Ultrahigh-strength hot stamping forming component

Abstract

The invention provides a hot stamping forming component. The martensite content of a steel plate base body of the component is larger than or equal to 95%. The average hardness of a laser cutting edge hardened layer of the component is smaller than or equal to 720 HV, the effective depth is smaller than or equal to 120 micrometers, and the ratio of the hardness peak value of the cutting edge hardened layer to the hardness of a steel plate base body is smaller than or equal to 1.15. The tensile strength is greater than or equal to 2050MPa, and the percentage elongation after fracture is greater than or equal to 4.9 The tensile test of the notched sample is carried out at the tensile speeds of 0.01 mm / min and 10 mm / min, and the breaking strength ratio at the two tensile speeds is greater than or equal to 0.90. After further coating and baking, the average hardness of a laser cutting edge hardened layer of the component is smaller than or equal to 700 HV, the effective depth is smaller than or equal to 100 microns, and the ratio of the hardness peak value of the cutting edge hardened layer to the hardness of a steel plate base body is smaller than or equal to 1.12; the tensile strength is greater than or equal to 1950MPa; the percentage elongation after fracture is greater than or equal to 5.5%; and the equivalent fracture strain in a plane state is greater than or equal to 0.175.

Description

Technical Field

[0001] The present invention relates to the technical field of steel materials, and in particular to an ultra-high strength hot stamping formed component and a manufacturing method thereof. Background Art

[0002] In order to obtain ultra-high-strength steel plates with a tensile strength exceeding 2000MPa, high-carbon content design is the most effective and economical means. However, an increase in carbon content means that the brittleness of the steel will increase, while the toughness will also decrease, and the sensitivity to hydrogen embrittlement will increase significantly. In particular, for hot-stamped components of steel plates with aluminum alloy coatings and a tensile strength of more than 2000MPa, hydrogen embrittlement fracture is a particularly prominent problem in their production and manufacturing process. The production and manufacturing process of hot-stamped components is mainly that the steel blank is heated and hot-stamped to obtain a hot-stamped semi-finished product, and then the hot-stamped component with the final contour is obtained by laser cutting, and then transported over long distances to the welding workshop for assembly and body-in-white welding. The laser-cut edges of the hot-stamped components after laser cutting are very prone to hydrogen embrittlement problems, especially during the welding process. Cracks are very likely to occur in the stress concentration area of ​​the laser-cut edge, and then rapidly expand to form brittle fractures, thereby causing the hot-stamped components to fail.

[0003] Chinese patent CN116287989A discloses a hot stamping steel, an aluminum-silicon coated hot stamping steel plate, and an automotive structural part. The tensile strength of the steel after hot stamping can exceed 2100 MPa. In order to achieve ultra-high strength and good toughness, the patented steel composition contains a large amount of Cr, Mo, and Ni. The addition of these high-hardenability alloying elements gives it extremely high hardenability. High hardenability will cause the steel to produce high phase transformation stress after the martensitic phase transformation, and even form phase transformation microcracks in the microstructure, thereby causing the toughness of the hot stamping component to decrease sharply and the risk of hydrogen embrittlement of the parts to increase significantly. In addition, Ni and Mo are expensive elements. Adding higher levels of Mo and Ni will lead to an increase in steel costs, making it difficult to meet the cost requirements of the automotive industry.

[0004] Chinese patent CN106399837A discloses an ultrafine-grained steel for hot stamping, a manufacturing process, a hot stamping process, and a hot stamping component. The steel has a tensile strength of 1800 to 2200 MPa after hot stamping. Although the patent emphasizes the technical effect of microalloy precipitation in reducing the carbon content of the martensite matrix and thus improving the toughness of hot stamping components, it does not consider the adverse effects of adding higher levels of alloying elements on the laser-cut edges of hot stamping components, especially the addition of elements such as Mn and Mo that simultaneously increase the carbon equivalent and hardenability of steel. When laser cutting components, a high-hardness martensite layer is produced on the cut edge, thereby increasing the risk of hydrogen embrittlement on the cut edge of the component. At the same time, the high-alloy design also makes it easy to produce hard and brittle martensite during the production process of the steel, which increases the difficulty of processing and plate shape control, and is not conducive to production cost control.

[0005] Chinese patent CN115478227A discloses a hot stamping steel plate, a hot stamping component, and a method for manufacturing the steel plate. The hot stamping component can achieve a tensile strength of 1750-2100 MPa. To avoid the formation of hard and brittle twinned martensite in the structure, the patent improves the toughness of the hot stamping steel. The patent focuses on controlling the final temperature of the martensitic phase transformation during alloy design. However, the patent also fails to address the significant impact of laser cutting on hydrogen embrittlement. Laser cutting can cause a hard and brittle martensitic layer to form on the cut edge of the hot stamping component, thereby reducing the ability of the cut edge of the hot stamping component to resist hydrogen embrittlement fracture.

[0006] In summary, although existing technologies can produce steel hot stamped components with tensile strengths exceeding 2000 MPa, none of these technologies recognize the significant increase in the risk of hydrogen embrittlement that is common in steel hot stamped components, especially those that have been laser cut. Furthermore, there is no effective solution to overcome the hydrogen embrittlement problem in steel hot stamped components. To meet the extremely high demands placed on the mechanical properties of steel hot stamped components by the current automotive industry, it is urgent to develop a hot stamped component with a tensile strength exceeding 2000 MPa and low hydrogen embrittlement sensitivity. Summary of the Invention

[0007] In order to solve the above technical problems, the present invention provides an ultra-high strength hot stamping component and a manufacturing method thereof, wherein the hot stamping component has a tensile strength exceeding 2000 MPa and low hydrogen embrittlement sensitivity.

[0008] In the first aspect, the present invention discloses a hot stamping formed component, wherein the martensite content of the steel plate matrix of the hot stamping formed component is ≥95%; the average hardness of the laser cutting edge hardened layer of the hot stamping formed component is below 720HV, the effective depth of the cutting edge hardened layer does not exceed 120μm, and the ratio of the hardness peak of the cutting edge hardened layer to the hardness of the steel plate matrix is ​​not higher than 1.15; the tensile strength of the hot stamping formed component is ≥2050MPa, and the elongation after fracture is ≥4.9%, wherein the tensile specimen is obtained from the hot stamping formed component by laser cutting.

[0009] Preferably, the martensite content of the steel plate matrix is ​​≥98%.

[0010] Preferably, the notched specimen is subjected to a tensile test at tensile speeds of 0.01 mm / min and 10 mm / min, and the ratio of the fracture strength at the two tensile speeds is ≥0.90, wherein the notched specimen is obtained from the hot stamping component by laser cutting, and the notched specimen is in the shape of a long strip, with the semicircular notches symmetrically arranged on the long side, and the notch radius is 2±0.1 mm to 3±0.1 mm.

[0011] Preferably, the ratio of the breaking strength at the two stretching speeds is ≥0.95.

[0012] In the second aspect, the present invention also discloses a hot stamping formed component, wherein the martensite content of the steel plate matrix of the hot stamping formed component is ≥95%; the average hardness of the laser cutting edge hardened layer of the hot stamping formed component is below 700HV, the effective depth of the cutting edge hardened layer does not exceed 100μm, and the hardness peak of the cutting edge hardened layer is not higher than 1.12 to the hardness of the steel plate matrix; the tensile strength of the hot stamping formed component is ≥1950MPa, and the elongation after fracture is ≥5.5%, wherein the tensile specimen is obtained from the hot stamping formed component by laser cutting; the equivalent fracture strain of the hot stamping formed component under plane strain is ≥0.175, wherein the notch specimen of the equivalent fracture strain test is obtained from the hot stamping formed component by wire cutting, and the notch specimen is long strip-shaped, with semicircular notches symmetrically arranged on the long side, and the notch radius is 5±0.1 mm.

[0013] Preferably, the martensite content of the steel plate matrix is ​​≥98%.

[0014] Preferably, at least one surface of the steel plate substrate of the hot stamping formed component in the first and second aspects of the present invention is covered with an aluminum alloy coating, the aluminum alloy coating has a thickness of 10-50 μm, and the steel plate substrate has a thickness of 0.7-2.5 mm.

[0015] Preferably, the steel plate substrate of the first and second aspects of the present invention has the following composition, which contains, by mass percentage, C: 0.365-0.455%, Mn: 0.50-1.35%, Si: 0.01-0.60%, Cr: 0.01-0.60%, Al: 0.10-0.60%, B: 0.001-0.010%, P: 0.001-0.020%, N: 0.001-0.010%, S: 0.001-0.010%, and the balance is Fe and unavoidable impurities; wherein the carbon equivalent C of the steel plate substrate is eq ≤0.68, manganese equivalent Mn eq 1.00~1.60, Carbon equivalent C eq =C+Mn / 6+Cr / 5+V / 14+Mo / 4+Ni / 40+Si / 24, Manganese equivalent Mn eq =Mn+1.29×Cr+3.28×Mo+0.46×Cu+0.37×Ni+0.07×Si.

[0016] More preferably, the sum of the mass percentages of Si, Cr, and Al in the steel plate matrix is ​​no more than 1.00%. More preferably, the sum of the mass percentages of Si, Cr, and Al in the steel plate matrix is ​​no more than 0.85%.

[0017] More preferably, the mass ratio of aluminum to carbon in the steel plate matrix, Al / C, is not less than 0.60. More preferably, the mass ratio of aluminum to carbon in the steel plate matrix, Al / C, is not less than 0.70.

[0018] More preferably, the steel plate matrix is ​​further composed of carbon equivalent C eq ≤0.65, manganese equivalent Mn eq More preferably, the steel plate matrix has a carbon equivalent of C eq ≤0.63, manganese equivalent Mn eq It is 1.00~1.40.

[0019] Further preferably, the components of the steel plate matrix are, by mass percentage, C: 0.365~0.435%, Mn: 0.50~1.35%, Si: 0.1~0.5%, Cr: 0.1~0.5%, Al: 0.2~0.5%, B: 0.001~0.010%, P: 0.004~0.010%, N: 0.001~0.010%, and S: 0.001~0.005%.

[0020] More preferably, the steel plate matrix further comprises at least one of V, Nb and Ti, wherein, in mass percentage, V is 0.001-0.20%, and the sum of the mass percentages of Nb and Ti is 0.001-0.100%.

[0021] More preferably, the steel plate matrix further comprises 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: 0.001-0.100%, Sn: 0.001-0.05 0%, Sb: 0.001~0.050%, As: 0.001~0.050%, Mg: 0.001~0.010%, Ca: 0.001~0.010%, Zr: 0.001~0.100%, O: 0.001~0.020%, REM: 0.001~0.050%, and the sum of the mass percentages of Ni, Mo, W, Cu, Co, Ta, Sn, Sb, As, Mg, Ca, Zr and REM is 0.001~0.500%.

[0022] Preferably, the laser cutting process of the hot stamping formed components described in the first and second aspects of the present invention is to perform laser cutting on the hot stamping formed components to obtain hot stamping formed components with final contour characteristics, wherein the laser cutting power is ≥800W, the cutting speed is ≥5m / min, and the gas pressure is ≤1bar.

[0023] Compared with the prior art, this application has at least the following beneficial effects: (1) The present application creatively discovered in mass production practice that the laser-cut edge of a hot stamping formed component is a high-risk area for hydrogen embrittlement. During the welding process, the stress concentration area of ​​the laser-cut edge is very likely to generate cracks due to hydrogen embrittlement and rapidly expand to form brittle fractures. The study found that the hydrogen embrittlement sensitivity of the hardened layer of the cut edge is strongly correlated with the cold crack sensitivity of the steel itself. At the same time, the characteristics of the hardened layer of the laser-cut edge are also significantly affected by the laser cutting process. To this end, the present application proposes to control the average hardness of the hardened layer of the laser-cut edge of the hot stamping formed component to be below 720HV, the ratio of the hardness peak to the average hardness of the steel plate matrix material is not greater than 1.15, and the effective depth of the hardened layer does not exceed 120μm, so as to achieve room temperature tensile testing of notched specimens taken from the hot stamping formed component at tensile speeds of 0.01mm / min and 10mm / min respectively. The fracture strength ratio under the two tensile speeds is greater than 0.90, ensuring that the specimen has a low risk of hydrogen-induced delayed cracking after laser cutting. After coating and baking, the average hardness of the laser-cut edge hardened layer is below 700 HV, the peak hardness ratio to the hardness of the steel substrate is no more than 1.12, and the effective depth of the hardened layer does not exceed 100 μm, ensuring that the laser-cut edge hardened layer of the specimen does not worsen the fracture strain during a car collision. This application, through carbon equivalent design and optimized control of laser cutting process parameters, ensures that the steel itself has low cold crack sensitivity while also achieving a distribution of low hardness and small effective depth in the laser-cut edge hardened layer of the component, thereby significantly improving the hydrogen embrittlement sensitivity of hot-stamped components.

[0024] (2) This application optimizes and adjusts the composition design of the steel plate matrix and the preparation process of the hot stamping formed component. In the hot stamping state, the martensite content of the steel plate matrix of the hot stamping formed component is ≥95%, the tensile strength is ≥2050MPa, and the elongation after fracture is ≥4.9%. After the hot stamping formed component is further baked or tempered, the tensile strength of the hot stamping formed component is ≥1950MPa, the elongation after fracture is ≥5.5%, and the equivalent fracture strain in the plane state is ≥0.175. This application optimizes the composition design of the steel plate matrix and the preparation process of the hot stamping formed component, so that the hot stamping formed component has a high tensile strength of 2000MPa while significantly improving the hydrogen embrittlement sensitivity.

[0025] (3) Based on the study of the microstructure of steel, this application found that Al has a larger atomic radius than Fe. Adding a certain amount of Al to the alloy forms a substitutional solid solution with Fe, which will achieve crystal lattice expansion. In the case of a high C design, the phase transformation stress of the martensite is reduced, and the martensite toughness is improved. The improvement of the toughness of the steel plate matrix can significantly inhibit the rapid expansion of cracks after initiation. Based on this, this application effectively reduces the harm of hydrogen embrittlement to hot stamping components by controlling the Al / C ratio to not less than 0.60, preferably not less than 0.70.

[0026] (4) In order to ensure that the steel has a high tensile strength of more than 2000 MPa, this applicant selected a carbon content of 0.365-0.455%. Under this high carbon content composition design, the toughness of the steel is more sensitive to the cooling conditions of the hot stamping component. The high cooling rate brings a greater degree of undercooling, which will promote the formation of twinned martensite, thereby damaging the toughness of the martensitic steel matrix. During the product development, this applicant 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. To this end, the present application rationally designs the hardenability of the steel, which can be expressed by the Mn equivalent. The present application designs the Mn equivalent to be 1.00~1.60, preferably 1.00~1.45, and more preferably 1.00~1.40, to control the hardenability of the material. The rational hardenability design not only ensures the proportion of martensite in the hot stamping formed components, but also inhibits the formation of twin martensite, ensuring that the steel can have a high tensile strength of more than 2000MPa while ensuring that the martensitic steel plate matrix still has sufficient toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some of the embodiments described in this application. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0028] Figure 1 Schematic diagram of notched tensile specimen used for hydrogen embrittlement risk assessment; Figure 2 Schematic diagram of notched specimen used for equivalent fracture strain test under plane strain state; Figure 3 Schematic diagram of the hardness test of the hardened layer on the cutting edge of the specimen; Figure 4 Schematic diagram of the core hardness test of the specimen; Figure 5 This is a metallographic photograph of the coating of the hot stamping formed component in Example 1 of the present invention; Figure 6 This is a metallographic photograph of the microstructure of the hot stamping component of Example 1 of the present invention; Figure 7 This is a metallographic photograph of the coating of the hot stamping formed component in Example 2 of the present invention; Figure 8 This is a metallographic photograph of the microstructure of the hot stamping component of Example 2 of the present invention; Figure 9 This is a SEM photograph of the microstructure of the hot stamping component of Example 8 of the present invention; Figure 10 This is a SEM photograph of the microstructure of the hot stamping component of Example 11 of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0030] Unless otherwise stated, all temperatures herein are degrees Celsius and all percentages are weight percentages. Unless otherwise noted, preferred embodiments can be freely combined as needed. It will be understood by those skilled in the art that the data and various parameters described in the examples are merely exemplary and do not constitute limitations of the present invention. The components used in the following examples and comparative examples are monomers or compounds known in the art, and the equipment used are all known in the art and can be obtained commercially or prepared by known techniques.

[0031] The present invention provides a hot stamping formed component, wherein the martensite content of the steel plate matrix of the hot stamping formed component is ≥95%, and the martensite content is preferably ≥98%.

[0032] The average hardness of the laser cutting edge hardened layer of the hot stamping formed component is below 720HV, preferably below 700HV, and more preferably below 680HV; the effective depth of the cutting edge hardened layer does not exceed 120μm, preferably does not exceed 100μm, and more preferably does not exceed 80μm; the ratio of the hardness peak of the cutting 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 characteristics of the laser cutting edge hardened layer of the hot stamping formed component directly affect the hydrogen embrittlement resistance of the component. Therefore, the present invention optimizes the design of the carbon equivalent C eq And optimize and adjust the laser cutting process parameters to ensure that the hardened layer on the cutting edge has the above-mentioned distribution characteristics of low hardness and small effective depth.

[0033] The tensile strength of the hot stamping formed component is ≥2050 MPa, and the elongation after fracture is ≥4.9%, wherein the tensile specimen is obtained from the hot stamping formed component by laser cutting.

[0034] Tensile tests were performed on notched specimens at tensile speeds of 0.01 mm / min and 10 mm / min. The fracture strength ratio at the two tensile speeds was ≥0.90, and preferably ≥0.95. The notched specimens were obtained from the hot stamped components by laser cutting. The notched specimens were long strips with semicircular notches symmetrically arranged on the long sides, and the notch radius was 2±0.1 mm to 3±0.1 mm. Furthermore, the hydrogen embrittlement risk of hot stamped components was defined based on the fracture strength ratio as follows: a ratio ≥0.95 indicates a low hydrogen embrittlement risk; a ratio 0.90 ≤ <0.95 indicates a medium hydrogen embrittlement risk; and a ratio <0.90 indicates a high hydrogen embrittlement risk.

[0035] The performance characteristics of hot stamping state, such as tensile strength, elongation after fracture, and hydrogen embrittlement risk of hot stamping formed components, are technical effects directly manifested by the core innovative measures of the present invention, such as optimizing the steel plate base alloy design and adjusting the laser cutting process parameters. In particular, the risk of hydrogen embrittlement, when the hot stamping formed component itself has a certain amount of diffusible hydrogen, for example, when the diffusible hydrogen content is not higher than 0.2ppm, a slow stretching of 0.01mm / min can cause hydrogen to diffuse and accumulate in the hardened layer of the laser cut edge, thereby causing hydrogen embrittlement fracture and reducing the fracture stress. However, under a fast stretching of 10mm / min, hydrogen does not have time to diffuse and accumulate, and the sample is not affected by hydrogen embrittlement, and the fracture stress does not decrease. Therefore, on the basis of meeting the alloy element ratio design of the present invention and adopting the hot working process of the present invention, the steel matrix of the present invention has good toughness and excellent characteristics of the hardened layer of the cut edge. The fracture strength ratio of the tensile specimens at the two pulling speeds is between 0.90 and 0.95, which is a medium hydrogen embrittlement risk. Even the fracture strength ratio of the specimens at the two pulling speeds can be above 0.95, achieving a low hydrogen embrittlement risk. After testing, it was found that all the hot stamping formed components in the hot stamping state of the present invention met the medium hydrogen embrittlement risk, and the hydrogen embrittlement risk of some preferred solutions reached the low hydrogen embrittlement risk.

[0036] In the actual production process, after the hot stamping formed components with final contour features after laser cutting are welded, they will also undergo body-in-white painting and electrophoresis. The baking treatment temperature during the painting and electrophoresis process is 150~180℃ and the time is 20~60min. After the hot stamping formed components that have been laser cut are further subjected to painting and baking or tempering treatment with the same effect, the average hardness of the laser cutting edge hardened layer of the hot stamping formed components is below 700HV, preferably below 680HV, and more preferably below 650HV; the effective depth of the cutting edge hardened layer does not exceed 100μm, preferably does not exceed 80μm, and more preferably does not exceed 60μm; the ratio of the hardness peak of the cutting edge hardened layer to the hardness of the steel plate substrate is not higher than 1.12, preferably not higher than 1.10, and more preferably not higher than 1.08. The hot stamping formed component has a tensile strength of ≥1950 MPa, an elongation after fracture ≥5.5%, and an equivalent fracture strain under plane strain of not less than 0.175, preferably not less than 0.185, and more preferably not less than 0.205.

[0037] After painting and baking, hot stamping components are equivalent to undergoing low-temperature tempering. The hardness of the hardened layer on the laser-cut edge of the component and the hardness of the martensite both decrease to a certain extent. The effective depth of the hardened layer and the ratio of the hardness peak of the hardened layer to the hardness of the martensite substrate also decrease accordingly. Considering that the body-in-white must undergo painting and baking, and that material properties will change to a certain extent after painting and baking, it is necessary to test the material properties of hot stamping components after baking or tempering. After baking, due to the effect of low-temperature tempering, the material stress is reduced, the toughness and plasticity of the martensite are improved, and the risk of hydrogen embrittlement of hot stamping components is significantly reduced.

[0038] Preferably, at least one surface of the steel plate substrate of the hot stamping formed component is covered with an aluminum alloy coating, the aluminum alloy coating has a thickness of 10 to 50 μm, and the steel plate substrate has a thickness of 0.7 to 2.5 mm.

[0039] Preferably, the steel plate matrix has the following composition, which contains, by mass percentage, C: 0.365-0.455%, Mn: 0.50-1.35%, Si: 0.01-0.60%, Cr: 0.01-0.60%, Al: 0.10-0.60%, B: 0.001-0.010%, P: 0.001-0.020%, N: 0.001-0.010%, S: 0.001-0.010%, and the balance is Fe and unavoidable impurities; wherein the carbon equivalent C of the steel plate matrix is eq ≤0.68, manganese equivalent Mn eq 1.00~1.60, Carbon equivalent C eq=C+Mn / 6+Cr / 5+V / 14+Mo / 4+Ni / 40+Si / 24, Manganese equivalent Mn eq =Mn+1.29×Cr+3.28×Mo+0.46×Cu+0.37×Ni+0.07×Si.

[0040] Further preferably, the total mass percentage of Si+Cr+Al in the steel plate matrix is ​​not higher than 1.00%, more preferably, not higher than 0.85%.

[0041] Further preferably, the mass ratio of aluminum to carbon Al / C in the steel plate matrix is ​​not less than 0.60, and more preferably, the mass ratio of aluminum to carbon Al / C is not less than 0.70.

[0042] More preferably, the steel plate matrix is ​​further composed of carbon equivalent C eq ≤0.65, manganese equivalent Mn eq More preferably, the steel plate matrix has a carbon equivalent of C eq ≤0.63, manganese equivalent Mn eq It is 1.00~1.40.

[0043] Further preferably, the components of the steel plate matrix are, by mass percentage, C: 0.365~0.435%, Mn: 0.50~1.35%, Si: 0.1~0.5%, Cr: 0.1~0.5%, Al: 0.2~0.5%, B: 0.001~0.010%, P: 0.004~0.010%, N: 0.001~0.010%, and S: 0.001~0.005%.

[0044] More preferably, the steel plate matrix further comprises at least one of V, Nb and Ti, wherein, in mass percentage, V is 0.001-0.20%, and the sum of the mass percentages of Nb and Ti is 0.001-0.100%.

[0045] More preferably, the steel plate matrix further comprises 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: 0.001-0.100%, Sn: 0.001-0.05 0%, Sb: 0.001~0.050%, As: 0.001~0.050%, Mg: 0.001~0.010%, Ca: 0.001~0.010%, Zr: 0.001~0.100%, O: 0.001~0.020%, REM: 0.001~0.050%, and the sum of the mass percentages of Ni, Mo, W, Cu, Co, Ta, Sn, Sb, As, Mg, Ca, Zr and REM is 0.001~0.500%.

[0046] Specifically, C: 0.365~0.455% Carbon is an important interstitial solid solution strengthening element in steel, enabling the material to achieve ultra-high strength and hardness. Therefore, the present invention adds a carbon content of 0.365% or more to ensure a tensile strength of over 2000 MPa. However, excessive addition of carbon promotes the formation of brittle twinned martensite, severely degrading toughness. Therefore, the carbon content of the present invention is controlled within a range of 0.365-0.455%, preferably 0.365-0.435%.

[0047] Mn: 0.50~1.35% Mn is an economical and effective element to improve the hardenability of steel. At the same time, the addition of Mn will significantly expand the austenite phase area, thereby affecting the martensite phase transformation process. Therefore, an appropriate amount of Mn is generally added to hot stamping steel. However, the addition of Mn has a negative impact on the C eq There is also an impact. Adding too much Mn will cause the C eq Increased hydrogen embrittlement sensitivity makes it difficult to ensure the laser-cut edge is not susceptible to hydrogen embrittlement. At the same time, adding more Mn will also cause the martensitic phase transformation to occur at lower temperatures, resulting in the massive generation of hard and brittle twin martensite, which reduces the toughness of the material. At the same time, the phase transformation stress within the material also increases, and severe banded segregation is likely to occur, deteriorating the performance of the steel. Therefore, the present invention sets the Mn content to 0.50-1.35%, which can take into account the carbon equivalent, manganese equivalent, and martensitic phase transformation temperature of the material.

[0048] Si: 0.01~0.60% The element Si has the effect of solid solution strengthening the matrix, and adding an appropriate amount can significantly improve the strength of the martensitic matrix. However, excessive Si addition can lead to the formation of difficult-to-remove oxides on the steel surface during production, affecting the surface quality of the final product. Therefore, the upper limit of Si content in the present invention is set at 0.60%, and further, it is set at 0.10-0.50%.

[0049] Cr: 0.01~0.60% The Cr element shifts the isothermal transformation C curve of steel to the right by hindering the nucleation and growth of cementite, significantly delaying the pearlite phase transformation. In addition, the Cr element reduces the decomposition rate of austenite, reduces the critical cooling rate of steel, and contributes to the formation of martensite. The effect of the Cr element on reducing the phase transition temperature of martensite is significantly lower than that of the Mn element. Therefore, the Cr element is more conducive to promoting the formation of dislocation martensite with good toughness. However, when the Cr element is added in excess, the oxide scale formed on the surface of the hot-rolled coil will be difficult to completely remove by pickling while increasing the alloy cost, affecting the surface quality of the final product. In addition, Cr is also an important alloying element that affects the carbon equivalent. Therefore, in the present invention, the Cr content is controlled to be below 0.60%, and further, the Cr content is controlled to be between 0.10 and 0.50%.

[0050] Al: 0.10~0.60% The addition of Al element can combine with N element to form AlN, which has the effect of solidifying N, thereby preventing the combination of N and B, and ensuring the effect of adding B to improve hardenability. In addition, Al can also increase the martensitic transformation temperature, which helps to reduce the formation of brittle twin martensite. However, when the addition amount of Al is too high, it will cause the problem of excessive resistance at the crystallizer mouth during continuous casting, affecting the production of ingots, and will increase the difficulty of controlling aluminum oxide inclusions in steel. Therefore, the Al content in the present invention is controlled between 0.10~0.60%, and further, it is controlled between 0.20~0.50%.

[0051] The sum of the mass percentages of Si, Cr, and Al should be no higher than 1.00%, preferably no higher than 0.85%. Si, Cr, and Al are all easily oxidized elements. Excessive additions of Si, Cr, and Al to steel can easily form surface oxides on the surface of hot-rolled coils that are difficult to pickle. These surface oxides are difficult to remove during subsequent pickling and cold rolling processes, thus affecting the surface quality of the steel sheet. Furthermore, during coating, these elements also form external oxidation on the surface of the steel sheet, causing plating defects and deteriorating the surface quality of the coated steel sheet. Therefore, in the present invention, the sum of the mass percentages of Si, Cr, and Al is controlled to be no higher than 1.00%, preferably no higher than 0.85%.

[0052] B: 0.001~0.010% The B element tends to segregate at the austenite grain boundaries, which can inhibit the phase transformation of austenite to ferrite. A relatively low addition amount can significantly improve the hardenability of the steel. However, a high B addition will lead to boron embrittlement, which is detrimental to the performance. Therefore, the B content in the present invention is set to 0.001~0.010%.

[0053] 0.001%≤V≤0.20%, 0.001%≤Nb+Ti≤0.100% The addition of V, Nb, and Ti can form carbides, nitrides, or carbonitrides with carbon and nitrogen. These uniform, fine precipitates pin austenite grain boundaries, refining the grains and improving the strength and toughness of the steel. Furthermore, the precipitates are dispersed throughout the steel matrix, exerting precipitation strengthening effects while acting as hydrogen traps to inhibit diffusible hydrogen in the steel matrix, slowing its segregation in stress concentration areas along the cut edges of hot-stamped components and reducing the hydrogen embrittlement sensitivity of the resulting hot-stamped components. Therefore, the components described in the present invention can be added in appropriate amounts. V, in particular, can also precipitate in large quantities during the hot stamping heating process, further consuming C in the matrix and promoting the formation of dislocation martensite. Furthermore, Ti and N have a strong binding force. Adding a certain amount of Ti to hot-stamped steel can form TiN with solid-solution N in the steel, preventing the combination of N and B, securing N and B, and ensuring hardenability. However, excessive addition of the above three microalloying elements will lead to a significant increase in cost. Therefore, in the present invention, the V content is controlled within the range of 0.001-0.20%, and the sum of the Nb and Ti contents is controlled within the range of 0.001-0.100%.

[0054] P: 0.001~0.020% Phosphorus (P) is an unavoidable impurity element in steel. As a solid-solution strengthening element, P can relatively inexpensively increase the strength of steel plates. On the other hand, when the P content exceeds 0.0200%, P can segregate at grain boundaries, significantly reducing toughness and causing other adverse effects. Therefore, the upper limit of P content is no greater than 0.020%, preferably no greater than 0.010%. Alternatively, considering that reducing P content to less than 0.001% increases smelting costs, the lower limit of P content may be no less than 0.001%.

[0055] S: 0.001~0.010% Like P, S is an unavoidable impurity element in steel. It reacts with Mn in the steel to form MnS inclusions. When the S content exceeds 0.010%, the large amount of MnS significantly impairs the ductility and toughness of the steel, degrading workability. Therefore, the upper limit of the S content is no greater than 0.010%, preferably no greater than 0.005%. Alternatively, considering that lowering the S content below 0.001% increases smelting costs, the lower limit of the S content may be no less than 0.001%.

[0056] N: 0.001~0.010% Nitrogen is also an unavoidable impurity element in steel. In particular, for steel containing B, its combination with B will significantly reduce the effect of B in improving hardenability. Therefore, it is necessary to reduce the content of Nitrogen as much as possible. Therefore, the content of Nitrogen in the present invention is controlled to be 0.001-0.010%.

[0057] Ni: 0.01~0.30% Ni is a hardenability improving element and can improve the low temperature toughness of steel, so its lower limit can be optionally set to 0.01%. A large amount of Ni addition is bound to increase the alloy cost and lead to C eq and Mn eq Therefore, the Ni content is set to no more than 0.30%.

[0058] Mo: 0.01~0.20% Mo can improve the hardenability of steel plates and prevent temper brittleness. It is preferably added at 0.01% or more, but excessive Mo addition will increase C eq and Mn eq , which in turn increases the hydrogen embrittlement sensitivity of the final hot stamped component and causes an increase in cost. Therefore, the Mo content is set to 0.20% or less.

[0059] W: 0.01~0.20% The addition of W significantly increases the strength of the steel sheet, and W-containing precipitates can serve as hydrogen traps. Therefore, an addition of 0.01% or more is preferred. However, W is a strong carbide-forming element. When the W content exceeds 0.20%, coarse and unevenly distributed carbides are formed, seriously impairing the performance of hot stamped components. Therefore, the W content is set to 0.20% or less.

[0060] Cu: 0.01~0.20% Cu improves the hardenability of the steel sheet, thereby increasing the strength of hot stamped components. To achieve this effect, the Cu content is preferably set to 0.01% or above. However, Cu tends to segregate at grain boundaries and cause copper brittleness, reducing the hot workability of the steel sheet. Therefore, the Cu content is set to 0.20% or below.

[0061] Co: 0.01~0.50% The addition of Co can increase the martensitic transformation temperature, facilitate martensite autotempering, and thus improve its toughness. Therefore, its lower limit can be preferably set to 0.001%. However, Co is a rare and precious element, and excessive addition will increase the cost of the steel plate. Moreover, Co promotes the graphitization of carbon in the steel, thereby impairing the toughness of hot stamped components. Therefore, the Co content is optionally set to 0.001% ≤ Co ≤ 0.50%.

[0062] Ta: 0.001~0.10% Ta, as a strong carbide-forming element, forms stable carbides with C, thereby refining grains and enhancing the strength and toughness of the steel sheet. To achieve this effect, the Ta content is preferably not less than 0.001%. However, if the Ta content exceeds 0.10%, a large amount of carbides will precipitate and tend to accumulate at grain boundaries, reducing the toughness of the steel sheet. Therefore, the Ta content is set to no more than 0.10%.

[0063] Sn: 0.001~0.05% The addition of Sn can refine the grains and improve the machinability of the steel plate by combining with other elements such as S. The preferred Sn addition level is no 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 no more than 0.05%.

[0064] Sb: 0.001~0.05% Sb also has the effect of refining grains, so to achieve this effect, the Sb addition is preferably 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 the steel, especially the plasticity and toughness. Therefore, the Sn content is set to no more than 0.05%.

[0065] As: 0.001~0.05% As has a certain strengthening effect on steel, which can increase its strength. However, As tends to accumulate at grain boundaries, increasing the brittleness of the steel plate and deteriorating its weldability. Therefore, the As content is set to 0.001 ≤ As ≤ 0.05%.

[0066] Mg: 0.001~0.010%, Ca: 0.001~0.010% Mg and Ca are commonly used for deoxidation during steelmaking. They can also form sulfides with sulfur, improving the number and morphology of inclusions within the steel sheet structure. Therefore, their addition level is preferably no less than 0.001%. However, when the Mg and Ca content exceeds 0.010%, large inclusions form within the steel sheet structure, impairing the toughness of hot stamped components. Therefore, the Mg and Ca content is set to no more than 0.01%.

[0067] Zr: 0.001~0.10% Zr is a strong carbide-forming element with similar effects to elements such as V, Nb, and Ti. When added in small amounts, it can refine grains and improve the low-temperature toughness of the steel plate. The preferred Zr addition level is no less than 0.001%. However, when the Zr addition level exceeds 0.10%, large carbides are formed within the steel plate structure, resulting in a decrease in the toughness of hot stamped components. Therefore, the Zr content is set to 0.001 ≤ Zr ≤ 0.10%.

[0068] O: 0.001~0.02% O forms coarse oxides in steel, which are detrimental to the toughness of hot stamped parts. Therefore, the lower the O content, the better. The O content is controlled to 0.001-0.02%, and more preferably below 0.006%.

[0069] REM: 0.001~0.05% REM improves deformability and toughness of hot stamped components by suppressing oxide formation. To achieve this effect, the REM content is preferably set to 0.001% or higher. However, the REM content should be controlled to no more than 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.

[0070] 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.

[0071] C eq =C+Mn / 6+Cr / 5+V / 14+Mo / 4+Ni / 40+Si / 24 In the present invention, the C content in the steel reaches 0.365~0.455%, which has a strong interstitial solid solution strengthening effect, so that the tensile strength of the hot stamping formed component reaches more than 2000MPa. Similar to the laser welding or resistance spot welding process, under the conditions of high heat input and ultra-high cooling rate of laser cutting, the high quenching stress in some cutting contour areas with stress concentration characteristics will cause the cutting edge hardened layer of the final hot stamping formed component to have a high risk of hydrogen embrittlement. For materials with high C content, the cold crack sensitivity of the material itself is strongly correlated with the hydrogen embrittlement sensitivity of the cutting edge hardened layer of its hot stamping formed component, that is, materials with high cold crack sensitivity are more likely to initiate cracks in their hardened layer after laser cutting under the combined action of thermal stress and martensitic phase transformation stress, thereby inducing hydrogen embrittlement cracking of the component. Based on this, the present invention proposes a method to control C eqThe requirements of the C content are that it reaches 0.365~0.455%, and the low carbon equivalent is obtained by controlling the addition ratio of alloying elements other than C to reduce the cold crack sensitivity of the hardened layer at the cutting edge, ensuring that the C eq Not more than 0.68, preferably not more than 0.65, further preferably not more than 0.63.

[0072] Mn eq =Mn+1.29Cr+3.28Mo+0.46Cu+0.37Ni+0.07Si The hardenability of the material affects the toughness of the material and the phase transformation stress during the cooling process. Therefore, it is hoped that the hardenability of the material is within an appropriate range. If too much alloying element is added, the hardenability is too good, which is not economical and will damage the toughness of the material. If the hardenability is too poor, non-martensitic structure will be easily generated during hot stamping, and the martensite ratio will be low, which will affect the strength. The inventors found that when the C content in the material is increased, the mechanical stability of the austenite will be significantly improved, and it will be more difficult to cause strain-induced ferrite phase transformation during high-temperature forming. Therefore, compared with 22MnB5, when the C content reaches 0.365~0.455%, ferrite is more difficult to generate during high-temperature forming, that is, high-C content materials do not need too high hardenability. It is sufficient to control the hardenability of the material to be close to that of 22MnB5, or even lower. While ensuring a high martensite ratio, the suppression of twin martensite is taken into account to improve the toughness of the matrix. The hardenability of the material can be controlled by the Mn equivalent (Mn eq ) indicates that the present invention controls Mn eq 1.00~1.60, preferably Mn eq 1.00~1.45, more preferably Mn eq It is 1.00~1.40.

[0073] The mass percentage ratio of Al / C is not less than 0.60, preferably not less than 0.70 Martensite is a supersaturated interstitial solid solution of carbon dissolved in α-Fe. The maximum solubility of carbon in austenite is 2.11%, while its solubility in α-Fe is only 0.0218%. During the transformation from austenite to martensite, if the carbon atoms dissolved in the octahedral interstices of austenite cannot diffuse out during rapid quenching, they will still accumulate in the octahedral interstices of α-Fe. Because the octahedral interstices of α-Fe are small, only 0.154 times the radius of an iron atom, carbon exceeding the maximum solubility of α-Fe will cause a large lattice distortion, resulting in volume expansion and phase transition stress. As the carbon content increases, more carbon further expands the lattice, causing increased volume expansion and increased phase transition stress in the material. The inventors recognized that Al has a larger atomic radius than Fe. In the case of a high-C design, adding a certain amount of Al to the alloy creates a substitution effect on Fe, expanding the crystal lattice. This reduces lattice distortion caused by interstitial solid solution of C atoms during martensite formation, reduces martensite transformation stress, and thus improves martensite toughness. Therefore, the present invention aims to control the Al / C mass percentage ratio to no less than 0.60, preferably no less than 0.70.

[0074] Preferably, the laser cutting process of the hot stamping formed component is to perform laser cutting on the hot stamping formed component to obtain a hot stamping formed component with final contour features, wherein the laser cutting power is ≥800W, the cutting speed is ≥5m / min, and the gas pressure is ≤1bar.

[0075] The hot stamping formed component disclosed in the present invention can be obtained by the following preparation method, which comprises the following steps: S1. Steelmaking: Weigh the raw materials according to the steel plate composition proposed in the present invention, smelt the raw materials by a vacuum induction furnace, an electric furnace or a converter, and obtain a steel billet that meets the requirements of the steel plate substrate composition of the present invention by continuous casting or continuous casting and rolling; S2. Hot rolling: The steel slab is heated to above 1100°C and held at this temperature for at least 2 hours. It is then hot-rolled in various passes at 800°C to 1250°C and coiled at 500°C to 700°C to form a hot-rolled coil. The hot-rolled coil is pickled to remove the oxide scale formed during the hot rolling process. S3 cold rolling: the pickled hot-rolled steel coil is cold rolled with a cold rolling reduction of 30% to 70% to obtain a cold-rolled steel coil with a thickness of 0.7 to 2.5 mm; S4. Annealing or coating: The cold-rolled steel coil is annealed or coated. If coating is used, the coating is an aluminum alloy coating with an Al content of more than 50% and a thickness of 10-50 μm. S5. Austenitization: The annealed or coated cold-rolled steel coil is processed into a steel sheet blank, which is heated to 850-950°C and held until fully austenitized to obtain a steel sheet blank for stamping. The heating and holding time is 3-10 minutes. During the heating and holding process, the dew point of the heating zone must be maintained below -10°C, preferably below -15°C, and more preferably below -20°C, thereby reducing the diffusible hydrogen content in the hot stamped component. S6. Stamping and quenching: The steel sheet blank to be stamped is transferred to a forming die for stamping, with the transfer time not exceeding 15 seconds. The temperature of the steel sheet blank placed on the die is not less than 750°C. After pressure quenching, the hot stamped component is removed from the die. S7. Laser cutting: Laser cutting the hot stamped component to obtain a hot stamped component with final contour features, wherein the laser cutting power is greater than 800 W, the cutting speed is not less than 5 m / min, and the gas pressure is not higher than 1 bar.

[0076] In addition, in the actual production process, after the hot stamping components with final contour features are laser cut and welded, the white body will be electrophoretically painted. The baking treatment temperature during the electrophoretic painting process is 150~180℃ and the time is 20~60min.

[0077] The following is a description of the performance tests in the examples.

[0078] Diffusible hydrogen content testing and hydrogen embrittlement risk assessment Hot stamping is performed in a heating furnace with a dew point control function to obtain a hot stamping component with a certain hydrogen content. The hydrogen content is tested using a Bruker diffusible hydrogen analyzer (TDS). Subsequently, a notch sample is machined from the hot stamping component using laser cutting. The schematic diagram of the notch sample is shown in the figure. Figure 1 As shown, the notched specimen is long and strip-shaped, with a length of not less than 70 mm, preferably 70-90 mm, and a width of 12-15 mm. The semicircular notches are symmetrically arranged on the long side. The notch radius can be set to 2.0±0.1-3.0±0.1 mm depending on the stress concentration factor, and the corresponding stress concentration factors are 1.9±0.02-1.5±0.02, respectively. Notch radii that are too large or too small do not meet the test requirements. In the following embodiments and comparative examples of the present invention, a notch radius of 2.5±0.1 mm is selected, corresponding to a stress concentration factor of 1.8±0.02. The notched specimen length is selected to be 80 mm, and the width is selected to be 12.5 mm.

[0079] Afterwards, the notched specimens were stretched at room temperature at tensile 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. The average value of at least three groups of each notched specimen was taken, and the fracture strength ratio was calculated. If the ratio is ≥0.95, it is judged as a low hydrogen embrittlement risk; when the ratio is 0.9≤<0.95, it is judged as a medium hydrogen embrittlement risk; if the ratio is <0.9, it is judged as a high hydrogen embrittlement risk.

[0080] Equivalent fracture strain test under plane strain state The hot stamping formed component was processed by wire cutting to produce a long strip notch specimen with a size of 140×20mm (length×width). The semicircular notch was set symmetrically on the long side, and the notch radius R was 5±0.1mm. The specimen schematic diagram is shown in the figure. Figure 2 As shown. Subsequently, testing was performed using a standard tensile testing machine at a stretching rate of 0.3 mm / min. The thickness of the original specimen at the notch before stretching was h0, and the thickness of the specimen at the tensile fracture after breaking was h. The equivalent fracture strain ε was calculated using the following formula. To minimize the impact of specimen processing on thickness reduction, the fracture thickness was measured in an area 1 / 2 the width near the center. The average of at least five test values ​​was taken. The notched specimen processing and testing methods for the following Examples and Comparative Examples of the present invention were all carried out in this manner.

[0081] Equivalent fracture strain calculation formula:

[0082] Cutting edge hardening layer characteristic test Reference Figure 3 and Figure 4 , Figure 3 This is a schematic diagram of the hardness test of the hardened layer on the cutting edge. Figure 4 The figure is a schematic diagram of the core hardness test. The hardness test of the cut edge hardened layer starts at a position of about 10μm from the edge of the specimen, with three rows of parallel points. Each row of points is tested along a straight line at a 30° angle to the edge of the specimen into the matrix. The load force is 50g, and the spacing between the load points is 40μm. The depth of the cut edge hardened layer is defined as the distance perpendicular to the edge and from the outermost edge to the first test point where the hardness value decreases to within ±20 of the average value of the core hardness. The average hardness of the cut edge hardened layer is the average of all hardness test points within the depth of the hardened layer (including the first test point from the outermost edge where the hardness value decreases to within ±20 of the average value of the core hardness). The peak hardness of the cut edge hardened layer is the maximum value of all hardness test points within the depth of the hardened layer (including the first test point from the outermost edge where the hardness value decreases to within ±20 of the average value of the core hardness). The hardness of the steel plate matrix is ​​the average of the five points of the core hardness test.

[0083] The present invention will be described in more detail below with reference to exemplary embodiments. The following examples or experimental data are intended to illustrate the present invention, and it should be clear to those skilled in the art that the present invention is not limited to these examples or experimental data.

[0084] Example 1 A hot stamping formed component is produced by the following production method, which comprises the following steps: S1 steelmaking: According to the T1 composition in Table 1 by vacuum induction furnace smelting, by continuous casting and forging to obtain a billet meeting the T1 composition in Table 1; S2. Hot rolling: The steel slab is heated to 1100°C and held for 2 hours. It is then hot-rolled at 800°C in various passes and coiled at 500°C to form a hot-rolled coil. The hot-rolled coil is pickled to remove the oxide scale produced during the hot rolling process. S3 cold rolling: the pickled hot-rolled steel coil was cold rolled with a cold rolling reduction of 60% to obtain a cold-rolled steel coil having a thickness of 1.2 mm; S4. Coating: The cold-rolled steel coil is coated with an aluminum alloy coating having an Al content of 50% and a thickness of 18 μm. S5. Austenitization: The coated cold-rolled steel coil is processed into a steel sheet blank, which is heated to 930°C and held until fully austenitized to obtain a steel sheet blank for stamping. The heating and holding time is 10 minutes, and the dew point of the heating zone must be maintained at -10°C during the heating and holding process. S6. Stamping and quenching: The steel sheet to be stamped is transferred to a forming die for stamping. The transfer time is 15 seconds. The temperature of the steel sheet to be stamped is 750°C. The steel sheet is cooled to below 200°C by press quenching and ejected from the die to obtain a hot stamped component. S7. Laser cutting: The hot stamping formed component is subjected to laser cutting to obtain a hot stamping formed component with final contour features, wherein the laser cutting power is 1000 W, the cutting speed is 7 m / min, and the gas pressure is 0.55 bar.

[0085] In order to simulate the baking process of the body-in-white painting electrophoresis process after the hot stamping formed components are welded, the hot stamping formed components with the final contour features after the above laser cutting are further baked at a temperature of 150°C and a time of 60 minutes.

[0086] In order to distinguish the hot stamping components before and after baking treatment, the hot stamping components with final contour features after laser cutting in step S7 are defined as hot stamping state hot stamping components, and the hot stamping components after baking treatment are defined as baked state hot stamping components.

[0087] In order to meet the sample size requirements of performance tests such as room temperature tensile testing, metallographic testing, hardened layer testing, diffusible hydrogen content testing and hydrogen embrittlement risk assessment, the hot stamping components in the hot stamping state and the hot stamping components in the baked state are processed according to the performance test requirements and performance tests are carried out separately.

[0088] Examples 2-12 (T2 to T9) and Comparative Examples 1-4 (CT1 to CT4) The process steps for preparing the hot-stamped components in Examples 2-12 and Comparative Examples 1-4 are identical to those in Example 1, differing only in the alloy composition of the steel plate substrate and the specific parameters of the heat treatment and laser cutting processes. For these alloy compositions and specific parameters, see Tables 1-3 for the corresponding Example and Comparative Example groups, respectively. It should be noted that in the laser cutting process corresponding to T8-2, due to the low laser power, the hot-stamped component could not be cut through, and thus a hot-stamped component with the final contour could not be obtained.

[0089] Table 1 Chemical composition of steel plate matrix (wt.%, balance Fe and impurities)

[0090] Table 2 Heat treatment process of steel billets with different alloy compositions

[0091] Table 3 Laser cutting process of different hot stamping components

[0092] Performance testing and result analysis The hot-stamped and baked hot-formed components prepared in Examples 1-12 and Comparative Examples 1-4 were processed into specimens meeting the dimensional requirements for performance testing, including room temperature tensile testing, metallographic examination, hardened layer testing, diffusible hydrogen content testing, and hydrogen embrittlement risk assessment. Diffusible hydrogen content testing, hydrogen embrittlement risk assessment, equivalent fracture strain testing, and cut-edge hardened layer characterization testing were performed. Specimen dimensional requirements, testing, and evaluation methods are described above for the performance testing in the Examples. Test results are shown in Tables 4-6. Tables 4 and 5 present the performance test results and cut-edge hardened layer distribution characteristics of hot-stamped component samples with different alloy compositions and heat treatment processes, respectively, while Table 6 presents the corresponding hydrogen embrittlement risk assessment results. It should be noted that baking reduces the diffusible hydrogen content and internal stress in hot-stamped components, and improves the toughness of the martensitic matrix structure, thus reducing the hydrogen embrittlement risk of hot-stamped components. Therefore, hydrogen embrittlement risk assessment was performed only on the hot-stamped specimens in the Examples and Comparative Examples, and not on the baked specimens.

[0093] Table 4 Performance test results of hot stamping components with different alloy compositions and heat treatment processes

[0094] Table 5 Distribution characteristics of the hardened layer on the cut edge of hot stamping components with different alloy compositions and heat treatment processes

[0095] Figure 5-6 as well as Figure 7-8 are metallographic photographs of the coating and microstructure of a portion of the hot stamping formed component in Examples 1 and 2 of the present invention, and Figure 9 and Figure 10 The SEM photos of the microstructures of the hot stamping components in Examples 8 and 11 are given respectively. It can be seen that Figure 5 and Figure 7 The coating thickness of hot stamping components is 18.8μm and 34.0μm respectively, while Figure 6 、 Figure 8-10 The microstructure of the steel plate matrix of the hot stamping formed component is mainly martensite, and the area ratio is more than 95%, thereby ensuring that the hot stamping formed component prepared by the present invention has ultra-high strength. In addition, observing the microstructure of the steel plate matrix of the hot stamping formed component in other embodiments, there is also a microstructure similar to that of Examples 1, 2, 8 and 11, and the microstructure of the steel plate matrix is ​​almost entirely martensite. By measuring the area ratio of the martensite structure in the test area, the martensite content in the steel plate matrix also reaches 95% or more. Since the metallographic photos or SEM photos of other embodiments are different from those of Example 1 Figure 6 or Example 8 Figure 9 The microstructure photos of other embodiments are very similar and will not be repeated here.

[0096] Table 6 Hydrogen embrittlement risk assessment

[0097] From the above test results, we can see that: 1) T1~T9 hot stamping components: C eq At 0.59~0.67, Mn eqWhen the mass percentage of Al / C is between 1.17 and 1.60, and the mass percentage of Al / C is between 0.63 and 1.22, the tensile strength of the hot stamped state reaches 2052-2198 MPa, and the elongation after fracture reaches 4.9-6.3%. The tensile strength of the baked state reaches 1950-2074 MPa, and the elongation after fracture reaches 5.5-7.1%. The equivalent fracture strain reaches 0.175-0.229. The hydrogen embrittlement risk of the hot stamped state is low or medium risk, indicating that the hot stamped components obtained under the alloy design and laser cutting process of the present invention have good strength, toughness and hydrogen embrittlement resistance. In particular, with the increase of C eq and Mn eq The decrease of C eq Not more than 0.65, Mn eq When the C is not more than 1.45, the component shows better toughness, the equivalent fracture strain is not less than 0.185, and the hydrogen embrittlement resistance is low. eq Not more than 0.63, Mn eq When the Al / C mass ratio is no more than 1.4, the equivalent fracture strain of the component is no less than 0.205, and the toughness is further improved. It can be expected that its hydrogen embrittlement resistance is also further improved. In addition, by comparison, it is found that when the Al / C mass ratio is no less than 0.70, the equivalent fracture strain of the component is no less than 0.191, which also reflects its effect on improving component toughness.

[0098] 2) T1~T9 hot stamping components: in hot stamping state, the hardness peak of the hardened layer of the cutting edge is 675~718HV, the effective depth is 60~110μm, and the ratio of the hardness peak of the hardened layer to the core hardness is 1.06~1.14; in baking state, the hardness peak of the hardened layer of the cutting edge is 654~699HV, the effective depth is 50~100μm, and the ratio of the hardness peak of the hardened layer to the core hardness is 1.05~1.12. In particular, when C eq Not more than 0.63, Mn eq When it does not exceed 1.40, in the hot stamping state, the peak hardness of the hardened layer on the cutting edge is 675~695HV, the effective depth is 60~100μm, and the ratio of the peak hardness of the hardened layer to the core hardness is 1.06~1.09.

[0099] 3) T8, T8-1 and T8-2: Under the same alloy composition, T8-2 uses the lowest cutting power. The reduction in heat input makes it impossible to complete the cutting of hot stamping components. T8-1 uses an overly slow cutting speed, the effective depth of the hardened layer is too large, and the ratio of the peak hardness of the hardened layer to the core hardness is too large, resulting in a decrease in the hydrogen embrittlement performance of the component.

[0100] 4) T9 and T9-1: Under the same alloy composition, T9-1 uses a higher gas pressure. The ultra-fast cooling causes the hardened layer to obtain an extremely high hardness peak. The ratio of the hardness peak of the hardened layer to the hardness of the core is also too large, which worsens the hydrogen embrittlement performance of the component.

[0101] 5) CT1: All alloys are within the scope of the present invention, but their C eq 、M eq The Al / C mass ratio does not meet the alloy composition design requirements of the present invention, the elongation after fracture and the plane fracture toughness of the component are lower than those of the embodiment of the present invention, and the high C eq This also leads to a larger ratio of the hardness peak of the hardened layer to the core hardness and a larger effective depth of the hardened layer, and the component has a high risk of hydrogen embrittlement.

[0102] 6) CT2: Compared with CT1, M eq and Al / C mass ratio meet the design requirements of the alloy composition of the present invention, but the Mn content and C eq Although the elongation after fracture and the equivalent fracture strain of the component are higher than those of CT1, they are still slightly lower than those of the present invention. In addition, the effective depth of the hardened layer and the hardness peak are both relatively high. Therefore, the component still has a high risk of hydrogen embrittlement.

[0103] 7) CT3: Compared with CT1 and CT2, C eq and Al / C mass ratio meet the alloy composition design requirements of the present invention, but Mn eq The mechanical properties of the component basically meet the design requirements of the present invention, except that the elongation after fracture and the equivalent fracture strain are slightly lower, and the ratio of the peak hardness of the hardened layer to the core hardness is relatively high. Therefore, the component shows a medium hydrogen embrittlement risk.

[0104] 8) CT4: Compared with T6, the two alloys have similar C eq and Mn eq However, the carbon content of CT4 is lower and the Al / C mass ratio is also very low. Therefore, the strength of CT4 is lower and the equivalent fracture strain is also slightly lower. The T6 of the present invention has better strength and toughness.

[0105] In summary, reasonable alloy composition design and laser cutting process ensure that the hardened layer has a reasonable distribution and the toughness and strength of the matrix material are good, which makes the hot stamping formed components show good strength, toughness and resistance to hydrogen embrittlement.

[0106] The materials used in the present invention are all commercial materials and can be purchased from commercial sources.

[0107] 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 in the scope of protection of the present invention.

Claims

1. A hot stamping component, characterized in that: The martensite content of the steel plate matrix of the hot stamping formed component is ≥95%; The average hardness of the laser cutting edge hardened layer of the hot stamping formed component is below 720 HV, the effective depth of the cutting edge hardened layer does not exceed 120 μm, and the ratio of the hardness peak of the cutting edge hardened layer to the hardness of the steel plate substrate is not higher than 1.15; The tensile strength of the hot stamping formed component is ≥2050 MPa, and the elongation after fracture is ≥4.9%, wherein the tensile specimen is obtained from the hot stamping formed component by laser cutting.

2. The hot stamping formed component according to claim 1, characterized in that The martensite content of the steel plate matrix is ​​≥98%.

3. The hot stamping component according to claim 1, wherein: The notched specimen was tensile tested at tensile speeds of 0.01 mm / min and 10 mm / min, and the ratio of the fracture strength at the two tensile speeds was ≥0.90, wherein the notched specimen was obtained from the hot stamping formed component by laser cutting, and the notched specimen was in the shape of a long strip, with the semicircular notch symmetrically arranged on the long side, and the notch radius was 2±0.1 mm to 3±0.1 mm.

4. The hot stamping formed component according to claim 3, characterized in that The breaking strength ratio at the two stretching speeds is ≥0.

95.

5. A hot stamping formed component, characterized in that: The martensite content of the steel plate matrix of the hot stamping formed component is ≥95%; The average hardness of the laser cutting edge hardened layer of the hot stamping formed component is below 700 HV, the effective depth of the cutting edge hardened layer does not exceed 100 μm, and the ratio of the hardness peak of the cutting edge hardened layer to the hardness of the steel plate substrate is not higher than 1.12; The hot stamping formed component has a tensile strength of ≥1950 MPa and an elongation after fracture of ≥5.5%, wherein the tensile specimen is obtained from the hot stamping formed component by laser cutting; The equivalent fracture strain of the hot stamping formed component under plane strain is ≥0.175, wherein the notched specimen for the equivalent fracture strain test is obtained from the hot stamping formed component by wire cutting, the notched specimen is in the shape of a long strip, the semicircular notches are symmetrically arranged on the long side, and the notch radius is 5±0.1 mm.

6. The hot stamped component according to claim 5, wherein: The martensite content of the steel plate matrix is ​​≥98%.

7. The hot stamping component according to any one of claims 1 to 6, characterized in that: At least one surface of the steel plate substrate of the hot stamping component is covered with an aluminum alloy coating, the aluminum alloy coating has a thickness of 10 to 50 μm, and the steel plate substrate has a thickness of 0.7 to 2.5 mm.

8. The hot stamping component according to any one of claims 1 to 6, characterized in that: The steel plate matrix has the following composition, which contains, by mass percentage, C: 0.365-0.455%, Mn: 0.50-1.35%, Si: 0.01-0.60%, Cr: 0.01-0.60%, Al: 0.10-0.60%, B: 0.001-0.010%, P: 0.001-0.020%, N: 0.001-0.010%, S: 0.001-0.010%, and the balance is Fe and unavoidable impurities; wherein the carbon equivalent C of the steel plate matrix is eq ≤0.68, manganese equivalent Mn eq 1.00~1.60, Carbon equivalent C eq =C+Mn / 6+Cr / 5+V / 14+Mo / 4+Ni / 40+Si / 24, Manganese equivalent Mn eq =Mn+1.29×Cr+3.28×Mo+0.46×Cu+0.37×Ni+0.07×Si.

9. The hot stamped component according to claim 8, wherein: The sum of the mass percentages of Si, Cr and Al in the steel plate matrix is ​​not higher than 1.00%.

10. The hot stamped component according to claim 8, wherein The sum of the mass percentages of Si, Cr and Al in the steel plate matrix is ​​not higher than 0.85%.

11. The hot stamped component according to claim 8, wherein The mass ratio of aluminum to carbon in the steel plate matrix, Al / C, is not less than 0.

60.

12. The hot stamped component according to claim 8, wherein The mass ratio of aluminum to carbon in the steel plate matrix, Al / C, is not less than 0.

70.

13. The hot stamped component according to claim 8, wherein The steel plate matrix further comprises the following components: carbon equivalent C eq ≤0.65, manganese equivalent Mn eq It is 1.00~1.

45.

14. The hot stamped component according to claim 8, wherein The steel plate matrix further comprises the following components: carbon equivalent C eq ≤0.63, manganese equivalent Mn eq It is 1.00~1.

40.

15. The hot stamped component according to claim 8, wherein The components of the steel plate matrix are, by mass percentage, C: 0.365-0.435%, Mn: 0.50-1.35%, Si: 0.1-0.5%, Cr: 0.1-0.5%, Al: 0.2-0.5%, B: 0.001-0.010%, P: 0.004-0.010%, N: 0.001-0.010%, and S: 0.001-0.005%.

16. The hot stamped component according to claim 8, wherein The steel plate matrix further comprises at least one of V, Nb and Ti, wherein, in terms of mass percentage, V is 0.001-0.20%, and the sum of the mass percentages of Nb and Ti is 0.001-0.100%.

17. The hot stamped component according to claim 8, wherein: The steel plate matrix further comprises 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: 0.001-0.100%, Sn: 0.001-0.050%, Sb: 0.001~0.050%, As: 0.001~0.050%, Mg: 0.001~0.010%, Ca: 0.001~0.010%, Zr: 0.001~0.100%, O: 0.001~0.020%, REM: 0.001~0.050%, and the sum of the mass percentages of Ni, Mo, W, Cu, Co, Ta, Sn, Sb, As, Mg, Ca, Zr and REM is 0.001~0.500%.

18. The hot stamped component according to any one of claims 1 to 6, characterized in that: The laser cutting process of the hot stamping formed component is to perform laser cutting on the hot stamping formed component to obtain a hot stamping formed component with final contour features, wherein the laser cutting power is ≥800W, the cutting speed is ≥5m / min, and the gas pressure is ≤1bar.

Images