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 components of the stainless steel layer comprise, in percentages 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, N: 0.1% or less, and the balance of Fe and other inevitable impurities; and the chemical components of the carbon steel layer comprise, in percentages by mass: C: 0.10-0.20%, Si: 0-2.0%, Mn: 0-2.0%, B: 0-0.010%, Ti: 0-0.10%, Nb: 0-0.050%, V: 0-0.05%, Cr: 0-0.5%, 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. Further disclosed in the present invention are a hot-stamped component and a manufacturing method therefor, so as to improve the corrosion resistance and delayed cracking resistance of the hot stamped component.

Description

A hot-formed composite steel plate, a hot-stamped component, and a method for manufacturing the same. Technical Field

[0001] This invention relates to a steel plate and a hot-stamped component, and more particularly to a hot-formed composite steel plate, a hot-stamped component, and a method for manufacturing the same. Background Technology

[0002] In recent years, high-strength steel has been mainly used for weight reduction in automotive hot forming steel, achieving weight reduction, low carbon emissions, and environmental protection. High strength and thinning, as well as energy conservation and emission reduction, have always been the main development trends in the automotive industry. As the strength level of parts increases, the traditional forming method of cold stamping becomes increasingly difficult to form, encountering challenges in terms of production costs and part manufacturability.

[0003] The production of some cold-formed composite plates can alleviate these problems, but achieving high strength in cold-formed steel plates requires special manufacturing processes, such as complex processes like secondary annealing, which are complicated and have uncontrollable costs.

[0004] Hot stamping is an emerging method for achieving high strength in products. It combines heat treatment and high-temperature forming to achieve high strength, significantly simplifying steel mill manufacturing processes and improving the formability of high-strength steel sheets. Commonly used hot-stamped products include: front and rear door side impact beams (beams), front and rear bumpers, A-pillar reinforcement plates, B-pillar reinforcement plates, C-pillar reinforcement plates, floor center tunnels, roof reinforcement beams, and other safety structural components. These hot-stamped products are characterized by high strength, complex shapes, good formability, high dimensional accuracy, and low springback.

[0005] With increasingly stringent regulations on corrosion resistance, more and more hot-formed parts require surface corrosion resistance. Hot-stamping steel is available in two surface conditions: bare sheet and coated sheet. Coated hot-stamping steel offers better corrosion resistance than bare sheet. However, the most commonly used zinc-based coating can develop cracks in the substrate during hot stamping, failing to maintain the steel's corrosion resistance. Another type, aluminum-silicon coating, offers insufficient corrosion resistance. While the aforementioned hot-formed structural steels have made significant progress, some performance shortcomings still need to be addressed, such as insufficient corrosion resistance to meet the requirements of hot-stamped parts. Summary of the Invention

[0006] This invention provides a hot-formed composite steel plate, a hot-stamped component, and a method for manufacturing the same, in order to solve the above-mentioned problems.

[0007] In a first aspect, embodiments of the present invention disclose 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;

[0008] 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;

[0009] The chemical composition of the carbon steel layer, by mass percentage, includes: C: 0.10–0.20%, Si: 0–2.0%, Mn: 0–2.0%, B: 0–0.010%, Ti: 0–0.10%, Nb: 0–0.050%, V: 0–0.05%, Cr: 0–0.5%, Ni: 0–1.0%, Cu: 0–1.0%, P: ≤0.02%, S: ≤0.02%, Al: 0.01–0.05%, N: ≤0.01%; the balance is Fe and other unavoidable impurities.

[0010] In some embodiments, after hot stamping, the microstructure of the stainless steel layer of the hot-formed composite steel sheet of the present invention is austenite, and the microstructure of the carbon steel layer is martensite, ferrite and retained austenite, with a volume fraction of 70-87% for martensite and a volume fraction of 2-8% for retained austenite.

[0011] Using the above technical solution, the hot-formed composite steel plate of the present invention has a stainless steel layer and a carbon steel layer. After hot stamping, the microstructure of the stainless steel layer is austenite, and the microstructure of the carbon steel layer is martensite, ferrite and retained austenite. The volume fraction of martensite is 70-87%, and the volume fraction of retained austenite is 2-8%. It has good corrosion resistance and high tensile strength.

[0012] In some embodiments, the hot-formed composite steel sheet of the present invention, after hot stamping, results in a hot-stamped component with a tensile strength of 900 MPa to 1250 MPa, a surface pitting corrosion potential less than or equal to 0.5 V, a strength-ductility product greater than or equal to 11000, and a 90° bending capacity R / t ≤ 2.5. In some embodiments, the resulting hot-stamped component has a tensile strength of 920 MPa to 1180 MPa. In some embodiments, the resulting hot-stamped component has a yield strength of 680 MPa to 960 MPa, such as 690 to 950 MPa. In some embodiments, the resulting hot-stamped component has an elongation ≥ 11.5%, such as 11.5% to 16.5%. In some embodiments, the resulting hot-stamped component has a strength-ductility product of 11000 to 18000. In some embodiments, the resulting hot-stamped component has a surface pitting corrosion potential of 0.25 to 0.45 V. In some embodiments, the hot stamping is performed at a heating temperature of 900–1000°C and a holding time of 0.5–5 min.

[0013] Optionally, the chemical element mass percentage of the carbon steel layer satisfies: 1.2% ≤ Mn + Cr ≤ 2.0%.

[0014] Optionally, a transition layer is included between the stainless steel layer and the carbon steel layer. This transition layer, extending outwards from the surface of the adjacent carbon steel layer, includes 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 4.5% of the thickness of the hot-formed composite steel sheet and less than or equal to 45 μm. In some embodiments, the thickness of the stainless steel carburization layer is 1.5 to 3.8% of the thickness of the hot-formed composite steel sheet, and this thickness is in the range of 20 to 45 μm.

[0015] Secondly, the present invention also discloses a hot-stamped component, the raw material of which includes the hot-formed composite steel plate as described in any embodiment of the first aspect. The hot-stamped component has a stainless steel layer and a carbon steel layer, wherein the microstructure of the stainless steel layer is austenite, and the microstructure of the carbon steel layer is martensite, ferrite, and retained austenite, with a volume fraction of 70-87% for martensite and 2-8% for retained austenite.

[0016] By adopting the above technical solution, the hot-stamped parts of the present invention have good hardenability, strength and resistance to delayed cracking, as well as corrosion resistance.

[0017] Optionally, the hot-stamped component has a tensile strength of 900 MPa to 1250 MPa, a surface pitting corrosion potential of less than or equal to 0.5 V, a strength-ductility product of greater than or equal to 11000, and a 90° bending capacity R / t ≤ 2.5. In some embodiments, the hot-stamped component has a tensile strength of 920 MPa to 1180 MPa. In some embodiments, the hot-stamped component has a yield strength of 680 MPa to 960 MPa, such as 690 to 950 MPa. In some embodiments, the hot-stamped component has an elongation of ≥11.5%, such as 11.5% to 16.5%. In some embodiments, the hot-stamped component has a strength-ductility product of 11000 to 18000. In some embodiments, the hot-stamped component has a surface pitting corrosion potential of 0.25 to 0.45 V.

[0018] Thirdly, the present invention also discloses a method for manufacturing a hot-formed composite steel plate, for manufacturing a hot-formed composite steel plate as described in any embodiment of the first aspect, comprising the following steps:

[0019] Slab manufacturing: Manufacturing slabs with carbon steel and stainless steel layers;

[0020] Billet assembly: Heating temperature is 1100~1260℃;

[0021] Composite rolling: First, heat to a heating temperature of 1100-1260℃ and hold for more than 0.6 hours (e.g., 0.6-5 hours or 0.6 hours to 280 minutes), then hot roll. The hot rolling heating temperature is controlled above Ar3 temperature, and the final rolling temperature is greater than or equal to 880℃ (e.g., 880-1000℃ or 880-910℃). Cool rapidly at a cooling rate of 30-100℃ / s (e.g., 30-90℃ / s), and control the coiling temperature at 500-600℃ (e.g., 520-600℃).

[0022] Cold rolling: Control the cold rolling reduction rate to 0-70% (e.g., 30-70%);

[0023] Annealing: The annealing temperature is 1050~1150℃, the holding time is greater than or equal to 30s (e.g. 30~100s or 40~80s), 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 (e.g. 20~200℃ / s).

[0024] By adopting the above technical solution, through precise control of the heating temperature in the billet assembly step, the heating temperature in the composite rolling step, and the heating temperature and holding time in the hot stamping step of the steel plate manufacturing process, it is beneficial to obtain the austenitic microstructure of the stainless steel layer and to control the thickness of the stainless steel carburized layer in the transition layer to be less than or equal to 60 micrometers, thereby improving the corrosion resistance and crack resistance of the hot stamped parts.

[0025] Optionally, 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℃.

[0026] Fourthly, the present invention also discloses a method for manufacturing a hot-stamped component, wherein a hot-formed composite steel plate manufactured by the method for manufacturing hot-formed composite steel plate according to any embodiment of the third aspect is subjected to hot stamping, wherein the heating temperature is 900-1000℃ (e.g., 920-980℃) and the holding time is controlled to be less than or equal to 5 min (e.g., 0.5-5 min).

[0027] By adopting the above technical solution, the corrosion resistance of hot-stamped parts is improved, and the surface pitting corrosion potential of hot-stamped parts is less than or equal to 0.5V.

[0028] Optionally, 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 or equal to 971℃, the holding time is less than or equal to 1.5 min.

[0029] Optionally, it also includes: low-temperature tempering, wherein the heating temperature for low-temperature tempering is 100–300°C and the tempering time is greater than 15 min. Attached Figure Description

[0030] Figure 1 shows a schematic diagram of the structure of the thermoformed composite steel plate of the present invention.

[0031] Figure 2 shows a schematic diagram of the structure of the thermoformed composite steel plate of the present invention.

[0032] In the diagram, 1 represents the carbon steel layer, 2 represents the stainless steel layer, 3 represents the carbon steel decarburization layer, and 4 represents the stainless steel carburization layer. Detailed Implementation

[0033] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0034] It should be noted that in this specification, similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0035] This invention describes the improvements and process parameters in each step of the manufacturing method of high-temperature carburized shaft gear steel. Other specific operational details can be found in existing processes.

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0037] While existing technologies can improve the corrosion resistance of hot-formed steel sheets through coating, the inventors have discovered that coating cracking during the hot-forming process still degrades the corrosion resistance of the steel sheet. Therefore, the inventors conceived of improving the corrosion resistance of hot-formed steel sheets through a composite of stainless steel and carbon steel. Specifically, they proposed a composite of austenitic stainless steel and carbon steel. Austenitic stainless steel refers to stainless steel with an austenitic structure at room temperature. Austenitic stainless steel exhibits excellent corrosion resistance, heat resistance, low-temperature strength, and mechanical properties, while also possessing good workability such as stamping and bending, exhibiting no heat treatment hardening, and being non-magnetic, making it widely used in industries such as petroleum, chemical, power, and nuclear energy. However, it was found that the achievable strength of austenitic stainless steel does not meet the requirements of hot-stamped parts, and the cost of stainless steel is difficult to control due to the addition of expensive alloys. Therefore, the inventors aim to provide a hot-formed composite steel sheet with a tensile strength greater than 900 MPa and good corrosion resistance, achieved through a combination of stainless steel and carbon steel. Meanwhile, hot-stamped steel with a strength of 900–1250 MPa is used for hot stamping in the energy-absorbing zones of parts. For these high-strength steels, in addition to strength, further improvements in elongation, bending, and other forming capabilities are needed. Higher elongation and better bending ability after hot forming contribute to improving the energy absorption capacity of hot-formed parts during impact. The inventors hope to further improve elongation, bending, and other forming capabilities. Higher elongation and better bending ability after hot forming contribute to improving the energy absorption capacity of hot-formed parts during impact.

[0038] In a first aspect, as shown in Figure 1, an embodiment of the present invention discloses a hot-formed composite steel plate, comprising a stainless steel layer 2 and a carbon steel layer 1, wherein the stainless steel layer 2 is located on the surface of the carbon steel layer 1. Specifically, when the hot-formed composite steel plate of the present invention comprises one stainless steel layer 2 and one carbon steel layer 1, the stainless steel layer 2 is located on the upper or lower surface of the carbon steel layer 1; when the hot-formed composite steel plate of the present invention comprises two stainless steel layers 2 and one carbon steel layer 1, similar to a sandwich structure, one stainless steel layer 2 is located on the upper surface of the carbon steel layer 1, and another stainless steel layer 2 is located on the lower surface of the carbon steel layer 1. The thickness ratio of the stainless steel layer 2 to the carbon steel layer 1 can be arbitrary.

[0039] The chemical composition of the stainless steel layer of the present invention, such as stainless steel layer 2, comprises, 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%, S: ≤0.03%, N: ≤0.1%, with the balance being Fe and other unavoidable impurities. In some embodiments, the C content of the stainless steel layer is 0.01–0.05%. In some embodiments, the Si content of the stainless steel layer is 0.2–0.6%. In some embodiments, the Mn content of the stainless steel layer is 1.2–1.6%. In some embodiments, the Ni content of the stainless steel layer is 6–13%. In some embodiments, the Cr content of the stainless steel layer is 14–20%. In some embodiments, the chemical composition of the stainless steel layer comprises, by mass percentage: C: 0.01–0.05%, Si: 0.2–0.6%, Mn: 1.2–1.6%, Ni: 6–13%, Cr: 14–20%, P: ≤0.04%, S: ≤0.03%, N: ≤0.1%, with the balance being Fe and other unavoidable impurities.

[0040] The carbon steel layer of the present invention, such as carbon steel layer 1, comprises, by mass percentage: C: 0.10–0.20%, Si: 0–2.0%, Mn: 0–2.0%, B: 0–0.010%, Ti: 0–0.10%, Nb: 0–0.050%, V: 0–0.05%, Cr: 0–0.5%, Ni: 0–1.0%, Cu: 0–1.0%, P: ≤0.02%, S: ≤0.02%, Al: 0.01–0.05%, N: ≤0.01%; the balance being Fe and other unavoidable impurities. In some embodiments, the Si content of the carbon steel layer is 0.2–1.6%. In some embodiments, the Mn content of the carbon steel layer is 0.8–2.0%. In some embodiments, the B content of the carbon steel layer is 0–0.007%. In some embodiments, the Ti content of the carbon steel layer is 0–0.08%. In some embodiments, the Nb content of the carbon steel layer is 0–0.03%. In some embodiments, the V content of the carbon steel layer is 0%. In some embodiments, the Cr content of the carbon steel layer is 0–0.45%. In some embodiments, the Ni content of the carbon steel layer is 0–0.3%. In some embodiments, the Cu content of the carbon steel layer is 0–0.5%. In some embodiments, the chemical composition of the carbon steel layer, by mass percentage, includes: C: 0.10–0.20%, Si: 0.2–1.6%, Mn: 0.8–2.0%, B: 0–0.007%, Ti: 0–0.08%, Nb: 0–0.030%, V: 0–0.01%, Cr: 0–0.45%, Ni: 0–0.3%, Cu: 0–0.5%, P: ≤0.02%, S: ≤0.02%, Al: 0.01–0.05%, N: ≤0.01%; the balance being Fe and other unavoidable impurities.

[0041] After hot stamping, the microstructure of the stainless steel layer of the hot-formed composite steel sheet is austenite, and the microstructure of the carbon steel layer is martensite, ferrite and retained austenite. The volume fraction of martensite is 70-87%, and the volume fraction of retained austenite is 2-8%.

[0042] In this invention, the stainless steel layer 2 is an alloy steel, mainly composed of iron, carbon, and at least 13% chromium. The addition of chromium provides antioxidant properties, giving the stainless steel layer 2 excellent corrosion resistance. The stainless steel layer 2 may also include nickel and other elements to enhance its structure and properties. The austenitic stainless steel layer 2 in this invention is a classic grade known to those skilled in the art, with relatively fixed composition requirements, and the composition of the stainless steel layer covers various austenitic stainless steel grades.

[0043] The carbon steel layer 1 of this invention is mainly composed of iron and carbon, with the carbon content affecting its hardness, strength, and ductility. The carbon content of the carbon steel layer 1 is between 0.10% and 0.20%, and may also contain a small amount of silicon. Research and analysis by the inventors have revealed that adding elements such as C, Si, Mn, Cr, and B to the carbon steel layer 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 of the hot-formed composite steel sheet consists of martensite, ferrite, and retained austenite, with a martensite volume fraction of 70-87% and a retained austenite volume fraction of 2-8%. Controlling the martensite volume fraction within the above range ensures the final strength. Furthermore, the martensite volume fraction is set to 70-84%. The higher the martensite content, the worse the elongation performance of the steel plate. As an austenite stabilizing element, the addition of a certain amount of Si can ensure that the final microstructure contains residual austenite and improve the elongation. By combining with the volume fraction of the martensite mentioned above, the steel plate can have a matching strength and elongation. Adding elements such as Nb and Ti to carbon steel layer 1 can suppress excessive grain size by utilizing the precipitation effect, and at the same time play a precipitation strengthening role. Adding Cu and Ni to carbon steel layer 1 can improve the potential difference between carbon steel layer and stainless steel layer, improve the interlayer cell effect, and improve corrosion resistance.

[0044] This invention optimizes the system composition design of stainless steel layer 2 and carbon steel layer 1. Specifically, stainless steel layer 2 adopts an austenitic microstructure, while carbon steel layer 1 adopts a high hardenability and high elongation hot-stamping steel composition. Carbon steel layer 1 provides the basis for specific mechanical properties of the hot-formed composite steel plate, and the austenitic stainless steel outer layer further improves bending performance. By rationally controlling the content of Cr, Ni, and Cu elements in stainless steel layer 2 and carbon steel layer 1, the stainless steel layer 2 and carbon steel layer 1 are well-matched, resulting in a hot-formed composite steel plate that not only has good tensile strength, elongation, and bending performance, but also high corrosion resistance.

[0045] In the hot-formed composite steel plate of the present invention, the design principles of each chemical element in the carbon steel layer 1 are as follows:

[0046] C: In the steel plate described in this invention, the addition of element C not only improves the strength of the steel but also increases the hardness of martensite, thus ensuring the occurrence of martensitic phase transformation. The inventors have found that when the mass percentage of C in the steel is below 0.1%, the strength of the steel plate is affected; while when the mass percentage of C in the steel is above 0.20%, it easily leads to excessively high martensite hardness and coarse grain size, which is detrimental to the ductility and toughness of the steel plate. Therefore, the mass percentage of C is controlled between 0.10% and 0.20%, preferably between 0.10% and 0.19%.

[0047] Si: In the steel plate described in this invention, Si dissolved in the steel can affect the interaction of dislocations and increase the work hardening rate. As an austenite stabilizing element, the addition of a certain amount of Si can ensure that the final microstructure contains retained austenite. Both effects can appropriately increase the elongation, which is beneficial to obtaining better formability of the steel. Based on this, in order to give full play to the beneficial effects of Si, the mass percentage of Si is controlled between 0 and 2.0%, such as between 0.1 and 2.0%.

[0048] Mn and Cr: In the steel plate described in this invention, the addition of Mn and Cr elements not only improves the hardenability of the steel but also effectively increases its strength. However, when the mass percentage of Mn and Cr elements in the steel is too high, the carbon equivalent will increase significantly, which negatively affects the weldability and resistance to delayed cracking of the steel. Therefore, the mass percentage of Mn element is controlled between 0% and 2.0%, such as 0.8% to 2.0%, and the mass percentage of Cr element is controlled between 0% and 0.5%.

[0049] Meanwhile, to ensure reasonable hardenability, limit the carbon equivalent and final microstructure strength after hot stamping, and guarantee the material's ductility, bending properties, toughness, and resistance to delayed cracking, the following requirements must be met: 1.2% ≤ Mn + Cr ≤ 2.0%.

[0050] Al: In the steel plate described in this invention, adding an appropriate amount of Al element can play a role in deoxidation and grain refinement. Therefore, in order to give full play to the beneficial effects of Al element, in this invention, the mass percentage content of Al element is controlled between 0.01% and 0.05%.

[0051] B: In the steel plate described in this invention, B is an element that can significantly improve the hardenability of steel. Adding B can promote martensite formation and ensure the strength of the steel plate after hot stamping. However, it should be noted that the B content in the steel should not be too high. After the grain boundary defects are filled, if more B is added, the precipitation of the "boron phase" at the grain boundaries will increase the grain boundary energy potentials. At the same time, the "boron phase" will also act as the nucleus of new phases, promoting an increase in the nucleation rate, which will lead to a decrease in the hardenability of the steel. Therefore, the mass percentage of B should be controlled between 0 and 0.010%.

[0052] Ti: In the steel plate described in this invention, the added strong carbide-forming element Ti exhibits a strong effect of inhibiting austenite grain growth at high temperatures. Simultaneously, the addition of Ti to the steel also helps refine the grains. Therefore, to maximize the beneficial effects of Ti, the mass percentage of Ti is controlled between 0 and 0.10% in this invention.

[0053] Nb and V: In the steel plate described in this invention, the added strong carbide-forming element Nb produces Nb carbide precipitation during hot rolling and continuous annealing, resulting in significant precipitation strengthening. Therefore, in this invention, the mass percentage content of Nb is controlled between 0% and 0.05%. Similarly, in this invention, the mass percentage content of V is controlled between 0% and 0.05%.

[0054] Cr, Cu, Ni: In the steel plate described in this invention, the addition of Cr, Cu, and Ni can improve the potential difference between the carbon steel layer and the stainless steel layer, improve the interlayer galvanic effect, and enhance corrosion resistance. Therefore, in this invention, the mass percentage content of Cu is controlled between 0% and 1.0%. Similarly, in this invention, the mass percentage content of Ni is controlled between 0% and 1.0%.

[0055] In the hot-formed composite steel sheet of the present invention, unavoidable impurity elements should be controlled to be as low as possible. However, considering the limitations of process level and manufacturing cost, unavoidable elements are controlled to be, for example, P ≤ 0.02%, S ≤ 0.02%, and N ≤ 0.01%.

[0056] As shown in Figure 2, the stainless steel layer 2 and the carbon steel layer 1 in the hot-formed composite steel plate of the present invention include a transition layer, which includes, in sequence, a carbon steel decarburization layer 3 and a stainless steel carbonization layer 4 along the surface of the carbon steel layer 1.

[0057] The inventors discovered that during long-term use, hot-formed composite steel sheets are prone to cracking or fracture due to continuous loads and stresses. Therefore, it is necessary to improve the delayed cracking resistance of hot-formed composite steel sheets. Delayed cracking resistance refers to the material's ability to resist crack propagation or fracture after being subjected to continuous loads or stresses. In-depth research revealed that the formation of a transition layer is caused by the diffusion of the compositional difference between the stainless steel and carbon steel layers. This transition layer consists of a decarburized carbon steel layer 3 and a carburized stainless steel layer 4. Extensive experimental research has revealed that the decarburized layer 3 of carbon steel, due to its strength falling between that of carbon steel and stainless steel, does not affect the performance of the hot-formed composite steel plate. In contrast, the carbon-enriched layer 4 of stainless steel has a high carbon equivalent (carbon equivalent refers to the carbon content of various alloying elements in steel. The carbon content is the primary factor determining the strength and weldability of carbon steel. The empirical formula for the carbon equivalent of carbon steel and alloy structural steel is: CE (percentage) value can be calculated using the following formula: CE=C+Mn / 6+(Cr+V+Mo) / 5+(Cu+Ni) / 15, where C, Mn, Cr, Mo, V, Ni, and Cu are the mass content of the corresponding elements in the steel). The stainless steel carburized layer 4 often results in a high-strength, low-toughness microstructure after hot stamping, which also reduces interlayer bonding strength, thus affecting the overall strength and elongation of the composite plate after hot forming. This leads to a decrease in the steel plate's strength, elongation, bending performance, and toughness. Furthermore, it often contains hydrogen traps such as microvoids, inclusions, or alloy carbides. Hydrogen diffuses and accumulates on the surface of these microvoids, inclusions, or alloy carbides in the interface transition layer, especially under residual stress, making the material more prone to hydrogen-induced delayed cracking and affecting its resistance to delayed cracking. To avoid these problems, this invention further controls the thickness of the stainless steel carburized layer 4 to be less than or equal to 4.5% of the thickness of the hot-formed composite steel plate and less than or equal to 45 μm. Experiments have verified that meeting this thickness requirement results in better resistance to delayed cracking, as demonstrated by hydrogen embrittlement tests on acid-etched ultra-high-strength steel and stamped parts conducted according to GMW17508.

[0058] Secondly, the present invention provides a hot-stamped component made from the hot-formed composite steel sheet described in the above embodiments. The hot-formed composite steel sheet provides the hot-stamped component with good hardenability, strength, resistance to delayed cracking, and corrosion resistance. Furthermore, after hot stamping, the carbon steel layer 1 of the hot-formed composite steel sheet has a microstructure of martensite + ferrite + retained austenite, which improves the strength performance of the hot-stamped component.

[0059] In the hot-stamped components of the above embodiments, the tensile strength is 900 MPa to 1250 MPa, the surface pitting corrosion potential is less than or equal to 0.5 V, the strength-ductility product (tensile strength × elongation) is greater than or equal to 11000, and the 90° bending capacity R / t ≤ 2.5 (R represents the minimum bending radius in mm; t represents the plate thickness in mm). The strength-ductility product is the product of tensile strength and elongation. The surface pitting corrosion potential can be used to evaluate the corrosion resistance of hot-stamped components; the lower the surface pitting corrosion potential, the better the corrosion resistance. Generally, a surface pitting corrosion potential not higher than 0.7 is considered to indicate good corrosion resistance.

[0060] Based on existing technologies, the inventors discovered through in-depth research that when existing hot-formed steel manufacturing methods are applied to hot-formed composite steel plates, the stainless steel layer 2 in the composite steel plate becomes incompatible, and the corrosion resistance and tensile strength of the steel plate fail to meet expectations. After various trials and experiments, the inventors determined the following technical solution and proposed a manufacturing method specifically applicable to hot-formed composite steel plates and hot-stamped parts with stainless steel and carbon steel layers.

[0061] Thirdly, the present invention provides a method for manufacturing a hot-formed composite steel plate, used to manufacture the hot-formed composite steel plates of the above embodiments, comprising the following steps:

[0062] (1) Slab manufacturing: Manufacturing slabs with carbon steel and stainless steel layers.

[0063] (2) Assembly: The heating temperature is 1100~1260℃.

[0064] (3) Composite rolling: First, heat to a heating temperature of 1100~1260℃, hold for 0.6~5 hours, and then perform hot rolling. The hot rolling heating temperature is controlled above 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 to 500~600℃.

[0065] (4) Cold rolling: Control the cold rolling reduction rate to 0-70%.

[0066] (5) Annealing: The annealing temperature is 1050~1150℃, the holding time is 30~100s, and the temperature is cooled to room temperature. In particular, rapid cooling is carried out in the temperature range of 500~900℃, and the cooling rate is controlled to be above 20℃ / s, such as 20~200℃ / s or 20~100℃ / s.

[0067] This invention ensures a suitable bond between the stainless steel and carbon steel layers by controlling the process conditions of the slab manufacturing, assembly, composite rolling, cold rolling, and annealing steps, thereby obtaining a multi-layered composite plate structure, which is also a prerequisite for achieving corrosion resistance. It also obtains a stainless steel layer 2 with an austenitic microstructure, thus improving the corrosion resistance of the steel plate. Furthermore, after the composite steel plate obtained by the above method is hot-stamped to form a hot-stamped component, the microstructure of the stainless steel layer 2 is austenitic, and the microstructure of the carbon steel layer 1 is martensite, ferrite, and retained austenite, improving the strength performance of the hot-stamped component.

[0068] The inventors also discovered through experimental comparison that in the composite rolling process, the lower the final rolling temperature and the higher the coiling temperature, the more carbides and σ phases precipitate at the grain boundaries. With other rolling process parameters remaining the same, a lower final rolling temperature and a higher coiling temperature make it easier for carbides and σ phases to precipitate, thus increasing the likelihood of intergranular corrosion. However, excessively high final rolling temperatures and excessively low coiling temperatures cannot be stably controlled. Therefore, it was ultimately determined that the final rolling temperature should be greater than 880–1000℃, with rapid cooling at a rate of 30–100℃ / s after rolling, and the coiling temperature controlled at 500–600℃.

[0069] Furthermore, the preparation method of this invention includes only one annealing step. In this annealing step, annealing is performed within a temperature range of 1050–1150°C, allowing the precipitated carbides to be re-dissolved, followed by rapid cooling to room temperature. Due to the rapid cooling rate, the dissolved carbon does not have enough time to combine with other alloying elements and precipitate, thereby improving its resistance to intergranular corrosion. When the solution temperature of the stainless steel layer 2 exceeds 1150°C, the grains become coarser, and the grain size grade decreases, which reduces the corrosion resistance of the strip. Therefore, this invention controls the annealing temperature to be between 1050 and 1150°C.

[0070] The inventors also discovered that by controlling the specific temperature in the above method, the thickness of the austenitic stainless steel carbonized layer 4 in the transition layer can be controlled to be less than or equal to 60 micrometers, thereby improving the delayed cracking resistance of the hot-formed composite steel plate and thus improving the corrosion resistance of the steel plate.

[0071] Specifically, to control the thickness 4 of the stainless steel carburized layer, it is necessary to control the interlayer component diffusion. Interlayer component diffusion is directly related to the product of temperature and time during high-temperature heating. Therefore, this invention first controls the billet heating temperature and hot rolling heating range to 1100–1260°C. Preferably, in the billet assembly and composite rolling steps, the billet heating temperature and hot rolling heating temperature are less than or equal to 1260°C, the billet heating temperature range is 1100–1260°C (e.g., 1200–1260°C), the hot rolling heating temperature range is Ar3–1260°C, and the billet holding time and hot rolling holding time are each 200–280 min; wherein, the billet high-temperature section holding time and the hot rolling high-temperature section holding time are 40–80 min, and the billet high-temperature section and the hot rolling high-temperature section are heating ranges of 1150–1260°C; through the above process, the thickness 4 of the stainless steel carburized layer in the transition layer can be further controlled to be less than or equal to 45 micrometers and less than or equal to 4.5% of the thickness of the hot-formed composite steel plate.

[0072] Through the above steps, hot-formed composite steel plates can be manufactured. This invention improves the manufacturing method of hot-formed composite steel plates, adjusts the process, and controls the thickness of the carbon-enriched layer, the combination and precipitation of dissolved carbon with other alloying elements in the stainless steel layer, and the dissipation of free hydrogen in the carbon steel layer. This enhances the corrosion resistance and delayed cracking resistance, as well as the overall strength and elongation of the hot-formed composite plate. This invention mainly improves the billet assembly and composite rolling processes. Specifically, in the composite rolling step, by controlling the product of the billet heating temperature and time and the hot rolling heating temperature and time, the diffusion of interlayer components is controlled, thereby controlling the thickness of the carbon-enriched layer. This results in the steel plate of this invention having better delayed cracking resistance and better strength and elongation of the hot-formed composite plate. Simultaneously, by controlling the annealing temperature and cooling regime during the manufacturing process, the precipitated carbides are re-dissolved and no longer precipitated, thus improving corrosion resistance.

[0073] In some implementations, the thickness ratio of all stainless steel layers to carbon steel layers used in the preform assembly is 1:10 to 1:4.

[0074] Fourthly, the present invention also discloses a method for manufacturing a hot-stamped component, including the method for manufacturing the hot-formed composite steel plate of any of the foregoing embodiments, and further including: hot stamping: the heating temperature is 900-1000℃, and the holding time is less than or equal to 5 minutes (e.g., 0.5-5 minutes).

[0075] Specifically, after the annealing step is completed and the hot-formed composite steel plate is obtained, hot stamping and low-temperature tempering steps are performed in sequence.

[0076] (6) Hot stamping: When the heating temperature is 900-1000℃, the holding time should be controlled to be less than or equal to 5 minutes, specifically 0.5-5 minutes. Excessive holding time in the hot stamping process will cause the grains to become coarse and the grain size grade to decrease, thus reducing the corrosion resistance of the strip steel. By controlling the holding time to be less than or equal to 5 minutes and the heating temperature, a reasonable austenitic structure is ensured for the surface stainless steel layer 2, guaranteeing corrosion resistance and ensuring that the surface pitting corrosion potential of the hot-stamped parts is less than or equal to 0.5V.

[0077] (7) Low-temperature tempering: The heating temperature for low-temperature tempering is controlled at 100–300°C, and the tempering time is greater than 15 min, specifically 20–120 min, to avoid the presence of higher free hydrogen solid solubility in the stainless steel layer 2, and to prevent the free hydrogen in the high-strength carbon steel structure after hot stamping from failing to dissipate properly. Due to the high free hydrogen solid solubility in the austenitic structure of the stainless steel layer, the free hydrogen in the inner carbon steel layer will not be able to dissipate properly, thus failing to maintain the delayed cracking resistance of the hot-stamped parts.

[0078] Through various trials and experiments, the inventors proposed adjusting the low-temperature tempering process in conjunction with controlling the thickness of the stainless steel carburized layer to further improve the corrosion resistance of hot-stamped parts. Preferably, in the hot-stamping step, when the heating temperature is 900–930°C, the holding time is less than or equal to 5 minutes, specifically 2–5 minutes; when the heating temperature is 931–950°C, the holding time is less than or equal to 4 minutes, specifically 2–4 minutes; when the heating temperature is 950–970°C, the holding time is less than or equal to 2.5 minutes, specifically 1–2.5 minutes; and when the heating temperature is greater than or equal to 971°C, the holding time is less than or equal to 1.5 minutes, specifically 0.5–1.5 minutes. This results in the surface pitting corrosion potential of the steel plate of this invention being less than or equal to 0.4V, thus exhibiting better corrosion resistance.

[0079] The coordination of the process conditions in the above embodiments ensures that the hot-stamped component of the present invention is composed of a suitable stainless steel layer 2 and a carbon steel layer 1, and also has good tensile strength, corrosion resistance, and delayed cracking resistance. The hot-stamped component passes the delayed cracking resistance test (tested according to GMW17508 standard for hydrogen embrittlement test of acid-impregnated ultra-high strength steel and stamped parts).

[0080] The manufacturing method of the hot-stamped component of the present invention will be described in further detail below.

[0081] Examples 1-5

[0082] The hot-stamped parts in Examples 1-5 were all manufactured using the following steps:

[0083] (1) Slab manufacturing: manufacturing slabs with carbon steel layers and slabs with stainless steel layers.

[0084] (2) Assembly: Carbon steel slab blanks and stainless steel slab blanks are combined into an assembly blank, and the heating temperature is controlled at 1100~1260℃.

[0085] (3) Composite rolling: First, heat to a heating temperature of 1100~1260℃, hold for 0.6~5 hours, and then hot roll. The hot rolling heating temperature is controlled above Ar3 temperature, the final rolling temperature is 880~1000℃, and the temperature is rapidly cooled at a cooling rate of 30~100℃ / s. The coiling temperature is controlled at 500~600℃.

[0086] (4) Cold rolling: Control the cold rolling reduction rate to 0-70%.

[0087] (5) Annealing: The annealing temperature is 1050-1150℃, the holding time is 30-100s, and the temperature is cooled to room temperature. The temperature range of 500-900℃ is rapidly cooled, and the cooling rate is controlled at 20-200℃ / s.

[0088] (6) Hot stamping: The heating temperature is 900-1000℃, and the holding time is controlled to be less than or equal to 5min.

[0089] Examples 2 and 4 also include a low-temperature tempering step, wherein the heating temperature for low-temperature tempering is controlled to be 100–300°C and the tempering time is greater than 15 min.

[0090] The hot-stamped part of Comparative Example 1 was manufactured using the following steps:

[0091] (1) Slab manufacturing: manufacturing slabs with carbon steel layers and slabs with stainless steel layers.

[0092] (2) Assembly: Carbon steel slab blanks and stainless steel slab blanks are combined into an assembly blank, and the heating temperature is controlled at 1230℃.

[0093] (3) Composite rolling: First, heat to a heating temperature of 1270℃ and hold for 350 minutes, then hot roll. The hot rolling heating temperature is controlled above Ar3 temperature, and the final rolling temperature is 880~1000℃. Cool quickly at a cooling rate of 30~100℃ / s and control the coiling temperature to 500~600℃.

[0094] (4) Cold rolling: Control the cold rolling reduction rate to 0-70%.

[0095] (5) Annealing: The annealing temperature is 1050-1150℃, the holding time is 30-100s, and the temperature is cooled to room temperature. The temperature range of 500-900℃ is rapidly cooled, and the cooling rate is controlled at 20-100℃ / s.

[0096] (6) Hot stamping: The heating temperature is 900-1000℃, and the holding time is controlled to be less than or equal to 5min.

[0097] The hot-stamped part of Comparative Example 2 was manufactured using the following steps:

[0098] (1) Slab manufacturing: manufacturing slabs with carbon steel layers and slabs with stainless steel layers.

[0099] (2) Assembly: Carbon steel slab blanks and stainless steel slab blanks are combined into an assembly blank, and the heating temperature is controlled at 1100~1260℃.

[0100] (3) Composite rolling: First, heat to a heating temperature of 1100~1260℃ and hold for 0.6~2 hours or more, then hot roll. The hot rolling heating temperature is controlled above Ar3 temperature, the final rolling temperature is 880~1000℃, and the temperature is rapidly cooled at a cooling rate of 30~100℃ / s. The coiling temperature is controlled at 500~600℃.

[0101] (4) Cold rolling: Control the cold rolling reduction rate to 0-70%.

[0102] (5) Annealing: The annealing temperature is 1050~1150℃, the holding time is 30~100s, and the temperature is cooled to room temperature. The temperature range of 500~900℃ is rapidly cooled, and the cooling rate is controlled at 20~100℃ / s.

[0103] (6) Hot stamping: The heating temperature is 990℃ and the holding time is controlled at 6.5min.

[0104] The steel plate compositions of the examples and comparative examples are shown in Table 1, and the process parameters are shown in Table 2.

[0105] Table 1 lists the chemical composition of the steel plates cast by the present invention, including the mass percentage of the chemical composition of the steel plates of Examples 1 to 5 and the mass percentage of the chemical composition of Comparative Examples 1 to 2 (%), with the remainder being Fe and other unavoidable impurities other than P, S, and N.

[0106] Table 1: Chemical composition (mass percentage) of hot-formed composite steel plates in different embodiments and comparative examples

[0107] (wt%, balance Fe and other unavoidable impurities besides P, S, and N)

[0108] Table 2-1

[0109] Table 2-2

[0110] The volume fraction of martensite, the volume fraction of retained austenite, the thickness of the stainless steel carburized layer, the percentage of the stainless steel carburized layer thickness to the total thickness of the composite steel plate, tensile strength, yield strength, elongation, plate thickness, surface pitting potential, and resistance to delayed cracking were measured for the examples and comparative examples. Specific data are shown in Table 3. The surface pitting potential was measured according to GB / T17899-1999, the method for measuring the pitting potential of stainless steel. The resistance to delayed cracking was tested according to GMW17508, the standard for hydrogen embrittlement testing of acid-etched ultra-high strength steel and stamped parts. Tensile strength, yield strength, elongation, and strength-ductility product were determined by tensile testing, using 50 mm gauge length specimens according to GB / T 228.1-2010, "Metallic materials, tensile testing—Part 1: Tests at room temperature." Minimum bending capacity was determined by a 90° bending test, according to GB / T 232-2010, the method for bending tests of metallic materials. The thickness of the carburized layer, the volume fraction of martensite, and the volume fraction of retained austenite in stainless steel were tested according to the standard test method GB / T 18876.1-2002, which uses automatic image analysis to determine the metallographic structure, inclusion content, and grade of steel and other metals.

[0111] Table 3: Measurement results of the examples and comparative examples

[0112] As shown in Table 3, the thickness of the stainless steel carburized layer of the hot-formed composite steel plate in each embodiment of the present invention is less than or equal to 4.5% of the thickness of the hot-formed composite steel plate and less than or equal to 45 μm. The volume fraction of martensite in the hot-stamped parts is 72-82%, the volume fraction of retained austenite is 3-7%, the tensile strength is 900 MPa-1230 MPa, the pitting corrosion potential is less than or equal to 0.5 V, the corrosion resistance is good, and all have good resistance to delayed cracking. The strength-ductility product is greater than 11000, and the 90° bending capacity R / t is less than or equal to 2.5.

[0113] Furthermore, some embodiments 1-4 further satisfy the following conditions: in the hot stamping step, when the heating temperature is 900-930℃, the holding time is less than or equal to 5 minutes; when the heating temperature is 931-950℃, the holding time is less than or equal to 4 minutes; when the heating temperature is 950-970℃, the holding time is less than or equal to 2.5 minutes; and when the heating temperature is greater than or equal to 971℃, the holding time is less than or equal to 1.5 minutes. At this point, the pitting corrosion potential can be further reduced to less than or equal to 0.4V, further improving corrosion resistance.

[0114] Examples 2 and 4 further satisfy the following: a low-temperature tempering step, wherein the heating temperature for low-temperature tempering is controlled at 100-300℃ and the tempering time is greater than 15 minutes, thereby further improving the delayed cracking resistance of the hot-stamped parts.

[0115] Regarding Comparative Example 1, the carbon steel layer 1 has a C content exceeding 0.20% and a Cr content exceeding 0.5%. Furthermore, in the composite rolling process, the hot rolling heating temperature is above 1260℃, the hot rolling holding time is above 280min, and the hot rolling high-temperature section holding time is above 80min, resulting in a stainless steel carbon-enhanced layer thickness greater than 45μm. Consequently, the steel plate's delayed cracking resistance evaluation is NG, and its strength-ductility product is less than 11000.

[0116] Regarding Comparative Example 2, the Ni content of its stainless steel layer 1 is less than 5%, the Cr content is less than 13%, and the Mn content is greater than 2.6%. In the hot stamping step, when the heating temperature is 990℃ and the holding time is controlled at 6.5min, which is greater than 5min, the surface pitting corrosion potential is 0.73V, resulting in poor corrosion resistance.

[0117] In summary, the present invention provides a method for manufacturing hot-stamped components. Through control of the billet assembly, composite rolling, hot stamping, and low-temperature tempering steps, specifically controlling the product of heating temperature and time in the billet assembly and composite rolling steps, and the product of temperature and time in the hot stamping step, and further controlling the heating temperature and tempering time in the low-temperature tempering step, this method allows for control over the thickness of the stainless steel carburized layer within a lower range when using stainless steel and carbon steel layers as the base material for the composite steel plate. This control also allows for control over the strength and toughness of the composite steel plate, as well as the austenite grain size on the surface of the composite steel plate. Consequently, while achieving high strength, this method also improves the corrosion resistance and delayed cracking resistance of the hot-stamped components, facilitating wider applications. These hot-stamped components have different strength levels ranging from 900 MPa to 1250 MPa, demonstrating promising application prospects and value.

[0118] While the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. Various changes in form and detail can be made by those skilled in the art, including several simple deductions or substitutions, without departing from the spirit and scope of the invention.

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: 0.10–0.20%, Si: 0–2.0%, Mn: 0–2.0%, B: 0–0.010%, Ti: 0–0.10%, Nb: 0–0.050%, V: 0–0.05%, Cr: 0–0.5%, Ni: 0–1.0%, Cu: 0–1.0%, P: ≤0.02%, S: ≤0.02%, Al: 0.01–0.05%, N: ≤0.01%; the balance being Fe and other unavoidable impurities.

2. The hot-formed composite steel plate as described in claim 1, characterized in that, The stainless steel layer has one or more of the following characteristics: The C content is 0.01–0.05%; The Si content is 0.2–0.6%; The Mn content is 1.2–1.6%; The Ni content is 6-13%; and The Cr content is 14-20%; Preferably, the chemical composition of the stainless steel layer, by mass percentage, includes: C: 0.01-0.05%, Si: 0.2-0.6%, Mn: 1.2-1.6%, Ni: 6-13%, Cr: 14-20%, P: ≤0.04%, S: ≤0.03%, N: ≤0.1%, with the balance being Fe and other unavoidable impurities.

3. The hot-formed composite steel plate as described in claim 1 or 2, characterized in that, The carbon steel layer has any one or more of the following characteristics: The Si content is 0.2%–1.6%; The Mn content is 0.8–2.0%; The content of B is 0-0.007%; The Ti content is 0–0.08%; The Nb content is 0–0.03%; The Cr content is 0–0.45%; The Ni content is 0-0.3%; and The Cu content is 0-0.5%; Preferably, the chemical composition of the carbon steel layer, by mass percentage, includes: C: 0.10–0.20%, Si: 0.2–1.6%, Mn: 0.8–2.0%, B: 0–0.007%, Ti: 0–0.08%, Nb: 0–0.030%, V: 0–0.01%, Cr: 0–0.45%, Ni: 0–0.3%, Cu: 0–0.5%, P: ≤0.02%, S: ≤0.02%, Al: 0.01–0.05%, N: ≤0.01%; 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 ≤ 2.0%.

5. The hot-formed composite steel plate 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 4.5% of the thickness of the hot-formed composite steel plate and less than or equal to 45 μm.

6. The hot-formed composite steel plate according to any one of claims 1-5, characterized in that, The hot-formed composite steel sheet, after hot stamping, has one or more of the following characteristics: (1) The microstructure of the stainless steel layer is austenite; (2) The microstructure of the carbon steel layer is martensite, ferrite and retained austenite, wherein the volume fraction of the martensite is 70-87% and the volume fraction of the retained austenite is 2-8%. (3) The tensile strength of the obtained hot stamping parts is 900MPa~1250MPa, the surface pitting corrosion potential is less than or equal to 0.5V, the strength-ductility product is greater than or equal to 11000, and the 90° bending capacity R / t≤2.5; (4) The yield strength of the obtained hot-stamped parts is 680MPa~960MPa; (5) The elongation of the obtained hot-stamped part is ≥11.5%.

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 a tensile strength of 900MPa to 1250MPa, a surface pitting corrosion potential of less than or equal to 0.5V, a strength-ductility product of greater than or equal to 11000, and a 90° bending capacity R / t ≤ 2.5; preferably, the hot-stamped component has a yield strength of 680MPa to 960MPa and an elongation of ≥11.5%.

9. The hot-stamped component as described in claim 7 or 8, characterized in that, The microstructure of the stainless steel layer of the hot-stamped component is austenite, and the microstructure of the carbon steel layer is martensite, ferrite and retained austenite, with the volume fraction of martensite being 70-87% and the volume fraction of retained austenite being 2-8%.

10. 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 20℃ / s.

11. The method for manufacturing the hot-formed composite steel plate as described in claim 10, 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℃.

12. The method for manufacturing the hot-formed composite steel plate as described in claim 10, characterized in that, The method has one or more of the following characteristics: (1) In the billet assembly step, the heating temperature is 1100~1260℃, the holding time is 200~280min, and the holding time of the high temperature section of the billet assembly is 40~80min; (2) 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 880-910℃. The temperature is rapidly cooled at a cooling rate of 30-100℃ / s or 30-90℃ / s, and the coiling temperature is controlled at 500-600℃ or 520-600℃. (3) In the cold rolling step, the cold rolling reduction rate is controlled to be 30-70%; In the annealing step, the annealing temperature is 1050-1150℃, the holding time is 30-100s or 40-80s, and the temperature is cooled to room temperature. The annealing is carried out rapidly within the temperature range of 500-900℃, and the cooling rate is controlled at 20-200℃ / s.

13. 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 10-12 is subjected to hot stamping, the hot stamping comprising: a heating temperature of 900-1000°C and a holding time of less than or equal to 5 min.

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

15. The method for manufacturing a hot-stamped part as described in claim 13 or 14, 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 15 minutes.

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