Delayed-cracking-resistant 1800MPa-grade zinc-based coated steel plate, manufacturing method thereof, hot forming method and component

Abstract

The invention provides a delayed cracking resistant 1800MPa level zinc-based coated steel plate, which comprises a substrate and a coating, the substrate comprises the following components in percentage by weight: 0.25%-0.35% of C, 0.15%-0.45% of Si, 1.50%-2.50% of Mn, less than or equal to 0.02% of P, less than or equal to 0.02% of S, 0.03%-1.50% of Al, 0.02%-0.10% of Nb, 0.02%-0.10% of Ti, less than or equal to 0.20% of V, less than or equal to 0.005% of B, 0.15%-0.60% of Cr, and Fe and other inevitable impurities; and the plating layer comprises the following components in percentage by mass: 0.15%-3.50% of Al and the balance of Zn. The invention further provides a manufacturing method of the delayed-cracking-resistant 1800MPa-grade zinc-based coated steel plate. The manufacturing method comprises the steps of smelting, casting, hot rolling and hot dipping. The invention further discloses a hot stamping method of the delayed-cracking-resistant 1800MPa-grade zinc-based coating steel plate. The hot stamping method comprises the steps of steel plate heating, steel plate cooling and hot stamping. According to the hot stamping forming part produced through the method, the strength of the steel plate is larger than 1800 MPa, the elongation is larger than 6%, and the steel plate subjected to hot stamping can meet the requirement that the steel plate does not crack after being bent for 120 hours at four points.

Description

Technical Field

[0001] The invention relates to the field of metal materials, and in particular to a delayed cracking resistant 1800MPa grade zinc-based coated steel plate and a manufacturing method, a hot forming method and components thereof. Background Art

[0002] The most commonly used hot-formed steel is 1500MPa grade steel, but with the increasing requirements for energy conservation, emission reduction and safety performance of automobiles, the strength of 1500MPa cannot meet the needs, so it is necessary to develop higher strength steel. The development of 1800MPa hot-formed steel is imminent, but with the increase in strength, there will be a problem of delayed cracking, that is, after stamping, hydrogen atoms from the service environment enter the steel and cause hydrogen aggregation, resulting in hydrogen-induced cracking, and the cracks expand under stress, resulting in delayed cracking.

[0003] Since hot forming is carried out under high temperature conditions, the steel plate will inevitably oxidize, and subsequent methods such as sandblasting and pickling are required to remove the iron oxide scale. To solve this problem, aluminum-silicon coated hot-formed steel plates have been developed. The aluminum-silicon coating can provide protection for the steel plate at high temperatures and avoid the formation of iron oxide scale. However, the aluminum-iron intermetallic compound generated by the reaction between the coating and the steel substrate during hot stamping is a brittle and hard phase and cannot provide electrochemical protection for the substrate.

[0004] Therefore, zinc-based coated hot-formed steel plates were proposed. Compared with traditional aluminum-silicon coated hot-formed steel plates, zinc-based coated hot-formed steel plates have better corrosion resistance. However, due to the low melting point of iron-zinc compounds, liquid phase brittleness problems will occur during the stamping process, causing parts to crack and fail.

[0005] To solve these problems, the present invention provides a hot stamping method for zinc-based coated steel plates and a zinc-based coated hot-formed steel plate. The formed parts have the protective effect of pure zinc coating on the steel plate, while solving the problems of liquid phase corrosion and delayed cracking of the steel substrate by the pure zinc coating. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a delayed cracking 1800MPa grade zinc-based coated steel sheet and its manufacturing method, hot forming method and components. The hot stamping parts produced by the method of the present invention have no liquid phase brittleness and liquid phase cracks, have good strength, toughness and delayed cracking resistance, and have excellent corrosion resistance.

[0007] The object of the invention is achieved in this way:

[0008] The present invention provides a delayed cracking resistant 1800MPa grade zinc-based coated steel plate, comprising a substrate and a coating, specifically as follows:

[0009] The zinc-based coated steel plate substrate has chemical compositions, by mass percentage, including: C: 0.25% to 0.35%, Si: 0.15% to 0.45%, Mn: 1.50% to 2.50%, P≤0.02%, S≤0.02%, Al: 0.03% to 1.50%, Nb: 0.02% to 0.10%, Ti: 0.02% to 0.10%, V≤0.20%, B≤0.005%, Cr: 0.15% to 0.60%, as well as Fe and some other inevitable impurities.

[0010] Furthermore, the substrate composition also includes one or more of the following elements: Mo≤1.00%, Cu≤0.50%, Ni≤1.00%;

[0011] Furthermore, the coating of the zinc-based coated steel sheet comprises, by mass percentage, chemical compositions of: Al: 0.15% to 3.50%, and the remainder Zn.

[0012] Furthermore, the coating composition also includes one or more of: Mg: 1.0% to 2%, Si: 0.05% to 0.50%, Ti: 0.03% to 0.50%, Re: 0.01% to 0.10%, and Mn: 0.5% to 3.0%.

[0013] The composition design reasons of the elements in the steel plate substrate are as follows:

[0014] C: 0.25%~0.35%

[0015] As the main alloying element, C contributes most to the strength of quenchable martensitic steel, providing strength, while forming precipitates with Nb and Ti elements in the steel to improve strength and refine grains; when the content is lower than 0.25%, sufficient low-temperature transformation phases such as martensite and bainite cannot be formed after hot forming; when the content is higher than 0.35%, the hardenability of the steel is improved, and the strength of the steel after hot forming is much greater than 1800MPa, the plasticity and toughness of the steel decrease, and the delayed fracture resistance performance decreases.

[0016] Mn: 1.50%~2.50%

[0017] The main function of Mn is to expand the austenite phase area, so that the zinc-based coated hot-formed steel plate can be hot stamped in a lower temperature range, and the martensite structure can be obtained. At the same time, the steel matrix is ​​solid-solution strengthened to improve the strength. When the Mn content is less than 1.50%, the strength of the steel is low, and the austenite state cannot be maintained at the hot stamping temperature. When the content is higher than 2.50%, the strength of the steel is much higher than the 1800MPa grade requirement.

[0018] Si: 0.15% to 0.45%

[0019] Si mainly inhibits the appearance of cementite, ensures that austenite does not undergo pearlite transformation during cooling, and exists at a lower temperature; at the same time, it solid-solution strengthens the steel matrix and improves strength. When the Si content is lower than 0.15%, the austenite is not stable enough during hot stamping and is prone to pearlite transformation. When the Si content is higher than 0.45%, selective oxidation will occur during continuous hot-dip plating, forming Si oxides on the surface of the steel plate, which will affect the hot-dip plating performance of the steel.

[0020] B≤0.005%, Cr: 0.15%~0.60%

[0021] To ensure hardenability, Ti, Cr and B are added. Due to the solute drag effect, it is difficult for Cr, Si and Mn elements to diffuse and migrate in steel, which can prevent the corrosion of the steel matrix by the liquid Zn in the coating during hot stamping heating and insulation, reduce the liquid phase brittleness, and thus improve the performance of zinc-based hot-formed steel sheets.

[0022] Cu≤0.50%

[0023] Adding Cu improves the corrosion resistance of steel, thereby preventing the penetration of H and improving the delayed fracture resistance of steel. The addition of Mo and Nb strengthens the steel matrix and refines the grains;

[0024] Mo≤1.00%, Ti: 0.02%~0.10%, V≤0.20%, Nb: 0.02%~0.10%

[0025] The addition of Mo, Ti, V and Nb can form fine dispersed precipitates such as TiN, TiC, NbC, VC, etc. in the steel, which can form hydrogen traps during service and improve the delayed fracture resistance of the steel.

[0026] Al: 0.03%~1.50%

[0027] The role of Al is similar to that of Si. It is better to use it together with Si to inhibit the appearance of cementite and ensure the stability of low-temperature austenite. However, the Al element will reduce the austenite phase area. At the same time, Al can form AlN precipitation with N in steel, refine the grains, act as a permanent hydrogen trap, absorb hydrogen atoms, and improve the delayed fracture resistance. Al: 0.03% to 1.50%. If the content is higher than 1.50%, it will affect the low-temperature stability of austenite. If the content is lower than 0.03%, it cannot ensure a good deoxidation effect and will increase the inclusion content in the steel.

[0028] The reasons for designing the composition of elements in the zinc-based coated steel plate coating are as follows:

[0029] Al: 0.15%~3.50%

[0030] Al: The addition of Al can generate aluminum oxide to cover the surface of the coating during the hot forming heating and heat preservation of the steel plate, forming a protective layer to prevent further oxidation of the coating. The Fe-Al phase is formed at the interface between the coating and the steel substrate. The existence of the Fe-Al phase will delay the corrosion of the zinc layer liquid to the steel substrate (especially the grain boundary of the steel) during the heating and heat preservation process of hot stamping, reduce the liquid phase brittleness, and improve the forming and bending properties of the steel. When the aluminum content is lower than 0.15%, it is not possible to form a sufficient Fe-Al inhibition layer to ensure the adhesion of the coating. When the aluminum content is higher than 3.50%, a thick aluminum oxide covering layer will be formed on the surface, affecting the subsequent pre-coating treatment.

[0031] Mg: 1.0%~2%

[0032] Mg: The addition of Mg element can greatly improve the corrosion resistance of the coating. At the same time, the magnesium oxide generated by magnesium oxidation can also cover the surface of the coating to form a protective layer to prevent further oxidation of the coating.

[0033] Si: 0.05% to 0.50%

[0034] Si: Si is enriched in the intermetallic compound layer, which hinders the mutual diffusion of Fe and Zn atoms through the liquid phase channel, and can form a compact inhibition layer structure, thereby reducing or even eliminating the liquid phase corrosion of the coating on the steel substrate, refining the structure of the coating and improving the coating performance.

[0035] Ti: 0.03%~0.50%

[0036] Ti: The addition of Ti can improve the corrosion resistance of the coating. In addition, Ti can form a protective film of titanium oxide, which has a strong bond with the substrate, good protection performance, and can repair damage by itself. Adding Si and Ti at the same time can generate a more compact inhibition layer and improve the ability of the steel plate to resist liquid phase corrosion. Ti can form an intermetallic compound with Al to improve the hardness of the coating.

[0037] Re: 0.01%~0.10%

[0038] Re: Improve the corrosion resistance of the coating, refine the grains, and facilitate the formation of a dense oxide film on the surface of the coating, providing protection during hot stamping.

[0039] Mn: 0.5%~3.0%

[0040] Mn: Improves the corrosion resistance of the coating, refines the grains, and increases the hardness of the coating.

[0041] Technical solution 2 of the present invention provides a method for manufacturing a delayed cracking resistant 1800MPa grade zinc-based coated steel plate, comprising smelting, casting, hot rolling, pickling and cold rolling, and hot-dip plating.

[0042] Hot rolling process:

[0043] Heating at 1220±40℃, keeping warm for 180±90 minutes, rough rolling at 1100±40℃, finishing rolling at 1060±40℃, final rolling at 870±40℃, coiling at 450~750℃; heating at 1220±40℃, keeping warm for 180±90 minutes to ensure uniform composition of the ingot and sufficient dissolution of precipitates such as Nb and Ti, rough rolling at 1100±40℃ to ensure sufficient deformation capacity, finishing rolling at 1060±40℃ to ensure good dephosphorization performance, final rolling at 870±40℃ to obtain relatively uniform and fine grain structure, coiling at 450~750℃ to reduce the thickness of the oxide scale, facilitate pickling, form a fine and uniformly distributed second phase precipitation, ensure uniform distribution of elements such as C and Mn in the steel, and ensure consistency of steel performance.

[0044] Pickling and cold rolling:

[0045] Pickling is used to completely remove the iron oxide scale. The cold rolling reduction rate is 30% to 70%. Rolling is difficult when the reduction rate is greater than 70%, and the grain refinement effect is not obvious when the reduction rate is less than 30%.

[0046] Hot dip coating process:

[0047] The composition of the plating solution is: Al: 0.15-3.50%, and it may also contain one or more of Mg: 1.0-2%, Si: 0.05-0.50%, Ti: 0.03-0.50%, Re: 0.01-0.10%, Mn: 0.5-3.0%, and the rest is Zn. The hot dip heating temperature is controlled at 750-900°C, and the zinc pot temperature is 450-520°C. The steel plate is pre-oxidized during the heating process, specifically, in the temperature range of 600-750°C, the surface of the steel plate is pre-oxidized using an oxidizing atmosphere (a furnace atmosphere with a high dew point or a furnace atmosphere containing oxygen), so that a layer of oxide film mainly composed of iron oxide is generated on the surface of the steel plate, which is reduced to active iron during the subsequent heating and heat preservation process. The active iron is easy to react with the aluminum element in the zinc pot to produce an alloy layer mainly composed of aluminum and iron.

[0048] Furthermore, the manufacturing method also includes pickling and cold rolling.

[0049] Technical solution three of the present invention provides a hot stamping method for a delayed cracking resistant 1800MPa grade zinc-based coated steel plate, comprising heating the steel plate, cooling the steel plate, and hot stamping.

[0050] 1) Steel plate heating: The zinc-based coated hot-formed steel plate is sent into a heating furnace for heating, and the heating and holding time is 180 seconds to 600 seconds in total, and the heating temperature is 800-930°C, preferably 850-890°C; if the heating time is less than 180 seconds, the austenitization of the steel plate is insufficient, and the reaction between the coating and the steel matrix is ​​insufficient, and it cannot be completely converted into Fe-Zn intermetallic compounds. If the heating time is more than 600 seconds, it will cause the coarsening of austenite grains and deteriorate the performance of the steel. At the same time, the Fe-Zn intermetallic compounds in the coating are all converted into α-Fe (Zn) solid solutions, which reduces the corrosion resistance of the steel and forms a very thick α-Fe layer, which will greatly reduce the strength of the steel. If the heating temperature is less than 800°C, austenitization cannot be achieved, and the alloying of the coating is not sufficient. If the heating temperature is higher than 930°C, it is consistent with the effect of too long holding time.

[0051] 2) Steel plate cooling: After the steel plate is insulated, it is cooled to the hot stamping temperature and stamping begins. The target temperature range for cooling is 500-850°C, preferably 600-720°C, and the cooling rate is greater than 10°C / s. If the target cooling temperature is lower than 500°C, it will cause the decomposition of austenite. If the target cooling temperature is higher than 850°C, the Fe-Zn intermetallic compound is in liquid state, which will cause liquid phase embrittlement. This problem can be completely avoided below 720°C. The purpose of a cooling rate greater than 10°C / s is to ensure the presence of austenite in the steel. Through low-temperature hot stamping, most of the grains (more than 80%) are controlled to form small-angle grain boundaries and subgrain boundaries (angle less than 20 degrees), thereby increasing the strength of the grain boundaries and reducing cracking and failure along the grain boundaries.

[0052] 3) Hot stamping: Hot stamping is performed immediately after the steel plate is cooled to the hot stamping temperature. The hot stamping cooling rate is greater than 15°C / s, and the cooling end temperature is controlled at 120-280°C, preferably 150-220°C.

[0053] The cooling end temperature is controlled above 120°C, and the residual heat can be used to age the parts after stamping is completed, which can improve the toughness of the parts to a certain extent; the cooling end temperature is controlled below 280°C because the transformation of martensite is incomplete above 280°C, and too high a residual heat aging temperature will reduce the strength of the steel.

[0054] Furthermore, the heating temperature during the steel plate heating process is 850-890° C.; the cooling target temperature range during the steel plate cooling process is 600-720° C.; and the cooling end point temperature during the hot stamping process is 150-220° C.

[0055] Technical solution four of the present invention provides a hot-formed component made of 1800MPa grade zinc-based coated steel plate resistant to delayed cracking, the steel base structure of the component is more than 96% martensite structure, and the balance is ferrite + residual austenite + bainite (residual austenite film (content of 0.5% to 1.5%), ferrite + bainite structure (1.5% to 3.5%)), the microstructure of the surface of the component has four layers (from the surface to the steel matrix in sequence), the first layer is the surface oxide layer: aluminum oxide + zinc oxide + iron oxide + manganese oxide and other oxides; the second layer is an iron-zinc intermetallic compound layer (such as Fe3Zn10, etc.); the third layer, an α-Fe (Zn) solid solution layer, the Zn content is greater than 5%, the thickness range is 10um to 50um, and the fourth layer is a steel matrix layer.

[0056] The second intermetallic compound layer and the third α-Fe(Zn) solid solution layer will preferentially electrochemically corrode the substrate, providing cathodic protection for the substrate. The α-Fe(Zn) solid solution layer has good plasticity and toughness, which can reduce or even eliminate the generation and expansion of microcracks and improve the toughness of the product.

[0057] The beneficial effects of the present invention are:

[0058] The present invention avoids the generation of pro-eutectic ferrite and pearlite through the design of high manganese and high silicon element composition, improves the strength and toughness of the steel matrix, and adds micro-alloy elements to refine the grains. In terms of technology, a hot stamping process of low-temperature heating and low-temperature deformation is adopted to control the formation of small-angle grain boundaries and sub-grain boundaries (angle less than 20 degrees) between most grains (more than 80%), improve the strength of the grain boundaries, and reduce cracking and failure along the grain boundaries.

[0059] 1. The present invention provides a hot-formed component of a zinc-based coated steel plate for hot forming. After hot pressing, the component has a yield strength greater than 1200 MPa, a tensile strength greater than 1800 MPa, an elongation greater than 6%, and excellent delayed fracture resistance.

[0060] 2. The coating is completely transformed into an iron alloy layer, with no coating evaporation, no liquid phase corrosion, and no hard Fe-Al intermetallic compounds.

[0061] 3. The matrix structure of the hot-formed parts is martensite + ferrite + bainite + retained austenite, retained austenite film (content of 0.5% to 1.5%), ferrite + bainite structure (1.5% to 2.5%).

[0062] 4. The hot stamped steel plate can meet the requirement of four-point bending without cracking for 120 hours (in hydrochloric acid solution with a pH value of 1). DETAILED DESCRIPTION

[0063] The present invention will be further described below by way of examples.

[0064] A method for manufacturing a delayed cracking 1800MPa grade zinc-based coated steel plate comprises smelting, casting, hot rolling and hot-dip coating.

[0065] Hot rolling process:

[0066] Heating at 1220±40℃, keeping warm for 180±90 minutes, rough rolling at 1100±40℃, finishing rolling at 1060±40℃, final rolling at 870±40℃, coiling at 450~750℃;

[0067] Hot dip coating process:

[0068] The plating solution composition is Al: 0.15-3.50%, the rest is Zn; it also includes one or more of Mg: 1.0-2%, Si: 0.05-0.50%, Ti: 0.03-0.50%, Re: 0.01-0.10%, Mn: 0.5-3.0%;

[0069] The hot dip heating temperature is 750-900°C, and the zinc pot temperature is 450-520°C. The steel plate is pre-oxidized during the heating process, specifically, the surface of the steel plate is pre-oxidized in an oxidizing atmosphere at a temperature range of 600-750°C.

[0070] A hot stamping method for a delayed cracking 1800MPa grade zinc-based coated steel plate comprises heating the steel plate, cooling the steel plate and hot stamping.

[0071] Steel plate heating:

[0072] The zinc-based hot-formed steel plate is sent into a heating furnace for heating, the heating and holding time is 180 seconds to 600 seconds in total, and the heating temperature is 800-930°C;

[0073] Steel plate cooling:

[0074] After the steel plate is insulated, it is cooled to the hot stamping temperature and stamping begins. The target temperature range for cooling is 500-850°C, and the cooling rate is greater than 10°C / s.

[0075] Hot stamping: Hot stamping is carried out immediately after the steel plate cools to the hot stamping temperature. The hot stamping cooling rate is greater than 15°C / s, and the cooling end temperature is controlled at 120-280°C.

[0076] Furthermore, the heating temperature during the steel plate heating process is preferably 850-890°C; the cooling target temperature range during the steel plate cooling process is preferably 600-720°C; and the cooling end point temperature during the hot stamping process is preferably 150-220°C.

[0077] A component made by a hot stamping method of a delayed cracking resistant 1800MPa grade zinc-based coated steel plate, wherein the component steel base structure is martensite + ferrite + bainite + residual austenite, the volume percentage of the residual austenite is 0.5% to 1.5%, and the volume percentage of the ferrite + bainite structure is 1.5% to 2.5% in total.

[0078] Furthermore, the microstructure of the component has four layers, namely 1, 2, 3, and 4 layers from the surface to the steel matrix. The 1st layer is the surface oxide layer: oxides such as aluminum oxide + zinc oxide + iron oxide + manganese oxide; the 2nd layer is the iron-zinc intermetallic compound layer; the 3rd layer is the α-Fe (Zn) solid solution layer, the Zn content is greater than 5%, the thickness range is 10um to 50um, and the 4th layer is the steel matrix layer.

[0079] Furthermore, the yield strength of the thermoformed component is greater than 1200 MPa, the tensile strength is greater than 1800 MPa, the elongation is greater than 6%, and the delayed fracture resistance is excellent.

[0080] Examples of the steel of the present invention are shown in Tables 1, 2, 3, 4 and 5.

[0081] Table 1: Chemical composition of the steel plate coating in the example

[0082]

[0083]

[0084] Table 2: Chemical composition of the steel plate substrate of the example

[0085]

[0086] Table 3 Manufacturing method of hot stamping steel plate

[0087]

[0088] Table 4: Process parameters and properties of example steel

[0089]

[0090] Table 5 Microstructure of hot stamping parts

[0091] More than 96% martensite structure, the balance is composed of ferrite + retained austenite + bainite (retained austenite film (0.5% to 1.5%), ferrite + bainite structure (1.5% to 3.5%)

[0092]

[0093] As can be seen from the above, the hot-formed parts of the hot-forming zinc-based coated steel sheet of the present invention have a yield strength greater than 1200MPa, a tensile strength greater than 1800MPa, an elongation greater than 6%, and excellent delayed fracture resistance after hot pressing. The coating of the parts is completely transformed into an iron alloy layer, there is no coating evaporation phenomenon, no liquid phase corrosion phenomenon, and no hard Fe-Al intermetallic compounds. The matrix structure of the hot-formed parts is martensite + ferrite + bainite + residual austenite, residual austenite film (0.5% to 1.5% content), ferrite + bainite structure (1.5% to 2.5%). At the same time, the steel plate after hot stamping can meet the requirement of no cracking in four-point bending for 120 hours (in a hydrochloric acid solution with a pH value of 1).

[0094] In order to describe the present invention, the present invention is appropriately and fully illustrated by the examples in the above. The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made should be included in the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A delayed cracking resistant 1800MPa grade zinc-based coated steel sheet, comprising a substrate and a coating, characterized in that: The substrate comprises the following components by weight percentage: C: 0.25% ~ 0.35%, Si: 0.15% ~ 0.45%, Mn: 1.50% ~ 2.50%, P ≤ 0.02%, S ≤ 0.02%, Al: 0.03% ~ 1.50%, Nb: 0.02% ~ 0.10%, Ti: 0.02% ~ 0.10%, V ≤ 0.20%, B ≤ 0.005%, Cr: 0.15% ~ 0.60%, as well as Fe and some other unavoidable impurities.

2. The delayed cracking 1800MPa grade zinc-based coated steel sheet according to claim 1, characterized in that: The substrate components also include one or more of the following elements: Mo≤1.00%, Cu≤0.50%, Ni≤1.00%.

3. The delayed cracking 1800MPa grade zinc-based coated steel sheet according to claim 1, characterized in that: The coating comprises the following components by mass percentage: Al: 0.15% to 3.50%, and the rest is Zn.

4. The delayed cracking 1800MPa grade zinc-based coated steel sheet according to claim 3, characterized in that: The components also include one or more of the following elements: Mg: 1.0% to 2%, Si: 0.05% to 0.50%, Ti: 0.03% to 0.50%, Re: 0.01% to 0.10%, and Mn: 0.5% to 3.0%.

5. A method for manufacturing a delayed cracking 1800MPa grade zinc-based coated steel sheet as claimed in any one of claims 1 to 4, comprising smelting, casting, hot rolling, pickling and cold rolling, and hot-dip coating, characterized in that: Hot rolling process: Heating at 1220±40℃, keeping warm for 180±90 minutes, rough rolling at 1100±40℃, finishing rolling at 1060±40℃, final rolling at 870±40℃, coiling at 450~750℃; Pickling and cold rolling: Cold rolling reduction rate 30% to 70%; Hot dip coating process: The hot-dip galvanizing heating temperature is 750-900°C, and the zinc pot temperature is 450-520°C; the steel plate is pre-oxidized during the heating process, specifically, the surface of the steel plate is pre-oxidized in an oxidizing atmosphere in the temperature range of 600-750°C.

6. A hot stamping method for the delayed cracking 1800MPa grade zinc-based coated steel sheet according to any one of claims 1 to 4, comprising heating the steel sheet, cooling the steel sheet, and hot stamping, wherein: Steel plate heating: The zinc-based hot-formed steel plate is sent into a heating furnace for heating, the heating and holding time is 180 to 600 seconds in total, and the heating temperature is 800 to 930°C; Steel plate cooling: After the steel plate is insulated, it is cooled to the hot stamping temperature and stamping begins. The cooling rate is greater than 10°C / s, and the target cooling temperature range is 500-850°C. Hot stamping: Hot stamping is carried out immediately after the steel plate cools to the hot stamping temperature. The hot stamping cooling rate is greater than 15°C / s, and the cooling end temperature is controlled at 120-280°C.

7. The hot stamping method of a delayed cracking 1800MPa grade zinc-based coated steel sheet according to claim 6, characterized in that: The heating temperature of the steel plate during heating is 850-890° C.; the target cooling temperature range of the steel plate during cooling is 600-720° C.; and the cooling end point temperature during hot stamping is 150-220° C.

8. A component made by hot stamping of a delayed cracking 1800MPa grade zinc-based coated steel sheet as claimed in claim 6, characterized in that: The steel matrix structure of the component is martensite+ferrite+bainite+retained austenite, the volume percentage of the retained austenite is 0.5% to 1.5%, and the volume percentage of the ferrite+bainite structure is 1.5% to 2.5% in total.

9. The component made by hot stamping method of a delayed cracking 1800MPa grade zinc-based coated steel sheet according to claim 8, characterized in that: The microstructure of the component has four layers, namely 1, 2, 3 and 4 layers from the surface to the steel matrix. The 1st layer is the surface oxide layer: oxides such as aluminum oxide + zinc oxide + iron oxide + manganese oxide; the 2nd layer is the iron-zinc intermetallic compound layer; the 3rd layer is the α-Fe (Zn) solid solution layer, the Zn content is greater than 5%, the thickness ranges from 10um to 50um, and the 4th layer is the steel matrix layer.

10. The component made by hot stamping method of a delayed cracking 1800MPa grade zinc-based coated steel sheet according to claim 8, characterized in that: The yield strength of the thermoformed component is greater than 1200 MPa, the tensile strength is greater than 1800 MPa, the elongation is greater than 6%, and the delayed fracture resistance is excellent.

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