2.2 gpa-grade al-si plated steel sheet, method for manufacturing the same, hot stamping method, and hot stamping formed part

Abstract

The application relates to the technical field of automobile steel plate production, in particular to a 2.2GPa-grade aluminum-silicon plated steel plate, a manufacturing method thereof, a hot stamping method and a hot stamping forming piece, molten steel meeting component requirements after smelting is subjected to hot dipping after being cast, hot-rolled and pickled, and through the synergistic design of components, structures and processes, an aluminum-silicon plated steel plate suitable for hot stamping forming is produced, the hot stamping forming piece obtained by adopting the steel plate and the matched hot stamping method contains more than 97% of martensite structure, the rest is ferrite + residual austenite + bainite, the plating layer is completely converted into a ferroalloy layer after hot stamping, the strength of the hot stamping forming piece can reach 2000-2400 MPa, the elongation is greater than 5%, the hot stamping forming piece has good strength and toughness matching, and simultaneously has excellent corrosion resistance and excellent anti-delayed cracking performance.

Description

Technical Field

[0001] This invention relates to the field of automotive steel sheet production technology, and in particular to an aluminum-silicon coated steel sheet for hot stamping, its manufacturing method, hot stamping method, and hot stamped parts. Background Technology

[0002] The core driving force behind the development of ultra-high strength steel comes from the automotive industry, especially the extreme pursuit of lightweighting and safety in the field of new energy vehicles, including the following aspects: The extreme need for lightweighting: New energy vehicles generally suffer from "range anxiety." To improve driving range, maximum weight reduction must be achieved in the body, chassis, and other structural components. High-strength materials allow for the use of thinner sheet metal while ensuring safety performance, resulting in significant weight reduction. The body of a new energy vehicle needs to provide sufficient support for the heavy battery pack while remaining lightweight itself, which places higher demands on the strength of the body structural components.

[0003] Extremely high safety standards: Current automotive crash regulations worldwide (such as CNCCAP and EURO-NCAP) are becoming increasingly stringent, with ever-higher requirements for passenger compartment protection. 2.2GPa grade steel is primarily used to manufacture critical crash-resistant structural components such as A-pillars, B-pillars, sill beams, and door anti-collision beams. In the event of a collision, these ultra-high-strength components effectively resist deformation, preventing intrusion into the passenger compartment and thus ensuring the survival space for occupants.

[0004] Cost and efficiency advantages: Compared with lightweight materials such as aluminum alloys and carbon fiber, ultra-high strength steel plates have significant advantages in terms of cost, production process compatibility (can be produced using existing stamping and welding production lines) and recyclability.

[0005] Hot stamping technology is a one-step process that combines stamping and hardening, avoiding the springback problem of traditional cold stamping of high-strength steel and resulting in high part forming precision. Currently, the strength of ultra-high-strength hot-formed steel has increased from the conventional 1.5 GPa level to 2.2 GPa level. This is not a simple matter of adjusting the composition; its production faces significant technical challenges, primarily the following: (1) The contradiction between strength and toughness: The higher the strength of a material, the more its fracture toughness and ductility will usually decrease significantly. A very hard but brittle material, like glass, cannot absorb energy through plastic deformation in a collision and will undergo catastrophic brittle fracture, which is absolutely unacceptable for automotive safety. The core challenge is how to ensure sufficient fracture elongation (usually required to be ≥5%) and excellent collision energy absorption capacity when the strength reaches the limit of 2.2 GPa.

[0006] (2) Risk of hydrogen-induced delayed cracking: When the strength of the steel plate exceeds 1.5 GPa, the steel becomes extremely sensitive to hydrogen embrittlement. During pickling, electroplating, or environmental corrosion, trace amounts of hydrogen atoms can penetrate the steel and accumulate at defects such as grain boundaries under extremely high internal stress, leading to sudden brittle fracture of the parts in a static state. As the strength increases, the sensitivity to hydrogen-induced cracking increases exponentially. It is necessary to strictly control the source of hydrogen from the composition and process, and at the same time improve the material's resistance to hydrogen embrittlement.

[0007] (3) Deterioration of welding and fatigue performance: The ultra-high strength narrows the spot welding process window, and the weld is prone to cracking, making it difficult to guarantee the joint strength. At the same time, the extremely high strength also means that it is more sensitive to micro-defects (such as inclusions and micropores), and the fatigue performance (the life of the part under alternating stress) faces a severe test.

[0008] (4) Formability and springback control: Although hot stamping is carried out at high temperatures, the rheological behavior of ultra-high strength materials in the austenitic state also needs to be precisely controlled. In addition, the micro-stress after quenching may lead to more complex springback, which in turn affects dimensional accuracy. Summary of the Invention

[0009] This invention provides a 2.2GPa grade aluminum-silicon coated steel sheet and its manufacturing method, hot stamping method, and hot stamped parts. Through the synergistic design of composition, microstructure, and process, an aluminum-silicon coated steel sheet suitable for hot stamping is produced. The hot stamped parts obtained by using this steel sheet and the matching hot stamping method can achieve a tensile strength of 2000-2400MPa and an elongation of more than 5%, exhibiting good strength and toughness matching, as well as excellent corrosion resistance and resistance to delayed cracking.

[0010] To achieve the above objectives, the present invention employs the following technical solution: A 2.2 GPa grade aluminum-silicon coated steel sheet, the chemical composition of the steel sheet by mass percentage is: C: 0.36%~0.40%, Si: 0.15%~0.50%, Mn: 1.00%~3.00%, P≤0.02%, S≤0.02%, Al: 0.03%~1.40%, Nb≤0.10%, Ti≤0.10%, V≤0.20%, Mo≤2.00%, B: 0.002%~0.006%, Cr: 0.15%~1.50%, Cu≤0.50%, Ni≤1.00%, with the remainder being Fe and other unavoidable impurities; The chemical composition of the aluminum-silicon coating, by mass percentage, is: Si: 5.0%–15.00%, Fe: 1.5%–2.6%; it also contains one or more of the following: Ti: 0.05%–0.50%, Re: 0.02%–0.20%, Mn: 0.5%–3.0%, Ni: 0.3%–3.0%, Sn: 0.02%–2.0%, Mg: 0.2%–3.0%; the remainder is Al.

[0011] The microstructure of the finished steel plate is pearlite + ferrite + bainite, wherein the volume content of pearlite is ≥50%.

[0012] A method for manufacturing a 2.2 GPa grade aluminum-silicon coated steel sheet includes the following processes: molten steel that meets the composition requirements after smelting is cast, hot-rolled, pickled, and then hot-dip coated; the hot rolling process parameters are: heating temperature 1180~1260℃, holding time 120~240min, roughing rolling start temperature 1060~1140℃, finishing rolling start temperature 1000~1080℃, finishing rolling finish temperature 840~920℃, and coiling temperature 450~650℃.

[0013] A method for manufacturing a 2.2 GPa grade aluminum-silicon coated steel sheet, wherein the hot-rolled steel sheet is pickled and then cold-rolled, and the hot-dip galvanizing process parameters of the cold-rolled steel sheet are as follows: the steel sheet is preheated to 600-750℃ before hot-dip galvanizing, and the surface of the steel sheet is pre-oxidized using an oxidizing atmosphere; the heating temperature of the steel sheet is controlled at 750-900℃ during hot-dip galvanizing, and the temperature of the aluminum pot is controlled at 630-720℃.

[0014] A hot stamping method for 2.2 GPa grade aluminum-silicon coated steel sheet includes the following steps: 1) Heat treatment of steel plate: The aluminum-silicon coated steel plate is sent into a heating furnace for heating. The heating time is 10-200s, the heating temperature is 800-980℃, and the holding time is 5-600s. 2) Hot stamping of steel plates: After heat preservation, the steel plates are cooled to 500-890°C at a cooling rate of more than 10°C / s and then stamped. The cooling rate during pressure holding and quenching is more than 15°C / s, and the final cooling temperature is 120-280°C.

[0015] A hot stamping method for 2.2 GPa grade aluminum-silicon coated steel sheet includes the following steps: 1) Steel plate heat treatment: The steel plate is rapidly heated to 900-980℃ at a heating rate of 50℃ / s or higher using induction heating or infrared heating, and the holding time is 5-100s. 2) Hot stamping of steel plates: After heat preservation, the steel plates are rapidly cooled to 750-880°C at a cooling rate of 30°C / s or higher, and then hot stamping is performed. The cooling rate during pressure holding and quenching is greater than 20°C / s, and the final cooling temperature is 180-350°C.

[0016] The hot-stamped parts obtained after hot stamping are subjected to tempering treatment at a temperature of 150–300℃ for 10–120 min.

[0017] A hot-stamped part is obtained by hot stamping the 2.2GPa grade aluminum-silicon coated steel sheet. The steel matrix of the hot-stamped part contains more than 97% martensite by volume, with the balance being ferrite + retained austenite + bainite. The martensite includes Mn-depleted martensite (MDM) and Mn-enriched martensite (MEM), and the difference in manganese mass content between MDM and MEM is ≥50%. The surface microstructure of the hot-stamped part has a three-layer structure, which consists of a surface oxide layer, an iron-aluminum-silicon intermetallic compound layer, and an α-Fe(Al) solid solution layer from the steel sheet surface to the steel matrix. The surface oxide layer is composed of aluminum oxide + iron oxide + manganese oxide.

[0018] The tensile strength of the hot-stamped parts is 2000-2400 MPa, and the elongation is greater than 5%; they do not break after 120 hours of four-point bending at 100% yield strength.

[0019] Compared with the prior art, the beneficial effects of the present invention are: Through the synergistic design of composition, microstructure, and process, an aluminum-silicon coated steel sheet suitable for hot stamping is produced. The hot-stamped parts obtained using this steel sheet and the matching hot stamping method contain more than 97% martensite, with the balance being ferrite + retained austenite + bainite. After hot stamping, the coating is completely transformed into an iron alloy layer. The strength of the hot-stamped parts can reach 2000-2400 MPa, with an elongation greater than 5%, exhibiting a good balance of strength and toughness, as well as excellent corrosion resistance and superior resistance to delayed cracking. Detailed Implementation

[0020] The present invention discloses a 2.2 GPa grade aluminum-silicon coated steel plate. The chemical composition of the steel plate, by mass percentage, is as follows: C: 0.36%–0.40%, Si: 0.15%–0.50%, Mn: 1.00%–3.00%, P≤0.02%, S≤0.02%, Al: 0.03%–1.40%, Nb≤0.10%, Ti≤0.10%, V≤0.20%, Mo≤2.00%, B: 0.002%–0.006%, Cr: 0.15%–1.50%, Cu≤0.50%, Ni≤1.00%, with the remainder being Fe and other unavoidable impurities.

[0021] The roles of each element in the steel plate (matrix) are as follows: As a major alloying element, carbon (C) contributes the most to the strength of quenched martensitic steel, primarily by providing strength.

[0022] The main function of Mn is to expand the austenite phase region and improve the hardenability of steel. In addition, this invention also utilizes the slow diffusion rate of Mn to form a heterogeneous structure in martensite, that is, to form Mn-depleted and Mn-rich regions in martensite, so that the steel can synergistically improve its strength and plasticity without relying on residual austenite.

[0023] Si primarily inhibits the formation of cementite, ensuring the stability of austenite; it also has a solid solution strengthening effect, improving the strength of steel.

[0024] To ensure hardenability, Ti, Cr, and B are added to the steel plate of this invention. Cu can also be added to improve the corrosion resistance of the steel. Elements such as Cu, Ti, Nb, and V can form second-phase particles such as TiN, TiC, and NbC, which can refine the grains, improve weldability, and act as permanent hydrogen traps, thereby preventing the penetration and diffusion of H and improving the steel's resistance to delayed fracture.

[0025] The addition of Mo strengthens the steel matrix and refines the grains, while also reducing the critical cooling rate during quenching.

[0026] The addition of Al can inhibit the formation of cementite and strengthen the steel matrix.

[0027] The addition of Ni can form NiAl nanoprecipitates, which strengthen the steel matrix, refine the grains, and improve the toughness of the steel.

[0028] The chemical composition of the aluminum-silicon coating, by mass percentage, is: Si: 5.0%–15.00%, Fe: 1.5%–2.6%; it also contains one or more of the following: Ti: 0.05%–0.50%, Re: 0.02%–0.20%, Mn: 0.5%–3.0%, Ni: 0.3%–3.0%, Sn: 0.02%–2.0%, Mg: 0.2%–3.0%; the remainder is Al.

[0029] The roles of each element in the aluminum-silicon coating are as follows: Al can generate aluminum oxide during the heating and heat preservation process of hot stamping of steel plates, which covers the coating surface as a protective layer to prevent further oxidation of the coating. At the same time, during the heating process, Al reacts with Fe in the substrate to generate FeAl intermetallic compounds.

[0030] The enrichment of silicon (Si) in the intermetallic compound layer hinders the interdiffusion of Fe and Al atoms, thereby forming a compact inhibitory layer structure. This reduces or even eliminates the liquid-phase erosion of the steel substrate by the coating, refines the coating structure, and improves coating performance. Simultaneously, Si can form composite oxides with Al on the coating surface, enhancing the corrosion resistance of the surface oxide layer. Furthermore, the addition of silicon lowers the melting point of the plating solution and improves its fluidity.

[0031] The addition of Ti can improve the corrosion resistance of the coating. Furthermore, Ti can form a titanium dioxide protective film, which has strong adhesion to the substrate, good protective performance, and can self-repair damage. The addition of Ti can refine the grain size and improve the plasticity and toughness of the coating. The simultaneous addition of Si and Ti can generate a more compact inhibition layer, improving the adhesion of the coating. Ti can also form intermetallic compounds with Al, increasing the hardness of the coating.

[0032] Re can improve the corrosion resistance of the coating, refine the grain, and facilitate the formation of a dense oxide film on the coating surface, providing protection during hot stamping.

[0033] Mn can improve the corrosion resistance of the coating, refine the grain size, and increase the hardness of the coating.

[0034] Ni can improve the corrosion resistance of the coating, refine the grain size, and enhance the plasticity and toughness of the coating.

[0035] Sn can improve the corrosion resistance of the coating and also improve its oxidation resistance at high temperatures.

[0036] Fe can reduce the alloying reaction time of the coating, reduce the heat reflection efficiency of the coating, and increase the heating rate during hot stamping.

[0037] The microstructure of the finished steel plate is pearlite + ferrite + bainite, wherein the volume content of pearlite is ≥50%.

[0038] The present invention discloses a method for manufacturing a 2.2 GPa grade aluminum-silicon coated steel sheet, comprising the following processes: molten steel that meets the composition requirements after smelting is cast, hot-rolled, pickled, and then hot-dip coated; the hot rolling process parameters are: heating temperature 1180~1260℃, holding time 120~240min, roughing rolling start temperature 1060~1140℃, finishing rolling start temperature 1000~1080℃, finishing rolling finish temperature 840~920℃, and coiling temperature 450~650℃.

[0039] The finishing rolling temperature was set at 840–920℃ to obtain austenite with finer grains. The coiling temperature was set at 450–650℃ to obtain a microstructure of ferrite, pearlite, and bainite. The C and Mn contents in each microstructure varied significantly, laying the foundation for the chemical heterogeneity in the subsequent martensitic microstructure. Studies revealed that the cold-rolled microstructure before rapid annealing mainly consisted of deformed ferrite, pearlite, and bainite. Furthermore, research showed a significant correlation between the manganese content and size of the cementite particles: large particles contained approximately 15 wt.% Mn, medium-sized particles approximately 10 wt.% Mn, and small particles (small particles or pearlite lamellae) approximately 6 wt.% Mn. The average manganese content in the ferrite matrix was approximately 0.5 wt.%. This uneven distribution of Mn laid the foundation for the formation of chemically heterogeneous martensite after rapid annealing.

[0040] Hot-rolled steel sheets can also be pickled before cold rolling. The hot-dip galvanizing process parameters for cold-rolled steel sheets are as follows: before hot-dip galvanizing, the steel sheet is preheated to 600-750℃, and the surface of the steel sheet is pre-oxidized using an oxidizing atmosphere; during hot-dip galvanizing, the heating temperature of the steel sheet is controlled at 750-900℃, and the temperature of the aluminum pot is controlled at 630-720℃. During the heating process, the cold-rolled steel sheet undergoes pre-oxidation treatment (600-750℃ range, oxidizing atmosphere), which causes an oxide film mainly composed of iron oxides to form on the surface of the steel sheet. During the subsequent heating and holding process, this oxide film is reduced to active iron, which readily reacts with aluminum elements in the zinc pot to form an alloy layer mainly composed of aluminum and iron.

[0041] The hot stamping method for a 2.2 GPa grade aluminum-silicon coated steel sheet according to the present invention includes the following steps: 1) Heat treatment of steel plate: The aluminum-silicon coated steel plate is sent into a heating furnace for heating for 10-200s, the heating temperature is 800-980℃ (preferably 880-940℃), and the holding time is 5-600s.

[0042] 2) Hot stamping of steel plate: After heat preservation, the steel plate is cooled to 500-890℃ (preferably 600-880℃) at a cooling rate of more than 10℃ / s and then stamped. The cooling rate during pressure holding and quenching is greater than 15℃ / s, and the final cooling temperature is 120-280℃ (preferably 150-220℃).

[0043] Preferably, the hot stamping method for a 2.2GPa grade aluminum-silicon coated steel sheet of the present invention includes the following steps: 1) Heat treatment of steel plate: The steel plate is rapidly heated to 900-980°C at a heating rate of 50°C / s or higher (preferably 80°C / s or higher) using rapid heating methods such as induction heating or infrared heating, and the holding time is 5-100s. 2) Hot stamping of steel plates: After heat preservation, the steel plates are rapidly cooled to 750-880°C at a cooling rate of 30°C / s or higher, and then hot stamping is performed. The cooling rate during pressure holding and quenching is greater than 20°C / s, and the final cooling temperature is 180-350°C.

[0044] Preferably, the hot-stamped parts obtained after hot stamping can also be tempered at a temperature of 150–300°C for 10–120 min.

[0045] The hot-stamped part of the present invention is obtained by the hot stamping method of the 2.2GPa grade aluminum-silicon coated steel sheet of the present invention. The steel base structure of the hot-stamped part contains more than 97% martensite by volume, and the balance is ferrite + retained austenite + bainite. The martensite structure includes Mn-depleted martensite (MDM) and Mn-enriched martensite (MEM), and the difference in manganese mass content between the two is more than 50%.

[0046] The surface microstructure of the hot-stamped part described in this invention has a three-layer structure, consisting of a surface oxide layer, an iron-aluminum-silicon intermetallic compound layer, and an α-Fe(Al) solid solution layer, arranged sequentially from the steel plate surface to the steel substrate. The surface oxide layer is composed of aluminum oxide, iron oxide, and manganese oxide. In other words, the layered structure of the hot-stamped part surface from the surface to the steel substrate is as follows: the first layer is a surface oxide layer (aluminum oxide + iron oxide + manganese oxide), the second layer is an iron-aluminum-silicon intermetallic compound layer, the third layer is an α-Fe(Al) solid solution layer, and the interior is the steel substrate layer.

[0047] Research has shown that the chemical heterogeneity within martensite induced by rapid annealing can synergistically improve the strength and ductility of steel without relying on retained austenite. A coexistence structure of Mn-depleted martensite (MDM) and Mn-enriched martensite (MEM) is formed in the steel. The orientation difference between these two types generates a large number of geometrically necessary dislocations (GNDs) at the interface, inducing continuous back stress hardening during tensile testing. Therefore, despite the very low amount of retained austenite (below 2%), the mechanical properties of the heterogeneous sample still surpass those of the homogeneous sample.

[0048] The heterostructure in martensite includes Mn-depleted martensite (MDM) and Mn-enriched martensite (MEM). MDM has multiple orientation variants, while MEM is confined to a single orientation variant. This significant crystallographic difference leads to a large number of geometric dislocations at the MDM / MEM interface. Unlike dual-phase steel, where geometrically necessary dislocations (GNDs) in ferrite grains can slip and reduce the yield strength, the inherently high dislocation density in the MDM region of the steel of this invention restricts GND migration, thereby maintaining a high yield strength. Furthermore, the hardness difference between MDM and MEM in the steel of this invention induces strain distribution during deformation, and the accumulated GNDs at the interface generate reverse stress, effectively delaying necking. Therefore, the hot-stamped part of this invention not only has a higher yield strength but also exhibits excellent ductility.

[0049] The hot-stamped part of the present invention has a tensile strength of 2000-2400 MPa and an elongation of more than 5%; it also has excellent corrosion resistance and delayed cracking resistance, and does not break after 120 hours of four-point bending at 100% yield strength.

[0050] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0051] The chemical composition of the steel plate in each embodiment is shown in Table 1, the chemical composition of the coating is shown in Table 2, and the hot stamping process parameters of the steel plate and the performance of the hot stamped parts are shown in Table 3.

[0052] Table 1 - Chemical composition of steel plates (wt.%): Table 2 - Chemical composition of the coating (wt.%): Table 3 - Hot stamping process parameters of steel plates and properties of hot stamped parts: Conclusion: The tensile strength of the hot-stamped parts prepared in each embodiment is greater than 2000 MPa, and the elongation is greater than 5%. The steel matrix is ​​martensite + a small amount of (ferrite + retained austenite + bainite), the coating is completely transformed into an iron alloy layer, and the VDA bending angle of the 1.0 mm thick steel plate is greater than 42°.

[0053] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A 2.2 GPa grade aluminum-silicon coated steel sheet, characterized in that, The chemical composition of the steel plate, by mass percentage, is as follows: C: 0.36%–0.40%, Si: 0.15%–0.50%, Mn: 1.00%–3.00%, P≤0.02%, S≤0.02%, Al: 0.03%–1.40%, Nb≤0.10%, Ti≤0.10%, V≤0.20%, Mo≤2.00%, B: 0.002%–0.006%, Cr: 0.15%–1.50%, Cu≤0.50%, Ni≤1.00%, with the remainder being Fe and other unavoidable impurities. The chemical composition of the aluminum-silicon coating, by mass percentage, is: Si: 5.0%–15.00%, Fe: 1.5%–2.6%; it also contains one or more of the following: Ti: 0.05%–0.50%, Re: 0.02%–0.20%, Mn: 0.5%–3.0%, Ni: 0.3%–3.0%, Sn: 0.02%–2.0%, Mg: 0.2%–3.0%; the remainder is Al. After smelting, the molten steel that meets the composition requirements is cast, hot-rolled, pickled, and then hot-dip galvanized. The hot rolling process parameters are as follows: heating temperature 1180~1260℃, holding time 120~240min, roughing rolling start temperature 1060~1140℃, finishing rolling start temperature 1000~1080℃, finishing rolling finish temperature 840~920℃, and coiling temperature 450~650℃.

2. The 2.2 GPa grade aluminum-silicon coated steel sheet according to claim 1, characterized in that, The microstructure of the finished steel plate is pearlite + ferrite + bainite, with the volume content of pearlite being ≥50%.

3. A method for manufacturing a 2.2 GPa grade aluminum-silicon coated steel sheet as described in claim 1 or 2, characterized in that, The process includes the following steps: molten steel that meets the composition requirements after smelting is cast, hot-rolled, pickled, and then hot-dip galvanized; the hot rolling process parameters are: heating temperature 1180~1260℃, holding time 120~240min, roughing rolling start temperature 1060~1140℃, finishing rolling start temperature 1000~1080℃, finishing rolling finish temperature 840~920℃, and coiling temperature 450~650℃.

4. The method for manufacturing a 2.2 GPa grade aluminum-silicon coated steel sheet according to claim 3, characterized in that, Hot-rolled steel sheets are pickled and then cold-rolled. The hot-dip galvanizing process parameters for cold-rolled steel sheets are as follows: the steel sheet is preheated to 600-750℃ before hot-dip galvanizing, and the surface of the steel sheet is pre-oxidized using an oxidizing atmosphere; the heating temperature of the steel sheet is controlled at 750-900℃ during hot-dip galvanizing, and the temperature of the aluminum pot is controlled at 630-720℃.

5. A hot stamping method for a 2.2 GPa grade aluminum-silicon coated steel sheet as described in claim 1, characterized in that, The steps include the following: 1) Heat treatment of steel plate: The aluminum-silicon coated steel plate is sent into a heating furnace for heating. The heating time is 10-200s, the heating temperature is 800-980℃, and the holding time is 5-600s. 2) Hot stamping of steel plates: After heat preservation, the steel plates are cooled to 500-890°C at a cooling rate of more than 10°C / s and then stamped. The cooling rate during pressure holding and quenching is more than 15°C / s, and the final cooling temperature is 120-280°C.

6. A hot stamping method for a 2.2 GPa grade aluminum-silicon coated steel sheet as described in claim 1, characterized in that, The steps include the following: 1) Steel plate heat treatment: The steel plate is rapidly heated to 900-980℃ at a heating rate of 50℃ / s or higher using induction heating or infrared heating, and the holding time is 5-100s. 2) Hot stamping of steel plates: After heat preservation, the steel plates are rapidly cooled to 750-880°C at a cooling rate of 30°C / s or higher, and then hot stamping is performed. The cooling rate during pressure holding and quenching is greater than 20°C / s, and the final cooling temperature is 180-350°C.

7. The hot stamping method for a 2.2 GPa grade aluminum-silicon coated steel sheet according to claim 5 or 6, characterized in that, The hot-stamped parts obtained after hot stamping are subjected to tempering treatment at a temperature of 150–300℃ for 10–120 min.

8. A hot-stamped part, obtained by the hot stamping method of the 2.2 GPa grade aluminum-silicon coated steel sheet as described in claim 5 or 6, characterized in that, The steel matrix of the hot-stamped part contains more than 97% martensite by volume, with the balance being ferrite + retained austenite + bainite. The martensite includes Mn-depleted martensite (MDM) and Mn-enriched martensite (MEM), and the difference in manganese mass content between MDM and MEM is ≥50%. The surface microstructure of the hot-stamped part has a three-layer structure, which consists of a surface oxide layer, an iron-aluminum-silicon intermetallic compound layer, and an α-Fe(Al) solid solution layer from the steel plate surface to the steel matrix. The surface oxide layer is composed of aluminum oxide + iron oxide + manganese oxide.

9. A hot-stamped part according to claim 8, characterized in that, The tensile strength of the hot-stamped parts is 2000-2400 MPa, and the elongation is greater than 5%; they do not break after 120 hours of four-point bending at 100% yield strength.

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