A 2000 mpa and above hot-stamped formed member

Abstract

The application provides a 2000MPa or more hot stamping forming component, a steel plate for manufacturing the same and a preparation method thereof, the steel plate comprises the following alloy components in percentage by mass: 0.365-0.455% of C, 0.50-1.35% of Mn, 0.01-0.6% of Si, 0.01-0.6% of Cr, 0.1-0.6% of Al, 0.001-0.01% of B, 0.001-0.02% of P, 0.001-0.01% of N, 0.001-0.01% of S, the balance of Fe and inevitable impurities, carbon equivalent is less than or equal to 0.68, manganese equivalent is 0.80-1.60, and the mass ratio of aluminum to carbon is greater than or equal to 0.5. Through austenitizing treatment and laser cutting process parameter design, the aluminum alloy plated hot forming component with the steel plate as a base body has a tensile strength of more than 2000MPa and low hydrogen brittleness sensitivity.

Description

Technical Field

[0001] This invention relates to the field of steel materials technology, and in particular to a hot-formed steel plate and aluminum alloy coated component with high tensile strength and low hydrogen embrittlement sensitivity, and the manufacturing method thereof. Background Technology

[0002] To obtain ultra-high strength steel plates with tensile strength exceeding 2000 MPa, high carbon content design is the most effective and economical method. However, increased carbon content means increased brittleness and decreased toughness, significantly increasing hydrogen embrittlement sensitivity. Hydrogen embrittlement is a particularly prominent problem in the manufacturing process of hot-formed steel components with aluminum alloy coatings and tensile strengths exceeding 2000 MPa. The manufacturing process of hot-formed components mainly involves heating and hot-stamping steel billets to obtain hot-stamped semi-finished products, followed by laser cutting to obtain hot-formed components with the final contour. These components are then transported long distances to the welding workshop for assembly and body-in-white welding. The laser-cut edges of the hot-formed components are highly susceptible to hydrogen embrittlement, especially during welding. Cracks easily form in the stress concentration areas of the laser-cut edges, rapidly propagating and leading to brittle fracture, ultimately causing the hot-formed component to fail.

[0003] Chinese patent CN116287989A discloses a hot-stamping steel, an aluminum-silicon coated hot-stamping steel sheet, and automotive structural parts. The tensile strength of this steel after hot forming can exceed 2100 MPa. To achieve ultra-high strength and good toughness, the patented steel composition includes a significant amount of Cr, Mo, and Ni. The addition of these high-hardenability alloying elements gives it extremely high hardenability. High hardenability leads to high phase transformation stress after the steel undergoes martensitic transformation, and may even form phase transformation microcracks in the microstructure. This results in a sharp decrease in the toughness of the hot-formed components and a significant increase in the risk of hydrogen embrittlement. Furthermore, Ni and Mo are expensive elements; adding high amounts of Mo and Ni will increase the cost of the steel, making it difficult to meet the cost requirements of the automotive industry.

[0004] Chinese patent CN106399837A discloses an ultra-fine grain hot-formed steel, its manufacturing process, hot-forming process, and hot-formed components. This steel, after hot forming, exhibits a tensile strength of 1800–2200 MPa. While this patent emphasizes the technical effect of microalloying precipitation in reducing the carbon content of the martensitic matrix and thus improving the toughness of hot-formed components, it fails to consider the adverse effects of adding high levels of alloying elements on the laser-cut edges of hot-formed components. In particular, the addition of elements such as Mn and Mo, which simultaneously increase the carbon equivalent and hardenability of the steel, leads to the formation of a high-hardness martensite layer at the cut edges during laser cutting, thereby increasing the risk of hydrogen embrittlement. Furthermore, the high-alloy design also makes the steel prone to the formation of hard and brittle martensite during production, increasing the difficulty of processing and shape control, and hindering production cost management.

[0005] Chinese patent CN115478227A discloses a hot-formed steel plate, a hot-formed component, and a method for manufacturing the steel plate. The tensile strength of the hot-formed steel component can reach 1750~2100MPa. This patent improves the toughness of the hot-formed steel to avoid the formation of hard and brittle twinned martensite within the microstructure. The patent focuses on controlling the end temperature of the martensitic phase transformation during alloy design. However, this patent also fails to consider the significant impact of laser cutting on hydrogen embrittlement. Laser cutting causes the cut edges of the hot-formed component to form a hard and brittle martensite layer, thereby reducing the ability of the cut edges of the hot-formed component to resist hydrogen embrittlement fracture.

[0006] In summary, while existing technologies can produce hot-formed steel components with tensile strengths exceeding 2000 MPa, they fail to address the significantly increased risk of hydrogen embrittlement, particularly in laser-cut components. Furthermore, current technologies lack effective solutions to overcome this problem. To meet the extremely high mechanical performance requirements of the automotive industry for hot-formed steel components, there is an urgent need to develop a hot-formed component with tensile strength exceeding 2000 MPa and low hydrogen embrittlement sensitivity, along with its manufacturing method. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a hot-formed component with high tensile strength and low hydrogen embrittlement sensitivity made of steel plate and aluminum alloy coating, and a method for processing and manufacturing the same. This method enables the hot-formed component with aluminum alloy coating to have a tensile strength exceeding 2000 MPa and low hydrogen embrittlement sensitivity.

[0008] In a first aspect, the present invention provides a hot-formed component with an aluminum alloy coating, characterized in that the hot-formed component comprises a steel plate substrate and an aluminum alloy coating, wherein the steel plate substrate comprises, by mass percentage: 0.365~0.455%C, 0.50~1.35%Mn, 0.01~0.60%Si, 0.01~0.60%Cr, 0.10~0.60%Al, 0.001~0.010%B, 0.001~0.020%P, 0.001~0.010%N, 0.001~0.010%S, with the balance being Fe and unavoidable impurity elements; Among them, carbon equivalent C eq ≤0.68, manganese equivalent Mn eq The mass ratio of aluminum to carbon (Al / C) is ≥0.50, ranging from 0.80 to 1.60. The carbon equivalent C eq Calculated according to formula (1), C eq =C+Mn / 6+Cr / 5+V / 14+Mo / 4+Ni / 40+Si / 24 formula (1); The manganese equivalent Mn eq Calculate according to formula (2), Mn eq =Mn+1.29×Cr+3.28×Mo+0.46×Cu+0.37×Ni+0.07×Si Formula (2); The average hardness of the laser-cut edge hardened layer of the thermoformed component is below 720 HV, the effective depth of the laser-cut edge hardened layer does not exceed 120 μm, and the ratio of the highest hardness of the laser-cut edge hardened layer to the hardness of the steel plate substrate is not higher than 1.15; the tensile strength of the thermoformed component is ≥2050 MPa, and the elongation after fracture is ≥4.9%.

[0009] Preferably, the thermoformed component is obtained by hot stamping and laser cutting; the martensite content of the steel plate substrate is ≥95%, and the thickness of the steel plate is 0.7~2.5mm; before hot stamping, the coating thickness is not greater than 33μm; after hot stamping, the coating thickness is not greater than 50μm.

[0010] Preferably, carbon equivalent C eq ≤0.63.

[0011] Preferably, the manganese equivalent (Mneq) is 1.45~1.60.

[0012] Preferably, the mass ratio of aluminum to carbon, Al / C, is ≥0.90.

[0013] With a diffusible hydrogen content not exceeding 0.2 ppm, the thermoformed component was subjected to room temperature notched tensile tests at tensile speeds of 0.01 mm / min and 10 mm / min, respectively, and the ratio of the fracture strength at the two tensile speeds was greater than 0.85.

[0014] After the thermoformed component undergoes coating, baking, or tempering treatment, the average hardness of the laser-cut edge hardened layer of the thermoformed component is below 700 HV, the effective depth of the laser-cut edge hardened layer does not exceed 100 μm, and the ratio of the highest hardness of the laser-cut edge hardened layer to the hardness of the steel plate substrate is not higher than 1.10; the tensile strength of the thermoformed component is ≥1950 MPa, the elongation after fracture is ≥5.5%, and the plane fracture strain is not less than 0.175.

[0015] Secondly, the present invention provides a method for preparing a thermoformed component with an aluminum alloy coating, comprising the following steps: S1. Steelmaking: Weigh the raw materials according to the composition of the steel plate, perform vacuum smelting on the raw materials, and obtain steel billets that meet the composition of the steel plate through continuous casting or continuous casting and rolling. S2. Hot rolling: The steel billet is heated to 1250°C and held for 2 hours, then hot rolled at 800°C to 1250°C, and then coiled at 500°C to 700°C to form a hot-rolled steel coil; S3. Cold rolling: The hot-rolled steel coil is cold-rolled with a reduction of 30% to 70% to obtain a cold-rolled steel coil with a thickness of 1.0 to 1.8 mm; S4. Coating: The cold-rolled steel coil is coated with an aluminum alloy coating, wherein the Al content in the coating is more than 50wt% and the coating thickness does not exceed 33μm. S5. Austenitization: The coated cold-rolled steel coil is heated to 850~950℃ and held until fully austenitized to obtain the steel plate blank to be stamped. The heating and holding time is 3~10min. During the heating and holding process, the dew point of the heating zone must be kept below -10℃. S6. Stamping and quenching: The steel plate blank to be stamped is transferred to the forming mold for stamping and forming. The transfer time shall not exceed 15s. The temperature of the steel plate blank to be stamped on the mold shall not be lower than 750℃. After pressure holding and quenching, the blank is removed from the mold to obtain a hot-formed semi-finished product.

[0016] Preferably, the method further includes the following step: S7. Laser cutting: laser cutting the thermoformed semi-finished product to obtain a thermoformed component with the final contour features, wherein the laser cutting power is above 750W, the cutting speed is not less than 5m / min, and the gas pressure is not higher than 1bar.

[0017] Preferably, the process further includes the following step: S8. Coating electrophoresis: After the thermoformed component is welded, it is coated with electrophoresis. The baking temperature during the coating electrophoresis process is 150~180℃ and the time is 20~60min.

[0018] Thirdly, the present invention provides a steel plate for manufacturing the above-mentioned aluminum alloy coated hot-formed components, wherein, by mass percentage, the steel plate comprises: 0.365~0.455%C, 0.50~1.35%Mn, 0.01~0.60%Si, 0.01~0.60%Cr, 0.10~0.60%Al, 0.001~0.010%B, 0.001~0.020%P, 0.001~0.010%N, 0.001~0.010%S, with the balance being Fe and unavoidable impurity elements; Among them, carbon equivalent C eq ≤0.68, manganese equivalent Mn eq The mass ratio of aluminum to carbon (Al / C) is ≥0.50, ranging from 0.80 to 1.60. The carbon equivalent C eq Calculated according to formula (1), C eq =C+Mn / 6+Cr / 5+V / 14+Mo / 4+Ni / 40+Si / 24 formula (1); The manganese equivalent Mn eq Calculate according to formula (2), Mn eq =Mn+1.29×Cr+3.28×Mo+0.46×Cu+0.37×Ni+0.07×Si Formula (2); The steel plate also contains at least one of V, Nb, and Ti, with V accounting for 0.001 to 0.20% by mass and the sum of the mass percentages of Nb and Ti being 0.001 to 0.100%.

[0019] More preferably, the steel plate further comprises at least one of Ni, Mo, W, Cu, Co, Ta, Sn, Sb, As, Mg, Ca, Zr, O, and REM, in the following mass percentages: Ni 0.01~0.30%, Mo 0.01~0.20%, W 0.01~0.20%, Cu 0.01~0.20%, Co 0.01~0.50%, Ta 0.001~0.10%, Sn 0.001~0.05%, Sb 0.001~0.05%, As 0.001~0.05%, Mg 0.001~0.010%, Ca 0.001~0.010%, Zr 0.001~0.10%, O 0.001~0.02%, REM. 0.001~0.05%, and the sum of the mass percentages of Ni, Mo, W, Cu, Co, Ta, Sn, Sb, As, Mg, Ca, Zr, and REM is 0.001~0.50%.

[0020] Compared with the prior art, this application has at least the following beneficial effects: (1) In a large number of production practices, this application has creatively discovered that the laser-cut edge of the hot stamping forming component is a high-risk area for hydrogen embrittlement. During the welding process, the stress concentration area of ​​the laser-cut edge is very prone to cracks due to hydrogen embrittlement and rapid expansion to form brittle fracture. Studies have found that the hydrogen embrittlement sensitivity of the hardened layer at the cut edge is strongly correlated with the cold cracking sensitivity of the steel itself, and the characteristics of the hardened layer at the laser cut edge are also significantly affected by the laser cutting process. Therefore, this application proposes that, under hot stamping conditions, the hot-formed component should meet the following requirements: martensite content of the steel substrate ≥ 95%, tensile strength ≥ 2050 MPa, elongation after fracture ≥ 4.9%, average hardness of the hardened layer at the laser cut edge below 720 HV, effective depth of the hardened layer not exceeding 120 μm, and the ratio of the highest hardness of the hardened layer to the hardness of the steel substrate not exceeding 1.15. With a diffusible hydrogen content not exceeding 0.2 ppm, room temperature notched tensile tests were conducted on the hot-formed component at tensile speeds of 0.01 mm / min and 10 mm / min, respectively, and the ratio of fracture strength at the two tensile speeds was greater than 0.85. After coating and baking, the average hardness of the hardened layer at the cut edge of the hot-formed component is below 700 HV, the effective depth of the hardened layer at the cut edge does not exceed 100 μm, and the ratio of the highest hardness of the hardened layer at the cut edge to the hardness of the steel substrate is not higher than 1.10. In the coated and baked state (or tempered state), the tensile strength of the hot-formed component is ≥1950 MPa, the elongation after fracture is ≥5.5%, and the plane fracture strain is not less than 0.175. This application, through the design of the steel plate composition and improvements in the manufacturing process of the aluminum alloy coated hot-formed component, significantly improves the hydrogen embrittlement sensitivity while maintaining a high tensile strength of 2000 MPa.

[0021] (2) Based on extensive production practice, this application has creatively discovered that the laser-cut edge of hot-formed components is a high-risk area for hydrogen embrittlement. During welding, the stress concentration area of ​​the laser-cut edge is highly susceptible to hydrogen embrittlement, which can cause cracks that rapidly propagate and lead to brittle fracture. Research has shown that the hydrogen embrittlement sensitivity of the hardened layer at the cut edge is strongly correlated with the cold cracking sensitivity of the steel itself, and the characteristics of the hardened layer at the laser-cut edge are also significantly affected by the laser cutting process. To address this, this application proposes controlling the carbon equivalent of the steel substrate to below 0.68, and controlling the ratio of the peak hardness in the hardened layer at the laser-cut edge to the average hardness of the steel substrate to be no greater than 1.15, and ensuring that the effective depth of the hardened layer does not exceed 120 μm. Through carbon equivalent design and control of laser cutting process parameters, the hardened layer at the cut edge is ensured to have a distribution characteristic of low hardness and small effective depth, thereby significantly improving the hydrogen embrittlement sensitivity of hot-formed components.

[0022] (3) Based on the study of the microstructure of steel, this application found that martensite is a supersaturated interstitial solid solution formed by C dissolving in α-Fe. C exceeding the maximum solubility of α-Fe will cause significant distortion of its crystal lattice, leading to volume expansion and phase transformation stress. As the C content increases, more C further expands the α-Fe crystal lattice, exacerbating volume expansion and further increasing the phase transformation stress of the material. Al has a larger atomic radius than Fe. In the case of high C design, adding a certain amount of Al to the alloy will have a substitution effect on Fe, which will expand the crystal lattice, thereby reducing the lattice distortion caused by C interstitial solid solution during martensitic phase transformation, reducing the phase transformation stress of martensite, and thus improving the toughness of martensite. The improvement of the toughness of the steel plate matrix can significantly inhibit the rapid propagation after crack initiation. Based on this, this application controls the Al / C ratio to be no less than 0.50, thereby effectively reducing the harm of hydrogen embrittlement to hot-formed components.

[0023] (4) In order to ensure that the steel has a high tensile strength of over 2000 MPa, this application selects a C content of 0.365~0.455%. Under this high C content composition design, the toughness of the steel is more sensitive to the cooling conditions of the hot-formed components. The high cooling rate leads to greater undercooling, which will promote the formation of twinned martensite, thereby damaging the toughness of the martensitic steel matrix. In the product development process, this application found that if the hardenability of the steel is poor, it will lead to the formation of non-martensitic structures (such as ferrite and bainite) in the steel plate after hot stamping, which will tend to reduce the strength of the steel. Therefore, this application rationally designs the hardenability of the steel. Hardenability can be expressed by Mn equivalent. This application designs the Mn equivalent to be between 0.80 and 1.60 to control the hardenability of the material. The rational hardenability design not only ensures the proportion of martensite in the hot-formed components, but also inhibits the formation of twinned martensite. While ensuring that the steel can have a high tensile strength of more than 2000MPa, the martensitic steel plate matrix still has sufficient toughness. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 A schematic diagram of a notched tensile specimen used for hydrogen embrittlement risk assessment. Figure 2 This is a schematic diagram of a notched tensile specimen used for plane fracture strain testing. Figure 3 This is a schematic diagram of the hardening layer and core hardness test at the cut edge; Figure 4 Here are typical SEM images of the coating on the thermoformed components of this invention; Figure 5 This is a typical SEM image of the microstructure of the thermoformed component of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0027] Unless otherwise stated, all temperatures are in degrees Celsius and all percentages are by weight. All components used in the following examples and comparative examples are monomers or compounds known in the art and are commercially available or prepared using known techniques.

[0028] This invention provides a steel plate with high tensile strength and low hydrogen embrittlement sensitivity. By weight percentage, the steel plate comprises: 0.365~0.455% C, 0.50~1.35% Mn, 0.01~0.60% Si, 0.01~0.60% Cr, 0.10~0.60% Al, 0.001~0.010% B, 0.001~0.020% P, 0.001~0.010% N, 0.001~0.010% S, with the balance being Fe and unavoidable impurity elements; wherein, the Si content is preferably 0.10~0.50%, the Cr content is preferably 0.10~0.50%, and the Al content is preferably 0.20~0.50%. Among them, carbon equivalent C eq ≤0.68, preferred C eq ≤0.65, more preferably C eq ≤0.63; Manganese equivalent Mn eq The preferred Mn content is controlled between 0.80 and 1.60. eq The ratio is 1.45; the mass ratio of aluminum to carbon (Al / C) is not less than 0.50, preferably not less than 0.90. Carbon equivalent C eq Calculated according to formula (1), C eq =C+Mn / 6+Cr / 5+V / 14+Mo / 4+Ni / 40+Si / 24 formula (1); Manganese equivalent Mn eq Calculate according to formula (2), Mn eq =Mn+1.29×Cr+3.28×Mo+0.46×Cu+0.37×Ni+0.07×Si Formula (2).

[0029] Preferably, the steel plate further comprises at least one of V, Nb, and Ti, wherein V is 0.001~0.20% by mass percentage, and the sum of the mass percentages of Nb and Ti is 0.001~0.100%. The purpose of adding V, Nb, and Ti is to refine the grains through precipitation, and the microalloyed precipitates can act as hydrogen traps to suppress the segregation of diffusible hydrogen in the matrix. In addition, the addition of V will precipitate a large amount of dispersed VC, reducing the C content of the matrix and thus reducing the martensitic lattice distortion. All of these factors improve the hydrogen embrittlement sensitivity of the hot-formed component.

[0030] The steel plate of the present invention may further include at least one of Ni, Mo, W, Cu, Co, Ta, Sn, Sb, As, Mg, Ca, Zr, O, and REM, wherein, by mass percentage, Ni 0.01~0.30%, Mo 0.01~0.20%, W 0.01~0.20%, Cu 0.01~0.20%, Co 0.01~0.50%, Ta 0.001~0.10%, Sn 0.001~0.05%, Sb 0.001~0.05%, As 0.001~0.05%, Mg 0.001~0.010%, Ca 0.001~0.010%, Zr 0.001~0.10%, and O. 0.001~0.02%, REM 0.001~0.05%, and the sum of the mass percentages of Ni, Mo, W, Cu, Co, Ta, Sn, Sb, As, Mg, Ca, Zr, and REM is 0.001~0.50%.

[0031] Specifically, C: 0.365~0.455% Carbon (C) is an important interstitial solid solution strengthening element in steel, enabling materials to achieve extremely high strength and hardness. Therefore, this invention adds more than 0.365% C to ensure a tensile strength of over 2000 MPa. However, excessive addition of C promotes the formation of brittle twinned martensite, severely deteriorating toughness. Therefore, the carbon content in this invention is controlled at 0.365~0.455%, preferably 0.365~0.435%.

[0032] Mn: 0.50~1.35% Manganese (Mn) is an economical and effective element for improving the hardenability of steel. Furthermore, the addition of Mn significantly expands the austenite phase region, thus affecting the martensitic transformation process. Therefore, an appropriate amount of Mn is commonly added to hot-stamped steel. However, the addition of Mn has a significant impact on the carbon content of the material. eq There are also effects; adding too much Mn will reduce the carbon content of the material. eq Increasing the Mn content makes it difficult to guarantee the hydrogen embrittlement sensitivity of the laser-cut edges. Furthermore, adding more Mn can cause the martensitic transformation to occur at lower temperatures, resulting in the formation of a large amount of hard and brittle twinned martensite, reducing the material's toughness. Simultaneously, it increases the internal phase transformation stress and easily leads to severe banded segregation, deteriorating the steel's performance. Therefore, this invention sets the Mn content to 0.50~1.35%, which can balance the material's carbon equivalent, manganese equivalent, and martensitic transformation temperature.

[0033] Si: 0.01~0.60% Si has the effect of solid solution strengthening of the matrix, and the addition of an appropriate amount can significantly improve the strength of the martensitic matrix. However, the addition of excessive Si will cause the formation of oxides on the surface of the steel during the production process that are difficult to eliminate, affecting the surface quality of the final product. Therefore, the upper limit of Si content in this invention is set to 0.60%, and further, to 0.10~0.50%.

[0034] Cr: 0.01~0.60% Cr significantly delays the pearlite transformation by shifting the isothermal transformation C-curve of steel to the right, thus hindering cementite nucleation and growth. Furthermore, Cr reduces the austenite decomposition rate, lowering the critical cooling rate of the steel and promoting martensite formation. The effect of Cr on lowering the martensite transformation temperature is significantly less than that of Mn; therefore, Cr is more conducive to promoting the formation of dislocation-type martensite with good toughness. However, excessive Cr addition increases alloying costs and makes it difficult to completely remove the oxide scale formed on the surface of hot-rolled coils through pickling, affecting the surface quality of the final product. In addition, Cr is also an important alloying element affecting carbon equivalent. Therefore, in this invention, the Cr content is controlled below 0.60%, and further, between 0.10% and 0.50%.

[0035] Al: 0.10~0.60% The addition of Al can combine with N to form AlN, effectively fixing N and preventing the combination of N and B, thus ensuring the added B improves hardenability. Furthermore, Al can increase the martensitic transformation temperature, helping to reduce the formation of brittle twinned martensite. However, excessive Al addition can cause excessive resistance at the crystallizer inlet during continuous casting, affecting billet production and increasing the difficulty of controlling alumina inclusions in the steel. Therefore, the Al content in this invention is controlled between 0.10% and 0.60%, and more specifically, between 0.20% and 0.50%.

[0036] B: 0.001~0.010% Boron readily segregates at austenite grain boundaries, which can suppress the phase transformation from austenite to ferrite. A low amount of boron can significantly improve the hardenability of steel. However, a high amount of boron can lead to boron embrittlement, which is detrimental to performance. Therefore, the boron content in this invention is set to 0.001~0.010%.

[0037] 0.001%≤V≤0.20%, 0.001%≤Nb+Ti≤0.100% The addition of V, Nb, and Ti elements can form carbides, nitrides, or carbonitrides with carbon and nitrogen. The uniform and fine precipitates pin the austenite grain boundaries, refining the grain size and improving the strength and toughness of the steel. Simultaneously, the precipitates are dispersed throughout the steel matrix, providing precipitation strengthening while also acting as hydrogen traps to inhibit diffusible hydrogen in the steel matrix, reducing its segregation in stress concentration areas at the cutting edges of hot-formed components and lowering the hydrogen embrittlement sensitivity of the final hot-formed component. Therefore, the components described in this invention can be added in appropriate amounts. In particular, V element can precipitate in large quantities during the heating process of hot stamping, further consuming C elements in the matrix and promoting the formation of dislocation-type martensite. Furthermore, Ti has a strong binding force with N. Adding a certain amount of Ti to hot-stamped steel can form TiN with the N in solid solution in the steel, preventing the combination of N and B elements, thus consolidating N and protecting B, ensuring hardenability. However, excessive addition of the above three microalloying elements will lead to a significant increase in cost. Therefore, in this invention, the V content is controlled in the range of 0.001~0.20%, and the sum of the Nb and Ti contents is controlled in the range of 0.001~0.100%.

[0038] P: 0.001~0.020% Phosphorus (P) is an unavoidable impurity element in steel. On the one hand, P, as a solid solution strengthening element, can relatively inexpensively improve the strength of steel plates. On the other hand, when the P content exceeds 0.0200%, P will segregate at grain boundaries, significantly leading to adverse effects such as decreased toughness. Therefore, the upper limit of P content is no more than 0.020%, preferably no more than 0.010%. Optionally, considering that reducing the P content to less than 0.001% would increase smelting costs, the lower limit of P content can be no less than 0.001%, and optionally no less than 0.004%.

[0039] S: 0.001~0.010% Similar to phosphorus (P), sulfur (S) is an unavoidable impurity element in steel. It reacts with manganese (Mn) in the steel to form MnS, becoming inclusions in the steel. When the S content exceeds 0.010%, a large amount of MnS will significantly impair the ductility and toughness of the steel, leading to a deterioration in workability. Therefore, the upper limit of the S content is no more than 0.010%, preferably no more than 0.005%. Similarly, optionally, considering that keeping the S content below 0.001% would increase smelting costs, the lower limit of the S content can be no less than 0.001%.

[0040] N: 0.001~0.010% Nitrogen (N) is an unavoidable impurity element in steel, especially for steel containing boron (B). Nitrogen combines with B to significantly reduce the effect of B in improving hardenability. Therefore, it is necessary to minimize the content of Nitrogen. Thus, the Nitrogen content in this invention is controlled at 0.001~0.010%.

[0041] Ni: 0.01~0.30% Ni is a hardenability-improving element and can improve the low-temperature toughness of steel. Therefore, its lower limit value can be optionally set at 0.01%. Adding a large amount of Ni will inevitably increase the cost of the alloy and lead to a decrease in C. eq and Mn eq The increase in Ni content leads to an increase in the hydrogen embrittlement sensitivity of the laser-cut edge. Therefore, the Ni content is set to no more than 0.30%.

[0042] Mo: 0.01~0.20% Mo can improve the hardenability of steel plates and prevent temper brittleness. It is preferable to add more than 0.01% Mo, but excessive Mo addition will increase carbon content. eq and Mn eq This leads to an increase in the hydrogen embrittlement sensitivity of the final thermoformed component, as well as an increase in cost. Therefore, the Mo content is set to be below 0.20%.

[0043] W: 0.01~0.20% The addition of W can significantly increase the strength of steel plates, and W-containing precipitates can serve as hydrogen capture sites; therefore, it is preferable to add 0.01% or more. However, W is a strong carbide-forming element, and when the W content exceeds 0.20%, coarse and unevenly distributed carbides will be formed, severely impairing the performance of hot-stamped components. Therefore, the W content is set to below 0.20%.

[0044] Cu: 0.01~0.20% Cu improves the hardenability of steel sheets, thereby increasing the strength of hot-stamped components. To achieve this effect, the Cu content is preferably set to 0.01% or more. However, Cu tends to segregate at grain boundaries and form copper embrittlement, reducing the hot workability of the steel sheet; therefore, the Cu content is set to 0.20% or less.

[0045] Co: 0.01~0.50% The addition of Co can increase the martensitic transformation temperature, which is beneficial for the self-tempering of martensite and thus improves its toughness. Therefore, its lower limit can preferably be set to 0.001%. However, Co is a rare and valuable element, and excessive addition will increase the cost of steel sheets. Moreover, Co promotes the graphitization of carbon in steel, which will impair the toughness of hot-stamped components. Therefore, optionally, the Co content is set to 0.001% ≤ Co ≤ 0.50%.

[0046] Ta: 0.001~0.10% Ta, as a strong carbide-forming element, can form stable carbides with C, thereby refining the grains and enhancing the strength and toughness of the steel plate. Therefore, to achieve this effect, the Ta content is preferably not less than 0.001%. Furthermore, when the Ta content exceeds 0.10%, a large amount of carbides will precipitate and easily accumulate at grain boundaries, leading to a decrease in the toughness of the steel plate. Therefore, the Ta content is set to not exceed 0.10%.

[0047] Sn: 0.001~0.05% The addition of Sn can refine the grain size and improve the machinability of steel plates by combining with elements such as S. Preferably, the Sn content is not less than 0.001%. However, Sn tends to segregate at grain boundaries, increasing the brittleness of the steel. Therefore, the Sn content is set to not exceed 0.05%.

[0048] Sb: 0.001~0.05% Sb also has the effect of refining grains, so to achieve this effect, the preferred Sb addition amount is not less than 0.001%. However, excessive addition will cause segregation at grain boundaries, which will also have an adverse effect on the properties of steel, especially plasticity and toughness. Therefore, the Sn content is set to not exceed 0.05%.

[0049] As: 0.001~0.05% As can strengthen steel to a certain extent, increasing its strength. However, as tends to accumulate at grain boundaries, leading to increased brittleness and deteriorated weldability. Therefore, the as content is set at 0.001 ≤ As ≤ 0.05%.

[0050] Mg: 0.001~0.010%, Ca: 0.001~0.010% Mg and Ca are commonly used for deoxidation during steel smelting and can also form sulfides with S, improving the quantity and morphology of inclusions in the steel sheet structure. Therefore, their addition amount is preferably not less than 0.001%. However, when the content of both Mg and Ca exceeds 0.010%, large-sized inclusions are formed in the steel sheet structure, damaging the toughness of hot-stamped components. Therefore, the content of Mg and Ca is set to not exceed 0.01%.

[0051] Zr: 0.001~0.10% Zr is a strong carbide-forming element, with effects similar to those of V, Nb, and Ti. Adding a small amount can refine the grain size and improve the low-temperature toughness of the steel plate. Preferably, the Zr content is not less than 0.001%. However, when the Zr content exceeds 0.10%, large-sized carbides form within the steel plate structure, leading to a decrease in the toughness of hot-formed components. Therefore, the Zr content is set to 0.001 ≤ Zr ≤ 0.10%.

[0052] O: 0.001~0.02% O forms coarse oxides in steel, which is detrimental to the toughness of hot-stamped components. Therefore, a lower O content is preferred, and the O content is controlled at 0.001~0.02%, more preferably below 0.006%.

[0053] REM: 0.001~0.05% REM (refined oxidizing agent) improves deformability and toughness of hot-stamped components by inhibiting oxide formation. To achieve this effect, the REM content is preferably set to 0.001% or more. However, the REM content should be controlled to not exceed 0.05% to avoid the formation of coarse oxides. In this invention, REM refers to a total of 17 elements including Sc, Y, and La series elements, and the REM content refers to the total content of these elements.

[0054] Optionally, 0.001≤Ni+Mo+W+Cu+Co+Ta+Sn+Sb+Ca+As+Mg+Ca+Zr+REM≤0.50%, thereby effectively controlling the raw material cost of steel.

[0055] C eq =C+Mn / 6+Cr / 5+V / 14+Mo / 4+Ni / 40+Si / 24 In this invention, the carbon content in the steel reaches 0.365~0.455%, exhibiting a strong interstitial solid solution strengthening effect, resulting in a tensile strength of over 2000 MPa for the hot-formed component. Similar to laser welding or resistance spot welding, under the high heat input and ultra-high cooling rate conditions of laser cutting, the high quenching stress in certain cutting contour areas with stress concentration characteristics will lead to a high risk of hydrogen embrittlement in the hardened layer at the cut edge of the final hot-formed component. For high-carbon materials, the material's inherent cold cracking sensitivity is strongly correlated with the hydrogen embrittlement sensitivity of the hardened layer at the cut edge of the hot-formed component. That is, materials with high cold cracking sensitivity are more prone to developing cracks in their hardened layer after laser cutting under the combined effects of thermal stress and martensitic phase transformation stress, thus inducing hydrogen embrittlement cracking in the component. Based on this, this invention proposes a method to control carbon content... eq The requirements are as follows: with a C content of 0.365~0.455%, the addition ratio of alloying elements other than C is controlled to obtain a low carbon equivalent, thereby reducing the cold cracking sensitivity of the hardened layer at the cutting edge and ensuring C content. eq The value should not exceed 0.68, preferably not exceed 0.65, and even more preferably not exceed 0.63.

[0056] Mn eq =Mn+1.29Cr+3.28Mo+0.46Cu+0.37Ni+0.07Si The hardenability of a material affects its toughness and phase transformation stress during cooling. Therefore, it is desirable for the hardenability to be within a suitable range. Excessive alloying elements result in overly high hardenability, which is uneconomical and detrimental to toughness. Conversely, poor hardenability leads to the formation of non-martensite structures during hot stamping, resulting in a low martensite ratio and reduced strength. The inventors discovered that increasing the carbon (C) content significantly improves the mechanical stability of austenite, making strain-induced ferrite phase transformation less likely during high-temperature forming. Therefore, compared to 22MnB5, when the C content reaches 0.365~0.455%, ferrite formation is more difficult during high-temperature forming. This means that high-C content materials do not require excessively high hardenability; controlling the hardenability to be close to, or even lower than, that of 22MnB5 is sufficient. This ensures a high martensite ratio while suppressing twinned martensite, thus improving the toughness of the matrix. The hardenability of a material can be controlled by the Mn equivalent (Mn... eq This indicates that the present invention aims to control Mn. eq Between 0.80 and 1.60.

[0057] Preferred, Mn eq Between 1.45 and 1.6.

[0058] The mass percentage ratio of Al / C is not less than 0.50, preferably not less than 0.90.

[0059] Martensite is a supersaturated interstitial solid solution formed by carbon (C) dissolving in α-Fe. The maximum solubility of C in austenite is 2.11%, while its solubility in α-Fe is only 0.0218%. During the austenite-to-martensite transformation, carbon atoms dissolved in the octahedral interstices of austenite, if unable to diffuse during rapid quenching, will remain aggregated within the octahedral interstices of α-Fe. Since the octahedral interstices of α-Fe are small, only 0.154 times the radius of an iron atom, C exceeding the maximum solubility of α-Fe will cause significant lattice distortion, leading to volume expansion and phase transformation stress. As the C content increases, more C further enlarges the lattice, intensifying volume expansion and increasing the phase transformation stress of the material. The inventors recognized that Al has a larger atomic radius than Fe. In high-carbon designs, adding a certain amount of Al to the alloy to substitute for Fe will expand the crystal lattice, reducing the lattice distortion caused by interstitial solid solution of C atoms during martensite formation. This reduces the phase transformation stress of martensite and thus improves its toughness. Therefore, the present invention aims to control the Al / C mass percentage ratio to be not less than 0.50, preferably not less than 0.90.

[0060] This invention provides a hot-formed component with an aluminum alloy coating. The hot-formed component comprises a steel plate substrate and an aluminum alloy coating. The steel plate substrate is the steel plate described above. The hot-formed component is obtained through hot stamping and laser cutting. The martensite content of the steel plate substrate is ≥95%, preferably ≥98%; the steel plate thickness is 0.7~2.5mm. Before hot stamping, the coating thickness is no greater than 33μm, and after hot stamping, the coating thickness is no greater than 50μm.

[0061] The average hardness of the laser-cut edge hardened layer of the hot-formed component is below 720 HV, preferably below 700 HV, and more preferably below 680 HV; the effective depth of the cut edge hardened layer does not exceed 120 μm, preferably not more than 100 μm, and more preferably not more than 80 μm; the ratio of the highest hardness of the cut edge hardened layer to the hardness of the steel plate substrate is not higher than 1.15, preferably not higher than 1.12, and more preferably not higher than 1.10. The tensile strength of the hot-formed component is ≥2050 MPa, and the elongation after fracture is ≥4.9%.

[0062] The characteristics of the hardened layer at the laser-cut edge of a thermoformed component directly affect the component's resistance to hydrogen embrittlement. Therefore, it is desirable to improve the resistance of the hardened layer through C... eq The design and control of laser cutting process parameters ensure that the hardened layer at the cut edge has a distribution characteristic of low hardness and small effective depth.

[0063] Under hot-stamped conditions, with a diffusible hydrogen content not exceeding 0.2 ppm, room-temperature tensile tests were conducted on notched specimens at tensile speeds of 0.01 mm / min and 10 mm / min, respectively. A ratio of the fracture strength of the specimens at the two tensile speeds greater than 0.95 indicates low hydrogen embrittlement risk; a ratio between 0.85 and 0.95 indicates medium hydrogen embrittlement risk; and a ratio below 0.85 indicates high hydrogen embrittlement risk.

[0064] The tensile strength, elongation after fracture, and hydrogen embrittlement risk of hot-formed components in the hot-stamped state are directly manifested through the core innovative measures of this invention. In particular, regarding hydrogen embrittlement risk, given the presence of diffusible hydrogen in the hot-formed component, slow stretching at 0.01 mm / min allows hydrogen to diffuse and accumulate in the hardened layer of the laser-cut edge, leading to hydrogen embrittlement fracture and a decrease in fracture stress. However, at rapid stretching at 10 mm / min, hydrogen does not have sufficient time to diffuse and accumulate, so the sample is unaffected by hydrogen embrittlement, and the fracture stress does not decrease. Therefore, if the alloy element ratio design is met and a reasonable hot-working process is employed, the matrix material has good toughness, and the hardened layer characteristics of the cut edge are suitable, then a fracture strength ratio above 0.95 indicates low hydrogen embrittlement risk, a ratio between 0.85 and 0.95 indicates medium hydrogen embrittlement risk, and a ratio below 0.85 indicates high hydrogen embrittlement risk. The hot-formed components in the stamped state of this invention all exhibit medium to low hydrogen embrittlement risk.

[0065] After coating and baking, the average hardness of the hardened layer at the cut edge of the thermoformed component is below 700 HV, preferably below 680 HV, and more preferably below 650 HV; the effective depth of the hardened layer at the cut edge does not exceed 100 μm, preferably not more than 80 μm, and more preferably not more than 60 μm; the ratio of the highest hardness of the hardened layer at the cut edge to the hardness of the martensitic substrate is not higher than 1.10, preferably not higher than 1.08. The tensile strength of the thermoformed component is ≥1950 MPa; the elongation after fracture is ≥5.5%; and the plane fracture strain is not less than 0.175, preferably not less than 0.185, and more preferably not less than 0.205.

[0066] After painting and baking, the component undergoes a low-temperature tempering process, resulting in a decrease in the hardness of both the hardened layer at the cut edges and the martensite. The effective depth of the hardened layer and the ratio of its maximum hardness to the hardness of the martensitic substrate also decrease accordingly. Considering that the body-in-white undergoes painting and baking at 170-180℃ for 20-30 minutes, it is necessary to test the material properties after baking. After baking, due to the tempering effect, material stress is reduced, martensitic toughness and plasticity are improved, and the risk of hydrogen embrittlement in the hot-formed component is significantly reduced.

[0067] This invention also provides a method for preparing a hot-formed aluminum alloy coated component, the method comprising the following steps: S1. Steelmaking: Weigh the raw materials according to the steel plate composition proposed in the present invention, perform vacuum smelting on the raw materials, and obtain steel billets that meet the steel plate composition of the first aspect of the present invention by continuous casting or continuous casting and rolling. S2. Hot rolling: The steel billet is heated to 1250℃ and held for 2 hours, then hot rolled at 800℃~1250℃, and then coiled at 500~700℃ to form a hot-rolled steel coil; S3. Cold rolling: The hot-rolled steel coil is cold-rolled with a reduction of 30% to 70% to obtain a cold-rolled steel coil with a thickness of 1.0 to 1.8 mm; S4. Coating: Cold-rolled steel coils are coated with aluminum alloy coating, with an Al content of more than 50% and a coating thickness of no more than 33μm.

[0068] S5. Austenitization: The coated cold-rolled steel coil is heated to 850~950℃ and held until fully austenitized to obtain the steel plate blank to be stamped. The heating and holding time is 3~10min. During the heating and holding process, the dew point of the heating zone must be kept below -10℃ to reduce the diffusible hydrogen content in the hot-formed component.

[0069] S6. Stamping and quenching: Transfer the steel plate blank to be stamped to the forming mold for stamping. The transfer time shall not exceed 15s. The temperature of the steel plate blank placed on the mold shall not be lower than 750℃. After holding pressure and quenching, the blank shall be demolded to obtain a hot-formed semi-finished product.

[0070] S7. Laser cutting: The above-mentioned thermoformed semi-finished product is laser-cut to obtain a thermoformed component with the final contour features, wherein the laser cutting power is above 750W, the cutting speed is not less than 5m / min, and the gas pressure is not higher than 1bar.

[0071] S8. Coating and electrophoresis: After the above-mentioned thermoformed components are welded, they are coated and electrophoresed. The baking temperature during the coating and electrophoresis process is 150~180℃ and the time is 20~60min.

[0072] The following is a description of the performance tests in the examples.

[0073] Diffusion-grade hydrogen content testing and hydrogen embrittlement risk assessment Hot stamping with a dew point control furnace is used to obtain a thermoformed semi-finished product with a certain hydrogen content. The hydrogen content is then tested using a Bruker diffusion hydrogen analyzer (TDS). Subsequently, notched tensile specimens are processed using laser cutting. A schematic diagram of the specimen is shown below. Figure 1 As shown, the materials were subjected to room temperature tensile tests at speeds of 0.01 mm / min and 10 mm / min, respectively. The fracture strength of the materials at the two different tensile speeds was recorded. If the tensile strength of the former was not less than 95% of that of the latter, it was considered to have a low risk of hydrogen embrittlement. If the ratio of the tensile strength of the former to that of the latter was 85% to 95%, it was considered to have a medium risk of hydrogen embrittlement. If the ratio was below 85%, it was considered to have a high risk of hydrogen embrittlement.

[0074] Planar fracture strain test The hot-stamped sheet metal was wire-cut into a strip-shaped specimen with dimensions of 140×20mm (length×width). The notch in the middle had a radius R of 5mm. A schematic diagram of the specimen is shown below. Figure 2 As shown. Subsequently, a standard tensile testing machine was used for testing at a tensile rate of 0.3 mm / min. The original specimen thickness at the notch before the test was h0, and the specimen thickness at the fracture surface after the test was completed was h. The equivalent fracture strain ε was calculated using the following formula. To avoid the influence of specimen processing on thickness reduction, the fracture surface thickness was measured in a region approximately 1 / 2 the width of the specimen near the center, and at least 5 sets of test values ​​were taken as the average value.

[0075] Equivalent fracture strain calculation formula: .

[0076] Cut edge hardened layer feature test Reference Figure 3 A schematic diagram of the hardening layer and core hardness test at the cut edge is shown. The hardness test starts from a position of ~10μm at the edge of the sample and proceeds along a straight line at a 30° angle to the edge of the sample into the matrix. The load force is 50g and the spacing between load points is 40μm. The depth of the hardening layer at the cut edge is defined as the distance perpendicular to the edge and from the outermost edge to the test point where the hardness value is equal to that of the sample core.

[0077] The present invention will now be described in more detail with reference to exemplary embodiments. The following embodiments or experimental data are intended to illustrate the present invention by way of example, and those skilled in the art should understand that the present invention is not limited to these embodiments or experimental data.

[0078] Example 1 A method for preparing a thermoformed aluminum alloy coated component includes the following steps: S1. Steelmaking: Steel billets that meet the T1 composition in Table 1 are obtained by vacuum induction furnace smelting according to the T1 composition in Table 1 and by continuous casting and forging. S2. Hot rolling: The steel billet is heated to 1250℃ and held for 2 hours, then hot rolled at 800℃ and coiled at 500℃ to form a hot-rolled steel coil; the hot-rolled steel coil is pickled to remove the oxide scale generated during the hot rolling process; S3. Cold rolling: The hot-rolled steel coil that has been pickled is cold-rolled with a reduction of 70% to obtain a cold-rolled steel coil with a thickness of 1.2mm. S4. Coating: Cold-rolled steel coils are coated with aluminum alloy coating, with an Al content of more than 50% and a coating thickness of 33μm. S5. Austenitization: The coated cold-rolled steel coil is heated to 850℃ and held until fully austenitized to obtain the steel plate blank to be stamped. The heating and holding time is 10 minutes. During the heating and holding process, the dew point of the heating zone must be kept at -10℃. S6. Stamping and quenching: Transfer the steel plate blank to be stamped to the forming mold for stamping. The transfer time is 15s. The temperature of the steel plate blank placed on the mold is 750℃. Hold the pressure and quench to cool to 200℃ before demolding to obtain a hot-formed semi-finished product. S7. Laser cutting: The above-mentioned thermoformed semi-finished products are processed by laser cutting to obtain thermoformed component samples with final contours for experiments such as room temperature tensile testing, metallographic inspection, hardened layer inspection, diffusible hydrogen content testing, and hydrogen embrittlement risk assessment. The laser cutting power is 1000W, the cutting speed is 7m / min, and the gas pressure is 0.55bar.

[0079] S8. Electrophoresis Coating: To simulate the electrophoresis coating process of the body-in-white after welding of the thermoformed components, the above-mentioned laser-cut thermoformed component samples were tempered at 150°C for 60 minutes. The temperature and time used in the tempering process of this invention are exactly the same as those in the coating baking process of this invention, and the description of the tempered state in this invention is equivalent to that of the baked state.

[0080] Examples 2-4 (T2~T4) and Comparative Examples 1-4 (CT1~CT4) The process steps for preparing aluminum alloy coated hot-formed components in Examples 2-4 and Comparative Examples 1-4 are exactly the same as those in Example 1. The only difference is the specific parameters of the chemical composition of the steel plate substrate, the heat treatment process, and the laser cutting process. The specific parameters are shown in the corresponding example groups and comparative example groups in Tables 1-3.

[0081] Table 1 Chemical composition of steel plate matrix (wt.%, balance is Fe and impurities)

[0082] Table 2 Heat treatment processes for different thermoformed semi-finished products

[0083] Table 3 Laser cutting processes for different thermoformed semi-finished products

[0084] Performance testing and results analysis The thermoformed semi-finished products obtained after stamping and quenching in step S6 were processed by laser cutting in Table 3 to obtain thermoformed component samples with final contours that could meet the requirements of room temperature tensile testing, metallographic inspection, hardened layer inspection, diffusible hydrogen content testing, and hydrogen embrittlement risk assessment. Diffusible hydrogen content testing, hydrogen embrittlement risk assessment, plane fracture strain testing, and hardened layer characteristic testing at the cut edge were performed respectively. The test results are shown in Tables 4 to 6.

[0085] Finally, the tempered hot-formed semi-finished product after the electrophoresis coating in step S8 was tested by wire cutting to obtain planar fracture strain test specimens. The test results are shown in Tables 4 and 5. Tables 4 and 5 show the performance test results and hardened layer distribution characteristics of hot-formed components under different compositions and hot working processes, respectively, while Table 6 shows the corresponding hydrogen embrittlement risk assessment results. It should be noted that since the diffusible hydrogen content and internal stress in the hot-formed component are reduced after tempering, and the toughness of the martensitic matrix is ​​improved, the hydrogen embrittlement risk of the component will be reduced. Therefore, the embodiments of this invention only evaluate the hydrogen embrittlement risk in the hot-stamped state.

[0086] Table 4 Performance test results of thermoformed components with different compositions and heat treatment processes

[0087] Table 5. Distribution characteristics of the hardened layer at the cut edge of thermoformed components under different compositions and heat treatment processes.

[0088] Figure 4 and 5 The images shown are SEM images of the coating and microstructure of a portion of the thermoformed component in Embodiment 1 of the present invention. It can be seen that the microstructure of the steel plate substrate is a fully martensitic structure.

[0089] Table 6 Hydrogen embrittlement risk assessment

[0090] From the above test results, we can conclude that: 1) T1~T4 thermoformed components: C eq In the range of 0.55 to 0.68, Mn eq With a mass ratio of 0.80 to 1.59 and an Al / C mass percentage of 0.63 to 0.96, the hot-stamped tensile strength reaches 2071 to 2120 MPa, and the elongation after fracture reaches 4.9 to 5.4%. The tempered tensile strength reaches 1965 to 2010 MPa, and the elongation after fracture reaches 5.7 to 6.1%. The planar fracture strain reaches 0.179 to 0.223. The hydrogen embrittlement risk in the hot-stamped state is low or medium, indicating that the hot-formed components obtained by the alloy design and laser cutting process of this invention exhibit good strength, toughness, and resistance to hydrogen embrittlement. In particular, with the increase in C... eq and Mn eq The decrease, when C eq Not exceeding 0.65, Mn eq When C does not exceed 1.45, the component exhibits superior toughness, with a plane fracture strain not less than 0.185, and all components show low hydrogen embrittlement risk. Furthermore, when C eq Mn is 0.55. eq When the Al / C mass ratio is 0.80, the plane fracture strain of the component reaches 0.223, indicating further improvement in toughness. It can be expected that its resistance to hydrogen embrittlement will also be further enhanced. In addition, a comparison shows that when the Al / C mass ratio is not less than 0.63, the plane fracture strain of the component is not less than 0.179, which also reflects its effect on improving the toughness of the component.

[0091] 2) T1~T4 thermoformed components: In the hot-stamped state, the maximum hardness of the hardened layer at the cut edges is 672~710 HV, the effective depth is 85~105 μm, and the ratio of the maximum hardness of the hardened layer to the core hardness is 1.06~1.13; in the baked state, the maximum hardness of the hardened layer at the cut edges is 646~688 HV, the effective depth is 70~95 μm, and the ratio of the maximum hardness of the hardened layer to the core hardness is 1.05~1.12. In particular, when C... eq Not exceeding 0.63, Mn eq When the hardness is not more than 1.36, in the hot stamping state, the maximum hardness of the hardened layer on the cut edge is 675HV, the effective depth is 105μm, and the ratio of the maximum hardness of the hardened layer to the hardness of the core is 1.06.

[0092] 3) CT1: All alloys are within the scope of this invention, but their C eq M eq The Al / C mass ratio does not meet the design requirements of this invention, and the elongation after fracture and planar fracture toughness of the components are lower than those of the embodiments of this invention, and the high C content... eq This also results in a larger ratio between the maximum hardness of the hardened layer and the hardness of the core, as well as a larger effective depth of the hardened layer, leading to a high risk of hydrogen embrittlement in the component.

[0093] 4) CT2: Compared to CT1, M eq Both the Al / C mass ratio and the C content meet the design requirements of this invention. eq The post-fracture elongation and planar fracture strain of the component are higher than CT1, but slightly lower than those of the present invention. Furthermore, the effective depth of the hardened layer and the maximum hardness are still relatively high. Therefore, the component still carries the risk of medium hydrogen embrittlement.

[0094] 5) CT3: Compared to CT1 and CT2, C eq Both Al / C mass ratios meet the design requirements of this invention, but Mn... eq The mechanical properties of the component are generally satisfactory, except that the elongation after fracture and the plane fracture strain are slightly low, and the ratio of the maximum hardness of the hardened layer to the hardness of the core is relatively high. Therefore, the component exhibits a medium risk of hydrogen embrittlement.

[0095] 6) CT4: Compared to T3, the two alloys have similar carbon content. eq and Mn eq However, CT4 has a lower carbon content and a lower Al / C mass ratio, resulting in lower strength. Therefore, the T3 of this invention has a superior combination of strength and toughness.

[0096] In summary, a reasonable alloy design and hot working process ensure that the hardened layer has a reasonable distribution and the matrix material performs well, thereby enabling the hot-formed components to exhibit good strength and toughness and resistance to hydrogen embrittlement.

[0097] All materials used in this invention are commercially available and can be purchased from retail sources.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A thermoformed component with an aluminum alloy coating, characterized in that, The hot-formed component comprises a steel plate substrate and an aluminum alloy coating. The steel plate substrate contains, by mass percentage: 0.365~0.455%C, 0.50~1.35%Mn, 0.01~0.60%Si, 0.01~0.60%Cr, 0.10~0.60%Al, 0.001~0.010%B, 0.001~0.020%P, 0.001~0.010%N, 0.001~0.010%S, with the balance being Fe and unavoidable impurity elements. Among them, carbon equivalent C eq ≤0.68, manganese equivalent Mn eq The mass ratio of aluminum to carbon (Al / C) is ≥0.50, ranging from 0.80 to 1.

60. The carbon equivalent C eq Calculated according to formula (1), C eq =C+Mn / 6+Cr / 5+V / 14+Mo / 4+Ni / 40+Si / 24Å(1)6 The manganese equivalent Mn eq Calculate according to formula (2), Mn eq =Mn+1.29×Cr+3.28×Mo+0.46×Cu+0.37×Ni+0.07×Si Formula (2); The average hardness of the laser-cut edge hardened layer of the thermoformed component is below 720 HV, the effective depth of the laser-cut edge hardened layer does not exceed 120 μm, and the ratio of the highest hardness of the laser-cut edge hardened layer to the hardness of the steel plate substrate is not higher than 1.15; the tensile strength of the thermoformed component is ≥2050 MPa, and the elongation after fracture is ≥4.9%.

2. The thermoformed component according to claim 1, characterized in that, The thermoformed component is obtained by hot stamping and laser cutting; the martensite content of the steel plate substrate is ≥95%, and the thickness of the steel plate is 0.7~2.5mm; before hot stamping, the coating thickness is not greater than 33μm; after hot stamping, the coating thickness is not greater than 50μm.

3. The thermoformed component according to claim 1, characterized in that, Carbon equivalent C eq ≤0.

63.

4. The thermoformed component according to claim 1, characterized in that, The manganese equivalent (Mneq) is 1.45~1.

60.

5. The thermoformed component according to claim 1, characterized in that, The mass ratio of aluminum to carbon, Al / C, is ≥0.

90.

6. The thermoformed component according to claim 1, characterized in that, With a diffusible hydrogen content not exceeding 0.2 ppm, the thermoformed component was subjected to room temperature notched tensile tests at tensile speeds of 0.01 mm / min and 10 mm / min, respectively, and the ratio of the fracture strength at the two tensile speeds was greater than 0.

85.

7. The thermoformed component according to claim 1, characterized in that, After the thermoformed component undergoes coating, baking, or tempering treatment, the average hardness of the laser-cut edge hardened layer of the thermoformed component is below 700 HV, the effective depth of the laser-cut edge hardened layer does not exceed 100 μm, and the ratio of the highest hardness of the laser-cut edge hardened layer to the hardness of the steel plate substrate is not higher than 1.10; the tensile strength of the thermoformed component is ≥1950 MPa, the elongation after fracture is ≥5.5%, and the plane fracture strain is not less than 0.

175.

8. The method for preparing the aluminum alloy coated hot-formed component according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: S1. Steelmaking: Weigh the raw materials according to the composition of the steel plate, perform vacuum smelting on the raw materials, and obtain steel billets that meet the composition of the steel plate through continuous casting or continuous casting and rolling. S2. Hot rolling: The steel billet is heated to 1250°C and held for 2 hours, then hot rolled at 800°C to 1250°C, and then coiled at 500°C to 700°C to form a hot-rolled steel coil; S3. Cold rolling: The hot-rolled steel coil is cold-rolled with a reduction of 30% to 70% to obtain a cold-rolled steel coil with a thickness of 1.0 to 1.8 mm; S4. Coating: The cold-rolled steel coil is coated with an aluminum alloy coating, wherein the Al content in the coating is more than 50wt% and the coating thickness does not exceed 33μm. S5. Austenitization: The coated cold-rolled steel coil is heated to 850~950℃ and held until fully austenitized to obtain the steel plate blank to be stamped. The heating and holding time is 3~10min. During the heating and holding process, the dew point of the heating zone must be kept below -10℃. S6. Stamping and quenching: The steel plate blank to be stamped is transferred to the forming mold for stamping and forming. The transfer time shall not exceed 15s. The temperature of the steel plate blank to be stamped on the mold shall not be lower than 750℃. After pressure holding and quenching, the blank is removed from the mold to obtain a hot-formed semi-finished product.

9. The preparation method according to claim 8, characterized in that, It also includes the following steps: S7. Laser cutting: The thermoformed semi-finished product is laser-cut to obtain a thermoformed component with the final contour features, wherein the laser cutting power is above 750W, the cutting speed is not less than 5m / min, and the gas pressure is not higher than 1bar.

10. The preparation method according to claim 9, characterized in that, It also includes the following steps: S8. Coating electrophoresis: After the thermoformed component is welded, it is coated with electrophoresis. The baking temperature during the coating electrophoresis process is 150~180℃ and the time is 20~60min.

11. A steel plate for manufacturing any one of the components according to claims 1-7, characterized in that: The steel plate comprises, by weight percentage: 0.365~0.455%C, 0.50~1.35%Mn, 0.01~0.60%Si, 0.01~0.60%Cr, 0.10~0.60%Al, 0.001~0.010%B, 0.001~0.020%P, 0.001~0.010%N, 0.001~0.010%S, with the balance being Fe and unavoidable impurity elements; Among them, carbon equivalent C eq ≤0.68, manganese equivalent Mn eq The mass ratio of aluminum to carbon (Al / C) is ≥0.50, ranging from 0.80 to 1.

60. The carbon equivalent C eq Calculated according to formula (1), C eq =C+Mn / 6+Cr / 5+V / 14+Mo / 4+Ni / 40+Si / 24Å(1)6 The manganese equivalent Mn eq Calculate according to formula (2), Mn eq =Mn+1.29×Cr+3.28×Mo+0.46×Cu+0.37×Ni+0.07×Si Formula (2); The steel plate also contains at least one of V, Nb, and Ti, with V accounting for 0.001 to 0.20% by mass and the sum of the mass percentages of Nb and Ti being 0.001 to 0.100%.

12. The steel plate according to claim 11, characterized in that: The steel plate further comprises at least one of Ni, Mo, W, Cu, Co, Ta, Sn, Sb, As, Mg, Ca, Zr, O, and REM, in the following mass percentages: Ni 0.01~0.30%, Mo 0.01~0.20%, W 0.01~0.20%, Cu 0.01~0.20%, Co 0.01~0.50%, Ta 0.001~0.10%, Sn 0.001~0.05%, Sb 0.001~0.05%, As 0.001~0.05%, Mg 0.001~0.010%, Ca 0.001~0.010%, Zr 0.001~0.10%, O 0.001~0.02%, REM. 0.001~0.05%, and the sum of the mass percentages of Ni, Mo, W, Cu, Co, Ta, Sn, Sb, As, Mg, Ca, Zr, and REM is 0.001~0.50%.

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