High-strength high-toughness hydrogen embrittlement resistant composite steel and method for manufacturing the same

Abstract

The application provides a high-strength and high-toughness hydrogen embrittlement resistant composite steel and a preparation method thereof. The preparation method of the composite steel comprises the following steps: obtaining a composite steel material by vacuum hot rolling of a martensitic steel and an austenitic steel in a sheath, the top layer and the bottom layer are both the martensitic steel, the middle part is the alternately stacked martensitic steel and austenitic steel, and the upper surface of the martensitic steel of the top layer and the lower surface of the martensitic steel of the bottom layer are hydrogen embrittlement resistant austenitic stainless steel. The preparation method of the application realizes a material system with high strength, high toughness and excellent hydrogen embrittlement resistance in a hydrogen-rich environment by constructing a multi-layer composite steel structure and optimizing the preparation process. The core part is high-strength martensitic hot forming steel and high-plasticity austenitic steel which are alternately compounded to form a strength and toughness synergistic structure; the upper and lower surfaces are made of low-cost hydrogen embrittlement resistant austenitic stainless steel, which effectively prevents hydrogen atoms from penetrating and inhibits crack propagation, and overcomes the mutual restriction among strength, toughness and hydrogen embrittlement resistance of single metal material.

Description

Technical Field

[0001] This application relates to the field of steel manufacturing technology, and in particular to a high-strength, high-toughness, hydrogen-embrittlement-resistant composite steel and its preparation method. Background Technology

[0002] Hydrogen energy, as a highly efficient, clean, and renewable secondary energy source, is widely considered a crucial direction for the future transformation of the energy system. With the advancement of the goals of "carbon peaking" and "carbon neutrality," the demand for hydrogen energy in transportation, industrial manufacturing, and aerospace continues to grow. my country's "Medium- and Long-Term Plan for the Development of the Hydrogen Energy Industry (2021-2035)" explicitly requires the coordinated development of the entire hydrogen energy chain, from production to storage, transportation, and utilization. Among these, the safety, economic viability, and efficient storage and transportation of hydrogen are the biggest obstacles hindering its industrialization.

[0003] Currently, materials used for hydrogen storage and transportation mainly include metallic materials and composite materials with carbon fiber wound linings. Carbon fiber wound composites have advantages such as high strength and light weight, but their manufacturing cost is high, the process is complex, and they exhibit significant anisotropy, generally limiting their application to small-scale, distributed hydrogen supply scenarios. For large-scale commercial hydrogen storage and transportation equipment, such as hydrogen pressure pipelines, stationary large-capacity hydrogen storage containers, and hydrogen refueling ships, cost-effective and technologically mature metallic materials, especially steel, are still necessary. Currently, hydrogen storage containers and long-tube trailers at domestic hydrogen refueling stations commonly use hydrogen-resistant Cr-Mo steel. However, traditional Cr-Mo steel is prone to hydrogen embrittlement in high-pressure hydrogen environments, manifesting as decreased impact toughness, accelerated fatigue crack propagation, and reduced critical cracking stress, severely restricting its safe and reliable application in high-pressure hydrogen storage and transportation equipment. Austenitic stainless steel, due to its good resistance to hydrogen embrittlement and excellent formability, is considered a potential candidate material for high-pressure hydrogen storage containers and pipelines. However, commercial austenitic stainless steel typically contains a high proportion of scarce alloying elements such as Cr, Ni, and Mo, making it difficult to meet the economic requirements for large-scale applications. In addition, austenitic stainless steels generally have low yield strength, making it difficult to provide sufficient structural load-bearing safety margin in high-pressure hydrogen environments. At the same time, the stability of the austenitic phase decreases at low temperatures, and its hydrogen embrittlement sensitivity increases accordingly, further limiting its application prospects under harsh hydrogen environments.

[0004] In the prior art, for example, invention patent application number 202411295809.1 proposes a hydrogen embrittlement-resistant Cr-Mo alloy steel and its preparation method. This patent obtains a novel Cr-Mo alloy steel with both high strength and excellent hydrogen embrittlement resistance by compositely adding appropriate microalloying elements such as Se, Cu, Nb, W, and RE. Invention patent application number 202410430874.4 proposes a hydrogen embrittlement-resistant austenitic stainless steel and its preparation method. This patent significantly improves the hydrogen embrittlement resistance of the material by adding rare earth element Y and strong carbide-forming element Nb to implement composite microalloying. Invention patent application number 202410397151.9 proposes an ultra-high strength hydrogen embrittlement-resistant austenitic stainless steel and its preparation method. Similarly, this patent also utilizes alloying design to significantly improve the hydrogen embrittlement resistance of the material by precipitating a large number of nano-sized non-coherent precipitates within the austenitic grains. In summary, most existing methods improve the hydrogen embrittlement resistance of materials through alloying, but they do not simultaneously and significantly improve the material's strength, toughness, and hydrogen embrittlement resistance. From the perspective of fundamental metallurgical principles, a single metallic material cannot fundamentally solve the problem of the inverse relationship between material strength, ductility, toughness, and hydrogen embrittlement resistance.

[0005] Therefore, how to break through the performance coupling limitations of traditional metallic materials in hydrogen environment through material design and structural innovation, and construct a material system with high strength, high toughness and excellent resistance to hydrogen embrittlement, has become a core scientific and engineering problem for the safe and reliable operation of hydrogen storage and transportation equipment. Summary of the Invention

[0006] To address the problems existing in the prior art, this application provides a high-strength, high-toughness, hydrogen embrittlement-resistant composite steel and its preparation method. Through composition design and process optimization, an advanced hydrogen storage material with high strength, high toughness, and excellent hydrogen embrittlement resistance is developed, and production stability is improved.

[0007] This application provides a method for preparing composite steel, which involves combining martensitic steel (HFS) and austenitic steel (TWIP) through a cladding vacuum hot rolling process to obtain a composite steel material. The top and bottom layers are both martensitic steel, and the middle layer consists of alternating stacks of martensitic steel and austenitic steel. The upper surface of the top layer of martensitic steel and the lower surface of the bottom layer of martensitic steel are hydrogen-embrittlement-resistant austenitic stainless steel (ASS).

[0008] Preferably, the martensitic steel comprises, by mass percentage: 0.2%–0.4% C, 0.5%–1.5% Mn, 0.2%–0.3% Si, 0.2%–0.3% Cr, 0.1%–0.3% V, 0.02%–0.04% Ti, 0.002%–0.004% B, unavoidable impurity elements ≤0.15%, and the balance being Fe.

[0009] Preferably, the austenitic steel comprises, by mass percentage: 0.5% to 0.8% C, 22.0% to 24.0% Mn, 0.2% to 1.5% Si, 0.1% to 0.3% Nb, unavoidable impurity elements ≤ 0.15%, and the balance being Fe.

[0010] Preferably, the hydrogen embrittlement resistant austenitic stainless steel comprises, by mass percentage: 0.02%–0.06% C, 8.0%–12.0% Mn, 0.2%–2.0% Si, 3.0%–6.0% Ni, 14.0%–20.0% Cr, 0.1%–0.4% N, 0.05%–0.2% Cu, unavoidable impurity elements ≤0.15%, and the balance being Fe.

[0011] Preferably, the preparation method includes the following steps:

[0012] Step 1: Prepare slabs according to the composition of the martensitic steel, the austenitic steel and the hydrogen embrittlement resistant austenitic stainless steel, cut them into plates of the same size, and remove surface oxide scale, impurities and oil stains.

[0013] Step 2: Stack the billet plates of martensitic steel and austenitic steel alternately, place the hydrogen embrittlement resistant austenitic stainless steel on the upper surface of the top layer of martensitic steel and the lower surface of the bottom layer of martensitic steel, and apply a release agent to the outer surface of the hydrogen embrittlement resistant austenitic stainless steel.

[0014] Step 3: After completing the assembly, place the composite billet into the sleeve and perform electron beam welding to seal the edges of the composite billet with the sleeve under high vacuum.

[0015] Step 4: Heat and hold the welded composite billet to ensure uniform structure and consistent internal and external temperatures, and then perform multiple hot rolling composite processes.

[0016] Step 5: Hold at 650~700℃ for 5~8 minutes, remove and perform warm rolling. After warm rolling, reduce the temperature to 250~350℃, return to the furnace and hold for 2~4 minutes, and repeat rolling until the total reduction rate is 10%~40%.

[0017] Step 6: Hold the warm-rolled composite material at 800~950℃ for 30~120min, cool it to achieve recrystallization and homogenization of the microstructure, and then temper it at 150~300℃ for 60~240min and cool it to release residual stress.

[0018] Preferably, in step one, continuous casting billets are prepared according to the compositions of the martensitic steel, the austenitic steel, and the hydrogen embrittlement-resistant austenitic stainless steel, respectively. Electroslag ingots are prepared using electroslag remelting technology with the continuous casting billets as electrodes. After forging and rolling, slabs of different thicknesses are prepared for later use.

[0019] Preferably, the thickness of the hydrogen embrittlement resistant austenitic stainless steel is 8~25mm, the thickness of the martensitic steel is 0.8~2.5mm, the thickness of the austenitic steel is 0.8~2.5mm, the layer thickness ratio of the hydrogen embrittlement resistant austenitic stainless steel, the martensitic steel and the austenitic steel is (5~25):1:1, and the total number of layers is 73~577.

[0020] Preferably, in step four, the heating temperature of the composite billet is 1150–1220℃, and the net holding time is 2–5 hours; the multi-pass hot rolling composite is performed with the roughing rolling starting temperature at 1080–1150℃, the finishing rolling temperature at 1020–1100℃, the total roughing reduction rate at 82%–92%, and the single-pass reduction rate at 10%–30%; the finishing rolling starting temperature at 960–1000℃, the finishing rolling temperature at 860–900℃, the total finishing reduction rate at 40%–70%, and the single-pass reduction rate at 5%–10%.

[0021] Preferably, the preparation method further includes step seven, which involves cold rolling the material obtained in step six at room temperature, annealing it at 600~950°C, and then cooling it.

[0022] This application provides a high-strength, high-toughness, hydrogen-embrittlement-resistant composite steel, which is a composite steel material obtained according to any of the above-described composite steel preparation methods.

[0023] The beneficial effects of this application are:

[0024] 1. The preparation method of this application achieves a material system with high strength, high toughness, and excellent resistance to hydrogen embrittlement in a hydrogen-rich environment by constructing a multi-layer composite steel structure and optimizing the preparation process. The core is composed of multiple alternating layers of high-strength martensitic hot-formed steel and high-ductility and toughness austenitic steel, forming a strong and tough synergistic structure; the upper and lower surfaces are made of low-cost austenitic stainless steel, which effectively prevents hydrogen atom penetration and inhibits crack propagation, overcoming the mutual constraints between strength, toughness, and resistance to hydrogen embrittlement in single metal materials or existing composite materials.

[0025] 2. The martensitic steel and hydrogen-embrittlement-resistant austenitic stainless steel used in the preparation method of this application are independently designed according to the service performance requirements of multi-layer composite plates, which effectively improves the performance of composite steel.

[0026] In martensitic steel, V, Ti and C form dispersed composite carbides mainly composed of VC and TiC during hot rolling and cooling. The composite carbides are mainly distributed inside the martensitic laths and at the lath interfaces, forming a lath-precipitate synergistic constraint structure together with the lath martensite. B element participates in the martensitic lath formation process in the form of interfacial segregation, which is used to stabilize the synergistic constraint structure.

[0027] In austenitic steel, Mn stabilizes austenite, while Nb precipitates in the form of NbC or Nb(C,N) to pin austenite grain boundaries, resulting in a fine-grained transition structure in the austenitic steel layer near the composite interface.

[0028] In hydrogen embrittlement resistant austenitic stainless steel, Ni and N work together to stabilize the austenitic matrix, Cr forms a continuous corrosion-resistant austenitic structure, and Cu exists in solid solution or in the form of fine Cu-rich regions to construct a surface structure that inhibits hydrogen penetration and homogenizes hydrogen distribution.

[0029] 3. The preparation method of this application adopts vacuum electron beam sealing, two-stage hot rolling and warm rolling composite process to ensure tight bonding and uniform structure of composite interface, improve yield and service reliability; through the adjustable design of layer thickness ratio and total number of layers, the composite steel structure and performance can be precisely matched to meet the needs of different hydrogen storage and transportation equipment and related hydrogen energy application fields, and provide a reliable material solution for large-scale hydrogen storage and transportation equipment.

[0030] 4. The high-strength, high-toughness, hydrogen-resistant multilayer composite steel of this application is suitable for high-pressure hydrogen pipelines, stationary hydrogen storage tanks, mobile hydrogen storage systems, and fuel cell power units, etc. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the composite blank structure with a casing in Example 1.

[0032] Figure 2 The images show the microstructure of the material obtained in Example 1. The top left image is the EBSD microstructure, the top right image is the SEM macrostructure, and the bottom image is the microstructure after tensile fracture.

[0033] Figure 3 The images show the EBSD microstructure of the material obtained in Comparative Example 1. The left image shows the macroscopic morphology of the tensile fracture surface, and the right image shows the microscopic morphology of the tensile fracture surface.

[0034] Figure 4 The images show the EBSD microstructure of the material obtained in Comparative Example 2. The left image shows the macroscopic morphology of the tensile fracture surface, and the right image shows the microscopic morphology of the tensile fracture surface. Detailed Implementation

[0035] To further understand this application, preferred embodiments of this application are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of this application, and not for limiting this application.

[0036] A method for preparing composite steel involves vacuum hot rolling martensitic steel (HFS) and austenitic steel (TWIP) together using a low-carbon steel cladding to obtain a composite steel material. The top and bottom layers are both martensitic steel, with alternating layers of martensitic and austenitic steel in the middle. The upper surface of the top layer of martensitic steel and the lower surface of the bottom layer of martensitic steel are made of hydrogen-embrittlement-resistant austenitic stainless steel (ASS). The overall structure of the composite steel is ASS / HFS / TWIP / HFS…HFS / TWIP / HFS / ASS, with a total of 73 to 577 layers.

[0037] Preferably, by mass percentage, the martensitic steel comprises: 0.2%–0.4% C, 0.5%–1.5% Mn, 0.2%–0.3% Si, 0.2%–0.3% Cr, 0.1%–0.3% V, 0.02%–0.04% Ti, 0.002%–0.004% B, unavoidable impurity elements ≤0.15%, single impurity <0.05%, and the balance being Fe. Martensitic steel with the above composition possesses both high strength and good plasticity, making it suitable as the main load-bearing layer of composite structures.

[0038] The design principles of the chemical elements in the HFS steel layer are as follows:

[0039] Carbon (C) is the most economical and effective element for enhancing the strength and hardness of steel. In HFS steel, C exists in two forms: dissolved carbon atoms and carbides. Increasing the dissolved carbon content in martensite can significantly improve its strength and hardness. Carbides can refine the microstructure, pin dislocations, and act as hydrogen traps, thereby improving the overall performance of the material. When the C content reaches 0.4%, its martensitic transformation mechanism changes from dislocation martensite to a mixed microstructure of dislocation and twinned martensite, with brittle twinned martensite accounting for 5%–10%. Furthermore, a high C content is extremely detrimental to weldability. Controlling the C content between 0.2% and 0.4% ensures the strength of HFS steel while avoiding the increased brittleness and decreased weldability caused by excessively high carbon content.

[0040] Mn: Manganese can reduce the M of steel. s The Mn content expands the austenite phase region and inhibits the transformation of austenite to ferrite, thus enhancing the hardenability of the steel. However, excessively high Mn content may lead to an increase in banded structures in the steel, worsening its ductility and toughness, and adversely affecting its weldability. Therefore, in this application, the Mn content of HFS steel is controlled at 0.5% to 1.5%.

[0041] B: Boron can significantly improve the hardenability of steel. The hardenability of steel is not directly determined by the total B content added to the steel, but rather by the content of solid-solution B, which improves hardenability. When the B content in steel is 0.002%–0.004%, its hardenability effect is hundreds to thousands of times greater than that of scarce alloying elements such as Ni, Cr, and Mo. Furthermore, B is inexpensive, saving production costs. Because B has a strong tendency to combine with N, the resulting BN has no effect on improving hardenability; therefore, it is necessary to use other strong nitride-forming elements (such as Ti) for treatment.

[0042] Silicon (Si) is a major deoxidizer in steel. Si can inhibit cementite formation, stabilize the precipitation of ε or η transition carbides, and promote C distribution into retained austenite, increasing austenite stability. However, excessive Si content can deteriorate the steel's ductility, toughness, and weldability. The silicon content in the HFS steel described in this application is designed to be 0.2%–0.3%.

[0043] Cr: Chromium improves the hardenability of steel by reducing the driving force of the austenite-to-pearlite / ferrite transformation. Simultaneously, Cr promotes the formation of a dense oxide film and dispersed carbides, helping to reduce grain boundary weakening and hydrogen accumulation tendency, thus enhancing the material's resistance to hydrogen embrittlement. The chromium content in the HFS steel described in this application is in the range of 0.2% to 0.3% to achieve a balance between strength, toughness, and service stability.

[0044] Ti: Titanium possesses an extremely strong ability to form nitrides and carbides, preferentially combining with nitrogen in steel to form thermally stable TiN. This effectively fixes nitrogen, preventing the formation of ineffective BN compounds and ensuring the effective role of dissolved B in hardenability. However, with high Ti and N contents, TiN tends to precipitate in the liquid phase, forming large primary particles. These coarse particles significantly reduce the toughness of the steel and induce brittle fracture. This application addresses this by strictly controlling the Ti to N ratio, ensuring w(Ti):w(N) is greater than 3.42, and limiting the Ti content to 0.02%–0.04%. This achieves nitrogen fixation while avoiding the formation of harmful liquid-precipitated TiN, ensuring stable hardenability and improving the overall mechanical properties of the steel.

[0045] Vanadium (V): As a typical strong carbide-forming element, vanadium can precipitate dispersed fine VC or (V,Ti)C carbides during rolling or heat treatment, playing a role in precipitation strengthening and inhibiting grain growth. It also reduces the brittleness risk associated with increased C content by consuming some C. Appropriate amounts of V can also improve the wear resistance and delayed cracking resistance of materials. However, excessive V content may lead to the precipitation of coarse carbides, weaken the stability of retained austenite, and increase material costs. This application controls the V content within the range of 0.1% to 0.3% to achieve good strengthening effects and microstructural stability.

[0046] Preferably, by mass percentage, the austenitic steel comprises: 0.5%–0.8% C, 22.0%–24.0% Mn, 0.2%–1.5% Si, 0.1%–0.3% Nb, unavoidable impurity elements ≤0.15%, single impurity <0.05%, and the balance being Fe. TWIP steel with the above composition exhibits excellent work hardening ability and elongation. As a control layer in a composite structure, it can significantly improve the overall plasticity and energy absorption capacity of the material.

[0047] The design principles of the chemical elements in the TWIP steel layer are as follows:

[0048] C: Carbon plays a role in solid solution strengthening in TWIP steel, and the addition of C also increases γ. The driving force required for martensitic phase transformation improves the stability of austenite, which is beneficial to ensuring the plasticity of TWIP steel.

[0049] Mn: Mn has a strong austenite stabilizing effect, which can significantly reduce the stacking fault energy (SFE) of steel, making the material more prone to mechanical twinning during deformation. This ensures the continuous occurrence of twinning-induced plasticity (TWIP) during deformation, achieving a synergistic improvement in high strength and high ductility. Simultaneously, the solid solution strengthening effect of Mn can improve the matrix strength of austenite, providing higher stress triggering conditions for twinning deformation. Furthermore, Mn promotes the solubility of carbon in austenite, which helps maintain microstructure stability and delays dynamic recrystallization, thereby improving the deformation uniformity of the material under complex stress conditions.

[0050] Silicon (Si): Silicon can inhibit cementite formation during cooling, reduce stacking fault energy, promote the formation of primary and secondary twins, and improve the strain hardening ability of TWIP steel. Furthermore, silicon acts as a deoxidizer in steel, increasing its strength and enhancing its oxidation resistance. Excessive silicon content may lead to reduced plasticity and the formation of a thicker oxide scale during hot rolling, affecting the surface properties of the sheet. Controlling the Si content between 0.2% and 1.5% can improve the steel's strength without compromising its ductility.

[0051] Niobium (Nb) readily combines with carbon (C) in steel to form highly stable NbC. Its dispersed precipitation effectively pins dislocations, inhibits recrystallization grain growth, refines grain size, and improves strength. Secondly, the solid solution strengthening effect of Nb complements the mechanical twinning-based plastic strengthening mechanism of TWIP steel, enhancing overall strength while maintaining high ductility. Furthermore, NbC precipitates can act as deep traps to capture diffusing hydrogen, reducing the tendency for hydrogen enrichment at grain boundaries and dislocations, and improving resistance to hydrogen embrittlement.

[0052] Preferably, by mass percentage, the hydrogen embrittlement resistant austenitic stainless steel comprises: 0.02% to 0.06% C, 8.0% to 12.0% Mn, 0.2% to 2.0% Si, 3.0% to 6.0% Ni, 14.0% to 20.0% Cr, 0.1% to 0.4% N, 0.05% to 0.2% Cu, unavoidable impurity elements ≤0.15%, single impurity <0.05%, and the balance being Fe.

[0053] The design principles of the chemical elements in the ASS steel layer are as follows:

[0054] C: In austenitic steel, carbon strengthens the matrix through solid solution, enhances the stability of austenite, and inhibits the formation of brittle phases, thereby improving resistance to hydrogen embrittlement. However, excessive carbon content reduces the plasticity and toughness of the steel and, during heat treatment, forms harmful precipitates with chromium along grain boundaries, providing favorable channels for hydrogen atom diffusion and reducing resistance to hydrogen embrittlement. Therefore, this application preferably controls the carbon content to 0.02%–0.06% to balance strengthening, microstructural stability, and resistance to hydrogen embrittlement.

[0055] Ni: Nickel is an austenite-forming element that significantly improves the stability of the austenite phase, inhibits the formation of brittle martensite or ferrite, thereby reducing the risk of hydrogen accumulation and crack initiation at the phase interface, while lowering the brittle transition temperature of steel and maintaining toughness at low temperatures. Nickel can also improve the diffusion path and rate of hydrogen in steel, making hydrogen distribution more uniform, reducing local stress concentration, strengthening grain boundary bonding, improving the grain boundary's resistance to hydrogen sensitivity, and increasing strength while maintaining or improving toughness. Combining the synergistic effects of Mn and N, this application controls the Ni content at 3.0% to 6.0%, ensuring a fully austenitic microstructure while also considering material cost, strength, toughness, and resistance to hydrogen embrittlement.

[0056] Mn: Manganese is an austenite-forming element that can stabilize the FCC austenite phase, significantly reducing the tendency of austenite to martensite transformation. It also increases the stacking fault energy (SFE) of steel, reduces the probability of plane slip, thereby weakening the effect of hydrogen atoms and reducing hydrogen embrittlement sensitivity. Manganese can also increase the solubility of nitrogen in austenite, improve matrix strength and microstructure stability, and is inexpensive, thus promoting material economy. It should be noted that excessively high manganese content may lead to intergranular element segregation, initiating intergranular cracking and deteriorating weldability and formability. Therefore, this application preferably controls the Mn content to 8.0%–12.0%.

[0057] Silicon (Si): In austenitic steel, silicon can inhibit the local enrichment of hydrogen atoms and improve resistance to hydrogen embrittlement by introducing vacancy defects and increasing lattice distortion, thereby hindering dislocation movement. Studies have shown that in Mn-containing steel, an appropriate amount of Si helps improve resistance to hydrogen embrittlement. However, when the Si content is too high (above 2%), it significantly reduces the stacking fault energy (SFE), increases the probability of strain-induced martensitic transformation and plane slip, and thus weakens the resistance to hydrogen embrittlement. Therefore, this application preferably controls the Si content to be between 0.2% and 2.0%.

[0058] Cr: Chromium is an important alloying element in low-cost hydrogen embrittlement-resistant austenitic stainless steel. Its main function is to form a dense Cr2O3 passivation film on the steel surface, effectively hindering the penetration of hydrogen atoms and reducing the hydrogen concentration in the steel matrix, thereby significantly enhancing the resistance to hydrogen embrittlement. Simultaneously, chromium helps maintain the uniformity of the all-austenitic structure by increasing the chemical stability of austenite and inhibiting the formation of ferrite and martensite. If the chromium content is below 14.0%, the passivation film is not fully formed, and hydrogen atoms easily penetrate the matrix, initiating hydrogen-induced cracking. If the chromium content exceeds 20.0%, it may reduce austenite stability, leading to the formation of δ-ferrite, and the precipitation of Cr-rich phases along grain boundaries during heat treatment or hot rolling, becoming hydrogen atom enrichment channels and reducing the resistance to hydrogen embrittlement. Therefore, this application preferably controls the Cr content between 14.0% and 20.0% to balance austenite stability, passivation film formation efficiency, and overall hydrogen embrittlement resistance.

[0059] Nitrogen (N) is a strong austenite-forming element that can inhibit the transformation of austenite to martensite, improve work hardening ability, and enhance the strength and resistance to hydrogen embrittlement of steel. Simultaneously, nitrogen can promote the formation of short-range ordered structures, enhance dislocation plane slip, and improve resistance to hydrogen embrittlement. However, excessively high nitrogen content may lead to increased brittleness in the steel. Therefore, this application preferably controls the nitrogen content at 0.1% to 0.4% to balance austenite stability, strengthening effect, and resistance to hydrogen embrittlement.

[0060] In annealed steel (ASS), copper not only improves the plasticity and processing properties of the material through solid solution and precipitation strengthening, ensuring formability during forging and rolling, but also forms a dense copper oxide layer on the matrix surface, effectively hindering hydrogen diffusion in the steel and enhancing its resistance to hydrogen embrittlement. However, excessive copper content can easily lead to enrichment along grain boundaries during heat treatment, causing surface cracking; while insufficient content results in inadequate strengthening and hydrogen barrier effects. Therefore, this application preferably controls the copper content to be between 0.05% and 0.2%.

[0061] In summary, the technical approach of this application in terms of materials addresses the challenge of simultaneously achieving high strength, high ductility, and resistance to hydrogen embrittlement in a hydrogen environment using traditional single steel grades and existing composite materials. Based on the understanding of the coupled and balancing relationship between the high hydrogen embrittlement sensitivity of high-strength steel, the low yield and tensile strength of high-ductility steel, and the tendency for hydrogen to accumulate in crystal defect regions or interfaces, a technical solution combining material composition design and a multi-layer composite structure is proposed. This application achieves synergistic optimization of strength and toughness by designing steel with specific chemical compositions and constructing a multi-layer composite structure. Simultaneously, by compositing low-cost stainless steel with excellent hydrogen embrittlement resistance onto the outer layer of the multi-layer steel, the resulting multi-layer composite steel significantly improves its resistance to hydrogen embrittlement while maintaining high strength and high ductility and toughness. Furthermore, by employing a cladding vacuum electron beam welding edge-sealing process and a two-stage hot-rolling composite process, combined with warm rolling, cold rolling, and heat treatment processes, the metallurgical bonding quality and interface structural stability between the layers are effectively guaranteed, thereby improving the comprehensive mechanical properties of the multi-layer composite steel during service in a hydrogen environment.

[0062] Preferably, the preparation method may include the following steps:

[0063] Step 1: Continuous casting billets are prepared according to the compositions of martensitic steel, austenitic steel, and hydrogen-embrittlement-resistant austenitic stainless steel, respectively. Electroslag ingots are then prepared using electroslag remelting technology with the continuous casting billets as electrodes. After forging and rolling, slabs of different thicknesses are prepared for later use. These are then cut into plates of the same size, and their surfaces are mechanically ground, degreased, and cleaned to remove oxide scale, impurities, and oil stains, achieving a surface roughness of 0.2~0.5μm.

[0064] Step two: Alternately stack martensitic and austenitic steel billets, placing hydrogen-embrittlement-resistant austenitic stainless steel on the upper surface of the top layer of martensitic steel and the lower surface of the bottom layer of martensitic steel. The preferred thicknesses of the hydrogen-embrittlement-resistant austenitic stainless steel are 8-25 mm, the martensitic steel is 0.8-2.5 mm, and the austenitic steel is 0.8-2.5 mm. The layer thickness ratio of the hydrogen-embrittlement-resistant austenitic stainless steel, martensitic steel, and austenitic steel is (5-25):1:1, with a total of 73-577 layers. Apply a release agent to the outer surface of the hydrogen-embrittlement-resistant austenitic stainless steel, specifically to the upper surface of the top layer and the lower surface of the bottom layer. The release agent can be boron nitride, with a thickness of 0.1-0.2 mm. After uniformly applying the release agent, bake at 120-150°C for 30-45 minutes.

[0065] Step 3: After completing the assembly, place the composite billet in a sleeve and perform electron beam welding to seal the edges under high vacuum. The preferred vacuum level is ≤5×10⁻⁶. -2Pa, weld penetration greater than 10mm. Electron beam welding parameters: bias voltage 1800~2200V; electron beam current 20~30mA; focusing 350~450mA; filament 15~18A; welding speed 300~450mm / min.

[0066] Step four: Heat the welded composite billet to 1150–1220℃ for 2–5 hours to ensure uniform microstructure and consistent internal and external temperatures. Then, perform multi-pass hot rolling. The roughing rolling temperature is 1080–1150℃, and the finishing rolling temperature is 1020–1100℃. The total roughing reduction is 82%–92%, and the single-pass reduction is 10%–30%, ensuring at least three passes have a reduction of ≥20%. After warming, the finishing rolling temperature is 960–1000℃, and the finishing rolling temperature is 860–900℃. The total finishing rolling reduction is 40%–70%, and the single-pass reduction is 5%–10%.

[0067] Step 5: Hold at 650~700℃ for 5~8 minutes, remove and perform warm rolling, with a single reduction of 0.1~0.3 mm. After warm rolling, the temperature drops to 250~350℃, and the furnace is reheated for 2~4 minutes. Repeat rolling until the total reduction rate is 10%~40%.

[0068] Step 6: Hold the warm-rolled composite material at 800~950℃ for 30~120min, cool it to achieve recrystallization and homogenization of the microstructure, and then temper it at 150~300℃ for 60~240min and cool it to release residual stress.

[0069] Step seven involves cold rolling the material obtained in step six at room temperature, annealing it at 600-950°C, and then cooling it. This triggers dynamic recrystallization, with deformation energy storage acting as the driving force to induce a large number of new grain nucleations, inhibiting grain growth and obtaining an ultrafine-grained structure. Furthermore, low-temperature tempering can be performed as needed to release residual stress.

[0070] Example 1

[0071] The martensitic steel in this embodiment comprises: 0.31% C, 1.22% Mn, 0.26% Si, 0.24% Cr, 0.21% V, 0.03% Ti, 0.0038% B, less than 0.02% of a single impurity element (P, S, O, N), and the balance being Fe.

[0072] The austenitic steel in this embodiment comprises: 0.61% C, 22.12% Mn, 0.26% Si, less than 0.03% of a single impurity element (P, S, O, N), and the balance being Fe.

[0073] The hydrogen embrittlement resistant austenitic stainless steel of this embodiment includes: 0.04% C, 10.0% Mn, 13.5% Cr, 4.5% Ni, 1.6% Si, 0.25% N, 1.2% Cu, and the total content of unavoidable P, S, and O impurities is ≤0.15%, the content of a single impurity is less than 0.05%, and the balance is Fe.

[0074] The preparation method of composite steel includes the following steps:

[0075] Step 1: Prepare continuous casting billets according to the composition of martensitic steel, austenitic steel and hydrogen embrittlement resistant austenitic stainless steel respectively. Use the continuous casting billets as electrodes to prepare electroslag ingots using electroslag remelting technology. After forging and rolling, prepare slabs of different thicknesses for later use.

[0076] All raw materials are strictly proportioned according to the designed mass percentages. The iron-based material uses high-quality pig iron or industrial pure iron with low sulfur and low phosphorus content to reduce impurities. Alloying elements such as Mn, Cr, Ni, Si, Cu, Nb, V, and Ti are selected from industrially available metals or ferroalloys based on their functional characteristics. Mn can be metallic manganese or low-carbon ferromanganese to balance cost and austenite stability. Cr and Ni use high-purity ferrochrome or ferronickel alloys to ensure passivation film formation and austenite stability. Microalloying elements V, Ti, and Nb are used in alloy form to control carbide / nitride precipitation behavior and reduce costs. Carbon sources are added through electrode graphite or carbon raisers. Nitrogen is introduced through the absorption of high-purity nitrogen gas during the AOD / VOD refining process or by adding nitrogen-containing ferroalloys (such as Fe–Cr–N). Regarding the order of addition, elements prone to oxidation and inclusion formation (Al, Si, Ti, V) are strictly added according to the principle of "strong deoxidation first, then weak deoxidation" to effectively reduce total oxygen content and inhibit inclusion formation. All raw materials are weighed and calibrated before batching to ensure that the deviation of major elements is controlled within ±0.02%~0.05wt.%.

[0077] 1) Preparation of HFS steel slab

[0078] First, a converter-LF refining-RH degassing route is adopted for smelting to reduce the content of harmful gases such as hydrogen, oxygen, and nitrogen. Before pouring the molten steel, the superheat is controlled at 25-35°C, and electromagnetic stirring in the crystallizer ensures uniform solute distribution. Then, continuous casting is carried out at a casting speed of 1.4-1.8 m / min to obtain a continuously cast billet with controllable defects and uniform composition. After surface treatment, the continuously cast billet is used as an electrode for electroslag remelting (ESR). The slag system is CaF2–Al2O3–CaO, ​​the remelting current is maintained at 800-1200 A, and the remelting rate is 120-180 kg / h to obtain an ESR ingot with low S, low O, and high purity. After homogenization at 1150-1200°C for 2-4 hours, the ESR ingot is forged, with the total deformation controlled at 40%-55% to break up the as-cast structure and refine the grains. Subsequently, multiple hot rolling passes were performed at 950~1050°C, with the final rolling temperature maintained in the range of 880~930°C. The steel was then cooled to room temperature in air to obtain a uniform tempered martensite precursor structure, ultimately producing a martensitic steel slab of the predetermined thickness.

[0079] 2) Preparation of TWIP steel slab

[0080] Austenitic high-manganese steel is smelted in a medium-frequency furnace and refined using AOD (argon-oxygen decarburization) to precisely control the content of elements such as C, Mn, Al, and Si. After AOD refining, the nitrogen content is generally stabilized at 0.01%~0.03%, ensuring a complete austenitization tendency. The molten steel is cast under protective conditions at a casting speed of 1.0~1.3 m / min to form a continuous casting billet with a thickness of 150~200 mm. During continuous casting, electromagnetic stirring in the crystallizer (M-EMS) is used to suppress Mn segregation. After milling, the continuous casting billet is used for electroslag remelting. The CaO content in the remelted slag is appropriately increased to improve the transformation of MnO inclusions. The electroslag ingot is homogenized at 1100~1150°C for 3~5 hours and then forged to the initial billet thickness, with the total reduction rate controlled at 45%~60%. Before rolling, the steel is reheated to 1000~1080°C and rolled in multiple passes to the target thickness. The final rolling temperature is maintained at 900°C±20°C to suppress the formation of high-temperature δ-ferrite and stabilize the austenitic structure. After rolling, air cooling or controlled cooling is used to prevent strain-induced phase transformation. Finally, an austenitic steel slab with uniform structure and low deformation energy storage is obtained.

[0081] 3) Preparation of ASS steel slab

[0082] ASS steel adopts an "ultra-low carbon + refining deoxidation + nitrogen strengthening" route. AOD+VOD combined refining significantly reduces C, O, and S content (C controlled at ≤0.03%, S and O generally reduced to ≤0.003%), and high-nitrogen protective nitrogen blowing achieves the target N content (0.1%~0.4%). The molten steel is continuously cast at a casting speed of 0.8~1.2 m / min. The crystallizer uses arc vibration and EMS control to reduce dendrite segregation and suppress MnS formation. The continuously cast billet undergoes electroslag remelting to further obtain high-purity metal. The slag system is Al2O3–CaO–CaF2, with a remelting voltage of 25~35V and a current of 900~1300A to ensure a stable molten pool and reduce inclusion content. The obtained electroslag ingots were held at 1150–1180°C for 2–3 hours and then forged into billets with a reduction rate of 40%–50% to break dendrites and eliminate segregation. Subsequently, they were hot-rolled at 1000–1100°C, with the final rolling temperature maintained at 950–1000°C, to obtain stable single-phase austenite and avoid Cr-enriched σ-phase or M-phase. 23 C6 precipitates along the grain boundaries. After rolling, air cooling is used to suppress the formation of high-temperature ferrite, ultimately yielding a hydrogen-resistant stainless steel slab with a pure microstructure, uniform grains, and a low hydrogen diffusion coefficient.

[0083] Martensitic and austenitic steel plates were cut into 400mm×300mm×1mm sizes, while hydrogen-embrittlement-resistant austenitic stainless steel plates were cut into 400mm×300mm×10mm sizes. The surfaces were mechanically ground using a wet-grit abrasive belt to thoroughly remove oxide scale and impurities, exposing fresh metal. The sides of the plates were also polished. Subsequently, the plates were ultrasonically cleaned for 20 minutes using anhydrous ethanol and acetone to remove grease and residual impurities. After cleaning, they were dried with clean air and stored in a clean environment for later use. The surface roughness was 0.2μm.

[0084] Step two involves alternately stacking martensitic and austenitic steel billets, with hydrogen-embrittlement-resistant austenitic stainless steel placed on the upper surface of the top layer of martensitic steel and the lower surface of the bottom layer. Specifically, this is an ASS / HFS / TWIP / HFS…HFS / TWIP / HFS / ASS structure, totaling 325 layers. A boron nitride release agent is applied to the outer surface of the hydrogen-embrittlement-resistant austenitic stainless steel to prevent the composite plate from adhering to the cladding after rolling. The release agent thickness is 0.15 mm, and after uniform application, the plate is baked at 130°C for 40 minutes.

[0085] Step 3: Select Q235B steel plate and process it into a grooved sleeve: the dimensions are 500mm×400mm×365mm, with a 401mm×301mm×345mm groove machined in the center, and a cover plate with dimensions of 500mm×400mm×10mm is also machined to ensure the surface is clean and free of contamination. After completing the assembly, place the composite billet into the sleeve.

[0086] like Figure 1 As shown, the composite blank with its sheath is placed inside a vacuum electron beam welder, fixed with a clamp, and then electron beam welded to seal the edges under high vacuum. The vacuum level is 5 × 10⁻⁶. -2 Pa, weld penetration greater than 10mm. The weld should be full, with no pits larger than 5mm appearing where the weld melt flows. The arc initiation and termination areas must be consistent and continuous, eliminating weld discontinuities. The weld surface should have good shape, free from cracks, inclusions, porosity, and surface depressions. The weld should be uniform and dense, free from porosity and cracks. Electron beam welding parameters: bias voltage 2000V; electron beam current 25mA; focusing 400mA; filament 16A; welding speed 350mm / min.

[0087] Step four involves heating the welded composite billet to 1200℃ for a net holding time of 2.5 hours to ensure uniform microstructure and consistent internal and external temperatures. This is followed by multi-pass hot rolling on a φ450 hot rolling mill at a rolling speed of 1 m / s. The roughing rolling starts at 1130℃ and finishes at 1050℃, with a total roughing reduction of 90% and a single-pass reduction of 10%–30%. The reductions for the first three passes are approximately 30%, 25%, and 23%, respectively. After roughing, the billet is air-cooled until it reaches 1000℃ before finishing. The finishing rolling starts at 1000℃ and finishes at 900℃, with a total finishing reduction of 40% and a single-pass reduction of 5%–8%. Immediately after rolling, the billet is water-cooled to room temperature.

[0088] Step 5: Hold at 700℃ for 5 minutes, remove and perform warm rolling with a single reduction of 0.15 mm. After rolling 2 passes, the temperature is reduced to 300℃, and the furnace is returned to hold for 2 minutes. Repeat rolling until the total reduction rate is 20%.

[0089] Step six: Hold the warm-rolled composite material at 850℃ for 20 minutes, then water-cool it to achieve recrystallization and microstructure homogenization. Next, temper it at 250℃ for 1 hour, followed by air cooling to release residual stress. Separate, clean, grind, and straighten the material to obtain the composite steel.

[0090] The material microstructure characteristics obtained in this embodiment are as follows: Figure 2 As shown in the figure, the EBSD IPF image and SEM interface morphology reveal a continuous and flat composite interface. No interface defects such as pores, inclusions, or delamination were observed, indicating that sufficient plastic contact and element interdiffusion occurred between the two metals under vacuum rolling and heat treatment, achieving a metallurgical interface dominated by atomic bonding. No significant remelted weld-like structures or brittle intermetallic compound continuous layers were observed near the interface. The grain size and matrix transition in the interface bonding zone are reasonable, showing uniform interface diffusion and a smooth microstructure transition, which is beneficial for suppressing interface stress concentration.

[0091] The fracture morphology reveals typical delamination and crack deflection characteristics during tensile fracture. After crack initiation within the martensite layer, its propagation towards the interface is halted by the austenite layer, exhibiting significant deflection and bifurcation, thus significantly elongating the crack propagation path and effectively dispersing the stress at the crack tip. Numerous plastic tear pits and deformation slip bands are visible within the austenite layer, indicating its significant role in plastic energy dissipation during tensile testing, playing a crucial toughening role in delaying failure. The repeated "crack deflection—crack passivation—energy dissipation" mechanism across multiple interfaces collectively enhances the overall fracture toughness of the material.

[0092] Example 2

[0093] The materials used in this embodiment are the same as those in Example 1. The preparation method of the composite steel is basically the same as that in Example 1. The only difference is that the number of layers in the core ASS / HFS / TWIP / HFS...HFS / TWIP / HFS / ASS is 157 in total, and the size of the sheath is adjusted accordingly. The size of the inner cavity of the sheath is changed to 401mm×301mm×177mm. Other process parameters and steps are consistent with those in Example 1.

[0094] Example 3

[0095] The materials used in this embodiment are the same as those in Example 1, and the preparation method of the composite steel is basically the same as that in Example 1. The only difference is that in step four, the initial rolling temperature of the rough rolling is 1080℃ and the final rolling temperature is 1000℃; the initial rolling temperature of the finish rolling is 950℃ and the final rolling temperature is 860℃. Other process parameters and steps are consistent with those in Example 1.

[0096] Example 4

[0097] The materials used in this embodiment are the same as those in Example 1. The preparation method of the composite steel is basically the same as that in Example 1. The only difference is that the warm rolling and heat preservation temperature at the beginning of step five is 650°C. Other process parameters and steps are consistent with those in Example 1.

[0098] Example 5

[0099] The materials used in this embodiment are the same as those in Example 1, and the preparation method of the composite steel is basically the same as that in Example 1. The only difference is that the warm-rolled composite material is heat-treated at 800°C in step six. Other process parameters and steps are consistent with those in Example 1.

[0100] Example 6

[0101] The materials used in this embodiment are the same as those in Example 1. The preparation method of the composite steel is basically the same as that in Example 1. The only difference is that in step seven, the material obtained in step six is ​​cold rolled at room temperature until the material thickness is 2 / 5 of the original thickness. Then, it is subjected to heat treatment of annealing at 850°C for 10 minutes and air-cooled.

[0102] Example 7

[0103] In this embodiment, the composite steel obtained in Example 6 is subjected to a heat treatment of tempering at 300°C for 60 minutes, followed by air cooling.

[0104] Comparative Example 1

[0105] The martensitic steel in this comparative example is the same as that in Example 1. It uses a single martensitic steel material for rolling and heat treatment without using a cladding. The size of the billet before rolling is consistent with that of the composite billet in Example 1, and the rolling and heat treatment process parameters are also consistent.

[0106] The tensile fracture characteristics of the material obtained in this comparative example are as follows: Figure 3 As shown, by Figure 3 Numerous fine cleavage facets can be observed, with dense distribution and clear boundaries, indicating that the fracture is mainly dominated by brittle cleavage mechanism. A small number of small dimples are only sparsely distributed in local areas, and the dimples are shallow and irregular, indicating that the degree of plastic deformation participation is extremely low. There is a lack of obvious crack deflection or passivation, resulting in limited absorption of fracture energy by the material, exhibiting typical high-strength and low-toughness fracture characteristics.

[0107] Comparative Example 2

[0108] The austenitic steel used in this comparative example is the same as that in Example 1. A single austenitic steel material is used for rolling and heat treatment without a cladding. The dimensions of the billet before rolling are consistent with those of the composite billet in Example 1, and the rolling and heat treatment process parameters are also consistent.

[0109] The fracture morphology characteristics of the material obtained in this comparative example are as follows: Figure 4 As shown, by Figure 4 Numerous uniformly distributed dimples were observed on the fracture surface. These dimples were stable in size, deep, and had smooth, continuous edges, indicating a typical microporous coalescence fracture mode. The high dimple density and uniform network distribution suggest that the material possesses sufficient microscopic plastic energy dissipation capacity during tensile deformation.

[0110] Comparative Example 3

[0111] The hydrogen embrittlement resistant austenitic stainless steel in this comparative example is the same as that in Example 1. It uses a single hydrogen embrittlement resistant austenitic stainless steel material for rolling and heat treatment without using a cladding. The size of the billet before rolling is consistent with that of the composite billet in Example 1, and the rolling and heat treatment process parameters are also consistent.

[0112] Comparative Example 4

[0113] The materials used in this comparative example are the same as those in Example 6, and the preparation method of the composite steel is basically the same as that in Example 6, except that step five is missing.

[0114] Comparative Example 5

[0115] The materials used in this comparative example are the same as those in Example 1, and the preparation method of the composite steel is basically the same as that in Example 1. The only difference is the ASS / HFS / TWIP / HFS…HFS / TWIP / HFS / ASS structure in step two, which has a total of 39 layers.

[0116] Tensile tests were conducted on samples of the multilayer composite steels prepared in Examples 1-7 and Comparative Examples 1-5, according to ASTM G129-00 standard, at a tensile strength of 5 × 10⁻⁶. -2 s -1 Slow-rate tensile testing (SSRT) was conducted using the strain rate specified in the test. Electrochemical hydrogen charging was employed, and all specimens were mechanically polished prior to hydrogen charging. The hydrogen charging solution was a NaOH aqueous solution containing 3% NaCl and 0.3% NH4SCN. The hydrogen charging current density was 5 mA / cm². 2 The samples were cathodically charged with hydrogen at a constant temperature of 90℃ for 24 hours. To prevent the hydrogen charging solution from evaporating and exposing the samples to air, the hydrogen charging solution was replenished periodically. After hydrogen charging, a zinc layer was electroplated on the surface of the specimen to slow down the escape of hydrogen atoms in the SSRT tensile test. SSRT tensile tests were performed at room temperature within 15 minutes after the electroplating was completed. Welding was performed using an input energy of 2.5 kJ / mm, and the impact toughness of the heat-affected zone of the weld was tested at -60℃. The test results are shown in Table 1.

[0117] According to GB / T8650-2006, hydrogen-induced cracking (HIC) tests were conducted on all samples, and the test results are shown in Table 2.

[0118] Table 1 Results of slow strain rate tensile test (SSRT) on multilayer composite steel plates

[0119]

[0120] Table 2 Results of hydrogen-induced cracking (HIC) test on multilayer composite steel plates

[0121]

[0122] The test results show that this application has achieved an excellent balance between the strength and toughness of the composite material and its resistance to hydrogen embrittlement through material and process design.

[0123] The above description of the disclosed embodiments enables those skilled in the art to implement or use this application. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from the principles of this application, and such improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A method for producing a composite steel, characterized by, A composite steel material is obtained by vacuum hot rolling martensitic steel and austenitic steel together. The top and bottom layers are both martensitic steel, and the middle layer consists of alternating stacks of martensitic steel and austenitic steel. The upper surface of the top layer of martensitic steel and the lower surface of the bottom layer of martensitic steel are hydrogen-embrittlement-resistant austenitic stainless steel. The martensitic steel, by mass percentage, comprises: 0.2%–0.4% C, 0.5%–1.5% Mn, 0.2%–0.3% Si, 0.2%–0.3% Cr, 0.1%–0.3% V, 0.02%–0.04% Ti, 0.002%–0.004% B, unavoidable impurity elements ≤0.15%, and the balance being Fe. The austenitic steel, by mass percentage, comprises: 0.5%–0.8% C, 22.0%–24.0% Mn, 0.2%–1.5% Si, 0.1%–0.3% Nb, unavoidable impurity elements ≤0.15%, and the balance being Fe. By weight percentage, the hydrogen embrittlement-resistant austenitic stainless steel comprises: 0.02%–0.06% C, 8.0%–12.0% Mn, 0.2%–2.0% Si, 3.0%–6.0% Ni, 14.0%–20.0% Cr, 0.1%–0.4% N, 0.05%–0.2% Cu, unavoidable impurity elements ≤0.15%, and the balance being Fe. Includes the following steps: Step 1: Prepare slabs according to the composition of the martensitic steel, the austenitic steel and the hydrogen embrittlement resistant austenitic stainless steel, cut them into plates of the same size, and remove surface oxide scale, impurities and oil stains. Step 2: Stack the billet plates of martensitic steel and austenitic steel alternately, place the hydrogen embrittlement resistant austenitic stainless steel on the upper surface of the top layer of martensitic steel and the lower surface of the bottom layer of martensitic steel, with a total number of layers of 73 to 577, and apply a release agent to the outer surface of the hydrogen embrittlement resistant austenitic stainless steel. Step 3: After completing the assembly, place the composite billet into the sleeve and perform electron beam welding to seal the edges of the composite billet with the sleeve under high vacuum. Step 4: Heat and hold the welded composite billet to ensure uniform structure and consistent internal and external temperatures, and then perform multiple hot rolling composite processes. Step 5: Hold at 650~700℃ for 5~8 minutes, remove and perform warm rolling. After warm rolling, reduce the temperature to 250~350℃, return to the furnace and hold for 2~4 minutes, and repeat rolling until the total reduction rate is 10%~40%. Step 6: Hold the warm-rolled composite material at 800~950℃ for 30~120min, cool it to achieve recrystallization and homogenization of the microstructure, and then temper it at 150~300℃ for 60~240min and cool it to release residual stress.

2. The method of manufacturing a composite steel according to claim 1, characterized in that, In step one, continuous casting billets are prepared according to the compositions of the martensitic steel, the austenitic steel, and the hydrogen embrittlement resistant austenitic stainless steel, respectively. Electroslag ingots are prepared by electroslag remelting technology using the continuous casting billets as electrodes. After forging and rolling, slabs of different thicknesses are prepared for later use.

3. The method of claim 1, wherein the steel is a high-strength steel. The thickness of the hydrogen embrittlement resistant austenitic stainless steel is 8~25mm, the thickness of the martensitic steel is 0.8~2.5mm, the thickness of the austenitic steel is 0.8~2.5mm, and the layer thickness ratio of the hydrogen embrittlement resistant austenitic stainless steel, the martensitic steel and the austenitic steel is (5~25)∶1∶1.

4. The method of claim 1, wherein the steel is a high-strength steel. In step four, the heating temperature of the composite billet is 1150–1220℃, and the net holding time is 2–5 hours; the multi-pass hot rolling composite is performed, with the roughing rolling starting temperature at 1080–1150℃, the finishing rolling temperature at 1020–1100℃, the total reduction rate of roughing rolling at 82%–92%, and the single-pass reduction rate at 10%–30%; the finishing rolling starting temperature is 960–1000℃, the finishing rolling temperature at 860–900℃, the total reduction rate of finishing rolling at 40%–70%, and the single-pass reduction rate at 5%–10%.

5. The method of claim 1, wherein the steel is a high-strength steel. It also includes step seven, which involves cold rolling the material obtained in step six at room temperature, annealing it at 600~950℃, and then cooling it.

6. A high-strength high-toughness hydrogen embrittlement resistant composite steel, characterized by, The composite steel material is obtained by the method for preparing composite steel according to any one of claims 1 to 5.

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