Hot-formed composite steel plate, and hot-stamped component and manufacturing method therefor

Abstract

Disclosed in the present invention is a hot-formed composite steel plate, comprising a stainless steel layer and a carbon steel layer, wherein the stainless steel layer is located on the surface of the carbon steel layer; the chemical composition of the stainless steel layer comprises, in percentage by mass: C: 0.01-0.15%, Si: 0.1-1.5%, Mn: 0.8-2.6%, Ni: 5-25%, Cr: 13-30%, P: 0.04% or less, S: 0.03% or less, and N: 0.1% or less, the balance being Fe and other inevitable impurities; and the chemical composition of the carbon steel layer comprises, in percentage by mass: C: 0.30-0.40%, Si: 0-1.3%, Mn: 0-2.0%, B: 0-0.010%, Ti: 0-0.20%, Nb: 0-0.20%, V: 0-0.20%, Cr: 0-1.0%, Ni: 0-1.0%, Cu: 0-1.0%, P: ≤ 0.02%, S: ≤ 0.02%, Al: 0.01-0.05%, and N: ≤ 0.01%, the balance being Fe and other inevitable impurities. Also disclosed in the present invention are a hot-stamped component and a manufacturing method therefor. Thus, the corrosion resistance and delayed cracking resistance of the hot-stamped component are improved.

Description

Hot-formed composite steel sheet, hot-stamped part and method for manufacturing the same TECHNICAL FIELD

[0001] The present application relates to a steel sheet and a hot-stamped part, in particular to a hot-formed composite steel sheet, a hot-stamped part and a method for manufacturing the same. BACKGROUND

[0002] In recent years, high-strength steel mainly used for hot forming of automobiles reduces weight, is low-carbon and environmentally friendly. High-strength thinning, energy saving and emission reduction have always been the main development trend of the automobile industry. With the increase of the strength level of parts, the forming difficulty of traditional forming methods such as cold stamping is getting higher and higher, and challenges are encountered in production cost and part manufacturability.

[0003] The production and manufacture of partially cold-formed composite sheets can alleviate such problems, but cold-formed steel sheets require special manufacturing processes to achieve high strength, such as complex processes such as secondary annealing for production, which is complex and uncontrollable in cost.

[0004] Hot stamping is a new way to achieve high strength of products, which is a combination of heat treatment and high-temperature forming to achieve high strength of products, which can greatly simplify the manufacturing process of the steel plant and improve the formability of high-strength steel sheets. Commonly used hot-stamped products mainly include front and rear door left and right bumper rods (beams), front and rear bumpers, A-pillar reinforcement plates, B-pillar reinforcement plates, C-pillar reinforcement plates, floor center channels, roof reinforcement beams and other safety structural parts. These hot-stamped products have the characteristics of high strength, complex shape, good formability, high dimensional accuracy and small springback.

[0005] With the improvement of corrosion resistance requirements, more and more hot-formed parts need surface corrosion resistance. The surface state of hot-stamped steel is divided into bare plate and plated steel plate. Hot-stamped steel plate with plating has better corrosion resistance than bare plate, but the most commonly used zinc-based plating will produce cracks to the substrate in hot stamping, which cannot maintain the corrosion resistance of the steel plate. The corrosion resistance of the other aluminum-silicon plating is insufficient. The aforementioned hot-formed structural steel has made great progress, but there are still some performance deficiencies in the use process that need to be solved, such as the corrosion resistance cannot meet the demand of hot-stamped parts. SUMMARY

[0006] The present application provides a hot-formed composite steel sheet, a hot-stamped part and a method for manufacturing the same to solve the above problems.

[0007] In a first aspect, the embodiments of the present application disclose a hot-formed composite steel sheet, comprising a stainless steel layer and a carbon steel layer, the stainless steel layer being located on the surface of the carbon steel layer.

[0008] The chemical composition of the stainless steel layer includes, by mass percentage, C: 0.01-0.15%, Si: 0.1-1.5%, Mn: 0.8-2.6%, Ni: 5-25%, Cr: 13-30%, P: 0.04% or less, S: 0.03% or less, N: 0.1% or less, and the balance of Fe and other inevitable impurities.

[0009] The chemical composition of the carbon steel layer includes, by mass percentage, C: 0.30-0.40%, Si: 0-1.3%, Mn: 0-2.0%, B: 0-0.010%, Ti: 0-0.20%, Nb: 0-0.20%, V: 0-0.20%, Cr: 0-1.0%, Ni: 0-1.0%, Cu: 0-1.0%, P: ≤0.02%, S: ≤0.02%, Al: 0.01-0.05%, N: ≤0.01%, and the balance of Fe and other inevitable impurities.

[0010] In some embodiments, after the hot stamping, the microstructure of the stainless steel layer is austenite, and the microstructure of the carbon steel layer is martensite and ferrite, with the volume fraction of the martensite being 90-97%.

[0011] With the above technical solution, the hot-formed composite steel plate has a stainless steel layer and a carbon steel layer, and after hot stamping, the microstructure of the stainless steel layer is austenite, and the microstructure of the carbon steel layer is martensite + ferrite, with the volume fraction of the martensite being 90-97%, good corrosion resistance, and high tensile strength.

[0012] In some embodiments, after the hot stamping, the hot-stamped part has a tensile strength of 1700-2100 MPa, such as 1700-2050 MPa, and a surface pitting corrosion potential of less than or equal to 0.5 V, such as 0.25-0.5 V.

[0013] In some embodiments, after the hot stamping, the hot-stamped part has a yield strength of 1500-1780 MPa and an elongation of ≥2.5%, such as 2.5-6.0%.

[0014] In this document, the heating temperature of the hot stamping is 900-1000°C, and the holding time is less than or equal to 5 min, such as 0.5-5 min.

[0015] Optionally, the mass percentage of the chemical elements of the carbon steel layer satisfies 1.2%≤Mn+Cr≤2.5%.

[0016] Optionally, the stainless steel layer and the carbon steel layer comprise a transition layer, the transition layer comprises, in order from the surface of the adjacent carbon steel layer outward, a carbon steel decarburization layer and a stainless steel carburization layer, the thickness of the stainless steel carburization layer is less than or equal to 5% of the thickness of the hot-formed composite steel sheet and less than or equal to 50 μm.

[0017] In a second aspect, the present application also discloses a hot-stamped part, the raw material for preparation comprising the hot-formed composite steel sheet according to any one of the embodiments of the first aspect.

[0018] With the above technical solution, the hot-stamped part has good hardenability, strength and resistance to delayed cracking, and corrosion resistance.

[0019] Optionally, the tensile strength of the hot-stamped part is 1700 MPa to 2100 MPa, and the surface pitting corrosion potential is less than or equal to 0.5 V.

[0020] In some embodiments, the microstructure of the stainless steel layer of the hot-stamped part is austenite, and the microstructure of the carbon steel layer is martensite and ferrite, the volume fraction of the martensite being 90% to 97%.

[0021] In some embodiments, the tensile strength of the hot-stamped part is 1700 MPa to 2100 MPa, such as 1700 MPa to 2050 MPa, and the surface pitting corrosion potential is less than or equal to 0.5 V, such as 0.25 to 0.5 V.

[0022] In some embodiments, the yield strength of the hot-stamped part is 1500 MPa to 1780 MPa, and the elongation is ≥2.5%, such as 2.5% to 6.0%.

[0023] In a third aspect, the present application also discloses a manufacturing method of a hot-formed composite steel sheet, for manufacturing the hot-formed composite steel sheet according to any one of the embodiments of the first aspect, comprising the following steps:

[0024] Manufacture of a slab: manufacture of a slab of the carbon steel layer and the stainless steel layer;

[0025] Slab assembly: heating temperature is 1100 to 1260 °C (such as 1200 to 1260 °C);

[0026] Composite rolling: first heated to a heating temperature of 1100 to 1260 °C (such as 1200 to 1260 °C), holding time is 0.6 hours or more (such as 0.6 to 5 hours, or 0.6 hours to 280 min), hot rolling is performed, the heating temperature of the hot rolling is controlled to be above the Ar3 temperature, the finish rolling temperature is greater than or equal to 880 °C (such as 880 to 1000 °C or 880 to 920 °C), rapid cooling is performed at a cooling speed of 30 to 100 °C / s (such as 30 to 80 °C / s), and the coiling temperature is controlled to be 500 to 600 °C;

[0027] cold rolling: the controlled cold rolling reduction is 0-70% (e.g. 20-70%);

[0028] annealing: the annealing temperature is 1050-1150℃, the holding time is greater than 30s (e.g. 40-100s or 40-80s), and the cooling is to room temperature, wherein, the rapid cooling is performed in the temperature range of 500-900℃, and the controlled cooling speed is greater than or equal to 20℃ / s (e.g. 20-200℃ / s or 50-200℃ / s).

[0029] By precisely controlling the heating temperature in the blanking step, the heating temperature in the compound rolling step, and the heating temperature and holding time in the hot stamping step, the austenite microstructure of the stainless steel layer is obtained, the thickness of the stainless steel carbonization layer in the transition layer is less than or equal to 70 microns, and the corrosion resistance and crack resistance of the steel plate are improved.

[0030] Optionally, in the blanking and compound rolling steps, the blanking heating temperature and the hot rolling heating temperature are less than or equal to 1260℃ (e.g. 1200-1260℃), and the blanking holding time and the hot rolling holding time are less than or equal to 280min (e.g. 100-280min or 120-280min); wherein, the blanking high-temperature section holding time and the hot rolling high-temperature section holding time are less than or equal to 80min (e.g. 20-80min), and the blanking high-temperature section and the hot rolling high-temperature section are the heating temperature interval of 1150-1260℃.

[0031] In a fourth aspect, the present application also discloses a manufacturing method of a hot stamped part, which performs hot stamping on the hot formed composite steel plate manufactured by the manufacturing method of the hot formed composite steel plate of any one of the embodiments of the third aspect, and the hot stamping comprises: the heating temperature is 900-1000℃, and the holding time is less than or equal to 5min (e.g. 0.5-5min, 1-5min or 2.5-4min).

[0032] By using the above technical solution, the corrosion resistance of the hot stamped part is improved, and the surface pitting corrosion potential of the hot stamped part is less than or equal to 0.5V.

[0033] Optionally, in the hot stamping step, when the heating temperature is 900-930℃, the holding time is controlled to be less than or equal to 5min; when the heating temperature is 931-950℃, the holding time is controlled to be less than or equal to 4min; when the heating temperature is 950-970℃, the holding time is controlled to be less than or equal to 2.5min; and when the heating temperature is greater than or equal to 971℃, the holding time is controlled to be less than or equal to 1.5min.

[0034] Optionally, the method further comprises: low temperature tempering, wherein the heating temperature of the low temperature tempering is 100-300 DEG C (for example, 120-250 DEG C), and the tempering time is greater than or equal to 20 min (for example, 20-100 min). BRIEF DESCRIPTION OF DRAWINGS

[0035] Fig. 1 shows a structural schematic diagram of the hot-formed composite steel plate according to the present application.

[0036] Fig. 2 shows another structural schematic diagram of the hot-formed composite steel plate according to the present application.

[0037] In the figure, 1 represents a carbon steel layer, 2 represents a stainless steel layer, 3 represents a carbon steel decarburization layer, and 4 represents a stainless steel carburization layer. DETAILED DESCRIPTION

[0038] The following will describe the embodiments of the present application by specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the disclosure. Although the description of the present application will be introduced in combination with the preferred embodiments, this does not mean that the features of the present application are limited to the embodiments. On the contrary, the purpose of introducing the present application in combination with the embodiments is to cover other options or modifications which can be extended based on the claims of the present application. In order to provide a deep understanding of the present application, many specific details will be included in the following description. The present application can also be implemented without using these details. In addition, in order to avoid confusion or obscure the focus of the present application, some specific details will be omitted in the description. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0039] It should be noted that in the present specification, similar reference numbers and letters represent similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0040] The present application describes the improvement points and process parameters in each step for the manufacturing method of high-temperature carburizing axle tooth steel, and other specific operation details can refer to the existing process.

[0041] In order to make the purpose, technical solutions and advantages of the present application more clear, the embodiments of the present application will be further described in detail below in combination with the drawings.

[0042] Although the corrosion resistance of hot-formed steel sheets can be improved by plating in the prior art, the inventors have found that hot-formed steel sheets after plating will still cause poor corrosion resistance due to cracking of the plating layer during hot forming. Thus, the inventors thought of improving the corrosion resistance of hot-formed steel sheets by combining stainless steel and carbon steel. In particular, by combining austenitic stainless steel and carbon steel, the austenitic stainless steel refers to stainless steel having an austenitic structure at room temperature. Austenitic stainless steel performs well in corrosion resistance, heat resistance, low temperature strength and mechanical properties, and has good stamping and bending workability, no heat treatment hardening phenomenon, no magnetism, and is widely used in the petroleum, chemical, power and atomic energy industries. However, it is found that the strength that can be achieved by austenitic stainless steel does not match the requirements of hot-stamped parts, and the cost of stainless steel is difficult to control due to the addition of precious alloy. Therefore, the inventors expect to provide a hot-formed composite steel sheet in which stainless steel and carbon steel are combined, the tensile strength is greater than 1700 MPa, and the hot-formed composite steel sheet has good corrosion resistance.

[0043] In a first aspect, as shown in FIG. 1, the embodiment of the present application discloses a hot-formed composite steel sheet, which comprises a stainless steel layer 2 and a carbon steel layer 1, and the stainless steel layer 2 is located on the surface of the carbon steel layer 1. Specifically, when the hot-formed composite steel sheet of the present application comprises one stainless steel layer 2 and one carbon steel layer 1, the stainless steel layer 2 is located on the upper surface or the lower surface of the carbon steel layer 1; when the hot-formed composite steel sheet of the present application comprises two stainless steel layers 2 and one carbon steel layer 1, it is similar to a sandwich structure, one stainless steel layer 2 is located on the upper surface of the carbon steel layer 1, and one stainless steel layer 2 is located on the lower surface of the carbon steel layer 1. Wherein, the thickness ratio of the stainless steel layer 2 and the carbon steel layer 1 can be arbitrary.

[0044] The stainless steel layer as the stainless steel layer 2 in the present application is an alloy steel mainly composed of iron, carbon and at least 13% of chromium. The addition of chromium provides oxidation resistance, so that the stainless steel layer 2 has excellent corrosion resistance. The stainless steel layer 2 can also include nickel and other elements to enhance its structure and performance. The stainless steel layer 2 with austenitic microstructure in the present application is a classic grade known to those skilled in the art, which has a relatively fixed composition requirement, and the composition of the stainless steel layer covers various austenitic stainless steel grades.

[0045] In some embodiments, the chemical composition of the stainless steel layer, such as stainless steel layer 2, includes, by mass percent: C: 0.01-0.15%, Si: 0.1-1.5%, Mn: 0.8-2.6%, Ni: 5-25%, Cr: 13-30%, P: ≤0.04%, S: ≤0.03%, N: ≤0.1%, and the balance of Fe and other inevitable impurities. In some embodiments, the content of C in the stainless steel layer is 0.01-0.05%. In some embodiments, the content of Si in the stainless steel layer is 0.3-0.6%. In some embodiments, the content of Mn in the stainless steel layer is 1.1-1.6%. In some embodiments, the content of Ni in the stainless steel layer is 7-13%. In some embodiments, the content of Cr in the stainless steel layer is 15-20%. In some embodiments, the chemical composition of the stainless steel layer includes, by mass percent: C: 0.01-0.05%, Si: 0.3-0.6%, Mn: 1.1-1.6%, Ni: 7-13%, Cr: 15-20%, P: ≤0.04%, S: ≤0.03%, N: ≤0.1%, and the balance of Fe and other inevitable impurities.

[0046] The carbon steel layer 1 of the present application is mainly composed of iron and carbon, and the content of carbon affects the hardness, strength and plasticity of the carbon steel layer 1. The carbon content of the carbon steel layer 1 is between 0.30% and 0.40%, and a small amount of silicon can also be contained. The inventors have found that the addition of elements such as C, Si, Mn, Cr, B, etc. in the carbon steel layer 1 can improve the hardenability of the material and ensure the formation of a martensitic structure after hot stamping. Specifically, after hot stamping, the microstructure of the carbon steel layer 1 is martensite and ferrite, wherein the volume fraction of martensite is greater than or equal to 90% and less than or equal to 97%. Controlling the volume fraction of martensite in the above range ensures the final strength. The addition of elements such as Nb and Ti in the carbon steel layer 1 can inhibit the grain from being too large and also play a role in precipitation strengthening. The addition of Cu and Ni in the carbon steel layer 1 can improve the potential difference between the carbon steel layer 1 and the stainless steel layer 2, improve the interlayer battery effect, and improve the corrosion resistance.

[0047] In some embodiments, the chemical composition of the carbon steel layer, such as carbon steel layer 1, includes, by mass percent: C: 0.30-0.40%, Si: 0-1.3%, Mn: 0-2.0%, B: 0-0.010%, Ti: 0-0.20%, Nb: 0-0.20%, V: 0-0.20%, Cr: 0-1.0%, Ni: 0-1.0%, Cu: 0-1.0%, P: ≤0.02%, S: ≤0.02%, Al: 0.01-0.05%, N: ≤0.01%, and the balance of Fe and other inevitable impurities.

[0048] The present application optimizes the system component design of the stainless steel layer 2 and the carbon steel layer 1, specifically, the stainless steel layer 2 adopts the stainless steel component system design with the microstructure of austenite, the carbon steel layer 1 adopts the high hardenability hot stamping steel component system design, the carbon steel layer 1 provides the basis for the specific mechanical properties of the hot forming composite steel plate, and the content of Cr, Ni and Cu elements in the stainless steel layer 2 and the carbon steel layer 1 is reasonably controlled, so that the stainless steel layer 2 and the carbon steel layer 1 are matched with each other, the hot forming composite steel plate can be obtained, which not only has good tensile strength, but also has high corrosion resistance.

[0049] In the hot forming composite steel plate of the present application, the design principles of each chemical element of the carbon steel layer 1 are as follows:

[0050] C: In the steel plate described in the present application, the addition of C element can not only improve the strength of the steel, but also improve the hardness of the martensite to ensure the occurrence of martensite phase change. The inventors have found that when the mass percentage of C element in the steel is less than 0.3%, the strength of the steel plate will be affected; and when the mass percentage of C element in the steel is higher than 0.40%, the hardness of the martensite is prone to be too high, and the grain size is coarse, which is not conducive to the toughness of the steel plate. Therefore, the mass percentage of C element is controlled between 0.30-0.40%.

[0051] Si: In the steel plate described in the present application, the addition of Si element can improve the hardenability of the steel. And the solid solution of Si in the steel can affect the interaction of dislocations, increase the work hardening rate, and appropriately improve the elongation, which is beneficial to the steel to obtain better formability. Therefore, in order to play the beneficial effect of Si element, the mass percentage of Si element is controlled between 0-1.3%, preferably, the mass percentage of Si element is controlled between 0.20-1.10 or 0.30-0.99%.

[0052] Mn, Cr: In the steel plate described in the present application, the addition of Mn and Cr elements can not only improve the hardenability of the steel, but also effectively improve the strength of the steel plate. When the mass percentage of Mn and Cr elements in the steel is too high, the carbon equivalent will be significantly improved, which has a negative impact on the welding performance and delayed cracking resistance of the steel. Therefore, the mass percentage of Mn element is controlled between 0-2%, preferably between 1-2%. The mass percentage of Cr element is controlled between 0-1.0%, preferably between 0.1%-0.8%.

[0053] At the same time, in order to ensure reasonable hardenability, limit the carbon equivalent and the final microstructure strength after hot stamping, ensure the toughness and delayed cracking resistance of the material, control 1.2%≤Mn+Cr≤2.3%.

[0054] Al: In the steel sheet described in the present invention, the addition of an appropriate amount of Al element in the steel can play a role of deoxidation and grain refinement. Therefore, in order to exert the beneficial effect of Al element, the mass percentage content of Al element is controlled in the present invention between 0.01-0.05%.

[0055] B: In the steel sheet described in the present invention, B is an element that can significantly improve the hardenability of the steel, and the addition of B element can promote the formation of martensite and ensure the strength of the steel sheet after hot stamping. However, it should be noted that the content of B element in the steel should not be too high. After the grain boundary defects are filled, if more B is added, the grain boundary energy will be increased due to the precipitation of "boron phase" at the grain boundary, and at the same time, the "boron phase" will also act as a core for new phase formation, promoting the increase of nucleation rate, resulting in the decrease of hardenability of the steel. Therefore, the mass percentage content of B element is controlled in the present invention between 0-0.010%. In some embodiments, the content of B in the carbon steel layer is 0-0.008%.

[0056] Ti: In the steel sheet described in the present invention, the addition of strong carbide-forming element Ti will show a strong effect of inhibiting the growth of austenite grains at high temperature, and the addition of Ti element in the steel also helps to refine the grains. Therefore, in order to exert the beneficial effect of Ti element, the mass percentage content of Ti element is controlled in the present invention between 0-0.20%. In some embodiments, the content of Ti in the carbon steel layer is 0.01-0.10%.

[0057] Nb, V: In the steel sheet described in the present invention, the addition of strong carbide-forming element Nb can produce carbide precipitation of Nb during hot rolling and continuous annealing, which can produce significant precipitation strengthening effect. Therefore, in the present invention, the mass percentage content of Nb element is controlled between 0-0.20%. In some embodiments, the content of Nb in the carbon steel layer is 0-0.06%. Therefore, in the present invention, the mass percentage content of V element is controlled between 0-0.20%. In some embodiments, the content of V in the carbon steel layer is 0-0.10%, such as 0%.

[0058] Cr, Cu, Ni: In the steel sheet described in the present invention, the addition of Cr, Cu, Ni can improve the potential difference between the carbon steel layer and the stainless steel layer, improve the interlayer battery effect, and improve the corrosion resistance. Therefore, in the present invention, the mass percentage content of Cr element is controlled between 0-1.0%, such as 0.1-0.8%. Therefore, in the present invention, the mass percentage content of Cu element is controlled between 0-1.0%, such as 0-0.6%. Therefore, in the present invention, the mass percentage content of Ni element is controlled between 0-1.0%, such as 0-0.3%.

[0059] In some embodiments, the chemical composition of the carbon steel layer according to the present application includes, in terms of mass percentage, C: 0.30-0.40%, Si: 0.2-1.1%, Mn: 1.0-2.0%, B: 0-0.008%, Ti: 0.01-0.10%, Nb: 0-0.06%, V: 0-0.10%, Cr: 0.1-0.8%, Ni: 0-0.3%, Cu: 0-0.6%, P: ≤0.02%, S: ≤0.02%, Al: 0.01-0.05%, N: ≤0.01%, and the balance of Fe and other inevitable impurities.

[0060] In the hot-formed composite steel sheet according to the present application, the inevitable impurity elements should be controlled as low as possible, but considering the process level and the limitation of manufacturing cost, therefore, the inevitable elements such as P ≤0.02%, S ≤0.02%, N ≤0.01% are controlled.

[0061] As shown in FIG. 2, the hot-formed composite steel sheet according to the present application includes, between the stainless steel layer 2 and the carbon steel layer 1, a transition layer which includes, in order from the surface of the carbon steel layer 1, a carbon steel decarburization layer 3 and a stainless steel carburization layer 4.

[0062] The inventors found that the hot-formed clad steel plate is prone to cracking or cracking during long-term use due to bearing continuous load and stress. Therefore, it is necessary to improve the resistance to delayed cracking performance of the hot-formed clad steel plate. The resistance to delayed cracking performance refers to the ability of the material to resist crack propagation or fracture after bearing continuous load or stress. After in-depth research, it is found that the transition layer is caused by the composition difference diffusion between the stainless steel and the carbon steel layer, which includes the carbon steel decarburization layer 3 and the stainless steel carburization layer 4. Through a large number of experimental researches, it is found that the carbon steel decarburization layer 3 does not affect the performance of the hot-formed clad steel plate because the strength is between that of carbon steel and stainless steel, while the carbon equivalent of the stainless steel carburization layer 4 is high (the carbon equivalent refers to the content of various alloying elements in steel converted into carbon. The carbon content is the main factor affecting the strength and weldability of carbon steel. The empirical formula of the carbon equivalent of carbon steel and alloy structural steel: the carbon equivalent CE (percentage) value can be calculated according to the following formula: CE = C + Mn / 6 + (Cr + V + Mo) / 5 + (Cu + Ni) / 15, wherein: C, Mn, Cr, Mo, V, Ni, and Cu are the mass content of the corresponding elements in the steel). The stainless steel carburization layer 4 often obtains high strength and low toughness structure after hot stamping, and also reduces the interlayer bonding force, which reduces the strength and toughness of the steel plate; there are also micro cavities, inclusions or alloy carbides and other hydrogen traps, hydrogen will diffuse to the surface of the micro cavities, inclusions or alloy carbides of the interface transition layer, especially in the case of residual stress, it is more prone to enrichment, which affects the resistance to delayed cracking performance. In order to avoid the above problems, the thickness of the stainless steel carburization layer 4 is controlled to be less than or equal to 5% of the thickness of the hot-formed clad steel plate and less than or equal to 50 μm. Experimental verification shows that the resistance to delayed cracking performance of the material is good, and the hydrogen embrittlement test of the pickling ultra-high strength steel and the stamping part can be carried out according to GMW17508. In some embodiments, the thickness of the stainless steel carburization layer 4 is 1.0-5.0% of the thickness of the hot-formed clad steel plate and is between 20-50 μm.

[0063] In the second aspect, the present application provides a hot stamped part prepared from the hot-formed clad steel plate of the above embodiments. The hot stamped part obtained by using the above hot-formed clad steel plate has good hardenability, strength and resistance to delayed cracking performance, and corrosion resistance, and the strength performance of the hot stamped part is improved after the hot-formed clad steel plate is hot stamped.

[0064] In the hot stamped part of the above embodiments, the tensile strength is 1700 MPa-2100 MPa, and the surface pitting corrosion potential is less than or equal to 0.5 V. The surface pitting corrosion potential can be used to evaluate the corrosion resistance of the hot stamped part. The smaller the surface pitting corrosion potential, the better the corrosion resistance. Generally, when the surface pitting corrosion potential is not higher than 0.7, it is considered that the corrosion resistance is good.

[0065] In some embodiments, the microstructure of the stainless steel layer of the hot stamped component is austenite, the microstructure of the carbon steel layer is martensite and ferrite, and the volume fraction of the martensite is 90% to 97%.

[0066] In some embodiments, the hot stamped component has a yield strength of 1500 MPa to 1780 MPa and an elongation of ≥ 2.5%, such as 2.5% to 6.0%.

[0067] According to the known prior art, the inventors have found, through in-depth research, that the manufacturing method of the hot forming steel in the prior art, when applied to the hot forming composite steel sheet, causes maladjustment of the stainless steel layer 2 in the composite steel sheet, and the corrosion resistance and tensile strength of the steel sheet cannot achieve the expected target. After various attempts and experiments, the inventors have determined the following technical solutions and proposed a manufacturing method specifically applicable to the hot forming composite steel sheet and the hot stamped component having a stainless steel layer and a carbon steel layer.

[0068] In a third aspect, the present application provides a manufacturing method of a hot forming composite steel sheet, for manufacturing the hot forming composite steel sheet of each of the above embodiments, comprising the following steps:

[0069] (1) Slab manufacturing: manufacturing a slab of the carbon steel layer and a slab of the stainless steel layer.

[0070] (2) Slab assembly: assembling the slab of the carbon steel layer and the slab of the stainless steel layer into a slab assembly, and controlling the heating temperature of the slab assembly to be 1100-1260℃.

[0071] (3) Composite rolling: first heated to a heating temperature of 1100-1260℃, and held for more than 0.6 hours, then hot rolled, with the hot rolling heating temperature controlled to be above the Ar3 temperature, the finish rolling temperature greater than 880℃, rapid cooling at a cooling rate of 30-100℃ / s, and the coiling temperature controlled to be 500-600℃.

[0072] (4) Cold rolling: controlling the cold rolling reduction rate to be 0-70%.

[0073] (5) Annealing: annealing at a temperature of 1050-1150℃, with a holding time of 30-100s, and cooling to room temperature, wherein the rapid cooling is performed in a temperature range of 500-900℃, and the cooling rate is controlled to be more than 20℃ / s, such as 20-200℃ / s or 20-100℃ / s.

[0074] The present application controls the process conditions of the slab manufacturing step, the slab assembling step, the composite rolling step, the cold rolling step and the annealing step to ensure the fit and bonding between the stainless steel layer and the carbon steel layer, to obtain a hot forming composite plate structure with multiple layers, and also to obtain the corrosion resistance. The microstructure of the stainless steel layer 2 is austenite, thereby improving the corrosion resistance of the steel plate. Meanwhile, after the composite steel plate obtained by the above method is subjected to hot stamping to form a hot stamped part, the microstructure of the stainless steel layer 2 is austenite, and the microstructure of the carbon steel layer 1 is martensite and ferrite, thereby improving the strength performance of the hot stamped part.

[0075] The inventors also found through experimental comparison that in the composite rolling step, the lower the finishing temperature, the higher the coiling temperature, and the more carbides and sigma phases are precipitated at the grain boundaries. When other rolling process parameters are the same, lower finishing temperature and higher coiling temperature are more likely to precipitate carbides and sigma phases, thereby more likely to cause intergranular corrosion. However, too high finishing temperature and too low coiling temperature cannot be stably controlled, so the present application finally controls the finishing temperature to be 880-1000°C (such as 880-920°C), and the steel is rapidly cooled at a speed of 30-100°C / s (such as 30-80°C / s) after rolling, and the coiling temperature is controlled to be 500-600°C.

[0076] Further, the preparation method of the present application only includes one annealing, and in the annealing step, annealing is performed at a temperature of 1050-1150°C to re-dissolve the precipitated carbides, and then rapidly cooled to room temperature. Due to the fast cooling speed, the dissolved carbon cannot combine with other alloying elements to precipitate, thereby improving the intergranular corrosion resistance of the steel plate. When the solid solution temperature of the stainless steel layer 2 is higher than 1150°C, the grain size becomes coarse, and the grain size grade decreases, which reduces the corrosion resistance of the steel plate. Therefore, the annealing temperature of the present application is controlled to be 1050-1150°C. The inventors also found that by controlling the specific temperature in the above method, the thickness of the austenitic stainless steel carbonizing layer 4 in the transition layer can be controlled to be less than or equal to 50 microns, thereby improving the delayed cracking resistance of the hot forming composite steel plate, and further improving the corrosion resistance of the steel plate.

[0077] Specifically, in order to control the thickness of the stainless steel carbonization layer 4, the interlayer composition diffusion must be controlled. The interlayer composition diffusion is directly related to the temperature-time product of high-temperature heating. Therefore, the present application first controls the billet heating temperature and the hot rolling heating range to be 1100-1260°C. Preferably, in the billet and composite rolling steps, the billet heating temperature and the hot rolling heating temperature are less than or equal to 1260°C, the billet heating temperature range is 1100-1260°C, the hot rolling heating temperature range is Ar3-1260°C, the billet holding time and the hot rolling holding time are each 36-300 min, such as 36 min-280 min or 200-280 min; wherein the billet high-temperature holding time and the hot rolling high-temperature holding time are each 20-80 min or 40-80 min, the billet high-temperature section and the hot rolling high-temperature section are the heating interval of the heating temperature 1150-1260°C; through the above process, the thickness of the stainless steel carbonization layer 4 in the transition layer can be further controlled to be less than or equal to 50 microns and less than or equal to 5% of the thickness of the hot-formed composite steel plate.

[0078] Through the above steps, a hot-formed composite steel plate can be manufactured. The present application improves the hot-formed composite steel plate manufacturing method, adjusts the process, controls the thickness of the stainless steel carbonization layer 4, the combination of the carbon and other alloy elements in solid solution in the stainless steel layer and the precipitation, and the escape of free hydrogen in the carbon steel layer, to improve the corrosion resistance and delayed cracking resistance of the steel plate. The present application mainly improves the billet and composite rolling. Specifically, in the composite rolling step, the product of the billet heating temperature and time and the product of the hot rolling heating temperature and time are controlled to control the interlayer composition diffusion and further control the carbonization layer thickness, so that the steel plate of the present application has good delayed cracking resistance. At the same time, the annealing temperature and cooling system of the annealing step in the manufacturing process are controlled, so that the precipitated carbide is re-dissolved and no longer precipitates, thereby improving the corrosion resistance.

[0079] In some embodiments, the thickness ratio of the carbon steel layer slab and the slab of all stainless steel layers is 4-10. When one layer of carbon steel layer and one layer of stainless steel layer are used, the thickness ratio of the two can be 9-10.

[0080] In a fourth aspect, the present application also discloses a method for manufacturing a hot-stamped part, which comprises the manufacturing method of the hot-formed composite steel plate of any of the preceding embodiments, and further comprises a hot stamping step, wherein the heating temperature of the hot stamping is 900-1000°C, and the holding time is less than or equal to 5 min.

[0081] Specifically, after the annealing step is completed and the hot-formed composite steel plate is obtained, the hot stamping and low-temperature tempering steps are sequentially performed.

[0082] (6) Hot stamping: the heating temperature is 900-1000 °C, and the holding time is controlled to be less than or equal to 5 min, specifically, the holding time is 0.5-5 min. If the holding time is too long in the hot stamping step, the grains will become coarse, and the grain size grade will decrease, which will reduce the corrosion resistance of the steel strip. The process control of the holding time less than or equal to 5 min and the heating temperature ensures that the surface stainless steel layer 2 obtains a reasonable austenitic structure, guarantees the corrosion resistance, and makes the surface pitting corrosion potential of the hot stamped part less than or equal to 0.5 V.

[0083] (7) Low temperature tempering: the heating temperature of the low temperature tempering is controlled to be 100-300 °C (such as 120-250 °C), and the tempering time is greater than or equal to 20 min, specifically, the tempering time is 20-120 min or 21-120 min, such as 20-100 min. Because the austenitic structure in the stainless steel layer has a high free hydrogen solid solubility, the free hydrogen in the inner carbon steel layer will not be able to escape normally, so that the delayed cracking resistance of the hot stamped part cannot be maintained. The inventors have made various attempts and experiments, and propose to adjust the low temperature tempering process, which is matched with the control of the thickness of the stainless steel carbonization layer, so as to further improve the delayed cracking resistance of the hot stamped part.

[0084] Preferably, in the hot stamping step, when the heating temperature is 900-930 °C, the holding time is less than or equal to 5 min, specifically, the holding time is 2-5 min; when the heating temperature is 931-950 °C, the holding time is less than or equal to 4 min, specifically, the holding time is 2-4 min; when the heating temperature is 950-970 °C, the holding time is less than or equal to 2.5 min, specifically, the holding time is 1-2.5 min; when the heating temperature is greater than or equal to 971 °C, the holding time is less than or equal to 1.5 min, specifically, the holding time is 0.5-1.5 min. Through the above process control, the austenitic stainless steel grain growth can be further avoided, so that the surface pitting corrosion potential of the steel sheet of the present application is less than or equal to 0.4 V, and has better corrosion resistance.

[0085] The mutual cooperation of the process conditions of the above-mentioned embodiments ensures that the hot stamped part of the present application is composed of the suitable stainless steel layer 2 and carbon steel layer 1, and also has good tensile strength, corrosion resistance and delayed cracking resistance. The hot stamped part passes the delayed cracking resistance test (according to the standard test of hydrogen embrittlement test of pickling super high strength steel and stamping parts according to GMW17508).

[0086] The manufacturing method of the hot stamped part of the present application will be further described in detail below.

[0087] Examples 1-5 and Comparative Examples 1-2

[0088] The hot stamped parts of Examples 1-5 are all prepared by the following steps:

[0089] (1) Slab manufacturing: manufacturing of slab of carbon steel layer and slab of stainless steel layer.

[0090] (2) Grouping: combining the slab of carbon steel layer and the slab of stainless steel layer into a group slab, and controlling the heating temperature to be 1100-1260°C.

[0091] (3) Compound rolling: heating to the heating temperature of 1100-1260°C first, and holding for 0.6-5 hours, and then hot rolling, controlling the heating temperature of the hot rolling to be above the Ar3 temperature, controlling the finish rolling temperature to be 880-1000°C, rapidly cooling at the cooling speed of 30-100°C / s, and controlling the coiling temperature to be 500-600°C.

[0092] (4) Cold rolling: controlling the cold rolling reduction to be 0-70%.

[0093] (5) Annealing: annealing at the temperature of 1050-1150°C, holding for 30-100s, and cooling to room temperature, wherein, rapidly cooling in the temperature range of 500-900°C, and controlling the cooling speed to be 20-100°C / s.

[0094] (6) Hot stamping: when the heating temperature is 900-1000°C, controlling the holding time to be less than or equal to 5min.

[0095] Examples 3 and 4 further include a low temperature tempering step, controlling the heating temperature of the low temperature tempering to be 100-300°C, and controlling the tempering time to be greater than 20min.

[0096] Comparative Example 1

[0097] (1) Slab manufacturing: manufacturing of slab of carbon steel layer and slab of stainless steel layer.

[0098] (2) Grouping: combining the slab of carbon steel layer and the slab of stainless steel layer into a group slab, and controlling the heating temperature to be 1280°C.

[0099] (3) Compound rolling: heating to the heating temperature of 1100-1260°C first, and holding for 0.6-5 hours, and then hot rolling, controlling the heating temperature of the hot rolling to be above the Ar3 temperature, controlling the finish rolling temperature to be 880-1000°C, rapidly cooling at the cooling speed of 30-100°C / s, and controlling the coiling temperature to be 500-600°C.

[0100] (4) Cold rolling: controlling the cold rolling reduction to be 0-70%.

[0101] (5) Annealing: annealing at the temperature of 1050-1150°C, holding for 30-100s, and cooling to room temperature, wherein, rapidly cooling in the temperature range of 500-900°C, and controlling the cooling speed to be 20-100°C / s.

[0102] (6) Hot stamping: the heating temperature is 900-1000 °C, and the holding time is controlled to be less than or equal to 5 min.

[0103] Comparative Example 2

[0104] (1) Slab manufacturing: manufacturing of a slab of carbon steel layer and a slab of stainless steel layer.

[0105] (2) Grouping: the carbon steel layer slab and the stainless steel layer slab are compounded into a group slab, and the heating temperature is controlled to be 1100-1260 °C.

[0106] (3) Compound rolling: first heated to a heating temperature of 1100-1260 °C, and the holding time is 0.6-2 hours, hot rolling is performed, the hot rolling heating temperature is controlled to be above Ar3 temperature, the finishing temperature is 880-1000 °C, rapid cooling is performed at a cooling speed of 30-100 °C / s, and the coiling temperature is controlled to be 500-600 °C.

[0107] (4) Cold rolling: the cold rolling reduction is controlled to be 0-70 %.

[0108] (5) Annealing: the annealing temperature is 1050-1150 °C, the holding time is 30-100 s, and cooling to room temperature, wherein, rapid cooling is performed in a temperature range of 500-900 °C, and the cooling speed is controlled to be 20-100 °C / s.

[0109] (6) Hot stamping: the heating temperature is 990 °C, and the holding time is 10 min.

[0110] The steel plate compositions of the examples and the comparative examples are shown in Table 1, and the process parameters are shown in Table 2-1 and Table 2-2.

[0111] Table 1 lists the chemical compositions of the cast steel plates of the present application, including the mass percentages of the steel plate chemical compositions of Examples 1 to 6 and the mass percentages of the chemical composition of Comparative Example 1 (%), and the rest is Fe and other unavoidable impurities except P, S and N.

[0112] Table 1: Mass percentages of chemical compositions of different examples and comparative examples of hot formed composite steel plates (wt%, the rest is Fe and other unavoidable impurities except P, S and N)

[0113] Table 2-1

[0114] Table 2-2

[0115] The volume fraction of martensite, the thickness of the stainless steel carburized layer, the thickness of the stainless steel carburized layer accounting for the total thickness of the composite steel plate, the tensile strength, the yield strength, the elongation, the plate thickness, the surface pitting potential and the delayed cracking resistance of the examples and the comparative examples were evaluated, and the specific data are shown in Table 3. Among them, the tensile strength, the yield strength and the elongation were detected according to GB / T 228.1-2010 "Metallic Materials-Tensile Testing-Part 1: Method of Test at Room Temperature" using a 50 gauge sample. The surface pitting potential was determined by GB / T 17899-1999 "Stainless Steel Pitting Potential Measurement Method", and the delayed cracking resistance was tested according to GMW17508 "Hydrogen Embrittlement Test Standard for Acid Immersion Ultra High Strength Steel and Stamping Parts". The thickness of the stainless steel carburized layer and the volume fraction of martensite were tested according to GB / T 18876.1-2002 "Standard Test Method for Determining Metallographic Structure, Inclusion Content and Grade of Steel and Other Metals by Automatic Image Analysis".

[0116] Table 3: Determination results of examples and comparative examples

[0117] As shown in Table 3, the thickness of the stainless steel carburized layer 4 of the hot forming composite steel plate of the examples 1-5 of the present application is less than or equal to 5% of the thickness of the hot forming composite steel plate and less than or equal to 50 μm; the volume fraction of martensite of the hot stamping parts of each example of the present application is 90%-97%, the tensile strength is 1710 MPa-2100 MPa, the surface pitting corrosion potential is less than or equal to 0.5 V, the corrosion resistance is good, and all have good delayed cracking resistance.

[0118] Further, some of the examples 1-4 further satisfy that in the hot stamping step, when the heating temperature is 900-930℃, the holding time is less than or equal to 5 min; when the heating temperature is 931-950℃, the holding time is less than or equal to 4 min; when the heating temperature is 950-970℃, the holding time is less than or equal to 2.5 min; and when the heating temperature is greater than 971℃, the holding time is less than or equal to 1.5 min. At this time, the surface pitting corrosion potential can be further reduced to less than or equal to 0.4 V, and the corrosion resistance is further improved.

[0119] Regarding example 4, it further satisfies that in the low temperature tempering step, the heating temperature of the low temperature tempering is 100-300℃, and the tempering time is greater than 20 min. The delayed cracking resistance of the hot stamping part is further improved, so that the surface pitting corrosion potential can be further reduced to 0.27 V.

[0120] With respect to Comparative Example 1, the heating temperature of the group blank in the group blanking and composite rolling step is above 1260℃, the holding time of the group blank is above 280min, and the holding time of the high temperature section of the group blank is above 80min, so that the stainless steel carbonized layer thickness is greater than 50μm and greater than 5% of the thickness of the hot formed composite steel plate, and the steel plate is NG in the delayed cracking resistance evaluation.

[0121] With respect to Comparative Example 2, the Ni content of the stainless steel layer is less than 5%, the Cr content is less than 13%, the Mn content is greater than 2.6%, and in the hot stamping step, when the heating temperature is 990℃, the holding time is controlled to be greater than 5min for 10min, so that the surface pitting corrosion potential is 0.72V, and the corrosion resistance is poor.

[0122] In summary, the present application provides a method for manufacturing a hot stamped part, which is controlled through a group blanking step, a composite rolling step, a hot stamping step, and a low temperature tempering step. The heating temperature and time product in the group blanking and composite rolling step and the temperature and time product in the hot stamping step are specifically controlled, and the heating temperature and tempering time in the low temperature tempering step are also controlled. When the steel plate of the stainless steel layer and the carbon steel layer is selected as the base material of the composite steel plate, the thickness of the stainless steel carbonized layer can be controlled in a lower range, the strength and toughness of the composite steel plate can be controlled, and the surface layer austenite grain size of the composite steel plate can be controlled, so that the high strength is obtained, and the corrosion resistance and delayed cracking resistance of the hot stamped part are improved, so as to be more widely applied subsequently. The hot stamped part has different strength levels from 1700MPa to 2100MPa, and has good application prospect and value.

[0123] Although the present application has been illustrated and described with reference to certain preferred embodiments thereof, it should be understood by those skilled in the art that the foregoing is a further detailed description of the application, and is not to be construed as limiting the application to the specific embodiments described. Various modifications and changes can be made thereto by those skilled in the art without departing from the spirit and scope of the application.

Claims

1. A hot-formed composite steel plate, characterized in that, It includes a stainless steel layer and a carbon steel layer, wherein the stainless steel layer is located on the surface of the carbon steel layer; The chemical composition of the stainless steel layer, by mass percentage, includes: C: 0.01–0.15%, Si: 0.1–1.5%, Mn: 0.8–2.6%, Ni: 5–25%, Cr: 13–30%, P: 0.04% and below, S: 0.03% and below, N: 0.1% and below, with the balance being Fe and other unavoidable impurities; The chemical composition of the carbon steel layer, by mass percentage, includes: C: 0.30–0.40%, Si: 0–1.3%, Mn: 0–2.0%, B: 0–0.010%, Ti: 0–0.20%, Nb: 0–0.20%, V: 0–0.20%, Cr: 0–1.0%, Ni: 0–1.0%, Cu: 0–1.0%, P: ≤0.02%, S: ≤0.02%, Al: 0.01–0.05%, N: ≤0.01%, with the balance being Fe and other unavoidable impurities.

2. The hot-formed composite steel plate as described in claim 1, characterized in that, The chemical composition of the stainless steel layer has one or more of the following characteristics: The content of C is 0.01-0.05%; The Si content is 0.3-0.6%; The Mn content is 1.1–1.6%; The Ni content is 7-13%; and The Cr content is 15-20%; Preferably, the chemical composition of the stainless steel layer, by mass percentage, includes: C: 0.01-0.05%, Si: 0.3-0.6%, Mn: 1.1-1.6%, Ni: 7-13%, Cr: 15-20%, P: ≤0.04%, S: ≤0.03%, N: ≤0.1%, balance Fe and other unavoidable impurities.

3. The hot-formed composite steel plate as described in claim 1 or 2, characterized in that, The chemical composition of the stainless steel layer has one or more of the following characteristics: The content of C is 0.30-0.40%; The Si content is 0.2%–1.1%; The Mn content is 1.0–2.0%; The content of B is 0-0.008%; The Ti content is 0.01–0.10%; The Nb content is 0–0.06%; The content of V is 0-0.10%; The Cr content is 0.1%–0.8%; The Ni content is 0-0.3%; and The Cu content is 0–0.6%; Preferably, the chemical composition of the carbon steel layer, by mass percentage, includes: C: 0.30–0.40%, Si: 0.2–1.1%, Mn: 1.0–2.0%, B: 0–0.008%, Ti: 0.01–0.10%, Nb: 0–0.06%, V: 0–0.10%, Cr: 0.1–0.8%, Ni: 0–0.3%, Cu: 0–0.6%, P: ≤0.02%, S: ≤0.02%, Al: 0.01–0.05%, N: ≤0.01%, with the balance being Fe and other unavoidable impurities.

4. The hot-formed composite steel plate according to any one of claims 1-3, characterized in that, The chemical element mass percentage of the carbon steel layer satisfies: 1.2% ≤ Mn + Cr ≤ 2.5%.

5. The hot-formed composite steel sheet according to any one of claims 1-4, characterized in that, Between the stainless steel layer and the carbon steel layer is a transition layer, which includes, along the surface of the adjacent carbon steel layer, a carbon steel decarburization layer and a stainless steel carbonization layer, wherein the thickness of the stainless steel carbonization layer is less than or equal to 5% of the thickness of the hot-formed composite steel plate and less than or equal to 50 μm.

6. The hot-formed composite steel sheet according to any one of claims 1-5, characterized in that, The hot-stamped component formed by hot stamping of the hot-formed composite steel plate has one or more of the following characteristics: (1) The microstructure of the stainless steel layer of the hot stamping component is austenite, and the microstructure of the carbon steel layer is martensite and ferrite, wherein the volume fraction of the martensite is 90% to 97%. (2) The tensile strength of the hot-stamped component is 1700 MPa to 2100 MPa, and the surface pitting corrosion potential is less than or equal to 0.5 V; and (3) The yield strength of the hot-stamped part is 1500MPa~1780MPa and the elongation is ≥2.5%, such as 2.5~6.0%.

7. A hot-stamped component, characterized in that, The raw materials for its preparation include the hot-formed composite steel sheet as described in any one of claims 1-6.

8. The hot-stamped component as described in claim 7, characterized in that, The hot-stamped component has one or more of the following characteristics: (1) The tensile strength of the hot-stamped part is 1700MPa~2100MPa, and the surface pitting corrosion potential is less than or equal to 0.5V; (2) The tensile strength of the hot-stamped component is 1700 MPa to 2100 MPa, and the surface pitting corrosion potential is less than or equal to 0.5 V; and (3) The yield strength of the hot-stamped part is 1500MPa~1780MPa and the elongation is ≥2.5%, such as 2.5~6.0%.

9. A method for manufacturing a hot-formed composite steel plate, characterized in that, The method for manufacturing the hot-formed composite steel sheet as described in any one of claims 1-6 comprises the following steps: Slab manufacturing: Manufacturing slabs with carbon steel and stainless steel layers; Billet assembly: Heating temperature is 1100~1260℃; Composite rolling: First, heat to a heating temperature of 1100-1260℃ and hold for more than 0.6 hours, then hot roll. The hot rolling heating temperature is controlled above the Ar3 temperature, and the final rolling temperature is greater than or equal to 880℃. Cool rapidly at a cooling rate of 30-100℃ / s and control the coiling temperature at 500-600℃. Cold rolling: Control the cold rolling reduction rate to 0-70%; Annealing: The annealing temperature is 1050~1150℃, the holding time is greater than 30s, and then cooled to room temperature. Rapid cooling is carried out in the temperature range of 500~900℃, and the cooling rate is controlled to be greater than or equal to 20℃ / s.

10. The method for manufacturing the hot-formed composite steel plate as described in claim 9, characterized in that, In the billet assembly and composite rolling steps, the billet heating temperature and the hot rolling heating temperature are less than or equal to 1260℃, and the billet holding time and the hot rolling holding time are less than or equal to 280min; wherein, the billet high-temperature section holding time and the hot rolling high-temperature section holding time are less than or equal to 80min, and the billet high-temperature section and the hot rolling high-temperature section are heating ranges with heating temperatures of 1150~1260℃.

11. The method for manufacturing the hot-formed composite steel plate as described in claim 9, characterized in that, The method has one or more of the following characteristics: (1) In the billet assembly step, the heating temperature is 1200~1260℃; (2) In the billet assembly step, the billet annealing time is 0.6 to 5 hours, or 0.6 hours to 280 minutes; (3) In the composite rolling step, the temperature is first heated to 1100-1260℃, and the holding time is 0.6-5 hours or 0.6 hours to 280 minutes. Hot rolling is then carried out. The hot rolling heating temperature is controlled above the Ar3 temperature, and the final rolling temperature is 880-1000℃ or 880-920℃. The temperature is rapidly cooled at a cooling rate of 30-100℃ / s or 30-80℃ / s, and the coiling temperature is controlled at 500-600℃. (4) In the cold rolling step, the cold rolling reduction rate is controlled to be 20-70%; (5) In the annealing step, the annealing temperature is 1050~1150℃, the holding time is 40~100s, such as 40~80s, and the temperature is cooled to room temperature. The temperature range is 500~900℃, and the cooling rate is controlled to be 20~200℃ / s or 50~200℃ / s.

12. A method for manufacturing a hot-stamped part, characterized in that, The hot-formed composite steel sheet manufactured by the manufacturing method of any one of claims 9-11 is subjected to hot stamping, wherein the heating temperature of the hot stamping is 900-1000°C or 900-970°C, and the holding time is less than or equal to 5 min, such as 0.5-5 min or 2.5-4 min.

13. The method for manufacturing a hot-stamped part as described in claim 12, characterized in that, In the hot stamping step When the heating temperature is 900-930℃, the holding time should be less than or equal to 5 minutes; when the heating temperature is 931-950℃, the holding time should be less than or equal to 4 minutes; when the heating temperature is 950-970℃, the holding time should be less than or equal to 2.5 minutes; when the heating temperature is greater than or equal to 971℃, the holding time should be less than or equal to 1.5 minutes.

14. The method for manufacturing a hot-stamped part as described in claim 12, characterized in that, The method further includes: low-temperature tempering, wherein the heating temperature for low-temperature tempering is 100-300°C and the tempering time is greater than 20 minutes.

15. The method for manufacturing a hot-stamped part as described in claim 12, characterized in that, The method further includes: low-temperature tempering, wherein the heating temperature for low-temperature tempering is 120–250°C and the tempering time is 20–100 min.

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