An ultra-high strength hot-stamped formed component

Abstract

The present application provides a hot-stamped component, the martensite content of the steel sheet substrate of the component is ≥ 95%; the average hardness of the laser cutting edge hardened layer of the component is ≤ 720 HV, the effective depth is ≤ 120 μm, the hardness peak value of the cutting edge hardened layer and the hardness ratio of the steel sheet substrate is ≤ 1.15; the tensile strength thereof is ≥ 2050 MPa and the elongation after fracture is ≥ 4.9%; the tensile test of the notched specimen is carried out at the tensile speed of 0.01 mm / min and 10 mm / min, the fracture strength ratio at the two speeds is ≥ 0.90. After further coating and baking, the average hardness of the laser cutting edge hardened layer of the component is ≤ 700 HV, the effective depth is ≤ 100 μm, the hardness peak value of the cutting edge hardened layer and the hardness ratio of the steel sheet substrate is ≤ 1.12; the tensile strength thereof is ≥ 1950 MPa and the elongation after fracture is ≥ 5.5%; the equivalent fracture strain in the flat state is ≥ 0.175.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel materials, and particularly relates to an ultra-high strength hot stamping forming component and a manufacturing method thereof. BACKGROUND

[0002] In order to obtain an ultra-high strength steel plate with a tensile strength exceeding 2000 MPa, a high carbon content design is the most effective and economical means. However, the increase of the carbon content means that the brittleness of the steel material will increase, the toughness will decrease, and the hydrogen embrittlement sensitivity will obviously increase. In particular, the steel plate with an aluminum alloy plating layer with a tensile strength exceeding 2000 MPa is a hot stamping forming component, and hydrogen embrittlement fracture is a particularly prominent problem in the production and manufacturing process. The production and manufacturing process of the hot stamping forming component mainly includes that a steel blank is heated and hot stamping formed to obtain a hot stamping forming semi-finished product, then a hot stamping forming component with a final contour is obtained through laser cutting, and the hot stamping forming component is transported to a welding workshop for assembly and body-in-white welding. The laser cutting edge of the hot stamping forming component after laser cutting is prone to hydrogen embrittlement problems, especially in the welding process, cracks are prone to occur in the stress concentration zone of the laser cutting edge, and then rapidly expand to form brittle fracture, thereby causing the hot stamping forming component to fail.

[0003] Chinese patent CN116287989A discloses a hot stamping steel material, an aluminum-silicon plating layer hot stamping steel plate, and an automobile structural member. The tensile strength of the steel material after hot stamping forming can exceed 2100 MPa. In order to obtain ultra-high strength and good toughness, the patent steel material composition adds a large amount of Cr, Mo, and Ni. The addition of these high hardenability alloy elements makes the steel material have extremely high hardenability, and the high hardenability will cause high phase transformation stress after the occurrence of the martensite phase change, and even form phase transformation micro-cracks in the microstructure, thereby causing the toughness of the hot stamping forming component to decrease sharply, and the hydrogen embrittlement risk of the part to increase obviously. In addition, Ni and Mo elements are expensive, and the addition of a high content of Mo and Ni will increase the cost of the steel material, which is difficult to meet the cost requirements of the automobile industry.

[0004] Chinese patent CN106399837A discloses a kind of ultrafine-grained hot stamping forming steel material, manufacturing process, hot stamping forming process and hot stamping forming component, the steel material has 1800~2200MPa tensile strength after hot stamping forming.The patent emphasizes the technical effect of micro-alloying precipitation on reducing the carbon content of martensite matrix and improving the toughness of hot stamping forming component, but it does not consider the adverse effects of adding high content of alloying elements on the laser cutting edge of hot stamping forming component, especially the addition of Mn and Mo, which increases the carbon equivalent and hardenability of the steel material, and makes the cutting edge produce high hardness martensite layer during laser cutting, thereby increasing the risk of hydrogen embrittlement of the cutting edge of the component.At the same time, high alloy design also causes the steel material to be prone to produce hard and brittle martensite during production, increasing the difficulty of processing and shape control, which is not conducive to production cost control.

[0005] Chinese patent CN115478227A discloses a kind of hot stamping forming steel plate, hot stamping forming component and steel plate manufacturing method, the tensile strength of the hot stamping forming component of the steel material can reach 1750~2100MPa.The patent improves the toughness of hot stamping forming steel material to avoid the generation of hard and brittle twin martensite in the structure, but the patent focuses on controlling the finish temperature of martensite transformation during alloy design, but the patent does not pay attention to the important influence of laser cutting on hydrogen embrittlement problem, laser cutting will cause the cutting edge of hot stamping forming component to form hard and brittle martensite layer, thereby reducing the ability of hot stamping forming component cutting edge to resist hydrogen embrittlement fracture.

[0006] In summary, although the existing technology can obtain a steel hot stamping forming component with tensile strength exceeding 2000MPa, the existing technology does not realize that the hydrogen embrittlement risk of steel hot stamping forming component, especially after laser cutting, is significantly increased, and the existing technology does not have a solution to effectively overcome the hydrogen embrittlement problem of steel hot stamping forming component.In order to meet the extremely high requirements of the current automobile industry for the mechanical properties of steel hot stamping forming component, it is urgent to develop a kind of hot stamping forming component with tensile strength exceeding 2000MPa and low hydrogen embrittlement sensitivity. SUMMARY

[0007] In order to solve the above technical problems, the present application provides a kind of ultra-high strength hot stamping forming component and its manufacturing method, the hot stamping forming component has more than 2000MPa tensile strength and low hydrogen embrittlement sensitivity.

[0008] In a first aspect, the present application discloses a hot-stamped component, wherein a martensite content of a steel plate substrate of the hot-stamped component is greater than or equal to 95%; an average hardness of a laser cutting edge hardened layer of the hot-stamped component is less than or equal to 720 HV; an effective depth of the laser cutting edge hardened layer is less than or equal to 120 μm; a hardness ratio of a hardness peak of the laser cutting edge hardened layer to a hardness of the steel plate substrate is less than or equal to 1.15; a tensile strength of the hot-stamped component is greater than or equal to 2050 MPa; and an elongation after fracture of the hot-stamped component is greater than or equal to 4.9%, wherein a tensile specimen is obtained from the hot-stamped component by laser cutting.

[0009] Preferably, the martensite content of the steel plate substrate is greater than or equal to 98%.

[0010] Preferably, a fracture strength ratio at two tensile speeds is greater than or equal to 0.90, wherein the two tensile speeds are 0.01 mm / min and 10 mm / min, the fracture strength ratio is obtained by tensile testing of a notched specimen, the notched specimen is obtained from the hot-stamped component by laser cutting, the notched specimen is in a strip shape, and semicircular notches are symmetrically arranged on both sides of a long side, and a notch radius is 2±0.1 mm to 3±0.1 mm.

[0011] Preferably, the fracture strength ratio at the two tensile speeds is greater than or equal to 0.95.

[0012] In a second aspect, the present application discloses a hot-stamped component, wherein a martensite content of a steel plate substrate of the hot-stamped component is greater than or equal to 95%; an average hardness of a laser cutting edge hardened layer of the hot-stamped component is less than or equal to 700 HV; an effective depth of the laser cutting edge hardened layer is less than or equal to 100 μm; a hardness ratio of a hardness peak of the laser cutting edge hardened layer to a hardness of the steel plate substrate is less than or equal to 1.12; a tensile strength of the hot-stamped component is greater than or equal to 1950 MPa; an elongation after fracture of the hot-stamped component is greater than or equal to 5.5%, wherein a tensile specimen is obtained from the hot-stamped component by laser cutting; and an equivalent fracture strain under plane strain of the hot-stamped component is greater than or equal to 0.175, wherein the equivalent fracture strain is obtained by testing a notched specimen, the notched specimen is obtained from the hot-stamped component by wire cutting, the notched specimen is in a strip shape, and semicircular notches are symmetrically arranged on both sides of a long side, and a notch radius is 5±0.1 mm.

[0013] Preferably, the martensite content of the steel plate substrate is greater than or equal to 98%.

[0014] Preferably, at least one surface of the steel plate substrate of the hot-stamped component in the first aspect and the second aspect is covered with an aluminum alloy plating layer, the aluminum alloy plating layer has a thickness of 10 μm to 50 μm, and the steel plate substrate has a thickness of 0.7 mm to 2.5 mm.

[0015] Preferably, the steel plate substrate of the first and second aspects of the present application has a composition consisting of, in mass percent, 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 consisting of Fe and unavoidable impurities; wherein the carbon equivalent C eq of the steel plate substrate is ≤0.68, and the manganese equivalent Mn eq is 1.00-1.60.

[0016] The carbon equivalent C eq of the steel plate substrate is C + Mn / 6 + Cr / 5 + V / 14 + Mo / 4 + Ni / 40 + Si / 24.

[0017] The manganese equivalent Mn eq of the steel plate substrate is Mn + 1.29xCr + 3.28xMo + 0.46xCu + 0.37xNi + 0.07xSi.

[0018] Further preferably, the sum of the mass percentages of Si, Cr, and Al in the steel plate substrate is not higher than 1.00%. More preferably, the sum of the mass percentages of Si, Cr, and Al in the steel plate substrate is not higher than 0.85%.

[0019] Further preferably, the mass ratio of Al to C, Al / C, in the steel plate substrate is not lower than 0.60. More preferably, the mass ratio of Al to C, Al / C, in the steel plate substrate is not lower than 0.70.

[0020] Further preferably, the steel plate substrate has a composition consisting of, in mass percent, 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 consisting of Fe and unavoidable impurities; wherein the carbon equivalent C eq of the steel plate substrate is ≤0.65, and the manganese equivalent Mn eq is 1.00-1.45. More preferably, the steel plate substrate has a composition consisting of, in mass percent, 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 consisting of Fe and unavoidable impurities; wherein the carbon equivalent C eq of the steel plate substrate is ≤0.63, and the manganese equivalent Mn eq is 1.00-1.40.

[0021] Further preferably, the steel plate substrate has a composition consisting of, in mass percent, 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 consisting of Fe and unavoidable impurities; wherein the carbon equivalent C eq of the steel plate substrate is ≤0.65, and the manganese equivalent Mn eq is 1.00-1.45. More preferably, the steel plate substrate has a composition consisting of, in mass percent, 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 consisting of Fe and unavoidable impurities; wherein the carbon equivalent C eq of the steel plate substrate is ≤0.63, and the manganese equivalent Mn eq is 1.00-1.40.

[0022] Further preferably, the component composition of the steel plate substrate further contains at least one of V, Nb and Ti, wherein the content of V is 0.001-0.20% by mass, and the total content of Nb and Ti is 0.001-0.100% by mass.

[0023] Further preferably, the component composition of the steel plate substrate further contains at least one of Ni, Mo, W, Cu, Co, Ta, Sn, Sb, As, Mg, Ca, Zr, O and REM, wherein the content of Ni is 0.01-0.30% by mass, the content of Mo is 0.01-0.20% by mass, the content of W is 0.01-0.20% by mass, the content of Cu is 0.01-0.20% by mass, the content of Co is 0.01-0.50% by mass, the content of Ta is 0.001-0.100% by mass, the content of Sn is 0.001-0.050% by mass, the content of Sb is 0.001-0.050% by mass, the content of As is 0.001-0.050% by mass, the content of Mg is 0.001-0.010% by mass, the content of Ca is 0.001-0.010% by mass, the content of Zr is 0.001-0.100% by mass, the content of O is 0.001-0.020% by mass, and the content of REM is 0.001-0.050% by mass, and the total content of Ni, Mo, W, Cu, Co, Ta, Sn, Sb, As, Mg, Ca, Zr and REM is 0.001-0.500% by mass.

[0024] Preferably, the laser cutting process of the hot-stamped component according to the first and second aspects of the present application is performed at a power of ≥800 W, a cutting speed of ≥5 m / min and a gas pressure of ≤1 bar.

[0025] Compared with the prior art, the present application has at least the following beneficial effects:

[0026] (1) The present application creatively finds in mass production practice that the laser cutting edge of a hot stamping formed component is a high-risk area for hydrogen embrittlement. In the welding process, the stress concentration area of the laser cutting edge is prone to crack due to hydrogen embrittlement and rapidly expand to form brittle fracture. It is found through research that the hydrogen embrittlement sensitivity of the hardening layer of the cutting edge is strongly related to the cold crack sensitivity of the steel itself, and the characteristics of the hardening layer of the laser cutting edge are also significantly affected by the laser cutting process. Therefore, the present application proposes to control the average hardness of the hardening layer of the laser cutting edge of the hot stamping formed component to be below 720 HV, the ratio of the hardness peak value to the average hardness of the steel plate base material is not greater than 1.15, and the effective depth of the hardening layer is not more than 120 μm, so as to realize the room temperature tensile test of the notched sample taken from the hot stamping formed component at a tensile speed of 0.01 mm / min and 10 mm / min, respectively. The fracture strength ratio at the two speeds is greater than 0.90, which ensures that the sample has a lower risk of hydrogen-induced delayed cracking after laser cutting. After baking, the average hardness of the hardening layer of the laser cutting edge is below 700 HV, the hardness ratio of the hardening layer of the laser cutting edge is not higher than 1.12, and the effective depth of the hardening layer is not more than 100 μm, which ensures that the hardening layer of the laser cutting edge does not deteriorate the fracture strain of the sample during automobile collision. The present application optimizes and controls the carbon equivalent design and the laser cutting process parameters to ensure that the cold crack sensitivity of the steel itself is low, and at the same time, the hardening layer of the laser cutting edge of the component has low hardness and small effective depth distribution characteristics, thereby significantly improving the hydrogen embrittlement sensitivity of the hot stamping formed component.

[0027] (2) The present application optimizes and adjusts the component design of the steel plate base and the preparation process of the hot stamping formed component. In the hot stamping state, the martensite content of the steel plate base of the hot stamping formed component is ≥95%, the tensile strength is ≥2050 MPa, and the elongation after fracture is ≥4.9%; after further baking or tempering treatment of the hot stamping formed component, the tensile strength of the hot stamping formed component is ≥1950 MPa, the elongation after fracture is ≥5.5%, and the equivalent fracture strain in the plane state is ≥0.175. The present application improves the component design of the steel plate base and the preparation process of the hot stamping formed component, so that the hot stamping formed component has a high tensile strength of 2000 MPa while significantly improving the hydrogen embrittlement sensitivity.

[0028] (3) Based on the research on the microstructure of steel, the application finds that Al has a larger atomic radius than Fe, and adding a certain amount of Al to the alloy will form a substitutional solid solution with Fe, which will expand the crystal lattice. In the case of high C design, the phase transition stress of martensite is reduced, and the toughness of the steel plate matrix is improved, which can significantly inhibit the rapid expansion of cracks after initiation. Based on this, the application effectively reduces the harm of hydrogen embrittlement problem to hot stamping forming components by controlling the Al / C ratio to be not less than 0.60, preferably not less than 0.70.

[0029] (4) In order to ensure that the steel has a high tensile strength of 2000 MPa or more, the C content is selected to be 0.365-0.455%. Under this high C content component design, the toughness of the steel is more sensitive to the cooling conditions of the hot stamping forming component. Higher cooling rate brings greater undercooling, which promotes the formation of twinned martensite, thereby damaging the toughness of the martensitic steel matrix. The application found in product development that if the hardenability of the steel is poor, it will lead to the generation 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, the application reasonably designs the hardenability of the steel, which can be represented by the Mn equivalent. The 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. Reasonable hardenability design not only ensures the proportion of martensite in the hot stamping forming component, but also inhibits the generation of twinned martensite, ensuring that the steel has a high tensile strength of 2000 MPa or more, while the martensitic steel plate matrix still has sufficient toughness. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings described below are only some embodiments described in the application, and those skilled in the art can also obtain other drawings from these drawings without creating any labor.

[0031] Figure 1 Schematic diagram of a notched tensile specimen for hydrogen embrittlement risk evaluation;

[0032] Figure 2 Schematic diagram of a notched specimen for equivalent fracture strain test under plane strain state;

[0033] Figure 3 Schematic diagram of specimen cutting edge hardening layer hardness test;

[0034] Figure 4 Schematic diagram of specimen core hardness test;

[0035] Figure 5 Coating metallographic photograph of the hot-stamping formed member of Example 1 of the present application;

[0036] Figure 6 Microstructure metallographic photograph of the hot-stamping formed member of Example 1 of the present application;

[0037] Figure 7 Coating metallographic photograph of the hot-stamping formed member of Example 2 of the present application;

[0038] Figure 8 Microstructure metallographic photograph of the hot-stamping formed member of Example 2 of the present application;

[0039] Figure 9 Microstructure SEM photograph of the hot-stamping formed member of Example 8 of the present application;

[0040] Figure 10 Microstructure SEM photograph of the hot-stamping formed member of Example 11 of the present application. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without any creative work fall within the scope of protection of the present application.

[0042] Unless otherwise specified, all the temperatures herein are in degrees Celsius, and all the percentages are weight percentages. Unless specifically indicated, each preferred scheme can be freely combined as needed. Those skilled in the art can understand that the data and various parameters recorded in the embodiments are only exemplary and do not constitute a limitation on the present application. Each component used in the following examples and comparative examples is a monomer or compound known in the art, and the equipment used is well known in the art, and can be obtained by commercial means or prepared by known technology.

[0043] The present application provides a hot-stamping formed member, the steel plate substrate of the hot-stamping formed member has a martensite content of ≥ 95%, preferably ≥ 98%.

[0044] The average hardness of the laser cut edge hardened layer of the hot stamped component is below 720 HV, preferably below 700 HV, further preferably below 680 HV; the effective depth of the laser cut edge hardened layer is not more than 120 pm, preferably not more than 100 pm, further preferably not more than 80 pm; the ratio of the hardness peak of the laser cut edge hardened layer to the hardness of the steel sheet substrate is not higher than 1.15, preferably not higher than 1.12, further preferably not higher than 1.10. The laser cut edge hardened layer characteristics of the hot stamped component directly affect the hydrogen embrittlement resistance of the component, therefore, the present application optimizes the design of the carbon equivalent C eq and optimizes the adjustment of the laser cutting process parameters, so as to ensure that the laser cut edge hardened layer has the above-mentioned low hardness and small effective depth distribution characteristics.

[0045] The tensile strength of the hot stamped component is ≥2050 MPa, and the elongation after fracture is ≥4.9%, wherein the tensile test sample is obtained from the hot stamped component by laser cutting.

[0046] The ratio of the breaking strength at a tensile speed of 0.01 mm / min to the breaking strength at a tensile speed of 10 mm / min is ≥0.90, preferably ≥0.95, wherein the notched test sample is obtained from the hot stamped component by laser cutting, the notched test sample is in the shape of a long strip, and a semicircular notch is symmetrically arranged on the left and right of the long side, and the notch radius is 2±0.1 mm to 3±0.1 mm. In addition, the hydrogen embrittlement risk of the hot stamped component is defined as follows in combination with the ratio of the breaking strength: the ratio ≥0.95 is low hydrogen embrittlement risk; 0.90≤the ratio<0.95 is medium hydrogen embrittlement risk; and the ratio<0.90 is high hydrogen embrittlement risk.

[0047] The tensile strength, the elongation after fracture and the hydrogen embrittlement risk of the hot stamping forming member in the hot stamping state are the technical effects directly shown by the present application after optimizing the alloy design of the steel plate substrate and adjusting the laser cutting process parameters. Especially the hydrogen embrittlement risk, in the case that the diffusible hydrogen content is not higher than 0.2 ppm, the slow tensile speed of 0.01 mm / min can make the hydrogen diffuse and gather in the hardened layer of the laser cutting edge, and then cause hydrogen embrittlement fracture to reduce the fracture stress, while under the fast tensile speed of 10 mm / min, the hydrogen does not have enough time to diffuse and gather, so 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 application and using the hot working process of the present application, the steel substrate of the present application has good toughness and excellent hardened layer characteristics of the cutting edge, and the fracture strength ratio of the tensile samples under the two tensile speeds is 0.90 to 0.95, which belongs to the medium hydrogen embrittlement risk, and even the fracture strength ratio of the samples under the two tensile speeds can be more than 0.95, reaching the low hydrogen embrittlement risk. Through testing, the hot stamping forming members in the hot stamping state of the present application all meet the medium hydrogen embrittlement risk, and the hydrogen embrittlement risk of the preferred schemes reaches the low hydrogen embrittlement risk.

[0048] In the actual production process, after the hot stamping forming member with the final contour characteristics is welded, it will also be subjected to white body coating electrophoresis, and the baking treatment temperature in the coating electrophoresis process is 150-180℃, and the time is 20-60 min. After the hot stamping forming member subjected to laser cutting is further subjected to coating baking or tempering treatment with the same effect, the average hardness of the hardened layer of the laser cutting edge of the hot stamping forming member is below 700 HV, preferably below 680 HV, and further preferably below 650 HV; the effective depth of the hardened layer of the cutting edge is not more than 100 μm, preferably not more than 80 μm, and further preferably not more than 60 μm; the hardness peak value of the hardened layer of the cutting edge is not higher than 1.12, preferably not higher than 1.10, and further preferably not higher than 1.08, compared with the hardness of the steel plate substrate. The tensile strength of the hot stamping forming member is ≥1950 MPa, the elongation after fracture is ≥5.5%, the equivalent fracture strain under plane strain is not less than 0.175, preferably not less than 0.185, and further preferably not less than 0.205.

[0049] After baking and painting, the hot stamping forming member is equivalent to being subjected to low-temperature tempering treatment, the hardness of the laser cutting edge hardened layer and the hardness of the martensite of the member are both decreased to a certain extent, and the effective depth of the hardened layer and the ratio of the peak hardness of the hardened layer to the hardness of the martensite substrate are also decreased. Considering that the body-in-white is subjected to baking and painting, and the material properties will change after baking and painting, it is necessary to detect the material properties of the hot stamping forming member after baking and tempering. After baking, due to the low-temperature tempering effect, the stress of the material is reduced, the toughness and plasticity of the martensite are improved, and the hydrogen embrittlement risk of the hot stamping forming member is significantly reduced.

[0050] Preferably, at least one surface of the steel plate substrate of the hot stamping forming member is covered with an aluminum alloy plating layer, the thickness of the aluminum alloy plating layer is 10-50 μm, and the thickness of the steel plate substrate is 0.7-2.5 mm.

[0051] Preferably, the steel plate substrate has the following component composition, containing, in 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 being Fe and inevitable impurities; wherein the carbon equivalent C eq of the steel plate substrate is ≤0.68, and the manganese equivalent Mn eq is 1.00-1.60.

[0052] The carbon equivalent C eq of the steel plate substrate is =C+Mn / 6+Cr / 5+V / 14+Mo / 4+Ni / 40+Si / 24.

[0053] The manganese equivalent Mn eq of the steel plate substrate is =Mn+1.29×Cr+3.28×Mo+0.46×Cu+0.37×Ni+0.07×Si.

[0054] Further preferably, the total mass percentage of Si+Cr+Al in the steel plate substrate is not higher than 1.00%, and more preferably, not higher than 0.85%.

[0055] Further preferably, the mass ratio of aluminum to carbon Al / C in the steel plate substrate is not lower than 0.60, and more preferably, the mass ratio of aluminum to carbon Al / C is not lower than 0.70.

[0056] Further preferably, the component composition of the steel plate substrate is further that the carbon equivalent C eq of the steel plate substrate is ≤0.65, and the manganese equivalent Mn eqThe value is 1.00~1.45. More preferably, the composition of the steel plate matrix is ​​further as follows: carbon equivalent C eq ≤0.63, manganese equivalent Mn eq The value is between 1.00 and 1.40.

[0057] More preferably, the composition of the steel plate matrix, by mass percentage, is: 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%, S: 0.001~0.005%.

[0058] More preferably, the composition of the steel plate matrix further contains at least one of V, Nb, and Ti, with V being 0.001 to 0.20% by mass percentage, and the sum of the mass percentages of Nb and Ti being 0.001 to 0.100%.

[0059] More preferably, the steel plate matrix further contains 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: 0.001~0.100%, 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%.

[0060] Specifically, C: 0.365~0.455%

[0061] 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%.

[0062] Mn: 0.50~1.35%

[0063] 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.

[0064] Si: 0.01~0.60%

[0065] 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%.

[0066] Cr: 0.01~0.60%

[0067] 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%.

[0068] Al: 0.10~0.60%

[0069] The addition of Al element can form AlN in combination with N element, which has the effect of fixing N, thereby preventing the combination of N and B and ensuring the effect of adding B to improve the hardenability. In addition, Al can also increase the martensite transformation temperature, which helps to reduce the generation of brittle twin martensite. However, when the addition amount of Al is too high, it will cause the problem of excessive crystallizer port resistance during continuous casting, which affects the production of casting blank, and increases the difficulty of controlling aluminum oxide inclusions in steel. Therefore, the content of Al in the present application is controlled between 0.10-0.60%, and further, it is controlled between 0.20-0.50%.

[0070] The total mass percentage of Si, Cr and Al is not higher than 1.00%, preferably not higher than 0.85%. Si, Cr and Al are all easily oxidized elements, and after being added too much in steel, they are easy to form surface oxides on the surface of hot-rolled steel coil, which are difficult to be pickled. Such surface oxides are difficult to be removed in the subsequent pickling and cold rolling process, thereby affecting the surface quality of the steel plate. At the same time, when coating and plating, the above elements also form external oxidation on the surface of the steel plate, causing plating defects and deteriorating the surface quality of the coated steel plate. Therefore, the total mass percentage of Si, Cr and Al in the present application is controlled to be not higher than 1.00%, preferably not higher than 0.85%.

[0071] B: 0.001-0.010%

[0072] B element is easy to segregate at the austenite grain boundary, which can inhibit the phase transformation of austenite to ferrite. Lower addition amount can significantly improve the hardenability of steel, and higher B addition will cause boron brittleness, which is not conducive to performance. Therefore, the content of B in the present application is set to 0.001-0.010%.

[0073] 0.001%≤V≤0.20%, 0.001%≤Nb+Ti≤0.100%

[0074] The addition of V, Nb and Ti elements can form carbides, nitrides or carbonitrides with carbon and nitrogen, and the uniform and fine precipitates can pin the austenite grain boundaries to refine the grains, which is beneficial to the improvement of the strength and toughness of the steel. Meanwhile, the precipitates are dispersedly distributed in the steel matrix, which can act as hydrogen traps to inhibit the diffusible hydrogen in the steel matrix, slow down the segregation of the diffusible hydrogen in the stress concentration area of the cutting edge of the hot stamping formed component, and reduce the hydrogen embrittlement sensitivity of the final hot stamping formed component. Therefore, the components in the application can be appropriately added. In particular, the V element can also be largely precipitated during the heating process of hot stamping, further consuming the C element in the matrix, and promoting the generation of dislocation type martensite. In addition, Ti has strong binding force with N, and the addition of a certain amount of Ti in the hot stamping steel can form TiN with the solid solution N in the steel, avoid the combination of N and B elements, and play a role in solid N and B to ensure the hardenability. However, the excessive addition of the above three micro-alloying elements will significantly increase the cost, and therefore, in the application, the content of V is controlled within the range of 0.001-0.20%, and the sum of the contents of Nb and Ti is controlled within the range of 0.001-0.100%.

[0075] P: 0.001-0.020%

[0076] P is an unavoidable impurity element in the steel. On the one hand, P can relatively cheaply improve the strength of the steel plate as a solid solution strengthening element. On the other hand, when the P content exceeds 0.0200%, P will segregate at the grain boundaries, thereby significantly causing adverse effects such as a decrease in toughness. Therefore, the upper limit of the P content is not greater than 0.020%, and preferably not greater than 0.010%. Alternatively, considering that reducing the P content to less than 0.001% will increase the smelting cost, therefore, the lower limit of the P content can be not less than 0.001%.

[0077] S: 0.001-0.010%

[0078] Like P, S is also an unavoidable impurity element in the steel, which will react with Mn in the steel to form MnS as inclusions in the steel. When the S content exceeds 0.010%, a large amount of MnS will significantly damage the ductility and toughness of the steel, and deteriorate the workability. Therefore, the upper limit of the S content is not greater than 0.010%, and preferably not greater than 0.005%. Similarly, alternatively, considering that reducing the S content to less than 0.001% will increase the smelting cost, therefore, the lower limit of the S content can be not less than 0.001%.

[0079] N: 0.001-0.010%

[0080] N is also an inevitable impurity element in steel, especially for steel containing B, which will significantly reduce the effect of B on improving hardenability, therefore, it is necessary to reduce the content of N as much as possible, and the content of N in the present application is controlled to be 0.001-0.010%.

[0081] Ni: 0.01~0.30%

[0082] Ni is a hardenability improving element, and Ni can improve the low temperature toughness of the steel, therefore, the lower limit value thereof can be optionally set to 0.01%, and a large amount of addition of Ni will inevitably cause the increase of alloy cost, and lead to the increase of C eq and Mn eq , and further improve the hydrogen embrittlement sensitivity of the laser cutting edge. Therefore, the content of Ni is set to be not more than 0.30%.

[0083] Mo: 0.01~0.20%

[0084] Mo can improve the hardenability of the steel plate and prevent temper brittleness, and preferably can be added by 0.01% or more, but excessive Mo addition will increase C eq and Mn eq , and further lead to the increase of hydrogen embrittlement sensitivity of the final hot stamping formed member, and cause the increase of cost, therefore, the content of Mo is set to be 0.20% or less.

[0085] W: 0.01~0.20%

[0086] The addition of W can significantly increase the strength of the steel plate, and the precipitates containing W can become the trapping point of hydrogen, therefore, it is preferred to add 0.01% or more. However, W is a strong carbide forming element, and when the content of W exceeds 0.20% or more, coarse and unevenly distributed carbides will be formed, which will seriously damage the performance of the hot stamping formed member, therefore, the content of W is set to be 0.20% or less.

[0087] Cu: 0.01~0.20%

[0088] Cu will improve the hardenability of the steel plate, and further improve the strength of the hot stamping formed member. In order to obtain this effect, the content of Cu is preferably set to be 0.01% or more. However, Cu is easy to segregate at the grain boundary and form a copper embrittlement phenomenon, which reduces the hot workability of the steel plate, therefore, the content of Cu is set to be 0.20% or less.

[0089] Co: 0.01~0.50%

[0090] The addition of Co can increase the martensite transformation temperature, favoring the self-tempering of the martensite and thus increasing its toughness. Therefore, the lower limit of the Co content can be set to 0.001%. However, Co is a rare and valuable element, and its excessive addition can increase the cost of the steel sheet, and Co can promote the graphitization of carbon in the steel and thus impair the toughness of the hot-stamped component. Therefore, the Co content can be set to 0.001%≤Co≤0.50%.

[0091] Ta: 0.001 ~ 0.10%

[0092] Ta, as a strong carbide-forming element, can form stable carbides with C and thus refine the grains, while increasing the strength and toughness of the steel sheet. Therefore, to obtain this effect, the Ta content is preferably not less than 0.001%. In addition, when the Ta content exceeds 0.10%, a large amount of carbides will be precipitated and easily agglomerate at the grain boundaries, resulting in a decrease in the toughness of the steel sheet. Therefore, the Ta content is set to not more than 0.10%.

[0093] Sn: 0.001 ~ 0.05%

[0094] The addition of Sn can refine the grains and improve the machinability of the steel sheet by cooperating with elements such as S. Therefore, the Sn content is preferably not less than 0.001%. However, Sn tends to segregate at the grain boundaries, increasing the brittleness of the steel. Therefore, the Sn content is set to not more than 0.05%.

[0095] Sb: 0.001 ~ 0.05%

[0096] Sb also has the effect of refining the grains. Therefore, to obtain this effect, the Sb content is preferably not less than 0.001%. However, excessive addition can cause segregation at the grain boundaries, adversely affecting the properties of the steel, particularly the plasticity and toughness. Therefore, the Sn content is set to not more than 0.05%.

[0097] As: 0.001 ~ 0.05%

[0098] As can strengthen the steel and thus increase its strength. However, As tends to accumulate at the grain boundaries, increasing the brittleness of the steel sheet and deteriorating the weldability. Therefore, the As content is set to 0.001≤As≤0.05%.

[0099] Mg: 0.001 ~ 0.010%, Ca: 0.001 ~ 0.010%

[0100] Mg and Ca are often used for deoxidation in steel material smelting, and can form sulfides with S to improve the number and morphology of inclusions in the steel sheet structure, so the addition amount thereof is preferably not less than 0.001%. However, when the contents of Mg and Ca are each more than 0.010%, large-sized inclusions are formed in the steel sheet structure, which causes damage to the toughness of the hot press-formed member, so the contents of Mg and Ca are set to not more than 0.01%.

[0101] Zr: 0.001 ~ 0.10%

[0102] Zr is a strong carbide-forming element, and has an effect similar to that of V, Nb, Ti, etc., and can refine grains and improve the low-temperature toughness of the steel sheet when added in a small amount, so the addition amount of Zr is preferably not less than 0.001%. However, when the addition amount of Zr exceeds 0.10%, large-sized carbides are formed in the steel sheet structure, which causes a decrease in the toughness of the hot press-formed member, so the content of Zr is set to 0.001 ≤ Zr ≤ 0.10%.

[0103] O: 0.001 ~ 0.02%

[0104] O forms coarse oxides in the steel, which is not good for the toughness of the hot press-formed member. Therefore, the lower the content of O is, the more preferable it is, so the content of O is controlled to 0.001 ~ 0.02%, and more preferably 0.006% or less.

[0105] REM: 0.001 ~ 0.05%

[0106] REM improves the deformability by suppressing the generation of oxides, and improves the toughness of the hot press-formed member. In order to obtain this effect, the content of REM is preferably set to 0.001% or more. However, the content of REM should be controlled to not more than 0.05% to avoid the generation of coarse oxides. In the present application, REM refers to a total of 17 elements including Sc, Y, and La-based elements, and the content of REM refers to the total of the contents of these elements.

[0107] Optionally, 0.001 ≤ Ni + Mo + W + Cu + Co + Ta + Sn + Sb + Ca + As + Mg + Ca + Zr + REM ≤ 0.50%, so as to effectively control the raw material cost of the steel.

[0108] C eq = C + Mn / 6 + Cr / 5 + V / 14 + Mo / 4 + Ni / 40 + Si / 24

[0109] 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-stamped components. 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-stamped 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-stamped 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.

[0110] Mn eq =Mn+1.29Cr+3.28Mo+0.46Cu+0.37Ni+0.07Si

[0111] 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 controls Mn. eq The value is 1.00~1.60, with Mn being the preferred choice. eq The value is 1.00~1.45, with Mn being more preferred. eq The value is between 1.00 and 1.40.

[0112] The Al / C mass percentage ratio shall not be less than 0.60, preferably not less than 0.70.

[0113] Martensite is a supersaturated interstitial solid solution formed by C dissolving in alpha-Fe, and the maximum solubility of C in austenite is 2.11%, and the solubility of C in alpha-Fe is only 0.0218%. In the process of austenite to martensite transformation, if the carbon atoms dissolved in the octahedral interstitial of austenite cannot diffuse out in the process of rapid quenching, they will still gather in the octahedral interstitial of alpha-Fe. Since the octahedral interstitial of alpha-Fe is small, only 0.154 times the radius of iron atom, therefore, C exceeding the maximum solubility of alpha-Fe will cause large lattice distortion, resulting in volume expansion and phase transformation stress. With the increase of C content, more C will further expand the lattice, resulting in more severe volume expansion and increased material phase transformation stress. The present inventor realizes that Al has a larger atomic radius than Fe, and in the case of high C design, adding a certain amount of Al in the alloy has a displacement effect on Fe, which will expand the crystal lattice, reduce the lattice distortion caused by the interstitial solubility of C atoms in martensite, and reduce the phase transformation stress of martensite, thereby improving the toughness of martensite. Therefore, the present application hopes to control the mass percentage ratio of Al / C to be not less than 0.60, preferably not less than 0.70.

[0114] Preferably, the laser cutting process of the hot-stamped formed component is laser cutting the hot-stamped formed component to obtain a hot-stamped formed component having a final profile feature, wherein the laser cutting has a power of > 800 W, a cutting speed of > 5 m / min, and a gas pressure of < 1 bar.

[0115] The hot-stamped formed component disclosed in the present application can be obtained by the following preparation method, which comprises the following steps:

[0116] S1. Steelmaking: weighing raw materials according to the components of the steel plate proposed in the present application, smelting the raw materials by a vacuum induction furnace, an electric furnace or a converter, and obtaining a billet meeting the component requirements of the steel plate base material through continuous casting or continuous casting and rolling;

[0117] S2. Hot rolling: heating the billet to above 1100 DEG C and keeping for more than 2 hours, then completing different passes of hot rolling at 800 DEG C to 1250 DEG C, and coiling at 500 DEG C to 700 DEG C to form a hot-rolled steel coil; pickling the hot-rolled steel coil to remove the oxide skin generated in the hot rolling process;

[0118] S3. Cold rolling: cold rolling the pickled hot-rolled steel coil, and the cold rolling reduction is 30% to 70%, to obtain a cold-rolled steel coil with a thickness of 0.7 to 2.5 mm;

[0119] S4. Annealing or plating: annealing or plating the cold-rolled steel coil, if plating is adopted, the plating layer is an aluminum alloy plating layer, the Al content in the plating layer is more than 50%, and the plating layer thickness is 10 to 50 microns;

[0120] S5. austenitizing: the cold-rolled steel coil after annealing or plating treatment is processed into a steel plate blank, heated to 850-950℃ and kept for 3-10 min to obtain a completely austenitized blank of the steel plate to be stamped, and the dew point of the heating zone during heating and keeping is kept below -10℃, preferably below -15℃, and further preferably below -20℃, so as to reduce the diffusible hydrogen content in the hot-stamped formed component;

[0121] S6. stamping and quenching: the above-mentioned blank of the steel plate to be stamped is transferred to a forming die for stamping and forming, the transfer time is not more than 15 s, and the temperature of the blank of the steel plate to be stamped placed on the die is not less than 750℃, and the hot-stamped formed component is obtained after pressure quenching and ejection from the die;

[0122] S7. laser cutting: the above-mentioned hot-stamped formed component is laser cut to obtain a hot-stamped formed component with final profile characteristics, wherein the power of laser cutting is above 800W, the cutting speed is not less than 5m / min, and the gas pressure is not higher than 1bar.

[0123] In addition, after the hot-stamped formed component with final profile characteristics obtained by laser cutting is welded, it will also be subjected to a white body coating electrophoresis, and the baking treatment temperature during the electrophoresis process is 150-180℃, and the time is 20-60min.

[0124] The following is an explanation of the performance test in the examples.

[0125] Diffusible hydrogen content testing and hydrogen embrittlement risk assessment

[0126] The hot-stamped formed component containing a certain hydrogen content is obtained by hot stamping and forming in a heating furnace with dew point control function, and the hydrogen content is tested by using a Brook diffusible hydrogen analyzer (referred to as TDS). Subsequently, a notched sample is machined from the hot-stamped formed component by laser cutting, and a schematic diagram of the notched sample is shown in Figure 1 The notched sample is a long strip 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 left and right of the long side, and the notch radius can be set to 2.0±0.1-3.0±0.1 mm according to the difference of the stress concentration factor, and the corresponding stress concentration factor is 1.9±0.02-1.5±0.02. Too large or too small notch radius does not meet the test requirements. In the following examples and comparative examples of the present application, the selected notch radius is 2.5±0.1 mm, and the corresponding stress concentration factor is 1.8±0.02. The length of the notched sample is selected to be 80 mm, and the width is selected to be 12.5 mm.

[0127] After that, the notched sample is respectively subjected to room temperature stretching at a stretching speed of 0.01 mm / min and 10 mm / min, the fracture strength of the material at the two different speeds is recorded, the fracture strength ratio is calculated by taking the average value of at least 3 groups of each notched sample, if the ratio is greater than or equal to 0.95, it is determined as low hydrogen embrittlement risk; if the ratio is greater than or equal to 0.9 but less than 0.95, it is determined as medium hydrogen embrittlement risk; if the ratio is less than 0.9, it is determined as high hydrogen embrittlement risk.

[0128] Equivalent fracture strain testing in plane strain state

[0129] The hot stamping forming member is processed into a long strip-shaped notched sample with a size of 140*20 mm (length*width) by wire cutting, a semicircular notch is symmetrically arranged on the left and right of the long side, the notch radius R is 5±0.1 mm, and the sample schematic diagram is as shown in Figure 2 Subsequently, a standard test stretcher is used for testing, the stretching rate is 0.3 mm / min, wherein the thickness h0 of the original sample at the notch before testing is stretched, the thickness h of the sample at the stretching fracture is tested, and the equivalent fracture strain ε is calculated by using the following formula. In order to avoid the influence of sample processing on thickness thinning, the fracture thickness measurement position is selected to be the 1 / 2 width area close to the center, and the test value is the average value of at least 5 groups. The notched sample processing and testing mode of each embodiment and comparative example of the present application are carried out in this way.

[0130] Equivalent fracture strain calculation formula:

[0131] Cut edge hardbanding layer characterization testing

[0132] Referring to Figure 3 and Figure 4 , Figure 3 is a hardness test schematic diagram of the cutting edge hardened layer, Figure 4 is a core hardness test schematic diagram. The hardness test of the cutting edge hardened layer starts from the position about 10 μm of the sample edge, 3 rows of points are tested in parallel, each row of points is tested along the straight line with an angle of 30° with the sample edge into the substrate, the load is 50 g, and the spacing of the load points is 40 μm. In addition, the depth of the cutting edge hardened layer is defined as the distance between the edge and the first detection point whose hardness value decreases to the average value of the core hardness ± 20. The average hardness of the cutting edge hardened layer is the average value of all hardness test points within the hardened layer depth (including the first detection point whose hardness value decreases to the average value of the core hardness ± 20 from the edge). The hardness peak value of the cutting edge hardened layer is the maximum value of all hardness test points within the hardened layer depth (including the first detection point whose hardness value decreases to the average value of the core hardness ± 20 from the edge). The hardness of the steel plate substrate is the average value of 5 points of the core hardness test.

[0133] The present application will be described in more detail below with reference to exemplary embodiments. The following examples or experimental data are intended to exemplify the application and to enable those skilled in the art to make and use the application. It is to be understood that the examples or experimental data do not limit the application, which is defined solely by the claims.

[0134] Example 1

[0135] A hot-stamped formed component is prepared by a preparation method comprising the following steps:

[0136] S1. Steelmaking: smelting according to the composition of T1 in Table 1 by vacuum induction furnace, and obtaining a billet satisfying the composition of T1 in Table 1 by continuous casting forging;

[0137] S2. Hot rolling: heating the billet to 1100°C for 2 hours, then completing the hot rolling of different passes at 800°C, and coiling at 500°C to form a hot-rolled coil; pickling the hot-rolled coil to remove the oxide skin generated during the hot rolling process;

[0138] S3. Cold rolling: cold rolling the pickled hot-rolled coil with a cold rolling reduction of 60% to obtain a cold-rolled coil with a thickness of 1.2 mm;

[0139] S4. Coating: coating the cold-rolled coil, the coating layer being an aluminum alloy coating layer with an Al content of 50% and a coating layer thickness of 18 μm;

[0140] S5. Austenitizing: processing the coated cold-rolled coil into a steel plate blank, heating to 930°C and holding until complete austenitization to obtain a steel plate blank to be stamped, the heating and holding time being 10 min, and the dew point of the heating zone being maintained at -10°C during the heating and holding process;

[0141] S6. Stamping and quenching: transferring the steel plate blank to be stamped to a forming die for stamping and forming, the transfer time being 15 s, the temperature of the steel plate blank to be stamped on the die being 750°C, and the pressure holding and quenching cooling to below 200°C to obtain a hot-stamped formed component;

[0142] S7. Laser cutting: laser cutting the hot-stamped formed component to obtain a hot-stamped formed component with final profile characteristics, wherein the power of the laser cutting is 1000 W, the cutting speed is 7 m / min, and the gas pressure is 0.55 bar.

[0143] To simulate the baking treatment of the hot-stamped formed component after completing the welding of the body-in-white during the electrophoresis process of the body-in-white coating, the hot-stamped formed component with final profile characteristics after laser cutting is further subjected to baking treatment at a temperature of 150°C for 60 min.

[0144] In order to distinguish the hot-stamped forming members before and after the baking treatment, the hot-stamped forming member with the final profile feature after the laser cutting in step S7 is defined as the hot-stamped state hot-stamped forming member, and the hot-stamped forming member after the baking treatment is defined as the baked state hot-stamped forming member.

[0145] In order to meet the requirements of sample size for performance tests such as room temperature tensile test, metallographic test, hardening layer test, diffusible hydrogen content test and hydrogen embrittlement risk evaluation, the hot-stamped state hot-stamped forming member and the baked state hot-stamped forming member are processed according to the requirements of performance tests, and the performance tests are carried out respectively.

[0146] Examples 2-12 (T2-T9) and Comparative Examples 1-4 (CT1-CT4)

[0147] The process steps of the preparation method of the hot-stamped forming members in Examples 2-12 and Comparative Examples 1-4 are exactly the same as those in Example 1, and the only difference is the alloy composition of the steel plate substrate and the specific parameters of the heat treatment process and the laser cutting process. The alloy composition and the specific parameters are shown in Table 1-3 respectively. It should be pointed out that the laser cutting process corresponding to T8-2 cannot cut the hot-stamped forming member through, because the laser power is too low, so the hot-stamped forming member with the final profile cannot be obtained.

[0148] Table 1 Chemical composition of steel plate substrate (wt.%, the balance is Fe and impurities)

[0149]

[0150] Table 2 Heat treatment process of steel blanks with different alloy compositions

[0151]

[0152] Table 3 Laser cutting process of different hot-stamped forming members

[0153]

[0154] Performance testing and results analysis

[0155] The hot stamping state and baked state hot stamping formed components prepared from the examples 1-12 and comparative examples 1-4 were respectively processed into samples meeting the size requirements of the performance tests of room temperature tensile, metallographic detection, hardening layer detection, diffusible hydrogen content test and hydrogen embrittlement risk evaluation, and were respectively subjected to diffusible hydrogen content test, hydrogen embrittlement risk evaluation, equivalent fracture strain test, and cutting edge hardening layer characteristic test. The sample size requirements, test and evaluation methods are described above in the description of the performance test of the examples, and the test results are shown in Tables 4-6. Tables 4 and 5 respectively show the performance test results and cutting edge hardening layer distribution characteristics of the hot stamping formed component samples under different alloy components and heat treatment processes, and Table 6 shows the corresponding hydrogen embrittlement risk evaluation results. It should be noted that the diffusible hydrogen content and internal stress of the hot stamping formed component after baking treatment are reduced, and the toughness of the martensitic matrix structure is improved, and the hydrogen embrittlement risk of the hot stamping formed component will be reduced, therefore, the hydrogen embrittlement risk evaluation of the examples and comparative examples of the present application is only performed on the hot stamping state samples, and the hydrogen embrittlement risk evaluation of the baked state samples is not performed.

[0156] Table 4 Performance test results of hot stamping formed components under different alloy components and heat treatment processes

[0157]

[0158] Table 5 Cutting edge hardening layer distribution characteristics of hot stamping formed components under different alloy components and heat treatment processes

[0159]

[0160] Figures 5-6 and Figures 7-8 are respectively metallographic photos of the plated layer and microstructure of the hot stamping formed component in examples 1 and 2 of the present application, and Figure 9 and Figure 10 respectively show SEM photos of the microstructure of the hot stamping formed component in examples 8 and 11. It can be seen that, Figure 5 and Figure 7 the plated layer thickness of the hot stamping formed component in examples 8 and 11 is respectively 18.8 μm and 34.0 μm, and Figure 6 , Figures 8-10The microstructure of the hot stamping component steel plate substrate is mainly martensite structure, and the area ratio is more than 95%, thereby ensuring that the hot stamping component prepared by the application has super-high strength. In addition, by observing the microstructure of the hot stamping component steel plate substrate in other embodiments, similar microstructures as in embodiments 1, 2, 8 and 11 are also present, and the microstructure of the steel plate substrate is almost all martensite. By measuring the area ratio of the martensite structure in the test area, the martensite content in the steel plate substrate also reaches 95% or more. Since the metallographic photos or SEM photos of other embodiments are extremely similar to those of embodiment 1 Figure 6 or embodiment 8, Figure 9 the microstructure photos of other embodiments are not repeated here.

[0161] Table 6 Hydrogen embrittlement risk evaluation

[0162]

[0163] From the above test results, it can be seen that:

[0164] 1) T1-T9 hot stamping components: C eq 0.59-0.67, Mn eq 1.17-1.60, the mass percentage ratio of Al / C is 0.63-1.22, the tensile strength of the hot stamping state is 2052-2198 MPa, the elongation after fracture is 4.9-6.3%, the tensile strength of the baking state is 1950-2074 MPa, the elongation after fracture is 5.5-7.1%, the equivalent fracture strain is 0.175-0.229, and the hydrogen embrittlement risk of the hot stamping state is low or medium risk, indicating that the hot stamping component obtained by the alloy design and laser cutting process of the application has good strength and toughness and hydrogen embrittlement resistance. In particular, as C eq and Mn eq decrease, when C eq is not more than 0.65 and Mn eq 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 hydrogen embrittlement risk. Further, when C eq is not more than 0.63 and Mn eq is not more than 1.4, the equivalent fracture strain of the component is not less than 0.205, and the toughness is further improved, and it can be expected that the hydrogen embrittlement resistance is also further improved. In addition, it is found by comparison that when the Al / C mass ratio is not less than 0.70, the equivalent fracture strain of the component is not less than 0.191, which also reflects the effect of improving the toughness of the component.

[0165] 2) T1-T9 hot stamping components: in hot stamping state, the peak hardness of the hardened layer of the cut edge is 675-718 HV, the effective depth is 60-110 pm, and the ratio of the peak hardness of the hardened layer to the core hardness is 1.06-1.14; in baked state, the peak hardness of the hardened layer of the cut edge is 654-699 HV, the effective depth is 50-100 pm, and the ratio of the peak hardness 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 not more than 1.40, in hot stamping state, the peak hardness of the hardened layer of the cut edge is 675-695 HV, the effective depth is 60-100 pm, and the ratio of the peak hardness of the hardened layer to the core hardness is 1.06-1.09.

[0166] 3) T8, T8-1 and T8-2: under the same alloy composition, T8-2 adopts the lowest cutting power, and the reduction of heat input causes the hot stamping component to fail to complete cutting, and T8-1 adopts too slow cutting speed, so that 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, thereby causing the hydrogen embrittlement performance of the component to decrease.

[0167] 4) T9 and T9-1: under the same alloy composition, T9-1 adopts a larger gas pressure, and the ultrafast cooling causes the hardened layer to obtain an extremely high peak hardness, and the ratio of the peak hardness of the hardened layer to the core hardness is also too large, thereby worsening the hydrogen embrittlement performance of the component.

[0168] 5) CT1: the alloys are all within the scope of the application, but the C eq , Mn eq and Al / C mass ratios all do not meet the requirements of the alloy composition design of the application, and the elongation after fracture and the plane fracture toughness of the component are both lower than those of the embodiments of the application, and the high C eq also causes the ratio of the peak hardness of the hardened layer to the core hardness to be too large and the effective depth of the hardened layer to be too large, and the component has a high hydrogen embrittlement risk.

[0169] 6) CT2: compared with CT1, the C eq , Mn eq and Al / C mass ratios all meet the requirements of the alloy composition design of the application, but the Mn content and C eq are too high, 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 application, and the effective depth of the hardened layer and the peak hardness are both too high, and therefore, the component still has a high hydrogen embrittlement risk.

[0170] 7) CT3: compared with CT1 and CT2, the C eqThe mechanical properties of the component are generally satisfactory, except that the elongation after fracture and the equivalent fracture strain are slightly low, and the ratio of the peak hardness of the hardened layer to the core hardness is high. Therefore, the component exhibits a medium risk of hydrogen embrittlement.

[0171] 8) CT4: Compared to T6, the two alloys have similar carbon content. eq and Mn eq However, CT4 has a lower carbon content and an extremely low Al / C mass ratio. Therefore, CT4 has lower strength and slightly lower equivalent fracture strain. The T6 of the present invention has superior strength and toughness.

[0172] In summary, a reasonable alloy composition design and laser cutting process ensure that the hardened layer has a reasonable distribution and that the matrix material exhibits good toughness and strength, thereby enabling the hot-stamped components to exhibit good strength, toughness, and resistance to hydrogen embrittlement.

[0173] All materials used in this invention are commercially available and can be purchased from retail sources.

[0174] 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 hot-stamped formed member, characterized by, The martensite content of the steel plate substrate of the hot-stamped formed component is ≥ 95%; The average hardness of the laser-cut edge hardened layer of the hot-stamped formed component is ≤ 720 HV, the effective depth of the laser-cut edge hardened layer is ≤ 120 μm, and the ratio of the hardness peak value of the laser-cut edge hardened layer to the hardness of the steel plate substrate is ≤ 1.15; The tensile strength of the hot-stamped formed component is ≥ 2050 MPa, and the elongation after fracture is ≥ 4.9%, wherein the tensile test sample is obtained from the hot-stamped formed component by laser cutting; The steel plate substrate has the following component composition, containing, in 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 being Fe and inevitable impurities; wherein the carbon equivalent C eq of the steel plate substrate is ≤0.68, and the manganese equivalent Mn eq is 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 x Cr + 3.28 x Mo + 0.46 x Cu + 0.37 x Ni + 0.07 x Si.

2. The hot-stamped formed member according to claim 1, characterized by The martensite content of the steel plate substrate is ≥ 98%.

3. The hot-stamped formed member according to claim 1, characterized by The ratio of the fracture strength at the two tensile speeds is ≥ 0.90, wherein the notched test sample is obtained from the hot-stamped formed component by laser cutting, the notched test sample is in a strip shape, and semicircular notches are symmetrically arranged on the left and right of the long side, and the notch radius is 2±0.1 mm to 3±0.1 mm.

4. The hot-stamped formed member according to claim 3, characterized by The ratio of the fracture strength at the two tensile speeds is ≥ 0.

95.

5. A hot-stamped formed member characterized by, The martensite content of the steel plate substrate of the hot-stamped formed component is ≥ 95%; The average hardness of the laser-cut edge hardened layer of the hot-stamped formed component is ≤ 700 HV, the effective depth of the laser-cut edge hardened layer is ≤ 100 μm, and the ratio of the hardness peak value of the laser-cut edge hardened layer to the hardness of the steel plate substrate is ≤ 1.12; The tensile strength of the hot-stamped formed component is ≥ 1950 MPa, and the elongation after fracture is ≥ 5.5%, wherein the tensile test sample is obtained from the hot-stamped formed component by laser cutting; The equivalent fracture strain of the hot-stamped formed component under plane strain is ≥ 0.175, wherein the notched test sample for the equivalent fracture strain test is obtained from the hot-stamped formed component by wire cutting, the notched test sample is in a strip shape, and semicircular notches are symmetrically arranged on the left and right of the long side, and the notch radius is 5±0.1 mm; The steel plate substrate has the following component composition, containing, in 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 being Fe and inevitable impurities; wherein the carbon equivalent C eq of the steel plate substrate is ≤0.68, and the manganese equivalent Mn eq is 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 x Cr + 3.28 x Mo + 0.46 x Cu + 0.37 x Ni + 0.07 x Si.

6. The hot-stamped formed member according to claim 5, characterized by The martensite content of the steel plate substrate is ≥ 98%.

7. The hot-stamped 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-stamped formed component is covered with an aluminum alloy plating layer, the thickness of the aluminum alloy plating layer is 10-50 μm, and the thickness of the steel plate substrate is 0.7-2.5 mm.

8. The hot-stamped component according to any one of claims 1 to 6, characterized in that The sum of the mass percentages of Si, Cr and Al in the steel plate substrate is ≤ 1.00%.

9. The hot-stamped component according to any one of claims 1 to 6, characterized in that The sum of the mass percentages of Si, Cr and Al in the steel plate substrate is ≤ 0.85%.

10. The hot-stamped component according to any one of claims 1 to 6, characterized in that The mass ratio of Al / C of aluminum and carbon in the steel plate substrate is ≥ 0.

60.

11. The hot-stamped component according to any one of claims 1 to 6, characterized in that The mass ratio of Al / C of aluminum and carbon in the steel plate substrate is ≥ 0.

70.

12. The hot-stamped component according to any one of claims 1 to 6, characterized in that The component composition of the steel plate substrate is further such that the carbon equivalent C eq ≤0.65, the manganese equivalent Mn eq is 1.00 to 1.

45.

13. The hot-stamped component according to any one of claims 1 to 6, characterized in that The component composition of the steel plate substrate is further such that the carbon equivalent C eq ≤0.63, the manganese equivalent Mn eq is 1.00 to 1.

40.

14. The hot-stamped component according to any one of claims 1 to 6, characterized in that The component composition of the steel plate substrate, in terms of mass percentage, is 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%.

15. The hot-stamped component according to any one of claims 1 to 6, characterized in that The component composition of the steel plate substrate further contains at least one of V, Nb and Ti, wherein V is 0.001-0.20% by mass, and the sum of Nb and Ti is 0.001-0.100% by mass.

16. The hot-stamped component according to any one of claims 1 to 6, characterized in that The component composition of the steel plate substrate further contains at least one of Ni, Mo, W, Cu, Co, Ta, Sn, Sb, As, Mg, Ca, Zr, O and REM, wherein Ni is 0.01-0.30% by mass, Mo is 0.01-0.20% by mass, W is 0.01-0.20% by mass, Cu is 0.01-0.20% by mass, Co is 0.01-0.50% by mass, Ta is 0.001-0.100% by mass, Sn is 0.001-0.050% by mass, Sb is 0.001-0.050% by mass, As is 0.001-0.050% by mass, Mg is 0.001-0.010% by mass, Ca is 0.001-0.010% by mass, Zr is 0.001-0.100% by mass, O is 0.001-0.020% by mass, and REM is 0.001-0.050% by mass, and the sum of Ni, Mo, W, Cu, Co, Ta, Sn, Sb, As, Mg, Ca, Zr and REM is 0.001-0.500% by mass.

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

Images