Galvanized hot-formed steel manufacturing method capable of avoiding LME problem

Abstract

The invention discloses a manufacturing method of galvanized hot-formed steel capable of avoiding the LME problem, and belongs to the technical field of manufacturing of high-strength steel for automobiles. According to the method, firstly, a zinc layer with the small thickness is obtained on the surface of the hot forming steel through electrogalvanizing, and the problem of liquid metal embrittlement caused by zinc melting in the hot stamping process of the zinc-based hot forming steel is solved; then the electro-galvanized plate is immersed in passivation treatment liquid for passivation film forming treatment, the situation that in the hot stamping process of the galvanized hot-formed steel, due to the fact that a plating layer is thin, oxide scales prone to stripping are generated, and consequently the surface quality is reduced is avoided, the problem that liquid metal is embrittled in the manufacturing process of the galvanized hot-formed steel is obviously solved, and the service life of the galvanized hot-formed steel is prolonged. And the method has a very good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of high-strength steel manufacturing for automobiles, and particularly relates to a method for manufacturing galvanized hot-formed steel that avoids the LME problem. Background Art

[0002] Lightweighting vehicles directly reduces emissions and fuel consumption, a development goal for today's automotive manufacturing industry. The use of high-strength and ultra-high-strength steels has become a major trend in automotive manufacturing. However, ultra-high-strength steels are susceptible to poor shape, high forming loads, and significant springback during cold working, hindering their use. Therefore, hot stamping is a key method for producing ultra-high-strength steel parts.

[0003] Conventional uncoated hot stamping parts can cause decarburization and oxidation scaling on the stamped steel surface during heating. To prevent oxidation and decarburization on the hot stamped steel surface and improve its high-temperature and corrosion resistance, coating technologies suitable for hot stamping steel have been developed. Currently, hot stamping coatings primarily include aluminum-silicon (Al-10Si) coatings, hot-dip pure zinc (GI) coatings, alloyed zinc-iron (GA) coatings, and electroplated zinc-nickel (Zn-10Ni) coatings.

[0004] There are two main existing hot stamping forming methods, namely direct hot stamping and indirect hot stamping. In direct hot forming, the steel plate is heated to a temperature higher than the austenitizing temperature and kept warm for a certain period of time so that the steel plate is fully austenitized. Afterwards, the heated steel plate is transferred to a forming mold and formed into a finished component in a one-step forming process and hardened by means of cooling the mold (the cooling rate of the mold is greater than the critical cooling rate of the steel plate). However, for low-melting-point coated hot stamping steels, such as GI, GA, ZnAlMg, etc., due to the low melting point of Zn, it is converted into liquid zinc during the high-temperature heating process of direct hot forming. Liquid metal brittleness (LME, Liquid Metal Embrittlement) cracks are easily generated during forming at high temperatures. Therefore, the direct hot forming method is difficult to achieve mass production of low-melting-point, high-corrosion-resistant coated hot-formed parts. Indirect hot forming is a method of forming the component to almost complete completion (generally 90% pre-forming) through a multi-step forming process, and then placing the almost formed component in a heating furnace to heat it until it is completely austenitized and kept warm for a period of time. The heated component is then transferred to a forming mold of the final size of the component for hot forming. The Chinese invention patent with application number 202310321793.6 discloses a method for preparing a zinc-based coated 1500MPa grade hot-formed steel bent pipe fitting. It adopts an indirect hot forming process, first bending and then quenching and cooling, which can control the processing accuracy of the pipe fittings and avoid the problem of LME generated by zinc-based coated hot-formed steel. However, the indirect hot forming method has limited adaptability to complex parts, and the cold stamping step of pre-forming is prone to cracking of deep-drawn or high-curvature parts.

[0005] As mentioned above, although the indirect hot forming method can solve the LME problem of galvanized hot-formed steel during high-temperature hot forming, the cost increases due to the complex process; its adaptability to complex parts is limited; it may also lead to problems such as reduced mechanical properties of hot-formed steel. It is very necessary to develop zinc-based hot-formed steel suitable for direct hot forming. Summary of the Invention

[0006] In order to solve the problem of liquid metal cracks in existing galvanized hot-formed steel due to the penetration of molten zinc into the substrate, the present invention aims to provide a method for manufacturing galvanized hot-formed steel that avoids the liquid metal embrittlement (LME) problem.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a method for manufacturing galvanized hot-formed steel to avoid the LME problem, comprising the following steps:

[0009] (1) pickling and cold rolling the hot-rolled steel plate to a thickness of 0.6 to 2.0 mm, performing continuous annealing at a temperature of 800 to 850° C. and a speed of 100 to 180 m / min, cooling, aging treatment at 400 to 450° C. for 400 to 1000 s, and then cooling to 150 to 180° C.;

[0010] (2) The steel plate obtained in step (1) is subjected to gravity electrogalvanizing, wherein the electroplating solution is a zinc sulfate aqueous solution, the zinc sulfate concentration is 100-120 g / L, the pH value is controlled at 1.3-1.8, the electroplating solution temperature is controlled at 50-70°C, and the current density is controlled at 1.5-3 A / dm 2 ;

[0011] (3) immersing the electrogalvanized sheet obtained in step (2) in a passivation treatment solution for passivation film formation treatment, wherein the passivation treatment solution comprises a main salt, a pH regulator, and the rest is water, the main salt is one or more of silicate, molybdate, tungstate or their hydrates, the pH value of the treatment solution is 6 to 8, the treatment temperature is 40 to 80° C., and the passivation treatment time is 20 to 1200 s, so that a passivation film is formed on the surface of the electrogalvanized sheet;

[0012] (4) The steel plate obtained in step (3) is hot formed at a heating temperature of 800-980°C and a holding time of 3-10 min, and then transferred to a stamping die in an air atmosphere or a nitrogen or argon doped with 0-0.5 vol.% H2. The cooling rate of the die is controlled to be above 25°C / s, the stamping pressure is 10-20 MPa, and the holding time is 3-20 s. After the holding time is completed, the die is lifted and the coated plate is taken out.

[0013] Based on the above technical solution, further, in step (1), the pickling temperature is controlled at 60-80°C and the speed is 80-220m / min.

[0014] Based on the above technical solution, further, the specific cooling process in step (1) is: first slowly cooling to 650-700°C at a cooling rate of 9-11°C / s; then rapidly cooling to 440-480°C at a cooling rate of 25-35°C / s.

[0015] Based on the above technical solution, further, after cooling to 150-180°C in step (1), it is leveled on a leveler, and the leveling elongation is controlled to be: 0.5-1.1%; conventional alkali washing, brushing, electrolytic degreasing and rinsing are performed, and the temperature of the degreasing liquid is controlled at 45-75°C, and the pH of the degreasing liquid is ≥9.5.

[0016] Based on the above technical solution, further, in step (2), the weight of the zinc layer is controlled to be 5-60 g / m 2 , preferably 5 to 30 g / m 2 .

[0017] Based on the above technical solution, further, in step (2), the running speed of the steel plate in the electrogalvanizing tank is 80 to 140 m / min.

[0018] Based on the above technical solution, further, the concentration of the main salt in the passivation treatment solution in step (3) is controlled at 2 to 20 g / L.

[0019] Based on the above technical solution, further, the pH regulator described in step (3) includes sodium hydroxide and nitric acid.

[0020] Based on the above technical solution, further, in step (3), the weight of the passivation film is controlled to be 0.4-1.0 g / m 2 , preferably 0.4 to 0.6 g / m 2 .

[0021] Based on the above technical solution, further, the cooling rate in step (4) is controlled at 25-35°C / s.

[0022] Based on the above technical solution, further, the preparation process of the hot-rolled steel plate described in step (1) is as follows:

[0023] 1) smelting to obtain molten steel, the chemical composition of the molten steel, calculated by mass percentage, is as follows: C: 0.01% to 0.25%, Mn: 0.30% to 1.5%, Si: 0.01% to 0.06%, Cr≤0.50%, Ti: 0.005% to 0.25%, Als≤0.02%, Ni≤0.50%, Cu≤0.30%, B≤0.005%, P≤0.03%, S≤0.03%, the balance being Fe and unavoidable impurities;

[0024] 2) The molten steel is poured to form a slab with a thickness of 210 to 230 mm, and the slab is heated at a temperature of 1100 to 1250°C for 1 to 3 hours, and then rough rolling and finish rolling are carried out. The starting temperature of the rough rolling is 1105 to 1150°C, and the starting temperature of the finish rolling is 980 to 1050°C. The slab is rapidly cooled to 500 to 800°C at a cooling rate of 15 to 40°C / s for coiling.

[0025] Based on the above technical solution, further, the chemical composition of the molten steel described in step 1) is calculated as follows by mass percentage: C: 0.01% to 0.10%, Mn: 0.20% to 0.40%, Si: 0.01% to 0.06%, Ti: 0.005% to 0.25%, Als: 0.01% to 0.02%, B: 0.001% to 0.005%, P≤0.03%, S≤0.03%, and the remainder is Fe and unavoidable impurities.

[0026] Based on the above technical solution, further, the chemical composition of the molten steel described in step 1) is as follows, by mass percentage: C: 0.10% to 0.25%, Mn: 0.30% to 0.70%, Si: 0.01% to 0.06%, Cr: 0.10% to 0.30%, Ti: 0.005% to 0.15%, Ni: 0.10% to 0.30%, Cu: 0.10% to 0.40%, B: 0.001% to 0.005%, P≤0.03%, S≤0.03%, and the remainder is Fe and unavoidable impurities.

[0027] Based on the above technical solution, further, in step 2), the hot rolling outlet temperature is 810-920°C.

[0028] Based on the above technical solution, further, the thickness of the hot-rolled steel plate in step 2) is 3.0 to 4.0 mm.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention adopts electro-galvanizing instead of hot-dip galvanizing to form a thinner zinc layer on the surface of the hot-formed steel, thereby avoiding the liquid metal embrittlement problem of the zinc-based hot-formed steel caused by zinc melting during the hot stamping process; then the electro-galvanized sheet is immersed in a passivation treatment solution for passivation film formation treatment, thereby avoiding the galvanized hot-formed steel during the hot stamping process. Due to the thin coating, the oxidized iron scale that is easy to peel off is generated, resulting in a decrease in surface quality. This significantly improves the liquid metal embrittlement problem of the galvanized hot-formed steel during the manufacturing process, and has very good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0032] Figure 1 This is a scanning electron microscope morphology of the surface of the electrogalvanized passivated sample prepared in Example 1;

[0033] Figure 2 This is a surface scanning electron microscope image of the electrogalvanized passivated sample prepared in Example 1 after hot forming;

[0034] Figure 3 Phase structure diagram of the electrogalvanized passivated samples after hot forming prepared in Example 1(a), Example 2(b) and Example 3(c);

[0035] Figure 4 This is a cross-sectional morphology of the electrogalvanized passivated sample prepared in Example 1 after hot forming;

[0036] Figure 5The energy spectra and Fe and Zn element distribution results of the electrogalvanized passivated samples prepared in Example 1(a), Example 2(b) and Example 3(c) after hot forming, where a, b, and c represent the energy spectra, a-1, b-1, and c-1 represent the Fe element distribution, and a-2, b-2, and c-2 represent the Zn element distribution;

[0037] Figure 6 This is the energy spectrum of the zinc-aluminum-magnesium coating sample prepared in comparative example 2 after hot forming, where (b) and (c) are the Fe element distribution and Zn element distribution results of the boxed area in Figure (a), respectively. DETAILED DESCRIPTION

[0038] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative work all fall within the scope of protection of the present invention.

[0039] Example 1

[0040] This embodiment provides a method for manufacturing galvanized hot-formed steel that avoids the LME problem, comprising the following steps:

[0041] (1) smelting to obtain molten steel, the chemical composition of the molten steel, by mass percentage: C: 0.12%, Mn: 0.60%, Si: 0.035%, Cr: 0.20%, Ti: 0.008%, Ni: 0.20%, Cu: 0.30%, B: 0.004%, P: 0.03%, S: 0.03%, the balance being Fe and unavoidable impurities;

[0042] (2) After pouring molten steel, a slab with a thickness of 220 mm is made; the slab is heated in a heating furnace at a temperature of 1200°C for 2 hours, and then rough rolling and finish rolling are carried out. The rough rolling start temperature is 1120°C, the finish rolling start temperature is 1000°C, the hot rolling outlet temperature is 820°C, and the plate thickness after hot rolling is 3.0 mm. The plate is then rapidly cooled to 650°C at a cooling rate of 15°C / s for coiling;

[0043] (3) Pickling and cold rolling are carried out, with the acid solution temperature controlled at 70°C and the pickling speed at 120m / min. After continuous cold rolling, the thickness is controlled at 1.5mm. Continuous annealing is carried out, with the annealing temperature controlled at 830°C and the annealing speed controlled at 150m / min. Cooling is carried out by the following method: first slowly cooling to 680°C at a cooling rate of 10°C / s; then rapidly cooling to 460°C at a cooling rate of 30°C / s, aging treatment at 440°C for 400s; and finally cooling to 170°C. Flattening is carried out on a flattening machine, and the smoothing elongation is controlled to be: 0.6%. Conventional alkaline washing, brushing, electrolytic degreasing and rinsing are carried out, with the degreasing solution temperature controlled at 60°C and the degreasing solution pH ≥ 9.5;

[0044] (4) The electroplating process adopts gravity zinc plating, the electroplating solution is zinc sulfate aqueous solution, the zinc sulfate concentration in the electroplating solution is 100g / L, the pH value is 1.4, the electroplating solution temperature is 50℃, and the current density is controlled at 2A / dm 2 The running speed of the steel plate in the electrogalvanizing tank is 100m / min; the zinc layer weight is controlled at 20g / m 2 ;

[0045] (5) The steel plate is immersed in the treatment solution for passivation film formation treatment to form a passivation film on the surface of the electro-galvanized plate. The treatment time is 30s and the treatment temperature is 70℃. The treatment solution includes main salt, pH regulator, and the rest is water. The main salt is Na2SiO3·9H2O13g / L, and the pH regulator is sodium hydroxide and nitric acid. The pH value of the treatment solution is regulated by the pH regulator to 6.5, and the weight of the passivation film is controlled to 0.5g / m 2 ;

[0046] (6) The treated steel plate is hot formed. The hot forming process conditions are as follows: heating temperature 880°C, holding time 3 min, transfer to a stamping die with a protective atmosphere of nitrogen or argon doped with 0.5 vol.% H2, circulating water is passed into the die, the water temperature is 25°C, the cooling rate is controlled at 30°C / s, the main cylinder pressure of the hydraulic press is 15 MPa, the hot stamping holding time is 15 s, and after the holding time is completed, the die is lifted and the coated plate is taken out.

[0047] Example 2:

[0048] This embodiment provides a method for manufacturing galvanized hot-formed steel that avoids the LME problem, comprising the following steps:

[0049] (1) smelting to obtain molten steel, the chemical composition of the molten steel, by mass percentage: C: 0.02%, Mn: 0.30%, Si: 0.03%, Ti: 0.20%, Cu: 0.30%, Als: 0.015%, B: 0.004%, P: 0.03%, S: 0.03%, the balance being Fe and unavoidable impurities;

[0050] (2) After pouring molten steel, a slab with a thickness of 220 mm is made; the slab is heated in a heating furnace at a temperature of 1200°C for 2 hours, and then rough rolling and finish rolling are carried out. The rough rolling start temperature is 1120°C, the finish rolling start temperature is 1000°C, the hot rolling outlet temperature is 800°C, and the plate thickness after hot rolling is 3.0 mm. The plate is then rapidly cooled to 650°C at a cooling rate of 20°C / s for coiling;

[0051] (3) Pickling and cold rolling are performed, with the acid solution temperature controlled at 70°C and the pickling speed at 120m / min. After continuous cold rolling, the thickness is controlled at 1.6mm. Continuous annealing is performed, with the annealing temperature controlled at 820°C and the annealing speed controlled at 130m / min. Cooling is performed by the following method: first slowly cooling to 680°C at a cooling rate of 10°C / s; then rapidly cooling to 450°C at a cooling rate of 30°C / s, aging treatment at 440°C for 400s; and finally cooling to 170°C. Leveling is performed on a leveling machine, and the smoothing elongation is controlled to be: 0.6%. Conventional alkaline washing, brushing, electrolytic degreasing and rinsing are performed, with the degreasing solution temperature controlled at 60°C and the degreasing solution pH ≥ 9.5;

[0052] (4) The electroplating process adopts gravity zinc plating, the electroplating solution is a zinc sulfate aqueous solution, the zinc sulfate concentration in the electroplating solution is 100g / L, the pH value is 1.5, the electroplating solution temperature is 55℃, and the current density is controlled at 1.5A / dm 2 The running speed of the steel plate in the electrogalvanizing tank is 120m / min; the zinc layer weight is controlled at 10g / m 2 ;

[0053] (5) Immerse the steel plate in the treatment solution for passivation film formation treatment to form a passivation film on the surface of the electro-galvanized plate. The treatment time is 30s and the treatment temperature is 70℃. The treatment solution includes main salt, pH regulator, and the rest is water. The main salt is Na2SiO3·9H2O5g / L and (NH4)2SO4 1.5g / L. The pH regulator is sodium hydroxide and nitric acid. The pH value of the treatment solution is regulated by the pH regulator to 7, and the weight of the passivation film is controlled to 0.5g / m 2 ;

[0054] (6) The treated steel plate is hot formed. The hot forming process conditions are as follows: heating temperature 910 °C, holding time 3 min, transfer to a stamping die with a protective atmosphere of nitrogen or argon doped with 0.5 vol.% H2, circulating water is passed into the die, the water temperature is 28 °C, the cooling rate is controlled at 26 °C / s, the main cylinder pressure of the hydraulic press is 12 MPa, the hot stamping holding time is 18 s, and after the holding time is completed, the die is lifted and the coated plate is taken out.

[0055] Example 3:

[0056] This embodiment provides a method for manufacturing galvanized hot-formed steel that avoids the LME problem, comprising the following steps:

[0057] Steps (1) to (5) are the same as in Example 1.

[0058] (6) The treated steel plate was hot formed. The hot forming process conditions were as follows: heating temperature 930 °C, holding time 3 min, transfer to a stamping die in an air atmosphere, circulating water in the die, water temperature 23 °C, cooling rate controlled at 33 °C / s, hydraulic press main cylinder pressure 16 MPa, hot stamping holding time 14 s, lift the die after holding, and remove the coated plate.

[0059] Example 4

[0060] This embodiment provides a method for manufacturing galvanized hot-formed steel that avoids the LME problem, comprising the following steps:

[0061] (1) smelting to obtain molten steel, the chemical composition of the molten steel, by mass percentage: C: 0.20%, Mn: 0.50%, Si: 0.035%, Cr: 0.15%, Ti: 0.008%, Ni: 0.15%, Cu: 0.25%, B: 0.004%, P: 0.03%, S: 0.03%, the balance being Fe and unavoidable impurities;

[0062] (2) After pouring molten steel, a slab with a thickness of 230 mm is made; the slab is heated in a heating furnace at a temperature of 1200°C for 2 hours, and then rough rolling and finish rolling are carried out. The rough rolling start temperature is 1150°C, the finish rolling start temperature is 1050°C, the hot rolling outlet temperature is 820°C, and the plate thickness after hot rolling is 3.2 mm. The plate is then rapidly cooled to 650°C at a cooling rate of 15°C / s for coiling;

[0063] (3) Pickling and cold rolling are performed, with the acid solution temperature controlled at 68°C and the pickling speed at 140m / min; after continuous cold rolling, the thickness is controlled at 1.8mm; continuous annealing is performed, with the annealing temperature controlled at 850°C and the annealing speed controlled at 120m / min; cooling is performed by the following method: first slowly cooling to 680°C at a cooling rate of 9°C / s; then rapidly cooling to 460°C at a cooling rate of 30°C / s, aging treatment at 440°C for 600s; and finally cooling to 170°C. Leveling is performed on a leveling machine, and the smoothing elongation is controlled to be: 0.8%. Conventional alkaline washing, brushing, electrolytic degreasing and rinsing are performed, with the degreasing solution temperature controlled at 65°C and the degreasing solution pH ≥ 9.5;

[0064] (4) The electroplating process adopts gravity zinc plating, the electroplating solution is zinc sulfate aqueous solution, the zinc sulfate concentration in the electroplating solution is 120g / L, the pH value is 1.4, the electroplating solution temperature is 60℃, and the current density is controlled at 3A / dm 2The running speed of the steel plate in the electrogalvanizing tank is 80m / min; the zinc layer weight is controlled at 50g / m 2 ;

[0065] (5) The steel plate is immersed in the treatment solution for passivation film formation treatment to form a passivation film on the surface of the electro-galvanized plate. The treatment time is 40s and the treatment temperature is 70℃. The treatment solution includes main salt, pH regulator, and the rest is water. The main salt is Na2MoO4·2H2015g / L, and the pH regulator is sodium hydroxide and nitric acid. The pH value of the treatment solution is regulated by the pH regulator to 6, and the weight of the passivation film is controlled to 0.6g / m 2 ;

[0066] (6) The treated steel plate is hot formed. The hot forming process conditions are as follows: heating temperature 950℃, holding time 3min, transfer to a stamping die in air atmosphere, circulating water is passed into the die, the water temperature is 25℃, the cooling rate is controlled at 25℃ / s, the main cylinder pressure of the hydraulic press is 10MPa, the hot stamping holding time is 20s, and after the holding time is completed, the die is lifted and the coated plate is taken out.

[0067] Comparative Example 1-2

[0068] In order to compare with the galvanized steel prepared by the present invention, we selected several common galvanized steels on the market as comparisons. Comparative Example 1 is a hot-dip galvanized sheet sold by a steel plant, and Comparative Example 2 is a hot-dip galvanized aluminum-magnesium sheet sold by a steel plant.

[0069] Example 5

[0070] Galvanized steel test pieces of Examples 1-4 and Comparative Examples 1-2 were prepared for crack resistance testing.

[0071] The coated test piece was cut to obtain a blank, which was then heated at 800-980°C for 3 minutes. The blank was then transferred to a press tool and hot stamped to produce an Ω-shaped component. The component was then cooled (at a cooling rate of 30°C / s) by circulating cooling water at 20-50°C through the die to achieve hardening through martensitic transformation.

[0072] Finally, the deformed portion of the component was cut and analyzed for cracks using a scanning electron microscope (SEM). A rating of 0 indicates excellent, with the presence of microcracks ranging from 0 to 20 μm in depth; 1 indicates the presence of microcracks ranging from 20 to 50 μm in depth; and 2 indicates very poor, with the presence of macrocracks greater than 50 μm in depth. The results are shown in Table 1.

[0073] Table 1 Performance test results of test pieces of Examples 1-4 and Comparative Examples 1-2

[0074]

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for manufacturing galvanized hot-formed steel to avoid the LME problem, characterized in that: The steps include: (1) pickling and cold rolling the hot-rolled steel plate to a thickness of 0.6 to 2.0 mm, performing continuous annealing at a temperature of 800 to 850° C. and a speed of 100 to 180 m / min, cooling, aging treatment at 400 to 450° C. for 400 to 1000 s, and then cooling to 150 to 180° C.; (2) The steel plate obtained in step (1) is subjected to gravity electrogalvanizing, wherein the electroplating solution is a zinc sulfate aqueous solution, the zinc sulfate concentration is 100-120 g / L, the pH value is controlled at 1.3-1.8, the electroplating solution temperature is controlled at 50-70°C, and the current density is controlled at 1.5-3 A / dm 2 ; (3) immersing the electrogalvanized sheet obtained in step (2) in a passivation treatment solution for passivation film formation treatment, wherein the passivation treatment solution comprises a main salt, a pH regulator, and the rest is water, the main salt is one or more of silicate, molybdate, tungstate or their hydrates, the pH value of the treatment solution is 6 to 8, the treatment temperature is 40 to 80° C., and the passivation treatment time is 20 to 1200 s, so that a passivation film is formed on the surface of the electrogalvanized sheet; (4) The steel plate obtained in step (3) is hot formed at a heating temperature of 800-980°C and a holding time of 3-10 min, and then transferred to a stamping die in an air atmosphere or a nitrogen or argon doped with 0-0.5 vol.% H2. The cooling rate of the die is controlled to be above 25°C / s, the stamping pressure is 10-20 MPa, and the holding time is 3-20 s. After the holding time is completed, the die is lifted and the coated plate is taken out.

2. The manufacturing method according to claim 1, characterized in that In step (1), the pickling temperature is controlled at 60-80°C and the speed is 80-220 m / min; the specific cooling process is: first slowly cooling to 650-700°C at a cooling rate of 9-11°C / s; then rapidly cooling to 440-480°C at a cooling rate of 25-35°C / s.

3. The manufacturing method according to claim 1, characterized in that In step (2), the zinc layer weight is controlled to be 5-60 g / m 2 , preferably 5 to 30 g / m 2 ; The running speed of the steel plate in the electrogalvanizing tank is 80~140m / min.

4. The manufacturing method according to claim 1, characterized in that The concentration of the main salt in the passivation treatment solution in step (3) is controlled at 2-20 g / L; the pH regulator includes sodium hydroxide and nitric acid; the weight of the passivation film is controlled at 0.4-1.0 g / m 2 , preferably 0.4 to 0.6 g / m 2 .

5. The manufacturing method according to claim 1, characterized in that The cooling rate in step (4) is controlled at 25-35°C / s.

6. The manufacturing method according to claim 1, characterized in that The preparation process of the hot-rolled steel plate described in step (1) is as follows: 1) smelting to obtain molten steel, the chemical composition of the molten steel, calculated by mass percentage, is as follows: C: 0.01% to 0.25%, Mn: 0.30% to 1.5%, Si: 0.01% to 0.06%, Cr≤0.50%, Ti: 0.005% to 0.25%, Als≤0.02%, Ni≤0.50%, Cu≤0.30%, B≤0.005%, P≤0.03%, S≤0.03%, the balance being Fe and unavoidable impurities; 2) The molten steel is poured to form a slab with a thickness of 210 to 230 mm, and the slab is heated at a temperature of 1100 to 1250°C for 1 to 3 hours, and then rough rolling and finish rolling are carried out. The starting temperature of the rough rolling is 1105 to 1150°C, and the starting temperature of the finish rolling is 980 to 1050°C. The slab is rapidly cooled to 500 to 800°C at a cooling rate of 15 to 40°C / s for coiling.

7. The manufacturing method according to claim 6, characterized in that The chemical composition of the molten steel in step 1) is as follows, by mass percentage: C: 0.01% to 0.10%, Mn: 0.20% to 0.40%, Si: 0.01% to 0.06%, Ti: 0.005% to 0.25%, Als: 0.01% to 0.02%, B: 0.001% to 0.005%, P≤0.03%, S≤0.03%, and the balance is Fe and unavoidable impurities.

8. The manufacturing method according to claim 6, characterized in that The chemical composition of the molten steel in step 1) is as follows, by mass percentage: C: 0.10%-0.25%, Mn: 0.30%-0.70%, Si: 0.01%-0.06%, Cr: 0.10%-0.30%, Ti: 0.005%-0.15%, Ni: 0.10%-0.30%, Cu: 0.10%-0.40%, B: 0.001%-0.005%, P≤0.03%, S≤0.03%, and the balance is Fe and unavoidable impurities.

9. The manufacturing method according to claim 6, characterized in that In step 2), the hot rolling outlet temperature is 810-920°C.

10. The manufacturing method according to claim 6, characterized in that The thickness of the hot-rolled steel plate in step 2) is 3.0 to 4.0 mm.

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