STEEL FOR HOT STAMPING, HOT STAMPING PROCESS AND HOT STAMPED COMPONENT

Abstract

The present invention presents a steel for hot stamping, a hot stamping process and a hot stamped component. The steel for hot stamping in weight percentage contains C: 0.2-0.4%, Si: 0-0.8%, Al: 0-1.0%, B: 0-0.005%, Mn: 0.5-3.0%, Mo: 0-1%, Cr: 0-2%, Ni: 0-5%, V: 0-0.4%, Nb: 0-0.2%, Ti: 0.01%, and impurity elements such as P, S, N unavoidable during smelting, wherein 29*Mo+16*Mn+14*Cr+5.3*Ni30% is satisfied when B0.0005%, and 0.4-1.0% Al is contained when 0.0005%<B0.005%.

Claims

1. A steel for hot stamping, wherein the steel for hot stamping in weight percentage contains C: 0.2-0.4%, Si: 0-0.8%, Al: 0.6%Al1.0%, B: 0.0005%<B0.005%, Mn: 0.5-3.0%, Mo: 0-1%, Cr: 0-2%, Ni: 0-5%, V: 0-0.4%, Nb: 0-0.2%, Ti: 0.01%, and impurity elements.

2. (canceled)

3. The steel for hot stamping according to claim 1, wherein in weight percentage the C content is 0.2-0.4%, the Si content is 0.1-0.5%, the Mn content is 0.8-2.2%, the Cr content is 0.1-0.5%, the B content is 0.0005-0.004%, the Ti content is 0-0.01% and the Al content is 0.6%Al1.0%.

4. The steel for hot stamping according to claim 1, wherein in weight percentage the C content is 0.3-0.4%, the Si content is 0.1-0.8%, the Mn content is 0.8-2.2%, the Cr content is 0-0.5%, the B content is 0.0005-0.004%, the Ti content is 0-0.01%, and the Al content is 0.6%Al0.9%.

5. The steel for hot stamping according to claim 1, wherein the steel for hot stamping is a hot-rolled steel sheet, a hot-rolled pickled sheet, a cold-rolled steel sheet, or a steel sheet with a coating.

6. A hot stamping process, comprising the following steps: a steel austenitizing step, in which the steel for hot stamping according to claim 1 or a pre-formed component of the steel for hot stamping is provided, and heated to 800-950 C. and then kept at this temperature for 1 to 10000 s; a steel transferring step, in which the steel or its pre-formed component after the above-mentioned steel austenitizing step is transferred to a hot stamping die, with the temperature of the steel maintained at 550 C. or higher during the transferring; and a hot stamping step, in which stamping, pressure holding and cooling are carried out, so that the steel in the die is cooled to 250 C. or lower at an average cooling rate of 10 C./s or higher, ensuring that the temperature of a component when the component exits the die is 250 C. or lower.

7. The hot stamping process according to claim 6, further comprising a tempering step after the hot stamping step, in which the formed component is heated to 150-200 C. and kept at this temperature for 10-40 minutes, or the formed component is heated to 150-280 C. in any manner and then kept at this temperature for 0.5-120 minutes, and then cooled in any manner.

8. The hot stamping process according to claim 7, wherein the tempering step is carried out by a painting process.

9. A hot stamped component, wherein the hot stamped component in weight percentage contains C: 0.2-0.4%, Si: 0-0.8%, Al: 0.6%Al1.0%, B: 0.0005%<B0.005%, Mn: 0.5-3.0%, Mo: 0-1%, Cr: 0-2%, Ni: 0-5%, V: 0-0.4%, Nb: 0-0.2%, Ti:0.01%, and impurity elements unavoidable during smelting.

10. (canceled)

11. The hot stamped component according to claim 9, wherein in weight percentage the C content is 0.24-0.4%, the Si content is 0.1-0.5%, the Mn content is 0.8-2.2%, the Cr content is 0.1-0.5%, the B content is 0.0005-0.004%, the Ti content is 0-0.01% and the Al content is 0.6%Al1.0%.

12. The hot stamped component according to claim 9, wherein in weight percentage the C content is 0.3-0.4%, the Si content is 0.1-0.8%, the Mn content is 0.8-2.2%, the Cr content is 0-0.5%, the B content is 0.0005-0.004%, the Ti content is 0-0.01% and the Al content is 0.6%Al0.9%.

13. The steel for hot stamping according to claim 3, wherein the steel for hot stamping is a hot-rolled steel sheet, a hot-rolled pickled sheet, a cold-rolled steel sheet, or a steel sheet with a coating.

14. The steel for hot stamping according to claim 4, wherein the steel for hot stamping is a hot-rolled steel sheet, a hot-rolled pickled sheet, a cold-rolled steel sheet, or a steel sheet with a coating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 shows the 20 C. impact fracture morphology of the exemplary steel for the present invention, NT1 steel.

[0038] FIG. 2 shows the 40 C. impact fracture morphology of the exemplary steel for the present invention, NT1 steel.

[0039] FIG. 3 shows the impact fracture morphology of the comparative steel, CS1 steel, when the impact data are normal.

[0040] FIG. 4 shows the impact fracture morphology of the comparative steel, CS1 steel, when the impact data are abnormal.

[0041] FIG. 5 shows the impact fracture morphology of the comparative steel, CS2 steel, when the impact data are abnormal.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0042] The technical solutions of the present invention will be described below in conjunction with the specific embodiments.

[0043] The steel for hot stamping of the present invention in weight percentage contains C: 0.2-0.4%, Si: 0-0.8%, Al: 0-1.0%, B: 0-0.005%, Mn: 0.5-3.0%, Mo: 0-1%, Cr: 0-2%, Ni: 0-5%, V: 0-0.4%, Nb: 0-0.2%, Ti: 0.01%, and impurity elements such as P, S, N unavoidable during smelting, wherein 29*Mo+16*Mn+14*Cr+5.3*Ni30% is satisfied when B0.0005%, and 0.4-1.0% Al is contained when 0.0005%<B0.005%. The function and basis for the proportion of each element of the present invention are described as follows.

[0044] C: Carbon can stabilize the austenite phase and reduce the A.sub.c3 temperature, thereby reducing the hot forming temperature. Carbon is an interstitial solid solution element, and its strengthening effect is much greater than that of a substitutional solid solution element. As the carbon content in the steel increases, the carbon content in the martensite after quenching will also increase, thereby improving the strength of the martensite. Therefore, under the condition of guaranteed hardenability, the strength can be effectively improved by increasing the carbon content. Increasing the carbon content is the most effective means to improve the strength of hot stamped steel, but as the carbon content increases, the toughness of steel sheet decreases and the welding performance deteriorates. Generally, the carbon content should not be too high. The carbon content of the steel of the present invention is 0.2-0.4%.

[0045] Si: Silicon is an effective deoxidizer and has a strong solid solution strengthening effect. It can also inhibit the precipitation of cementite during the tempering process and improve the tempering stability of steel. Too high silicon content may cause surface quality problems, and thus the silicon content of the steel of the present invention is 0-0.8%.

[0046] Al: In order to prevent the generation of large-size TiN inclusions, a composition design containing no Ti or trace amount of Ti is adopted in the present invention. Aluminum is a strong deoxidizing element and has a strong binding force with N. In the present invention, when the B content is greater than 0.0005%, in order to prevent the generation of BN and exert the effect of B segregated at the austenite grain boundary for improving the hardenability, Al of a relatively high content is to be added to bind with N. After painstaking research, the inventors have found that the generation of BN can be avoided by adding 0.4% or more Al. Too much addition of Al will increase the A.sub.c3 temperature of steel, and will cause the problem that the resistance at the opening of the continuous casting crystallizer increases. Therefore, when the B content is greater than 0.0005%, the Al content of the steel of the present invention is required to be 0.4-1.0%; when the B content is less than 0.0005%, there is no need to keep B by using Al, and the Al content can be less than 0.4% or Al may not be added.

[0047] B: B can segregate at the austenite grain boundaries, thus inhibiting the generation of ferrite and improving the hardenability of steel during hot stamping. Higher than 0.0005% B can just play the role of inhibiting the generation of ferrite, too high content of B will cause boron embrittlement, so the B content of the steel of the present invention can be 0-0.005%; when 29*Mo+16*Mn+14*Cr+5.3*Ni30%, the hardenability of steel can be guaranteed, and the B content can be lower than 0.0005% or B may not be added.

[0048] Mn: Manganese is the most commonly used alloying element for improving the hardenability and can expand the austenite zone and lower the A.sub.c3 temperature, which is beneficial to lowering the hot stamping temperature and refine the original austenite grains. Mn has a strong binding force with O and S, and is a good deoxidizer and desulfurizer, which can reduce or eliminate the hot brittleness of steel caused by sulfur and improve the hot workability of steel. Too high Mn content will reduce the oxidation resistance of steel, and at the same time deteriorate the welding and forming performance. The content of manganese in the steel of the present invention is 0.5-3.0%.

[0049] Mo: molybdenum can significantly improve the hardenability of steel, 0.2% and more molybdenum can effectively inhibit the generation of ferrite and significantly improve the hardenability of steel. Molybdenum can also improve the weldability and corrosion resistance of steel. Limited to cost, the Mo content should not be too high. The content of Mo in the steel of the present invention can be 0-1.0%.

[0050] Alloying elements such as Cr and Ni: elements, such as chromium, nickel can improve the hardenability of steel and improve the strength and hardness of steel. A mixed addition of Cr and Ni can significantly improve the hardenability of steel, but for cost consideration, the total content should not be too high, the Cr content can be 0-2%, and the Ni content can be 0-5%.

[0051] When the B content is lower than 0.0005%, in order to improve the hardenability of the steel sheet, a certain amount of elements, such as Mn, Mo, Cr, Ni, may be added. The above-mentioned four elements have different effects on the hardenability of the steel sheet. According to their effects on the hardenability, the elements are multiplied by corresponding coefficients. The inventor has found through diligent research that when 29*Mo+16*Mn+14*Cr+5.3*Ni30%, the hardenability of the steel sheet in a normal hot stamping process can be guaranteed.

[0052] V, Nb: a small amount of vanadium and niobium can form dispersed refined grain of carbides, nitrides and carbonitrides, thereby improving the strength and toughness of steel and consuming the carbon content of the martensite matrix, which can further improve toughness; and because these fine compounds are dispersed among the phases, precipitation strengthening can occur. An excessively high V and Nb addition amount has no obvious effect, and increases the cost. The V content in the steel of the present invention is 0-0.4%, and the Nb content is 0-0.2%.

[0053] Ti: Ti has a strong binding force with N. When Ti is used to fix N, in order to ensure a complete fixation of nitrogen, it must be satisfied that the weight ratio of Ti to N w(Ti)/w(N)3.4, wherein w(Ti) and w(N) represent respectively the weight percentages of Ti and N in steel. When the stoichiometric ratio of Ti to N is equal to 1, w(Ti)/w(N) is approximately equal to 3.4. When this condition is met, N in the steel can be completely reacted by Ti to precipitate TiN without causing a combination of the residual N in solid-solution state in the steel with B and a formation of BN. If the N content increases, Ti of a higher content must be added. However, the inventors of the present application have found that the volume fraction of coarse TiN particles (with particle size1 m) in steel is proportional to w(Ti)*w(N), wherein w(Ti)*w(N) represents the product of mass percentages of Ti and N in steel. If w(Ti)*w(N) exceeds the product of their solid solubilities, TiN particle inclusions will be precipitated in the molten steel before the molten steel solidifies, the size of which can reach more than 10 microns. TiN has a high dissolution temperature, and does not dissolve during the austenitization process at around 900 C., and remains in the microstructure of the final formed component. Coarse TiN hard particles or TiN particles with high density will become crack source when the material is deformed, leading to cleavage and fracture of hot stamped martensitic steel and severely reducing the impact toughness of the steel sheet. Therefore, in the present invention, it is required that the Ti content in steel is less than 0.01%, or Ti may not be added.

[0054] N: Nitrogen is an interstitially solubilizing element that can significantly improve the strength of steel, and is an austenite stabilizing element, which expands the austenite region and lower the A.sub.c3 temperature. N is apt to combine with strong nitride forming elements such as Ti and Al to form nitrides. TiN is a nitride precipitated from liquid and is apt to form large-size particles, which deteriorates the impact toughness of steel. In the present invention, no Ti or trace amount of Ti is added, which avoids the formation of large-size TiN. In the present invention, Al is used to fix N. Since AlN is a nitride precipitated from solid, under the influence of the formation kinetics, it can form fine and dispersed AlN inclusions, without serious impact on toughness. Therefore, in the present invention it is required that the N content in steel is just less than 0.01%.

[0055] P: In general, phosphorus is a harmful element in steel, which will increase the cold brittleness of steel, deteriorate the weldability, reduce the plasticity, and deteriorate the cold bending performance. In the steel of the present invention, the P content is required to be less than 0.02%.

[0056] S: Sulfur is also a harmful element in general, causing hot brittleness of the steel and reducing the ductility and welding performance of the steel. In the steel of the present invention, the S content is required to be less than 0.015%.

[0057] As a preferred embodiment of the steel of the present invention, the C content is 0.20-0.38%, the Si content is 0.1-0.5%, the Mn content is 0.8-2.2%, the Cr content is 0.1-0.5%, the Mo content is 0.2-0.6%, and the Ti content is 0-0.01%.

[0058] As another preferred embodiment of the steel of the present invention, the C content is 0.24-0.4%, the Si content is 0.1-0.5%, the Mn content is 0.8-2.2%, the Cr content is 0.1-0.5%, the B content is 0.0005-0.004%, the Ti content is 0-0.01%, and the Al content is 0.4-0.8%.

[0059] The steel of the present invention is smelted into steel ingots according to the designed composition, and subjected to 1200 C. homogenization for 5 hours, hot-rolled to the thickness of 3 mm in 5 to 8 passes with a final rolling temperature higher than 800 C., air-cooled to 650 C. and furnace-cooled, and subjected to simulated coiling, and cooled to room temperature and then pickled, cold-rolled to 1.5 mm, and subjected to a hot stamping experiment.

[0060] Table 1 shows the respective composition of the exemplary steels NT1-NT14 of the present invention and the comparative steels CS1, CS2. The Ti content in all exemplary steels of the present invention is less than 0.01%, NT1-NT10 have no B or has a B content of less than 0.0005%, and elements, such as Mn, Mo, Cr, Ni are added to ensure the hardenability of steel; the B content in NT11-NT14 is greater than 0.0005%, and a certain amount of Al is added to combine with N to avoid the generation of BN. The comparative steels CS1 and CS2 have the composition of the hot stamping steel in current industrial production. Steel CS1 has a B content of 0.002%, a N content of 0.0045%, and 0.039% Ti is added to combine with N; CS2 contains 0.0025% B, and 0.03% Ti is added to combine with N, and the N content is 0.0044%. The critical cooling rates were measured by heating materials to the austenitizing temperature by a thermodilatometre and cooling at a rate of 10, 15, 20, 25, and 30 C./s and observing resulting microstructures. A cooling rate was determined to be critical cooling rate when full martensite microstructure was obtained.

[0061] Conventional hot stamping equipment is used to produce 22MnB5, the critical cooling rate of which is about 30 C./s. The critical cooling rates of the comparative steels CS1 and CS2 lie in the range of 2530 C./s. The critical cooling rates of the exemplary steels NT1-NT14 of the present invention are all less than or equal to this value, indicating that the steel composition of the present invention can meet the requirements of conventional hot stamping equipment for the hardenability, and all exemplary steels can obtain full martensite microstructure after hot stamping with the process shown in Table 2.

[0062] Table 1 indicates the composition (mass percentage) and critical cooling rate ( C./s) of the exemplary steels of the present invention and the comparative steels.

TABLE-US-00001 Critical 29*Mo + 16*Mn + Cooling No. C Si Al B Mn Mo Cr Ni V Nb Ti 14*Cr + 5.3*Ni N Rate NT1 0.30 0.3 2.0 0.2 0.2 0.05 37.8 0.0046 25-30 NT2 0.35 0.2 2.0 0.5 0.3 39.0 0.0039 25-30 NT3 0.31 0.4 2.0 2.1 43.1 0.0043 20-25 NT4 0.33 0.2 1.1 0.4 0.6 0.07 37.6 0.0052 25-30 NT5 0.26 0.2 1.2 0.5 0.9 0.2 38.5 0.0049 20-25 NT6 0.28 0.3 1.0 1.2 0.7 0.06 36.5 0.0035 20-25 NT7 0.31 0.3 1.3 0.3 0.5 0.2 0.05 36.5 0.0047 15-20 NT8 0.27 0.2 1.2 0.1 3.0 38 0.0041 20-25 NT9 0.29 0.4 1.7 1.8 0.1 52.4 0.0052 15-20 NT10 0.32 0.2 0.8 0.2 0.7 1.1 0.3 34.2 0.0044 15-20 NT11 0.27 0.2 0.45 0.0009 2 0.05 0.0046 25-30 NT12 0.33 0.2 0.45 0.0021 2 0.2 0.2 0.05 0.0048 15-20 NT13 0.32 0.2 0.6 0.0015 1.6 0.2 0.05 0.0045 20-25 NT14 0.31 0.2 0.86 0.0010 2 0.2 0.05 0.0043 15-20 CS1 0.33 0.2 0.0015 1.5 0.2 0.039 0.0045 25-30 CS2 0.23 0.2 0.0025 1.2 0.030 0.0044 25-30

[0063] The hot stamping process of the present application includes the following steps:

[0064] Steel austenitizing: providing the steel for hot stamping with the above-mentioned alloying elements or its pre-formed component, and heating it to 800-950 C. and keeping it at this temperature for 1 to 10000 s, wherein the heating method for said process step can be but not limited to roller hearth furnace, box heating furnace, induction heating, and resistance heating;

[0065] Steel transferring: transferring the above-mentioned heated steel onto a hot stamping die, ensuring that the temperature of the steel is equal to or higher than 550 C. while being transferred to the die;

[0066] Hot stamping: choosing a reasonable press tonnage according to the size of the above-mentioned steel sheet, with a stamping pressure value of, for example, 1-40 MPa, and determining the pressure holding time according to the sheet thickness, which, for example, it is kept at 4-40 s. For example, the pressure holding time of sheet with thickness of 1.2 mm can be set to 5-15 s, and the pressure holding time of sheet with thickness of 1.8 mm can be set to 7-20 s. For example, the die surface temperature is kept at 200 C. or lower by the cooling system of the die, so that the steel is cooled to 250 C. or lower at an average cooling rate of not less than 10 C./s in the die to ensure that the temperature of a component is equal to or lower than 250 C. when the component exits the die.

[0067] After the hot stamping, tempering can also be carried out. For example, during the painting process, the formed component is heated to 150-200 C. and kept at this temperature for 10-40 minutes; or the above-mentioned formed component is heated to 150-280 C. in any manner and kept at this temperature for 0.5-120 minutes and then cooled in any manner.

[0068] Table 2 shows the hot stamping process parameters of the exemplary steels NT1 to NT14 of the present invention and the comparative steels CS1 and CS2. All of the steels are kept at 870-900 C. for 5 minutes, and then the blanks are taken out and placed on the hot stamping die, the blank temperature is about 700 C. when the die closes, the stamping pressure is 10 MPa, the pressure is kept for 6 s, the temperature of a component when the component exits the die is about 100 C., and then the blanks are air cooled to room temperature, and tempered at 170 C. for 20 minutes. This process can be realized with conventional hot stamping equipment.

[0069] Table 2 indicates the hot stamping process parameters of the exemplary steels of the present invention.

TABLE-US-00002 Component tempearture Blank when Austenitizing Stamping tempearture Pressure component Tempering Steel temperature Austenitizing pressure/ when die Holding exits die temperature/ Tempering No. C. time/min MPa closes C. Time/s C. C. time/min NT1 900 5 10 690 6 92 170 20 NT2 900 5 10 702 6 103 170 20 NT3 910 5 10 695 6 108 170 20 NT4 910 5 10 710 6 95 170 20 NT5 900 5 10 691 6 97 170 20 NT6 890 5 10 699 6 102 170 20 NT7 900 5 10 702 6 105 170 20 NT8 880 5 10 706 6 98 170 20 NT9 870 5 10 685 6 94 170 20 NT10 910 5 10 703 6 105 170 20 NT11 900 5 10 698 6 103 170 20 NT12 910 5 10 707 6 94 170 20 NT13 900 5 10 690 6 101 170 20 NT14 910 5 10 709 6 107 170 20 CS1 900 5 10 693 6 102 170 20 CS2 900 5 10 703 6 104 170 20

[0070] Table 3 shows the mechanical properties of the exemplary steels NT1 to NT14 of the present invention and the comparative steels CS1 and CS2 after hot stamping. The tensile specimens are ASTM standard specimens with a gauge length of 50 mm, and the strain rate for the tensile mechanical properties testing is 2 mm/min. The yield strength is the stress value that produces 0.2% residual deformation. The impact specimen is a three-layered impact specimen. The impact test is carried out not less than 30 times for each type of steel, with random sampling locations.

[0071] The experimental results show that all exemplary steels of the present invention have a yield strength of 1200 MPa, a tensile strength of 1500 MPa, and a elongation of 7%, which are equivalent to the performance of the comparative steels, and the performance of some exemplary steels is even slightly improved compared with the performance of the comparative steels.

[0072] Most of the data of the comparative steel CS1 at 20 C. are at or above 60 J.Math.cm.sup.2, the impact toughness at 40 C. is mostly higher than 55 J.Math.cm.sup.2, but an abnormal data rate of about 10% exists. The abnormal data show that the impact toughness at 20 C. is about 29 J.Math.cm.sup.2, and the impact toughness at 40 C. is about 26 J.Math.cm.sup.2. After the impact fracture analysis, as shown in FIG. 4, a large amount of TiN inclusions have been found at the fracture where the impact value was abnormal, with particle size above 1 m, and some even have a particle size as high as 10 m, indicating that the existence of large-size TiN has become the crack source, which seriously reduces the impact toughness.

[0073] Most of the data of the impact toughness of the comparative steel CS2 at 40 C. and 20 C. are concentrated around 60 J.Math.cm.sup.2, but an abnormal data rate of about 5% exists. The abnormal data show that the impact toughness is only about 40 J.Math.cm.sup.2. As shown in FIG. 5, a large amount of TiN have been found at the abnormal fracture of CS2, with particle size above 5 m, indicating that the reason for abnormal reduction of the impact toughness of CS2 lies in the generation of large-size TiN caused by a relatively high content of N.

[0074] From the analysis of the comparative steels CS1 and CS2, it can be seen that the generation of TiN will deteriorate the toughness of the steel. Since the size and distribution of TiN are normally distributed according to the probability, both CS1 and CS2 containing coarse TiN inclusions will be in abnormal condition, with toughness reduced to about 40 J.Math.cm-2 or below.

[0075] In order to reduce the generation of TiN, the N or Ti content in the steel can be reduced. As the N content in steel is limited by metallurgy quality, the reduction of the N content will inevitably lead to a substantial increase in steelmaking costs. The content of Ti in the steel of the present invention is lower than 0.01%, and the content of TiN can be kept at a very low level without producing large-size TiN particles, so that the problem of insufficient toughness caused thereby can be avoided. The exemplary steels NT1-NT14 of the present invention have respectively an impact toughness value 60 J.Math.cm-2 or above at 20 C. and an impact toughness of 50 J.Math.cm.sup.2 or above at 40 C., and no abnormal values exist. FIG. 1 shows the 20 C. impact fracture morphology of NTT steel, and FIG. 2 shows the 40 C. impact fracture morphology of NTT steel, wherein no inclusions have been found at the fracture. This morphology represents the impact fracture morphology of all exemplary steels of the present invention, indicating that the inclusions in the steel of the present invention will not significantly affect the impact toughness.

[0076] Table 3 indicates the mechanical properties of the exemplary steels of the present invention.

TABLE-US-00003 Impact Impact Yield Tensile Toughness Toughness Strength Strength Elonga- at 20 C. at 40 C. Steel No. MPa MPa tion % J .Math. m.sup.2 J .Math. m.sup.2 NT1 1380 16 1851 15 8.0 0.2 65.4 3.0 56.6 4.5 NT2 1610 19 1973 12 7.9 0.3 64.1 1.7 55.2 3.5 NT3 1426 11 1860 18 8.7 0.3 63.5 3.2 56.3 1.4 NT4 1518 17 1880 20 7.2 0.2 63.4 1.5 55.8 0.5 NT5 1218 19 1560 14 7.9 0.3 66.4 2.8 56.4 2.7 NT6 1288 16 1651 16 8.1 0.3 63.1 1.9 55.2 3.8 NT7 1426 11 1885 19 8.5 0.1 63.5 3.0 54.7 1.9 NT8 1242 23 1665 11 7.5 0.2 63.9 1.7 55.5 0.9 NT9 1334 20 1801 20 8.2 0.3 63.8 2.9 56.9 4.2 NT10 1472 13 1884 17 7.6 0.3 66.1 2.0 54.8 3.8 NT11 1380 9 1743 13 7.7 0.3 65.2 1.4 54.8 0.8 NT12 1521 19 1965 23 8.7 0.3 63.2 1.4 53.8 0.8 NT13 1471 15 1887 22 7.9 0.2 66.9 1.9 56.7 3.6 NT14 1429 18 1847 12 7.8 0.3 60.1 2.5 55.2 3.4 Normal 1574 12 1905 13 8.5 0.3 64.0 3.2 55.1 1.4 CS1 Abnormal 1568 11 1901 14 8.2 0.2 29.0 1.5 26.4 2.1 CS1 Normal 1156 17 1541 23 7.5 0.3 61.0 4.6 58.0 2.2 CS2 Abnormal 1144 16 1504 8 7.2 0.3 42.1 1.3 41.6 5.9 CS2

[0077] As shown in Table 3, the hot stamped component of the present invention can also obtain good mechanical properties while ensuring a good impact toughness. Specifically, a yield strength of 1200-1800 MPa, a tensile strength of 1500-2150 MPa and an elongation of 7-10%, a 40 C. impact toughness of 45 J.Math.cm.sup.2 can be achieved. The mechanical properties are equivalent to those of existing Ti-containing steel for hot stamping and even slightly improved. Among them, NT12 and NT14, in particular, can achieve a high strength under the condition of relatively low composition proportion of expensive alloys. Their mechanical properties are: tensile strength184712 MPa, elongation7.80.3%, 40 C. Charpy impact toughness (CVN)53.80.8 J.Math.cm.sup.2.

[0078] The hot stamped component of the present invention can be used for the high-strength component of automobile, including but not limited to A-pillar, B-pillar, bumper, roof frame, underbody frame, and vehicle door bumper bar of automobile.

[0079] The above embodiments and experimental data are intended to illustrate the present invention exemplarily. It should be clear to those skilled in the art that the present invention is not limited to these embodiments, and various modifications can be made without departing from the protection extent of the present invention.