Hot forming steel as well as preparation method and application thereof

Abstract

The invention provides hot forming steel and a preparation method and application thereof. The hot forming steel comprises the following components in percentage by mass: 0.19-0.38 wt% of C; 0.8 to 2.0 wt% of Si; mn: 0.8 to 2.0 wt%; p: less than or equal to 0.025 Wt%; s: less than or equal to 0.01 Wt%; al: < = 0.2 Wt%; b: 0.0015 to 0.0050 wt% of the total weight of the raw materials; the steel comprises the following components in percentage by weight: 1.5-4.0% of Cr, 0.01-0.3% of Nb, 0.01-0.3% of Ti and the balance of Fe and inevitable impurities. According to the hot forming steel and the preparation method thereof, the hot forming steel which not only has high-temperature oxidation resistance, but also has relatively good cracking resistance and relatively high strength is obtained by selecting proper components, contents and a preparation method, so that a prepared hot forming part also has the properties, and the technical problems existing in related technologies are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of steel smelting, and in particular to a hot-formed steel, a preparation method and application thereof. Background Art

[0002] Hot-formed parts play a key role in automobile manufacturing, especially for new energy vehicles. In order to achieve weight reduction, emission reduction and improve passive safety performance, they are faced with the problem of how to optimize the structure and materials of hot-formed parts.

[0003] However, the current hot stamping process and hot bulging forming technology have certain limitations. Although the above processes can produce two-dimensional parts and simple tubular structures, it is still difficult to produce large-sized parts. As a result, more complex or large-sized hot-formed parts need to be formed into two-dimensional parts and simple tubular structures first, welded, heated as a whole, and then water-cooled in quenching liquid. However, such hot-formed parts are prone to deformation and cracking.

[0004] In summary, there is an urgent need for a hot-formed steel, a preparation method and an application thereof to solve the problems existing in the related technologies. Summary of the invention

[0005] The main purpose of the present invention is to provide a hot-formed steel, a preparation method and application thereof, so as to solve the technical problems of deformation and cracking existing in the production of more complex or large-sized hot-formed parts in the related art.

[0006] To achieve the above-mentioned object, the present invention provides a hot-formed steel, whose components, measured by mass percentage, include: C: 0.19-0.38Wt%; Si: 0.8-2.0Wt%; Mn: 0.8-2.0Wt%; P: ≤0.025Wt%; S: ≤0.01Wt%; Al: ≤0.2Wt%; B: 0.0015-0.0050Wt%; Cr: 1.5-4.0Wt%, Nb: 0.01-0.3Wt%, Ti: 0.01-0.3Wt%, and the balance is Fe and unavoidable impurities.

[0007] Preferably, its components, by mass percentage, include: C: 0.19-0.38Wt%; Si: 1.3-2.0Wt%; Mn: 0.8-2.0Wt%; P: ≤0.025Wt%; S: ≤0.01Wt%; Al: ≤0.2Wt%; B: 0.0020-0.0050Wt%; Cr: 3.0-4.0Wt%, Nb: 0.01-0.3Wt%, Ti: 0.01-0.3Wt%, and the balance is Fe and unavoidable impurities.

[0008] The beneficial effects of the present invention are:

[0009] The present invention provides a hot-formed steel that not only has high-temperature oxidation resistance but also has good crack resistance and high strength by selecting appropriate components and contents. The hot-formed parts prepared based on the hot-formed steel provided by the present invention have excellent performance in all aspects, thereby solving the technical problems of deformation, cracking and rusting that exist in the related art when producing more complex or large-sized hot-formed parts.

[0010] The present invention also provides a method for preparing the hot-formed steel, comprising:

[0011] Continuously casting the molten steel to obtain a continuous casting billet, wherein the composition of the continuous casting billet is the same as that of the hot-formed steel;

[0012] The continuous casting billet is sequentially subjected to hot rolling and pickling and cold rolling to obtain hot-formed steel; the pickling and cold rolling includes pickling, cold rolling, annealing, flattening and coiling.

[0013] Preferably, the hot rolling temperature in the hot rolling step is 880-960°C.

[0014] Preferably, in the annealing step, the annealing temperature is 630-730° C. and the temperature is kept for 10-20 hours.

[0015] The beneficial effects of the present invention are:

[0016] The hot-formed steel obtained by the above preparation method has relatively uniform performance and relatively stable product quality. In addition, due to the pickling, the steel surface is free of oxide scale, smooth and flat, with good quality, which is convenient for subsequent processing and forming operations.

[0017] The present invention also provides the application of the hot-formed steel or the hot-formed steel obtained by the above-mentioned preparation method in the preparation of parts, including:

[0018] The hot-formed steel is hot stamped to obtain components, and the components are welded and heat-treated as a whole to obtain parts; the heat treatment includes heating, shaping, cooling and painting.

[0019] Preferably, in the heating step, the heating temperature is 880-950° C. and the heating time is 240-450 seconds.

[0020] Preferably, in the heating step, a protective gas atmosphere is adopted throughout the whole process, and the oxygen content in the protective gas atmosphere is ≤6%, and the dew point is ≤-15°C.

[0021] Preferably, the cooling step includes: placing the heated parts on a fixed bracket for air cooling or wind cooling.

[0022] The beneficial effects of the present invention are:

[0023] The present invention is based on a specific material in hot-formed steel with high-temperature oxidation resistance, good crack resistance and high strength, and adopts a method of first forming, welding as an assembly and then heat treating the entire part, thereby obtaining parts with excellent comprehensive performance, and the overall strength level of the parts can also be achieved. In addition, since welding is performed first and then heat treating, this method eliminates the heat-affected zone of the weld point and weld, and can simultaneously achieve the improvement of material strength and the strengthening of the tubular structure, greatly improving the overall rigidity. On this basis, the use of this hot-formed part can further achieve the thinning and weight reduction of the automobile. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0025] Figure 1 is a schematic diagram of the oxide layer thickness of a part made of hot-formed steel in Example 1 of the present invention;

[0026] Figure 2 1 is a comparison diagram of the high temperature oxidation resistance of the hot-formed steel and 22MnB5 steel in Example 1 of the present invention; (a) corresponds to 22MnB5 steel, and (b) corresponds to the hot-formed steel in Example 1.

[0027] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with the implementation methods and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] It should be noted that all directional indications (such as up, down, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components in a certain specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0030] In addition, in the present invention, the descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0031] Furthermore, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in the field. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0032] The invention provides a hot-formed steel, the components of which are, by mass percentage, C: 0.19-0.38Wt%; Si: 0.8-2.0Wt%; Mn: 0.8-2.0Wt%; P: ≤0.025Wt%; S: ≤0.01Wt%; Al: ≤0.2Wt%; B: 0.0015-0.0050Wt%; Cr: 1.5-4.0Wt%, Nb: 0.01-0.3Wt%, Ti: 0.01-0.3Wt%, and the balance is Fe and unavoidable impurities.

[0033] In some embodiments, the components thereof include, by mass percentage: C: 0.19-0.38Wt%; Si: 1.3-2.0Wt%; Mn: 0.8-2.0Wt%; P: ≤0.025Wt%; S: ≤0.01Wt%; Al: ≤0.2Wt%; B: 0.0020-0.0050Wt%; Cr: 3.0-4.0Wt%, Nb: 0.01-0.3Wt%, Ti: 0.01-0.3Wt%, and the remainder is Fe and unavoidable impurities.

[0034] Furthermore, the hot-formed steel comprises, by mass percentage, the following: C: 0.21±0.01Wt%; Si: 1.32±0.01Wt%; Mn: 1.2±0.1Wt%; P: 0.012±0.001Wt%; S: 0.002±0.0001Wt%; Al: 0.03±0.001Wt%; B: 0.0038±0.0001Wt%; Cr: 3.1±0.1Wt%, Nb: 0.052±0.001Wt%, Ti: 0.03±0.001Wt%, and the balance is Fe and unavoidable impurities.

[0035] The study found that the existing materials have poor high-temperature oxidation resistance and cracking resistance. In the process of tubular structural parts made of this raw material, heating the whole body after welding, and then cooling in the quenching liquid, different parts have different cooling speeds, which leads to deformation and cracking of the whole part due to excessive stress. In addition, it is difficult to remove rust from the inner wall of the closed part by shot blasting, and the subsequent anti-rust paint has poor adhesion, which is easy to rust and cause part failure.

[0036] Based on this, the present invention provides a method of selecting appropriate components and contents to obtain a hot-formed steel that not only has high-temperature oxidation resistance but also has good crack resistance and high strength, so that the hot-formed parts prepared using this material also have the above-mentioned properties, thereby solving the technical problems of deformation, cracking and rusting that exist in the related art when producing more complex or large-sized hot-formed parts.

[0037] Among them, C (carbon): carbon is the most important element that determines the mechanical properties of steel. Carbon atoms are often interstitially dissolved in the iron atom lattice, thereby playing an interstitial solid solution strengthening role. When carbon atoms and alloying elements form carbides and are dispersed in the crystal, they play a precipitation strengthening role. When the carbon content of steel is increased, as the amount of pearlite increases, the strength and hardness of the steel increase, while the plastic toughness decreases. Therefore, the C content is controlled at 0.19-0.38Wt% in this application.

[0038] Si (silicon): Silicon is a non-carbide forming element, which basically exists in the matrix in the form of interstitial solid solution. Therefore, silicon plays a strong role in solid solution strengthening, which can improve the strength and hardness of the material, while its toughness and plasticity are reduced. In addition, silicon can also be used as an auxiliary element to improve oxidation resistance. At high temperatures, a protective and dense SiO2 film is formed on the surface of silicon-containing heat-resistant steel. Silicon can also improve the hardenability of the material, reduce the requirements for cooling rate, and make the material meet the process requirements of air cooling hardening. Therefore, the content of Si is controlled at 1.3-2.0Wt% in this application.

[0039] Mn (manganese): Manganese is a strengthening element that can form a solid solution with the iron atoms in the steel and change its lattice structure, thereby increasing the hardness of the steel. In addition, manganese can also make the grain boundaries of the steel finer and the grain size smaller through the solid solution strengthening effect, thereby increasing the strength of the steel. This makes manganese-containing steel have higher tensile strength and hardness. Manganese can also form stable oxides and silicates in the steel, thereby forming a layer of dense oxide film and silicate film, which improves the oxidation resistance and corrosion resistance of the steel. In addition, the solid solution of manganese in steel can improve the thermal stability of the steel, prevent the steel from undergoing phase change and structural changes at high temperatures, and is beneficial to subsequent processes such as hot stamping. Therefore, the content of Mn is controlled at 0.8~2.0Wt% in this application.

[0040] B (boron): Boron can be added to steel as a trace element. It can promote the chemical reaction of steel, improve the uniformity of steel, make the composition of steel more uniform, and thus make the performance of steel more stable. In addition, the addition of boron is also conducive to improving the hardenability of steel, reducing the requirements for cooling rate, and making the material meet the process requirements of air cooling hardening. Therefore, the content of B is controlled at 0.0020-0.0050wt% in this application.

[0041] Cr (chromium): Chromium can significantly improve the hardenability of steel. At the same time, chromium is a carbide-forming element. For example, M3C and M23C6 carbides contain a certain amount of chromium. The combination of chromium and carbon effectively alleviates the decarburization sensitivity of steel, increases the activation energy of carbon, thereby reducing the graphitization tendency of steel and refining the grain size. On the other hand, chromium forms a dense and stable oxide Cr2O3 with strong adhesion inside the steel, which not only improves the oxidation resistance of the steel, but also hinders the growth of M3C carbides, thereby improving the high-temperature oxidation resistance of the steel. Therefore, in this application, the Cr content is controlled at 3.0-4.0Wt%.

[0042] Nb (Niobium): Niobium can form interstitial phases such as NbC or NbN in steel. During the recrystallization process, NbC and NbN have the effect of inhibiting grain growth, thereby greatly increasing the recrystallization time point and the recrystallization temperature of austenite, expanding the temperature range of the non-recrystallization zone, promoting the deformation of austenite grains and the "accumulation" of defects, and ultimately playing a role in grain refinement. Therefore, the content of Nb is controlled at 0.01 to 0.3 wt% in this application.

[0043] Ti (titanium): Titanium can react with nitrogen, oxygen and other elements in steel to form fine titanium nitride and titanium oxide particles. These particles can act as nucleating agents for austenite in steel, prompting austenite to nucleate and grow at a lower temperature, thereby refining the grain structure of the steel. The refined grain structure can significantly improve the strength, toughness and fatigue properties of steel. In addition, titanium can combine with carbon, nitrogen, oxygen and other elements in steel to form stable titanium carbide, titanium nitride and titanium oxide compounds. These compounds can effectively improve the corrosion resistance of steel, especially the ability to resist acidic and alkaline environments; titanium in steel can reduce the tendency of carbide precipitation during welding and reduce the embrittlement of the heat-affected zone of welding. This helps to improve the toughness and strength of the welded joint and enable titanium-containing steel to perform better during the welding process. Therefore, the titanium content is controlled at 0.01-0.3Wt% in this application.

[0044] It is worth pointing out that in the present application, Si, B, and Cr have a good synergistic effect in improving the hardenability of the steel. By controlling the appropriate content of the three, it is beneficial to reduce the requirements of the steel for the subsequent cooling rate, and under air cooling conditions, it can achieve the same strength grade as 22MNB5 after hot stamping.

[0045] Furthermore, in the present application, Si, Mn, and Cr have a good synergistic effect in improving the high-temperature oxidation resistance of steel. The SiO2 film formed by Si, the solid solution formed by Mn, and the Cr2O3 film formed by Cr in the steel constitute three lines of defense against oxidation corrosion, which effectively improves the stability of the steel under high-temperature heat treatment.

[0046] Furthermore, in the present application, both Nb and Ti have excellent crystallization refining effects. They refine the grain structure through precipitates to improve the toughness and resistance to hydrogen-induced delayed cracking of the steel, and in addition, they also improve the strength and fatigue properties of the steel.

[0047] The present invention also provides a method for preparing the hot-formed steel, comprising:

[0048] Continuously casting the molten steel to obtain a continuous casting billet, wherein the composition of the continuous casting billet is the same as that of the hot-formed steel;

[0049] The continuous casting billet is sequentially subjected to hot rolling and pickling cold rolling to obtain hot-formed steel; the pickling cold rolling includes pickling, cold rolling, annealing, flattening and coiling.

[0050] In some embodiments, the hot rolling temperature in the hot rolling step is 880-960°C.

[0051] In some embodiments, the annealing temperature in the annealing step is 630-730° C. and the temperature is maintained for 10-20 hours.

[0052] The hot-formed steel obtained by the above preparation method has relatively uniform performance and relatively stable product quality. In addition, due to the pickling, the steel surface is free of oxide scale, smooth and flat, with good quality, which is convenient for subsequent processing and forming operations.

[0053] The present invention also provides the application of the hot-formed steel or the hot-formed steel obtained by the above-mentioned preparation method in the preparation of parts, including:

[0054] The hot-formed steel is hot stamped to obtain components, and the components are welded and heat-treated as a whole to obtain parts; the heat treatment includes heating, shaping, cooling and painting.

[0055] In the present invention, by using hot-formed steel with high-temperature oxidation resistance, good crack resistance and high strength, and adopting the method of forming first, welding as an assembly and then heat treating the whole, it can be achieved that the parts are all 1500MPa strength level; in the present invention, since welding is done first and then heat treating, this method eliminates the heat-affected zone of the weld joint and weld, and can simultaneously achieve the improvement of material strength and the strengthening of the tubular structure, greatly improving the overall rigidity. On this basis, the use of this hot-formed part can further achieve the reduction of automobile thickness and weight. In addition, taking Example 1 as an example, see Figure 1 As shown, the average oxide layer thickness of the parts made of the hot-formed steel of the present invention is 0.87 um, which meets the use requirements.

[0056] In some embodiments, the heating temperature in the heating step is 880-950° C., and the heating time is 240-450 s.

[0057] After welding, the components are heated to the target temperature, so that the steel begins to change phase, gradually changing from solid to austenite, and the temperature is evenly maintained for a period of time. This ensures that the overall temperature is uniform, avoids local overheating or overcooling, and ensures that the steel parts are cooled evenly in the subsequent cooling process, thereby obtaining ideal structure and performance.

[0058] In addition, during the heating process, the stress inside the steel part will gradually release and decrease, reducing the risk of cracks and deformation during the subsequent cooling process.

[0059] In some embodiments, during the heating step, a protective gas atmosphere is adopted throughout the entire process, and the oxygen content in the protective gas atmosphere is ≤6%, and the dew point is ≤-15°C.

[0060] By selecting the appropriate oxygen content and dew point, the oxidation of materials in the furnace can be reduced, and the thickening of the oxide layer and powdering and shedding can be avoided.

[0061] In some embodiments, the cooling step includes: placing the heated parts on a fixed bracket for air cooling or wind cooling.

[0062] Air cooling or wind cooling can prevent parts from contacting the quenching liquid and causing contamination of the parts, ensuring that the surface quality meets the requirements of direct coating; compared with water cooling process, air cooling and wind cooling can cool each part more evenly, which is beneficial to reduce deformation caused by thermal stress of parts.

[0063] Example

[0064] The following examples more specifically describe the disclosure of the present application, which are intended for illustrative purposes only, as it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0065] Example 1: Preparation of hot-formed steel: A method for preparing hot-formed steel comprises continuously casting molten steel to obtain a continuous casting billet;

[0066] The continuous casting billet was hot rolled and pickled and cold rolled in sequence to obtain a hot-formed steel with a thickness of 1.2 mm (the hot-formed steel obtained in this embodiment and the steel of type 22MnB5 were heated at 950°C for 3 minutes and then cooled. The results are as follows Figure 2 The pickling cold rolling includes pickling, cold rolling, annealing (hood annealing), leveling and coiling. The hot-formed steel includes, by mass percentage: C: 0.21Wt%; Si: 1.32Wt%; Mn: 1.2Wt%; P: 0.012Wt%; S: 0.002Wt%; Al: 0.03Wt%; B: 0.0038Wt%; Cr: 3.1Wt%, Nb: 0.052Wt%, Ti: 0.03Wt%, and the balance is Fe and unavoidable impurities.

[0067] In this embodiment, the hot rolling temperature in the hot rolling step is 920°C.

[0068] In this embodiment, the annealing temperature in the annealing step is 660° C. and the annealing time is 15 hours.

[0069] Parts preparation: hot stamping hot-formed steel to obtain parts, welding the parts and heating, shaping, cooling and painting the whole to obtain a 1.2×40×50×300mm square tube;

[0070] In the heating step, the heating temperature is 930° C. and the heating time is 300 s.

[0071] In the heating step, a protective gas atmosphere is adopted throughout the whole process, and the oxygen content in the protective gas atmosphere is ≤6%, and the dew point is ≤-15°C.

[0072] The cooling step is to place the heated parts on a fixed support for air cooling or wind cooling.

[0073] Embodiment 2: The difference from Embodiment 1 is that the hot-formed steel comprises, in mass percentage, the following: C: 0.19Wt%; Si: 2.0Wt%; Mn: 0.8Wt%; P: 0.025Wt%; S: 0.005Wt%; Al: 0.02Wt%; B: 0.0015Wt%; Cr: 4.0Wt%, Nb: 0.01Wt%, Ti: 0.01Wt%, and the remainder is Fe and unavoidable impurities.

[0074] Embodiment 3: The difference from Embodiment 1 is that the hot-formed steel comprises, in percentage by mass: C: 0.38Wt%; Si: 0.8Wt%; Mn: 2.0Wt%; P: 0.012Wt%; S: 0.01Wt%; Al: ≤0.015Wt%; B: 0.0050Wt%; Cr: 1.5Wt%, Nb: 0.3Wt%, Ti: 0.3Wt%, and the remainder is Fe and unavoidable impurities.

[0075] Embodiment 4: The difference from Embodiment 1 is that the hot-formed steel comprises, in percentage by mass: C: 0.25Wt%; Si: 1.5Wt%; Mn: 1.0Wt%; P: 0.025Wt%; S: 0.001Wt%; Al: 0.05Wt%; B: 0.0020Wt%; Cr: 1.9Wt%, Nb: 0.05Wt%, Ti: 0.2Wt%, and the remainder is Fe and unavoidable impurities.

[0076] Comparative example 1: The difference from Example 1 is that the hot-formed steel comprises, in mass percentage, the following: C: 0.25Wt%; Si: 0.5Wt%; Mn: 3.0Wt%; P: 0.025Wt%; S: 0.001Wt%; Al: 0.05Wt%; B: 0.0020Wt%; Cr: 1.0Wt%, Nb: 0.1Wt%, Ti: 0.15Wt%, and the balance is Fe and unavoidable impurities.

[0077] Comparative Example 2: The difference from Example 1 is that the hot-formed steel comprises, in mass percentage, the following: C: 0.31Wt%; Si: 3.0Wt%; Mn: 0.5Wt%; P: 0.025Wt%; S: 0.001Wt%; Al: 0.05Wt%; B: 0.0020Wt%; Cr: 5.0Wt%, Nb: 0.01Wt%, Ti: 0.25Wt%, and the balance is Fe and unavoidable impurities.

[0078] Comparative Example 3: The difference from Example 1 is that the hot-formed steel comprises, by mass percentage, C: 0.20Wt%; Si: 1.6Wt%; Mn: 1.1Wt%; P: 0.015Wt%; S: 0.002Wt%; Al: 0.09Wt%; B: 0.0026Wt%; Cr: 2.9Wt%, Ti: 0.40Wt%, and the balance is Fe and unavoidable impurities. (Nb is not included)

[0079] Comparative Example 4: The difference from Example 1 is that the hot-formed steel comprises, by mass percentage, C: 0.31Wt%; Si: 3.0Wt%; Mn: 0.5Wt%; P: 0.025Wt%; S: 0.001Wt%; Al0.05Wt%; B: 0.0020Wt%; Cr: 5.0Wt%, Nb: 0.4Wt%, and the balance is Fe and unavoidable impurities. (Ti is not contained).

[0080] The hot-formed steels and corresponding parts prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to performance tests (the performance tests included the yield strength, tensile strength, elongation required in GB / T 34566-2017, and the surface quality of parts and oxide layer thickness not clearly specified in the standard), wherein the performance results of the hot-formed steels are shown in Table 1, and the performance results of the corresponding parts are shown in Table 2.

[0081] Table 1 Performance results of hot-formed steels obtained in Examples 1-4 and Comparative Examples 1-4

[0082]

[0083]

[0084] Table 2 Performance results of parts obtained from Examples 1-4 and Comparative Examples 1-4

[0085] project Yield strength / MPa Tensile strength / MPa Elongation / A50% Oxide layer thickness / um Surface condition Example 1 1170 1570 10.5 0.87 Smooth Example 2 1035 1410 7.5 0.82 Smooth Example 3 1565 1980 6.0 1.7 Smooth but yellowish Example 4 1100 1480 8.0 1.2 Smooth Comparative Example 1 870 1160 11.2 3.1 Blue Gray Comparative Example 2 1470 1870 4.5 0.80 There are black spots Comparative Example 3 1080 1490 5.5 0.93 Smooth Comparative Example 4 1505 1810 4.0 0.85 There are black spots

[0086] The above technical solutions of the present invention are only preferred embodiments of the present invention, and the patent scope of the present invention is not limited thereto. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A hot-formed steel, characterized in that: Its components include, by mass percentage: C: 0.19-0.38Wt%; Si: 0.8-2.0Wt%; Mn: 0.8-2.0Wt%; P: ≤0.025Wt%; S: ≤0.01Wt%; Al: ≤0.2Wt%; B: 0.0015-0.0050Wt%; Cr: 1.5-4.0Wt%, Nb: 0.01-0.3Wt%, Ti: 0.01-0.3Wt%, and the balance is Fe and inevitable impurities.

2. The hot-formed steel according to claim 1, characterized in that: Its components include, by mass percentage: C: 0.19-0.38Wt%; Si: 1.3-2.0Wt%; Mn: 0.8-2.0Wt%; P: ≤0.025Wt%; S: ≤0.01Wt%; Al: ≤0.2Wt%; B: 0.0020-0.0050Wt%; Cr: 3.0-4.0Wt%, Nb: 0.01-0.3Wt%, Ti: 0.01-0.3Wt%, and the balance is Fe and unavoidable impurities.

3. A method for preparing the hot-formed steel according to claim 1 or 2, characterized in that: include: Continuously casting the molten steel to obtain a continuous casting billet, wherein the composition of the continuous casting billet is the same as the hot-formed steel according to claim 1 or claim 2; The continuous casting billet is sequentially subjected to hot rolling and pickling cold rolling to obtain hot-formed steel; the pickling cold rolling includes pickling, cold rolling, annealing, flattening and coiling.

4. The preparation method according to claim 3, characterized in that: The hot rolling temperature in the hot rolling step is 880-960°C.

5. The preparation method according to claim 3, characterized in that: In the annealing step, the annealing temperature is 630-730° C. and the temperature is kept for 10-20 hours.

6. Application of the hot-formed steel according to claim 1 or 2 or the hot-formed steel obtained by the preparation method according to any one of claims 3 to 5 in the preparation of parts, characterized in that: include: The hot-formed steel is hot stamped to obtain components, and the components are welded and heat-treated as a whole to obtain parts; the heat treatment includes heating, shaping, cooling and painting.

7. The use according to claim 6, characterized in that: In the heating step, the heating temperature is 880-950° C. and the heating time is 240-450 seconds.

8. The use according to claim 6, characterized in that: In the heating step, a protective gas atmosphere is adopted throughout the whole process, and the oxygen content in the protective gas atmosphere is ≤6%, and the dew point is ≤-15°C.

9. The use according to claim 6, characterized in that: The cooling step includes: placing the heated parts on a fixed support for air cooling or wind cooling.

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