusion and enrichment of carbon from the supersaturated martensite to the untransformed austenite, thereby stabilizing the austenite; finally, the steel is cooled to room temperature, and the final structure is a mixed structure of martensite and retained austenite or a mixed structure of ferrite, martensite and retained austenite, thereby achieving excellent strength and ductility matching.

[0005] In the prior art, Japanese Patent Application Publication No. 2006-265671 discloses an alloyed hot-dip galvanized high-tension steel sheet having excellent workability and liquid metal embrittlement crack resistance, which is a plated steel sheet on which an alloyed hot-dip galvanizing is applied, wherein the base steel has a composition comprising C: 0.04 to 0.25 wt%, Si: 0.01 to 2.0 wt%, Mn: 0.5 to 3.0 wt%, P: 0.1 wt% or less, S: 0.03 wt% or less, further comprising one or two or more of Ti: 0.001 to 0.1 wt%, Nb: 0.001 to 0.1 wt%, V: 0.01 to 0.3 wt%, Mo: 0.01 to 0.5 wt%, Zr: 0.01 to 0.5 wt%, and the balance being Fe and inevitable impurities, and has a metallographic structure comprising ferrite at an area ratio of 40 to 95%, one or two or more of bainite, pearlite, and martensite, and retained austenite at a volume ratio of 1 to 10%.

[0006] Japanese Patent Application Publication No. 2008-231493 discloses a method for manufacturing an alloyed hot-dip galvanized steel sheet for spot welding, which comprises hot-rolling a base steel containing, in wt%, C: 0.05 to 0.20%, Si: 0.5 to 2.0%, Mn: 1.0 to 2.5%, and the balance being Fe and inevitable impurities, cooling the hot-rolled steel sheet at a cooling rate of 30°C / sec or more after hot-rolling, and coiling the hot-rolled steel sheet at 450 to 580°C, so that the grain boundary oxidation depth of the hot-rolled steel sheet is 5 μm or less, cold-rolling the hot-rolled steel sheet, and performing an alloyed hot-dip galvanizing treatment on the cold-rolled steel sheet at an adhesion amount of 3 g / m 2 The cold-rolled steel sheet is subjected to an Fe-based plating treatment, and the cold-rolled steel sheet is subjected to an alloyed hot-dip galvanizing treatment, so that the grain boundary oxidation depth of the alloyed hot-dip galvanized steel sheet is 5 μm or less.

[0007] SUMMARY

[0008] The object of the present application is to provide a 980MPa-grade zinc-plated steel sheet for automobiles resistant to spot-welding liquid metal embrittlement and a method for manufacturing the same.

[0009] To achieve the above object, the technical solution of the present application is as follows:

[0010] The present application provides a 980MPa-grade zinc-plated steel sheet for automobiles resistant to spot-welding liquid metal embrittlement, which is divided into a roll-pressed steel sheet and a stamping steel sheet.

[0011] The roll-pressed steel sheet comprises, by mass percent, C: 0.13% to 0.16%, Mn: 1.60% to 2.30%, Si: 0.80% to 1.00%, Al: 0.035 to 0.06%, P: 0.008% to 0.015%, S≤0.003%, and the balance of Fe and inevitable impurities.

[0012] The stamping steel sheet comprises, by mass percent, C: 0.18% to 0.25%, Mn: 1.80% to 2.50%, Si: 0.80% to 1.80%, Al: 0.05% to 0.80%, P: 0.008% to 0.015%, S≤0.003%, and the balance of Fe and inevitable impurities.

[0013] In the above technical solution, further, the steel sheet comprises, by mass percent, Ti: 0.005% to 0.025%, Nb: 0.005% to 0.025%, and Ti+Nb≤0.03%, and B: 0.002% to 0.005%.

[0014] In the above technical solution, further, the steel sheet comprises at least one of Ni, Cr, and Mo, wherein, by mass percent, Ni: 0.10% to 0.30%, Cr: 0.10% to 0.30%, and Mo: 0.10% to 0.30%, and Mn+Ni+Cr+Mo≤2.60%.

[0015] The reasons for designing the chemical components and contents of the steel sheet of the present application are as follows:

[0016] C: C is the most economical strengthening element in steel, which improves the hardenability of the steel plate and thus improves the strength of the steel plate. In the Q&P steel of the present application, C is the most critical factor, which affects the undercooled austenite phase change behavior. The relatively rich C in the undercooled austenite during the cooling stage ensures the content of the transformed martensite during the transformation, and at the same time, the untransformed undercooled austenite relies on the C diffusion of the surrounding martensite to improve the stability during the isothermal partitioning stage, and thus remains as residual austenite. However, too high C content will increase the risk of hot rolling edge cracking and cold rolling edge cracking in industrial production. In addition, too high C content will lead to the formation of a high proportion of twinned martensite at the spot welding nugget, which will deteriorate the welding performance.

[0017] Mn: Mn is a common economical strengthening element in steel, which improves the solid solution strengthening effect and improves the hardenability of the steel plate to improve the overall strength of the steel plate. In the Q&P steel of the present application, Mn element mainly plays a role in reducing the critical zone cooling rate and increasing the proportion of martensite during the rapid cooling stage; at the same time, it cooperates with C addition to improve the stability of austenite phase. However, the addition content of Mn element should not exceed the scope of the present application, considering the problem of C / Mn segregation caused by too high Mn content.

[0018] Si: Si element is a common economical strengthening element, which ensures the base strength of ferrite; at the same time, Si addition will increase the AC3 point of the steel plate, effectively adjusting the annealing process window during continuous annealing stage, to ensure appropriate ferrite and austenite proportion in the critical zone under the industrial continuous annealing temperature; in the Q&P steel of the present application, the main role of Si addition is that sufficient Si addition can inhibit the formation of carbides during overaging stage, to avoid the performance reduction of the steel plate due to carbide precipitation. It is worth noting that in the case of producing galvanized products, too high Si content will lead to "leakage" of the galvanized surface and other surface quality problems.

[0019] Al: Al is limited in conventional steel plates, and is generally used as a deoxidizer during smelting process. In the present application, higher content of Al is added instead of Si during the production and manufacturing stage of galvanized products, to play a role in inhibiting carbide precipitation; however, the content of Al replacing Si should not be too high, and too high addition will lead to difficulties in tapping during continuous casting crystallization stage, upward shift of the soaking window during continuous annealing / continuous galvanizing, and other problems that increase the difficulty of production.

[0020] Ti: In conventional steel plates, the role of Ti is to fix nitrogen, and in the present application, appropriate addition of Ti element is used as a strength supplement. Some planned components cannot meet the strength requirement, and rely on the precipitation of Ti element to play the role of fine-grain strengthening and precipitation strengthening to supplement the strength.

[0021] Nb: Nb is a micro-alloy strengthening element, which plays a role in refining grains and improving strength; in the present application, Nb is added in combination with Ti to fill the gap of low strength caused by some design components; however, the content of Nb should not be too high, and too high content will lead to too high degree of fine-grain during hot rolling, too high strength of hot rolled coil, and increased difficulty of cold rolling.

[0022] P: P element is an impurity element in steel, which is easy to segregate at grain boundary, when the content of P in steel is high, Fe2P particles are easy to form, which reduces the plasticity and toughness of steel, therefore, the lower the content of P is, the better. In the application, the content of P is controlled to be P≤0.0015%.

[0023] S: S element is an impurity element in steel, which is easy to combine with Mn to form MnS inclusions, thus deteriorating the plasticity of the steel plate, therefore, the lower the content of S is, the better. In the application, the content of S is controlled to be S≤0.003%.

[0024] Ni: Ni is a solid solution strengthening element, which, like C and Mn, improves the stability of austenite; meanwhile, Ni improves the corrosion resistance of the steel plate to a certain extent. In the optional components of the application, Ni can be added in an appropriate amount to improve the corrosion resistance.

[0025] Cr and Mo: Cr and Mo are solid solution strengthening elements, which strengthen the steel plate. In the application, Cr and Mo improve the hardenability of the steel plate, delay the formation of pearlite and bainite in the cooling stage, and promote the formation of martensite; meanwhile, Cr and Mo change the type of iron oxide scale in the coiling process, limit the oxidation in the steel plate, and improve the surface quality of the steel plate. In the application, Cr and Mo balance the edge cracks in hot rolling and the edge cracking in cold rolling after Mn is added.

[0026] Mn+Ni+Cr+Mo≤2.6%: As mentioned above, alloying elements such as Ni, Cr, and Mo are alternative elements to supplement Mn, and their main function in the application is to improve the stability of austenite and supplement the stability of austenite. However, considering multiple dimensions such as cost, steel pouring difficulty, hot rolling difficulty, and cold rolling difficulty, the overall addition should meet the integrated purpose of low cost, easy production, and high yield.

[0027] B: B is segregated at the grain boundary of austenite during welding, which strengthens the grain boundary and helps to improve the resistance to liquid metal embrittlement cracking. Therefore, B can also be contained as needed. However, if the content of B is greater than 0.005%, carbides and nitrides are generated, the above effect is saturated, and the hot workability is reduced. If there is a soft decarburized layer on the surface of the base material, the stress is reduced, and cracks are not easy to occur.

[0028] In the above technical solution, further, the yield strength of the roll-formed steel plate is ≥780 MPa, the tensile strength is ≥980 MPa, the elongation is 12% to 15%, and the hole expansion rate is 40% to 70%.

[0029] The yield strength of the stamping steel plate is ≥600 MPa, the tensile strength is ≥980 MPa, and the elongation is 20% to 23%.

[0030] Another aspect of the present application provides a method for preparing the 980MPa-grade zinc-plated steel sheet for resisting spot-welding liquid metal embrittlement for automobiles, which comprises the following steps:

[0031] (1) Continuous casting: the continuous casting is performed according to the chemical composition of the steel, and the casting temperature is 1580-1620℃;

[0032] (2) Hot rolling: the heating temperature is 1230-1280℃, the furnace time is 180-240min, the rough rolling temperature is 1150-1200℃, the finish rolling temperature is 1070-1130℃, the final rolling temperature is ≥920℃, and the coiling temperature is 550-600℃;

[0033] (3) Cold rolling: the rolling reduction is 46.7-48.6%;

[0034] (4) Continuous annealing and zinc plating:

[0035] The continuous annealing and zinc plating process of the roll-formed steel sheet is as follows:

[0036] The cold-rolled steel sheet is heated to 900-950℃, isothermally treated for 80-180s, is slowly cooled to 750-820℃ at a cooling rate of 1.2-3.6℃ / s, is rapidly cooled to 250-400℃ at a rate of 15-25℃ / s, is then aged by increasing the temperature to 450-470℃ at a rate of 20℃ / s or more, is zinc-plated in a zinc pot, and is finally alloyed and zinc-plated by increasing the temperature to 480-520℃.

[0037] The continuous annealing and zinc plating process of the stamping-formed steel sheet is as follows:

[0038] The cold-rolled steel sheet is heated to 820-860℃, isothermally treated for 60-120s, is slowly cooled to 700-740℃ at a cooling rate of 1.2-3.6℃ / s, is rapidly cooled to 250-350℃ at a rate of 18-25℃ / s, is then over-aged by increasing the temperature to 380-420℃ at a rate of 20℃ / s or more, is isothermally treated for 20-40s, is increased to 455-470℃ to enter a zinc pot, and is finally alloyed and zinc-plated by increasing the temperature to 480-520℃.

[0039] In the above technical solution, further, in step (1), the thickness of the casting blank is 220-280mm.

[0040] In the above technical solution, further, in step (2), the thickness of the intermediate blank is 50-80mm.

[0041] The present application has the following beneficial effects:

[0042] (1) The roll-pressed and punched steel plates prepared by the application have the advantage of resisting point welding liquid metal embrittlement, wherein the yield strength of the roll-pressed steel plate is greater than or equal to 780 MPa, the tensile strength is greater than or equal to 980 MPa, the elongation is 12% to 15%, and the hole expansion rate is 40% to 70%; the yield strength of the punched steel plate is greater than or equal to 600 MPa, the tensile strength is greater than or equal to 980 MPa, the elongation is 20% to 23%, and the anti-LME-QP980 MPa product is obtained;

[0043] (2) The application has the advantages of low cost and high performance in the dual-carbon strategy;

[0044] (3) The application proposes a gradient distribution process idea and is applied in industry. DETAILED DESCRIPTION

[0045] The application will be described in more detail by examples, which are only a description of the best mode of the application and do not have any limitation on the scope of the application.

[0046] The chemical composition of the steel plate in the examples of the application is listed in Table 1.

[0047] The chemical composition of the steel in Table 1, wt%

[0048] The preparation method of the steel plate in the above examples includes the following steps:

[0049] (1) Continuous casting: the steel is continuously cast according to the chemical composition, the casting temperature is 1580 to 1620℃, and the cast blank is obtained, the thickness of the cast blank is 220 to 280mm;

[0050] (2) Hot rolling: the heating temperature is 1230 to 1280℃, the furnace time is 180 to 240min, the rough rolling temperature is 1150 to 1200℃, the intermediate blank thickness is 50 to 80mm, the finish rolling temperature is 1070 to 1130℃, the final rolling temperature is greater than or equal to 920℃, and the coiling temperature is 550 to 600℃; the heating temperature is controlled at 1230 to 1280℃, the furnace time is 180 to 240min, the purpose is to promote the full solid solution of the alloy and control the banded structure caused by segregation. The purpose of two-stage rolling in the finish rolling stage is to promote the recrystallization behavior of the original austenite grains and inhibit the coarsening of the unrecrystallized austenite grains; the coiling temperature is controlled at 550 to 600℃, the purpose is to prevent the formation of Si-rich oxides on the surface of the steel plate after adding Si content, and then cause excessive internal oxidation layer and grain boundary oxidation layer;

[0051] (3) Cold rolling: the thickness of the cold rolled sheet is 1.4 / 1.6 / 1.8 mm, 1.4 mm sheet thickness corresponds to 2.8 mm hot rolled steel sheet, 1.6 and 1.8 mm sheet thickness corresponds to 3.0-3.5 mm hot rolled steel sheet, the rolling reduction is 46.7-48.6%; too low rolling reduction cannot guarantee enough cold rolling deformation energy storage, leading to insufficient ferrite recrystallization effect in continuous annealing stage; too high rolling reduction greatly increases the load of the cold rolling mill, which cannot guarantee the realization of the target thickness;

[0052] (4) Continuous annealing and galvanizing:

[0053] The continuous annealing and galvanizing process of the roll-formed steel sheet is as follows:

[0054] The cold rolled sheet is heated to 900-950 °C, isothermally held for 80-180 s, is slowly cooled to 750-820 °C at a cooling rate of 1.2-3.6 °C / s, is rapidly cooled to 250-400 °C at a rate of 15-25 °C / s, is then aged at a temperature of 450-470 °C at a rate of 20 °C / s or more, is galvanized in a zinc pot, and finally is alloyed and galvanized at a temperature of 480-520 °C.

[0055] The roll-formed steel sheet is fully austenitized at the galvanizing soaking stage (heated to 820-860 °C, isothermally held for 60-120 s), the ferrite content is controlled within 5% by slowly cooling to 750-820 °C, so as to prevent the strength from being reduced due to too high ferrite content and prevent the strength from being too high due to too low ferrite content; more importantly, the C concentration gradient of the supercooled austenite after slow cooling and before rapid cooling is ensured, thereby determining the transformation amount of the subsequent bainite and martensite; then the steel sheet is cooled to 250-400 °C at a high cooling rate, 25%-30% of martensite structure and the remaining untransformed supercooled austenite structure are obtained, too low martensite content leads to reduced strength of the steel sheet, and too high martensite content leads to reduced residual austenite content.

[0056] The continuous annealing and galvanizing process of the stamping steel sheet is as follows:

[0057] The cold rolled sheet is heated to 820-860 °C, isothermally held for 60-120 s, is slowly cooled to 700-740 °C at a cooling rate of 1.2-3.6 °C / s, is rapidly cooled to 250-350 °C at a rate of 18-25 °C / s, is then over-aged at a temperature of 380-420 °C at a rate of 20 °C / s or more, is isothermally held for 20-40 s, is heated to 455-470 °C to enter the zinc pot, and finally is alloyed and galvanized at a temperature of 480-520 °C.

[0058] The stamping type is in the galvanizing soaking stage (heating 820-860℃, isothermal 60-120s), so that 35%-45% of critical zone ferrite structure is obtained, the strength of the balanced steel plate is balanced and the C concentration in austenite under the austenitizing degree is ensured; the slow cooling temperature is to 700-740℃, 5%-10% of oriented epitaxial ferrite is obtained, the ferrite content is prevented from being too high to reduce the strength, and the ferrite content is prevented from being too low to be too high; more importantly, the C concentration gradient of the supercooled austenite after slow cooling and before fast cooling is ensured, and then the transformation amount of the subsequent process bainite and martensite is determined; then the higher cooling speed is used to cool to 250-350℃, 25%-30% of martensite structure and the remaining untransformed supercooled austenite structure are obtained, and the martensite content is too low to reduce the strength of the steel plate, and the martensite content is too high to reduce the residual austenite content.

[0059] Table 2 lists the continuous casting and hot rolling process parameters of the example steel plate, Table 3 lists the cold rolling and continuous annealing process parameters of the example steel plate, and Table 4 lists the mechanical properties of the example steel plate.

[0060] Table 2 hot rolling process of the example steel

[0061] Table 3 cold rolling, annealing and galvanizing process of the example steel

[0062] Table 4 mechanical properties of the example steel

[0063] The above examples are only preferred examples of the present application, and are not limited to the embodiments. The protection scope of the present application should be limited to the scope defined by the claims. Other different forms of changes or variations can be made on the basis of the above description. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A 980 MPa grade zinc-coated steel sheet for automobiles excellent in resistance to spot weld liquid metal embrittlement, characterized by, The steel plate is divided into a roll-pressed steel plate and a stamping steel plate; The roll-pressed steel plate comprises, in mass percentage, C: 0.13% to 0.16%, Mn: 1.60% to 2.30%, Si: 0.80% to 1.00%, Al: 0.035 to 0.06%, P: 0.008% to 0.015%, S≤0.003%, and the balance of Fe and inevitable impurities; The stamping steel plate comprises, in mass percentage, C: 0.18% to 0.25%, Mn: 1.80% to 2.50%, Si: 0.80% to 1.80%, Al: 0.05% to 0.80%, P: 0.008% to 0.015%, S≤0.003%, and the balance of Fe and inevitable impurities.

2. The 980 MPa grade zinc-coated steel sheet for automobiles according to claim 1, characterized by, The steel plate further comprises, in mass percentage, Ti: 0.005% to 0.025%, Nb: 0.005% to 0.025%, and Ti+Nb≤0.03%, and B: 0.002% to 0.005%.

3. The 980 MPa grade zinc-coated steel sheet for automobiles according to claim 1 or 2, characterized by, The steel plate further comprises at least one of Ni, Cr and Mo, wherein, in mass percentage, Ni: 0.10% to 0.30%, Cr: 0.10% to 0.30%, Mo: 0.10% to 0.30%, and Mn+Ni+Cr+Mo≤2.60%.

4. The 980 MPa grade zinc-coated steel sheet for automobiles according to claim 1 or 2, characterized by, The roll-pressed steel plate has a yield strength of ≥780 MPa, a tensile strength of ≥980 MPa, an elongation of 12% to 15%, and a hole expansion ratio of 40% to 70%. The stamping steel plate has a yield strength of ≥600 MPa, a tensile strength of ≥980 MPa, and an elongation of 20% to 23%.

5. A method of manufacturing a 980 MPa grade zinc-coated steel sheet for automotive use, which is resistant to liquid metal embrittlement by spot welding according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: (1) continuous casting: the steel is cast according to the chemical composition of the steel, and the casting temperature is 1580 to 1620 ℃; (2) hot rolling: the heating temperature is 1230 to 1280 ℃, the furnace time is 180 to 240 min, the rough rolling temperature is 1150 to 1200 ℃, the finish rolling temperature is 1070 to 1130 ℃, the final rolling temperature is ≥920 ℃, and the coiling temperature is 550 to 600 ℃; (3) cold rolling: the rolling reduction is 46.7% to 48.6%; (4) continuous annealing and galvanizing: The continuous annealing and galvanizing process of the roll-pressed steel plate is as follows: The cold-rolled steel plate is heated to 900 to 950 ℃, isothermally treated for 80 to 180 s, is slowly cooled to 750 to 820 ℃ at a cooling rate of 1.2 to 3.6 ℃ / s, is rapidly cooled to 250 to 400 ℃ at a rate of 15 to 25 ℃ / s, is then aged at a temperature of 450 to 470 ℃ at a temperature rising rate of 20 ℃ / s, is galvanized in a zinc pot, and is finally alloyed and galvanized at a temperature of 480 to 520 ℃; The continuous annealing and galvanizing process of the stamping steel plate is as follows: The cold-rolled steel plate is heated to 820-860℃, isothermally treated for 60-120s, slowly cooled at a rate of 1.2-3.6℃ / s to 700-740℃, rapidly cooled at a rate of 18-25℃ / s to 250-350℃, then overaged at a rate of 20℃ / s to 380-420℃, isothermally treated for 20-40s, then heated to 455-470℃ to enter a zinc pot, and finally heated to 480-520℃ to perform galvanizing.

6. The production method according to claim 5, wherein In step (1), the thickness of the cast slab is 220-280mm.

7. The preparation method according to claim 5, characterized in that, In step (2), the thickness of the intermediate slab is 50-80mm.

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