Hot-pressed parts with tensile strength of ≥ 1000 MPa and their manufacturing method

Abstract

A hot pressed part having a tensile strength of 1000MPa or more and a manufacturing method thereof, the chemical composition of which is, in weight percent, C 0.05-0.20%, Si 0.02-1.00%, Mn 0.5-2.0%, P≦0.10%, S≦0.05%, Al 0.01-0.30%, Nb 0.01-0.0.04%, Ti 0.01-0.06%, Cr:0.12-0.50%, B 0.001-0.05%, and the balance being Fe and other unavoidable impurities, and which simultaneously satisfies the conditions of 0.24%≦C+Mn / 6≦0.45%, 0.05%≦Nb+Ti+B×10≦0.15%. The obtained hot pressed parts have an average grain size of initial austenite ≦10μm, a VDA cold bending angle ≧80°, and impact toughness at room temperature ≧80J / cm 2 , yield strength≧800MPa, tensile strength≧1000MPa, and elongation at break≧6%. Hot-pressed parts have high strength and high toughness, and are widely used in the automobile, ship, machinery and other industries.

Description

[Technical Field]

[0001] The present invention relates to the technical field of automotive materials, specifically to hot-pressed parts with a tensile strength of ≥ 1000 MPa and a method for producing the same. [Background technology]

[0002] As the natural environment deteriorates and petroleum resources become increasingly scarce, green and safety are becoming the main development trends in the automotive manufacturing industry. Current research has shown that as the strength grade of automotive steel increases, especially for steel sheets with tensile strengths above 1000 MPa, cold forming formability deteriorates significantly, resulting in poor piercing accuracy and even tearing in some areas. Hot-pressed parts, characterized by high strength, high formability, and low strain recovery, are an important technological solution for reducing the weight of automotive structures. Demand for hot-pressed parts is increasing due to their wide application in safety structural parts such as A / B pillars, bumpers, and center aisles in body-in-white vehicles.

[0003] Currently, hot-pressed products in the market are mainly of the 1500 MPa strength grade, and in terms of toughness, the VDA cold bending angle is about 50°, and the impact toughness at room temperature is about 40 J / cm 2 In comparison, 1000MPa hot-pressed products have higher toughness, making them suitable for energy-absorbing piercings, which require even greater toughness. 1000MPa-grade high-toughness hot-pressed products have better impact performance in terms of material performance, function as energy-absorbing areas in structural reinforcement, and combine the advantages of high strength and good local impact resistance. Currently, 1000MPa strength-grade hot-pressed steel is known, but it has drawbacks, such as the addition of multiple precious elements to achieve high strength and toughness, and the need for complex multi-stage control processes in its manufacture.

[0004] Chinese Patent CN107810281B discloses a "steel for press hardening and press hardened parts made from such steel." While press hardened parts with tensile strengths exceeding 950 MPa and cold bending angles exceeding 75° can be obtained, the steel contains a large amount of microalloys, and high-temperature annealing is used in the production of the steel sheet, while two-stage controlled cooling is used in the hot pressing process to produce the parts. This makes the manufacturing process complicated and difficult to implement in practice.

[0005] Chinese Patent CN105829562B discloses a "hot-pressed steel plate member, its manufacturing method, and a steel plate for hot pressing." The alloy contains 0.060-0.20% Ti, and 90% of the total Ti is required to precipitate. Furthermore, a two-stage cooling process is used after hot pressing. The resulting hot-pressed member achieves a strength of only 980 MPa or more, and there is no mention of the hot-pressed member having high toughness.

[0006] Chinese patent CN104838030B discloses "Hot-pressed parts with improved toughness and manufacturing methods thereof." The alloy contains B≦0.001% and other noble alloys, mainly Mo, which improve the ability to obtain martensite during quenching, achieving high strength.

[0007] As described above, conventional high-strength hot press steels have problems such as insufficient toughness and poor impact energy absorption. Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to provide a highly tough hot-pressed part having a tensile strength of ≥ 1000 MPa and a method for manufacturing the same. The hot-pressed part thus obtained has a yield strength of ≥ 800 MPa, a tensile strength of ≥ 1000 MPa, an elongation at break of ≥ 6%, a VDA cold bending angle of ≥ 80°, and an impact toughness at room temperature of ≥ 80 J / cm. 2Hot-pressed parts have high strength and high toughness, which solves the problems of conventional high-strength hot-pressed parts, such as insufficient toughness and poor collision energy absorption, and are widely used in industries such as automobiles, ships, and machinery. [Means for solving the problem]

[0009] To achieve the above objectives, the present invention provides the following technical solutions: A hot-pressed part having a tensile strength of 1000 MPa or more, the chemical composition of which is, in weight percent, C: 0.05-0.20%, Si: 0.02-1.00%, Mn: 0.5-2.0%, P≦0.10%, S≦0.05%, Al: 0.01-0.30%, Nb: 0.01-0.04%, Ti: 0.01-0.06%, Cr: 0.12-0.50%, B: 0.001-0.05%, the balance being Fe and other unavoidable impurities, and simultaneously satisfying the following conditions: 0.24%≦C+Mn / 6≦0.45%; 0.05%≦Nb+Ti+B×10≦0.15%; The hot-pressed part is Old Average austenite grain size ≦10μm, VDA cold bending angle ≧80°, room temperature impact toughness ≧80J / cm 2 Hot-pressed parts with tensile strength ≥ 1000 MPa.

[0010] Furthermore, the hot-pressed part may further contain, as components, one or more of Ni: 0.01 to 1.0%, Mo: 0.01 to 0.5%, and V: 0.01 to 0.5%, in weight percent.

[0011] Preferably, the P content is ≦0.05%. Preferably, the S content is ≦0.01%.

[0012] Hot-pressed parts according to the present invention minute In the structure, the area ratio of martensite and bainite is 75% or more, and the remainder is made up of ferrite, retained austenite, or a mixture of both.

[0013] The hot-pressed part according to the present invention has a yield strength of ≥ 800 MPa, a tensile strength of ≥ 1000 MPa, and an elongation at break of ≥ 6%.

[0014] In some embodiments, the hot-pressed part of the present invention has a yield strength of 830 MPa or more, a tensile strength of 1020 MPa or more, and an elongation at break of 7.0% or more. In some embodiments, the hot-pressed part of the present invention has a yield strength of 830-1150 MPa, a tensile strength of 1020-1300 MPa, and an elongation at break of 7.0-9.0%.

[0015] In some embodiments, the hot-pressed part of the present invention has a VDA cold bending angle of ≥ 85°. In some embodiments, the hot-pressed part of the present invention has a VDA cold bending angle of ≥ 90°. In some embodiments, the hot-pressed part of the present invention has a VDA cold bending angle of 85-120°.

[0016] In some embodiments, the hot-pressed part of the present invention has an impact toughness of ≥ 85 J / cm at room temperature. 2 In some embodiments, the hot-pressed part of the present invention has an impact toughness of ≥ 90 J / cm at room temperature. 2 In some embodiments, the hot-pressed part of the present invention has an impact toughness of 80 to 115 J / cm at room temperature. 2 is.

[0017] In the composition design of the present invention: C: An important element for increasing strength and hardness. A carbon content of 0.05% or more ensures the strength and hardenability of steel sheets and hot-pressed parts, and enables the tensile strength of hot-pressed parts to meet the target requirements. However, since an increase in carbon content can deteriorate the plasticity, toughness, weldability, etc. of hot-pressed parts, in the present invention, the C content is set to 0.05 to 0.20%.

[0018] Si: Adding a certain amount of Si dissolves in ferrite and austenite, increasing the strength and hardness of the hot-pressed part. Since the galvanic properties of the hot-pressed part are affected when the Si content exceeds 1.0%, the Si content is set to 0.02-1.0% in the present invention. In one embodiment, the Si content is set to 0.05-0.7%.

[0019] Mn: Has the effects of deoxidizing and desulfurizing, and can further increase the hardness and strength of hot-pressed parts. Mn is a strong austenite-stabilizing element, and can significantly increase the hardenability of hot-pressed parts. To ensure the strength of hot-pressed parts, the Mn content in steel is set to 0.5% or more. However, if the Mn content exceeds 2.0%, the manufacturability and weldability of hot-pressed parts may deteriorate. Therefore, in the present invention, the Mn content is set to 0.5 to 2.0%.

[0020] C+Mn / 6 is an important alloying element and fully reflects the material's strength, toughness, and weldability. If C+Mn / 6 < 0.24%, the hot-pressed parts cannot ensure high tensile strength and the material lacks the ability to form martensite. If C+Mn / 6 > 0.48%, the martensite structure in the hot-pressed parts will have high C and Mn contents, which will lead to the formation of high-carbon martensite and significantly reduce the toughness of the material. Since weldability is significantly reduced when C+Mn / 6 exceeds 0.45%, the present invention specifies a limit of 0.24%≦C+Mn / 6≦0.45%.

[0021] P, S: Both P and S are harmful elements, and segregation of P element causes low-temperature brittleness in hot-pressed parts. Segregation of S element at high temperatures reduces plasticity and may cause low-temperature brittleness. The main purpose of the design of this invention is to significantly improve the toughness of the material, so P≦0.10% and S≦0.05%, and preferably P≦0.05% and S≦0.01%.

[0022] Al: As a deoxidizing element, it is preferable that the hot-pressed part contains 0.01% or more Al. However, if the hot-pressed part contains a large amount of Al, coarse oxides are formed, which deteriorates the overall performance of the hot-pressed part. Therefore, in the present invention, the Al content is set to 0.01 to 0.3%. In some embodiments, the Al content is set to 0.01 to 0.25%.

[0023] Nb: An important microalloy element. Nb has a solid-solution strengthening effect. On the other hand, Nb has a very strong bonding strength with both C and N and can form stable compounds with them, which refines crystal grains, improves the strength and toughness of hot-pressed parts, and at the same time, gives hot-pressed parts good cold bending properties. Furthermore, Nb carbonitrides act as hydrogen traps and can reduce susceptibility to hydrogen-induced cracking. Therefore, in the present invention, the Nb content is set to 0.01 to 0.04%. If the Nb content is less than 0.01%, the grain refinement effect is insufficient, and if it exceeds 0.04%, the cost of the product increases.

[0024] Ti: An important microalloy element. It has a strong affinity with nitrogen, oxygen, and carbon, and is an element with good deoxidation and nitrogen fixation properties, preventing the formation of BN by boron and nitrogen. Ti also has a grain refinement effect, improving the toughness of the material. However, if the Ti content is too high, bulk nitrides are likely to form, deteriorating the toughness and plasticity. Therefore, in the present invention, the Ti content is set to 0.01 to 0.06%, which can improve the toughness and plasticity of hot-pressed parts.

[0025] B: Its main effect is to significantly increase the hardenability of steel, thereby saving other precious metals. There is an optimum range for the addition of B to increase hardenability, and if the amount exceeds a certain level, the effect of increasing hardenability becomes less obvious. Therefore, in the present invention, the B content is set to 0.001 to 0.05%. In some embodiments, the B content is set to 0.001 to 0.005%.

[0026] As components, Nb, Ti, and B elements refine the grain structure of hot pressed parts in different ways, and Nb / Ti precipitated carbon-nitrogen compounds refine the grains in the production of hot pressed parts, while B improves hardenability, and the synergistic effect of the two improves toughness. Nb / Ti have similar effects, and the order of addition is the same, but B, although a small amount, has the effect of significantly improving hardenability. When the alloying component is Nb+Ti+B×10<0.05%, the structure of hot pressed parts is not significantly refined. In particular, Old If the average austenite grain size exceeds 10 μm, high toughness cannot be achieved. If Nb+Ti+B×10>0.15%, the effect of refining the grain size will not be apparent even if the alloy content is further increased, while the alloy cost will increase. Therefore, in the present invention, the range is set to 0.05%≦Nb+Ti+B×10≦0.15%.

[0027] Cr: Effectively improves the hardenability of hot-pressed parts. Similar to Mn, Cr further improves the strength and toughness of hot-pressed parts. Furthermore, the addition of Cr prevents surface oxidation due to high temperatures during subsequent hot-pressing. Therefore, in the present invention, the Cr content is set to 0.12 to 0.5%.

[0028] Ni, Mo, and V: All of these elements stably guarantee the strength and toughness of hot-pressed parts. Ni is important for increasing the strength of steel, lowering the low-temperature brittle transition temperature of steel, and improving impact toughness. Mo significantly improves the hardenability of steel, refines austenite grains, prevents temper embrittlement, and improves the strength and toughness of hot-pressed parts. V refines austenite grains as a fine carbon nitride, improving the toughness of steel. Therefore, Ni, Mo, and V can simultaneously guarantee high strength and good toughness for hot-pressed parts.

[0029] Considering the alloy cost of the steel and the saturation degree of the effect of the elements, the present invention may further include one or more alloying elements selected from the group consisting of 0.01-1.0% Ni, 0.01-0.5% Mo, and 0.01-0.5% V. In some embodiments, the steel of the present invention has Ni≦0.3%, Mo≦0.3%, and V≦0.2%.

[0030] The composition of the present invention is based on the design concept of low carbon microalloying, and the solid solution strengthening by C and the C / Mn combination improves hardenability and ensures the strength of hot pressed parts. The addition of small amounts of microalloys such as Nb, Ti, and B improves the hardenability and the strength of hot pressed parts. Old The grain size of a hot-pressed part containing austenite grains is further refined to obtain a hot-pressed part with high strength and high toughness. Preferably, alloying elements such as Ni, Mo, and V are partially added to further increase the strength and toughness of the hot-pressed part.

[0031] The method for producing a hot-pressed part having a tensile strength of 1000 MPa according to the present invention comprises the following steps: 1) Smelting and casting Smelting according to the above ingredients and casting into slabs; 2) Hot rolling, Volume Pickling The heating and discharge temperature of the slab is 1100-1260°C, and the final rolling temperature is 830-880°C; Volume The rolling temperature is 580-650℃, and after pickling, the hot-rolled slab is obtained. 3) Cold rolling and annealing The total reduction in cold rolling is 40-80%, and the annealing temperature is 720-780°C; 4) Hot press forming The heating temperature of the annealed steel sheet is Ac3 to 960°C, and the heating time is 2 to 10 minutes; then, it is transferred to a mold and press-formed, and the forming temperature is ≥ 700°C; Thereafter, the material is cooled to 200°C or below at a cooling rate exceeding 30°C / s to obtain a hot-pressed part.

[0032] In some implementations, the slab heating and discharge temperature is 1150-1260°C.

[0033] Furthermore, in step 3), in the steel sheet structure after the annealing, the area ratio of martensite and carbide particles dispersedly distributed in a network shape is 10 to 40%, and the area of ​​a single martensite or carbide particle is 25 μm 2 is less than.

[0034] Furthermore, in step 3), in the steel sheet structure after the annealing, 80% or more of the crystal grains have an aspect ratio of 0.5 to 2.0.

[0035] After the annealing in step 3), the steel sheet is plated to obtain a steel sheet having a plated layer, and the average weight of one side of the plated layer is 20 to 120 g / m 2 is.

[0036] Preferably, the plating layer is a pure zinc plating layer, a zinc-iron alloy plating layer, a zinc-based alloy plating layer containing Al and Mg, or an aluminum-silicon alloy plating layer.

[0037] Furthermore, before the hot press forming in step 4), the steel plate and other strength grade steel for hot press parts are welded using laser butt welding technology to form a butt-welded part.

[0038] In some embodiments, the heating time in step 4) is 200 to 600 seconds.

[0039] In some embodiments, the molding temperature in step 4) is 700 to 820°C.

[0040] In some embodiments, the cooling rate in step 4) is 35-60° C. / s. The steel slab produced with the above-mentioned composition is subjected to hot rolling, cold rolling and annealing to become an unplated steel sheet, or to hot rolling, cold rolling and annealing, and then to plating by any method to become a plated steel sheet.

[0041] The present invention controls the production process of hot-pressed parts, and the slab heating and discharge temperatures during hot rolling are set to 1100-1260°C. If the heating temperature is lower than 1100°C, the microalloy cannot be sufficiently melted. If the heating temperature exceeds 1260°C, the crystal grains tend to coarsen, resulting in a deterioration in toughness. By setting the final rolling temperature to 830-880°C, the final rolling is performed within the non-recrystallization zone of austenite, resulting in a refined crystal grain structure.

[0042] In the present invention, since a small amount of Nb and Ti microalloy is added, in order to increase the precipitation of niobium titanium carbide during winding, the winding temperature is set to 580 to 650°C. In this way, NbC and TiC distributed on a nano-scale are precipitated at a high rate, and the obtained NbC and TiC are easily quenched during the subsequent heating in hot pressing. Old The growth of austenite grains can be suppressed, Old It is advantageous for refining the austenite grain size. If the coiling temperature is below 580°C, the niobium titanium carbide will not precipitate well, and the steel sheet will have high strength after hot rolling, making cold rolling difficult. If the coiling temperature exceeds 650°C, the grains will become coarse, which is unfavorable for controlling the grain refinement throughout the entire process, and oxidation will occur on some surfaces of the steel sheet, which is unfavorable for controlling the subsequent pickling process and will affect the galvanizability of the steel sheet.

[0043] The total reduction in cold rolling should be 40-80%. If the total reduction in cold rolling is less than 40%, the structure will not be destroyed and the effect of refining the grains will not be obvious. If the total reduction in cold rolling is more than 80%, the residual hardness in the steel sheet will be high and there will be a lot of band-like structure, which will be unfavorable for subsequent production and will significantly deteriorate the toughness of the hot-pressed part.

[0044] Annealing after hot rolling further controls the grain size and shape of the steel sheet and ensures high toughness of hot-pressed parts. Based on the composition design, an annealing temperature of 720-780°C ensures that more than 80% of the grains in the steel sheet structure after annealing are nearly equiaxed, meaning that the aspect ratio of the grain shape satisfies 0.5-2.0. A high proportion of equiaxed grains reduces banded structure, refines the initial steel sheet structure, and allows for a refined structure in subsequent hot-pressed parts. Annealing temperatures above 780°C significantly increase the grain size.

[0045] By setting the annealing temperature at 720 to 780°C, fine martensite and carbide particles are dispersed along the ferrite crystal boundaries in the structure. Both martensite and carbide are high-carbon phases. In addition, in the structure, 2 Since fine particles of less than 10 to 40% account for 10 to 40%, the effective grain boundary area increases significantly. Since the high carbon phase and the effective grain boundary are the preferred nucleation sites of austenite, this is favorable for increasing the nucleation rate of austenite, promoting nucleation. Old The austenite grain size is refined. If the area ratio of martensite and carbide particles in the structure exceeds 40%, the quality of the steel sheet after annealing is high, which is unfavorable for subsequent punching. If the area ratio of martensite and carbide particles in the structure is less than 10%, the grain boundary area cannot be effectively increased. As mentioned above, if the grain size is not controlled, high-toughness hot-pressed parts cannot be obtained, so the steel sheet must be annealed at 720-780°C.

[0046] In the present invention, if the heating temperature of the hot-pressed steel sheet is less than AC3, the steel sheet structure cannot be fully austenitized. If the heating time is less than 2 minutes, the austenitization of the steel sheet and the dissolution of carbides are insufficient. If the hot-pressing temperature exceeds 960°C or the heating time exceeds 10 minutes, the austenite grains become coarse, significantly reducing the toughness of the hot-pressed part. If the deformation temperature of the steel sheet is less than 700°C, deformation is difficult and large amounts of ferrite and other structures are likely to precipitate. Therefore, in order to ensure the design requirements for strength and toughness of the hot-pressed part, the cooling rate after hot-pressing must be 30°C / s, which is higher than the critical cooling rate for obtaining a martensite structure, and the steel sheet must be quenched to below 200°C.

[0047] The steel sheet obtained after annealing may be an unplated sheet, or an alloy plating layer may be applied to the surface of the steel sheet to reduce the effects of iron oxide film on the surface due to heating of the steel sheet and subsequent deterioration of corrosion resistance. The coating amount of the plating layer is 20 to 120 g / m 2 The coating weight of the plating layer is 20 g / m 2 When the coating weight is less than 120g / m, it is difficult to control during production, and the corrosion resistance of the hot stamped parts is poor. 2 Above this value, corrosion resistance becomes saturated and the cost increases.

[0048] The plating layer may be a pure zinc plating layer, or a zinc-iron alloy plating layer such as Zn-Fe, Zn-Al, Zn-Mg, or Zn-Al-Mg.Furthermore, it may be a zinc-based alloy plating layer containing Al and Mg, or an aluminum-silicon alloy plating layer such as an aluminum-silicon alloy plating layer containing 0-4% Fe, 5-11% Si, and the balance being aluminum and unavoidable impurities.

[0049] The beneficial effects of the present invention are as follows: The composition of the present invention mainly adopts the design concept of low carbon micro-alloying, and improves hardenability through solid solution strengthening by C and C / Mn combination, ensuring the strength of hot-pressed parts. By adding small amounts of micro-alloys such as Nb, Ti, and B, and controlling them to 0.24%≦C+Mn / 6≦0.45% and 0.05%≦Nb+Ti+B×10≦0.15%, the grain size of the hot-pressed parts is significantly refined, and the strength of the hot-pressed parts is improved. Old The average austenite grain size is set to 10 μm or less, improving the toughness of high-strength hot-pressed parts. This solves the problems of conventional high-strength hot-pressed parts, such as insufficient toughness and poor collision energy absorption, and is therefore widely used in industries such as automobiles, ships, and machinery.

[0050] In the manufacturing process of the present invention, a small amount of microalloy components is added and the winding temperature is set to 580 to 650°C, whereby NbC and TiC are precipitated at a high rate, and the obtained NbC and TiC are easily melted during the subsequent heating of the hot press. Old Suppresses the growth of austenite grains, Old The austenite grain size is refined. Furthermore, by setting the annealing temperature at 720 to 780°C, 80% or more of the crystal grains in the structure of the steel sheet obtained after annealing become substantially equiaxed. In this way, after the steel sheet is hot-pressed, Old The austenite grain size is refined, Old The average austenite grain size is ≦10μm, and the toughness of the high-strength hot-pressed parts is significantly improved. The hot-pressed parts have a yield strength of ≧800MPa, a tensile strength of ≧1000MPa, and a VDA cold bending angle of ≧80° and room temperature impact toughness of ≧80J / cm. 2 is. [Brief explanation of the drawings]

[0051] [Figure 1] FIG. 1 shows a scanning electron microscope microstructure photograph of a hot-pressed part according to an embodiment of the present invention. [Figure 2] FIG. 2 shows a photograph of the prior austenite structure of a hot-pressed part according to an embodiment of the present invention. [Figure 3]FIG. 3 shows a metallographic photograph of the steel sheet after annealing in the example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0052] The present invention will be further described with reference to the following examples, in which the VDA cold bending angle measurement standard is VDA238-100, bending test for metallic material sheets; the impact toughness measurement standard is GB / T 229, Charpy impact test method for metallic materials; and the mechanical properties measurement standard is GB / T 228.1, Tensile test for metallic materials, Part 1: Room temperature tensile test method.

[0053] Specific components and process parameters of the examples of the present invention are shown in Tables 1 and 2, and the performance of the hot-pressed parts of each example is shown in Table 3.

[0054] Figure 1 shows a scanning electron microscope image of a hot-pressed part. minute As can be seen from FIG. 1, the structure of the hot-pressed part according to the present invention is minute The structure is martensite, bainite, and a small amount of retained austenite, with the area ratio of martensite and bainite being 75% or more.

[0055] As can be seen from Figure 2, Old The average grain size of austenite is ≦10 μm. As can be seen from FIG. 3, in the steel sheet structure after annealing, the aspect ratio of the shape of approximately 85% of the grains satisfies 0.5 to 2.0, the martensite and carbide particles are dispersed in a network, and the area ratio of the martensite and carbide particles exceeds 25%, and the single grain area is ≦25 μm. 2 is less than.

[0056] As can be seen from the performance in Table 3, the hot-pressed parts according to the present invention have a yield strength of ≥ 800 MPa, a tensile strength of ≥ 1000 MPa, a VDA cold bending angle of ≥ 80°, and an impact toughness at room temperature of ≥ 80 J / cm 2 , and the elongation at break is ≧6%.

[0057] [Table 1]

[0058] Table 2

[0059] Table 3

Claims

1. A hot-pressed part having a tensile strength of ≥ 1000 MPa, the chemical composition of which is, in weight percent, C: 0.05-0.20%, Si: 0.02-1.00%, Mn: 0.5-2.0%, P≦0.10%, S≦0.05%, Al: 0.01-0.30%, Nb: 0.01-0.04%, Ti: 0.01-0.06%, Cr: 0.12-0.50%, B: 0.001-0.05%, the balance being Fe and other unavoidable impurities, and simultaneously satisfying the following conditions: (1) 0.24%≦C+Mn / 6≦0.45%; and (2) 0.05%≦Nb+Ti+B×10≦0.15%; In formula (1) and formula (2), C, Mn, Nb, Ti, and B represent the weight percentages of C element, Mn element, Nb element, Ti element, and B element, respectively. The hot-pressed part has an average grain size of prior austenite ≦10 μm, a VDA cold bending angle ≧80°, and an impact toughness at room temperature ≧80 J / cm ２ A hot-pressed part having a tensile strength of ≧1000 MPa.

2. The hot-pressed part having a tensile strength of 1000 MPa or more according to claim 1, further comprising, in weight percent, one or more of Ni: 0.01 to 1.0%, Mo: 0.01 to 0.5%, and V: 0.01 to 0.5%.

3. 2. The hot-pressed part according to claim 1, wherein the P is ≦0.05% and / or the S is ≦0.01%.

4. The hot-pressed part having a tensile strength of 1000 MPa or more according to claim 1, characterized in that the Si content is 0.05 to 0.7%, and / or the Al content is 0.01 to 0.25%, and / or the B content is 0.001 to 0.005%.

5. 5. The hot-pressed part having a tensile strength of ≧1000 MPa according to any one of claims 1 to 4, characterized in that in the microstructure of the hot-pressed part, an area ratio of martensite and bainite is ≧75%, and the remainder consists of ferrite, retained austenite, or a mixture of both.

6. The hot-pressed part according to any one of claims 1 to 4, wherein the hot-pressed part has a yield strength of 800 MPa, a tensile strength of 1000 MPa, and a breaking elongation of 6%.

7. The hot-pressed part having a tensile strength ≥ 1000 MPa according to claim 6, characterized in that the hot-pressed part has a yield strength ≥ 830 MPa, a tensile strength ≥ 1020 MPa, and a breaking elongation ≥ 7.0%.

8. The hot-pressed part having a tensile strength of 1000 MPa or more according to claim 7, characterized in that the hot-pressed part has a yield strength of 830 to 1150 MPa, a tensile strength of 1020 to 1300 MPa, and a breaking elongation of 7.0 to 9.0%.

9. The hot-pressed part has a VDA cold bend angle ≥ 85°; and / or the hot-pressed part has a room temperature impact toughness ≥ 85 J / cm ２ The hot-pressed part having a tensile strength of ≧1000 MPa according to any one of claims 1 to 4.

10. 10. The hot pressed part having a tensile strength > 1000 MPa according to claim 9, wherein the VDA cold bend angle of the hot pressed part is > 90°.

11. 10. The hot pressed part with a tensile strength ≥ 1000 MPa according to claim 9, wherein the VDA cold bend angle of the hot pressed part is between 85° and 120°.

12. The room temperature impact toughness of the hot pressed part is ≥ 90 J / cm ２ 10. The hot pressed part according to claim 9, wherein:

13. The room temperature impact toughness of the hot pressed part is 80 to 115 J / cm ２ 10. The hot pressed part according to claim 9, wherein:

14. The method for producing a hot-pressed part with a tensile strength of ≥ 1000 MPa according to any one of claims 1 to 4, characterized in that it comprises the following steps: 1) Smelting and casting smelting according to the composition of any one of claims 1 to 4 and casting into slabs; 2) Hot rolling, coiling, pickling The heating and unloading temperature of the slab is 1100-1260°C, and the final rolling temperature is 830-880°C; The coiling temperature is 580 to 650°C, and the hot-rolled slab is obtained after pickling. 3) Cold rolling and annealing The total reduction in cold rolling is 40 to 80%, and the annealing temperature is 720 to 780°C; 4) Hot press forming After annealing, the steel sheet was ３ Heating to 960°C or less, heating time is 2 to 10 minutes; then transferring to a mold and press forming, molding temperature is 700°C or more; Thereafter, the product is cooled to 200°C or less at a cooling rate exceeding 30°C / s to obtain a hot-pressed part.

15. In step 3), the area ratio of martensite and carbide particles dispersedly distributed in a network form in the structure of the steel sheet after annealing is 10 to 40%, and the area of ​​a single martensite or carbide particle is 25 μm ２ 15. The method for producing a hot-pressed part with a tensile strength ≥ 1000 MPa according to claim 14, wherein the tensile strength is less than 1000 MPa.

16. 15. The method for producing a hot-pressed part having a tensile strength of 1000 MPa or more according to claim 14, wherein in step 3), 80% or more of the crystal grains in the structure of the steel sheet after annealing have an aspect ratio of 0.5 to 2.

0.

17. After the annealing in step 3), the steel sheet is plated to obtain a steel sheet having a plating layer, and the average weight of one side of the plating layer is 20 to 120 g / m ２ The method for producing a hot-pressed part having a tensile strength of ≥ 1000 MPa according to claim 14, characterized in that

18. 15. The method for manufacturing a hot-pressed part having a tensile strength ≥ 1000 MPa according to claim 14, wherein the plating layer is a pure zinc plating layer, a zinc-iron alloy plating layer, a zinc-based alloy plating layer containing Al and Mg, or an aluminum-silicon alloy plating layer.

19. 15. The method for manufacturing a hot-pressed part with a tensile strength of ≥ 1000 MPa as claimed in claim 14, characterized in that before the hot-press forming in step 4), the steel plate and other strength grade steel plates for hot-pressed parts are welded by laser butt welding technology to form a hot-pressed butt-welded part.

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