High-strength and high-toughness steel suitable for high-humidity and harsh hydrogen environment and preparation method of high-strength and high-toughness steel

Abstract

The invention relates to high-toughness steel adapting to a high-damp-heat harsh hydrogen environment and a preparation method, and belongs to the technical field of steel preparation. The high strength and toughness steel comprises the following chemical components in percentage by mass: 0.40%-0.55% of C, 0.20%-1.50% of Si, 0.55%-1.50% of Mn, 0.70%-1.50% of Cr, 0.50%-1.50% of Ni, 0.15%-0.35% of Mo, 0.025%-0.065% of Al, less than or equal to 0.015% of P, less than or equal to 0.010% of S and the balance of Fe and inevitable impurities. By optimizing the alloy element ratio and synergistic effect, the strength, toughness and delayed fracture resistance of the steel are remarkably improved, and the long-life service requirement of the steel in the severe hydrogen environment is met at the strength level of 1200-1400 MPa.

Description

Technical Field

[0001] This application relates to the technical field of steel preparation, and particularly to a high-strength and tough steel suitable for high-humidity, high-temperature, and harsh hydrogen environments and a preparation method thereof. Background Art

[0002] Driven by the strategic goals of "carbon peak and carbon neutrality" (dual carbon), energy conservation, emission reduction, and green development have become the inevitable requirements for the global energy transformation. As the core pillar of the green energy system, wind power will play a dominant role in the future power generation structure. Compared with onshore wind power, offshore wind power has 20% - 40% higher energy efficiency of wind energy resources, and also has advantages such as not occupying land, high wind speed, less dust, large power generation, stable operation, and zero dust emissions, making it suitable for large-scale development. At the same time, the strategic position of China's marine resources (including oil and gas, wind energy, and minerals) has become increasingly prominent, becoming an important direction for national energy security and economic development.

[0003] However, large-scale marine resource development requires safe, reliable, and long-life infrastructure as a prerequisite. However, the extreme marine environment with high humidity, high temperature, strong radiation, and high chloride ion concentration seriously threatens the long-term service safety of infrastructure. Developing advanced steel materials with ultra-high strength, excellent corrosion resistance, and hydrogen embrittlement resistance has become the key breakthrough to break through the technical bottleneck of marine engineering equipment and support the deep integration of the "dual carbon" goal and the marine power strategy. Summary of the Invention

[0004] This application provides a high-strength and tough steel suitable for high-humidity, high-temperature, and harsh hydrogen environments and a preparation method thereof to solve the following technical problems: how to solve the hydrogen embrittlement problem of high-strength steel in high-humidity, high-temperature, and harsh hydrogen environments.

[0005] In a first aspect, an embodiment of this application provides a high-strength and tough steel suitable for high-humidity, high-temperature, and harsh hydrogen environments. In terms of mass fraction, the chemical composition of the high-strength and tough steel is as follows: C: 0.40% - 0.55%, Si: 0.20% - 1.50%, Mn: 0.55% - 1.50%, Cr: 0.70% - 1.50%, Ni: 0.50% - 1.50%, Mo: 0.15% - 0.35%, Al: 0.025% - 0.065%, P ≤ 0.015%, S ≤ 0.010%, and the balance is Fe and unavoidable impurities.

[0006] Optionally, in terms of mass fraction, the chemical composition of the high-strength and tough steel further adds at least one of Nb: 0.05% - 0.15%, V: 0.06% - 0.30%, and Ti: 0.030% - 0.085%.

[0007] Optionally, the chemical composition of the high-strength and high-toughness steel satisfies: 0.15 ≤ (1.2[Nb] + 1.48[V] + 0.48[Ti])·[C] ≤ 0.30, where [Nb], [V], [Ti], and [C] represent the mass fractions of Nb, V, Ti, and C, respectively.

[0008] Optionally, in terms of volume fraction, the microstructure of the high-strength and high-toughness steel is: lower bainite: 70% - 75%, martensite 10% - 15%, austenite 10% - 15%.

[0009] Optionally, the grain size of the austenite is 0.05μm - 0.50μm, and the austenite is in the form of thin films and / or blocks.

[0010] Optionally, when the hydrogen content of the high-strength and high-toughness steel is greater than 3 ppm, under a constant load of 0.8Rp 0.2 , the delayed fracture time > 100 h.

[0011] Optionally, the tensile strength of the high-strength and high-toughness steel is 1200 Mpa - 1400 Mpa.

[0012] In a second aspect, the present application provides a method for preparing the high-strength and high-toughness steel described in the first aspect, and the method includes:

[0013] Obtaining a billet with the described chemical composition;

[0014] Successively heating, rolling, performing a first isothermal heat treatment, and a second isothermal heat treatment on the billet to obtain the finished high-strength and high-toughness steel.

[0015] Optionally, the temperature of the first isothermal heat treatment is (Ms + 10°C) - (Ms + 15°C), and the time of the first isothermal heat treatment is 10 min - 30 min.

[0016] Optionally, the temperature of the second isothermal heat treatment is (Ms (剩余奥氏体) + 5°C) - (Ms (剩余奥氏体) + 10°C), and the time of the second isothermal heat treatment is 30 min - 60 min.

[0017] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0018] The embodiment of the present application provides a high-strength and tough steel suitable for a harsh hydrogen environment with high humidity and heat. In terms of mass fraction, the chemical composition of the high-strength and tough steel is as follows: C: 0.40% - 0.55%, Si: 0.20% - 1.50%, Mn: 0.55% - 1.50%, Cr: 0.70% - 1.50%, Ni: 0.50% - 1.50%, Mo: 0.15% - 0.35%, Al: 0.025% - 0.065%, P ≤ 0.015%, S ≤ 0.010%, and the balance is Fe and unavoidable impurities. By optimizing the alloy element ratio and synergistic effect, precisely controlling the contents of Ni (nickel), Cr (chromium), and Mo (molybdenum) elements, regulating the phase transformation thermodynamics and kinetics of carbide-free bainite, a uniform and fine bainite / martensite duplex structure is formed; stabilizing the retained austenite content, using its high hydrogen solubility to buffer the local hydrogen concentration and inhibit the initiation of hydrogen-induced cracks; avoiding the precipitation of carbides along the grain boundaries and reducing the hydrogen diffusion channels. The strength, toughness, and resistance to delayed fracture of the steel are significantly improved, enabling it to meet the long-life service requirements in a harsh hydrogen environment at the strength level of 1200 Mpa - 1400 MPa. Brief Description of the Drawings

[0019] The drawings herein are incorporated into the specification and form a part of this specification, showing the embodiments in line with the present application, and are used together with the specification to explain the principles of the present application.

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0021] Figure 1 It is a schematic flow chart of a preparation method of a high-strength and tough steel suitable for a harsh hydrogen environment with high humidity and heat provided by the embodiment of the present application. Detailed Embodiments

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0023] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual values within that range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, and this applies regardless of the range; in addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0024] In this text, terms including "comprising" etc. mean "including but not limited to". Relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "And / or" describes the association relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, or B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "a plurality" means two or more; "at least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single items (pieces) or plural items (pieces); for example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both mean: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. "Parts representation method" such as parts by weight, parts by mass, etc. represents the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0025] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in this text can be obtained through market purchase or can be prepared by existing methods.

[0026] In a first aspect, an embodiment of the present application provides a high-strength and tough steel suitable for a harsh hydrogen environment with high humidity and high temperature. In terms of mass fraction, the chemical composition of the high-strength and tough steel is as follows: C: 0.40% - 0.55%, Si: 0.20% - 1.50%, Mn: 0.55% - 1.50%, Cr: 0.70% - 1.50%, Ni: 0.50% - 1.50%, Mo: 0.15% - 0.35%, Al: 0.025% - 0.065%, P ≤ 0.015%, S ≤ 0.010%, and the balance is Fe and inevitable impurities.

[0027] The positive effect of limiting the mass fraction of C to 0.40% - 0.55%: C is one of the most important hardening elements in steel. Within this mass fraction range, C can significantly improve the hardenability of the steel, thereby enhancing the overall performance of the steel. When the mass fraction of C is lower than 0.40%, the hardenability of the steel may be insufficient, resulting in insufficient hardness for large-sized materials and affecting the strength of the steel. While when the mass fraction of C exceeds 0.55%, it may lead to excessive carbides, thus reducing the cold deformation performance and toughness-plasticity of the steel. Therefore, limiting the mass fraction of C within the range of 0.40% - 0.55% can maintain good toughness while ensuring strength.

[0028] The positive effect of limiting the mass fraction of Si to 0.20% - 1.50%: Si dissolves in ferrite (α-Fe), and lattice distortion is caused by the difference in atomic size (Si atoms have a larger radius). This lattice distortion hinders dislocation movement, thereby increasing the strength and hardness of the steel. Within this mass fraction range, the strengthening effect of Si is significant and helps to improve the overall strength of the steel. Si can also hinder the diffusion of carbon atoms, delay the formation and aggregation of cementite, and enable the steel to maintain higher strength during the tempering process. When the Si content is appropriate (within the range defined in this technical solution), the addition of Si can increase the strength of the steel without significantly reducing its toughness and plasticity. When the mass fraction of Si is higher than 1.50%, it may deteriorate the toughness and plasticity of the steel.

[0029] The positive effect of limiting the mass fraction of Mn to 0.55% - 1.50%: Mn is a commonly used deoxidizing element in steel. At the same time, it can effectively improve the hardenability of the steel during quenching and high-temperature tempering and quenching processes. The improvement of hardenability helps to ensure that the steel can uniformly obtain the required structure and properties when used in large sizes, avoiding performance unevenness problems caused by insufficient hardenability. Although Mn is beneficial for improving hardenability, when the mass fraction of Mn is higher than 1.50%, it may increase the risk of center segregation during continuous casting and exacerbate the tendency of grain boundary segregation during quenching and tempering treatment, thereby promoting temper brittleness.

[0030] Positive effects of limiting the mass fraction of Cr to 0.70% - 1.50%: Cr is one of the key elements to enhance the corrosion resistance of steel. Adding 0.70% - 1.50% of Cr to steel can form a dense chromium oxide film, effectively isolating water and oxygen, thereby improving the corrosion resistance of steel in humid environments. This is particularly important for steel used in high humidity and heat environments and can extend its service life.

[0031] Positive effects of limiting the mass fraction of Ni to 0.50% - 1.50%: Within this mass fraction range, there are effects of controlling slab cracks and improving corrosion resistance; when the value of the mass fraction is greater than the maximum value of the range endpoints, it will lead to higher development material costs and greater difficulty in controlling surface defects of rolled products. When the value of the mass fraction is less than the minimum value of the range endpoints, it will lead to easy occurrence of rolling cracks in the slab, affecting the product forming performance.

[0032] Positive effects of limiting the mass fraction of Mo to 0.15% - 0.35: Mo is a strong carbide - forming element that can significantly improve the hardenability of steel. During the preparation of high - strength and tough steel, the improvement of hardenability helps to ensure that the steel can still obtain uniform structure and properties under large cross - section sizes, thereby improving the overall mechanical properties of the steel. In addition, the addition of Mo can refine the grains of the steel and improve its strength. At the same time, Mo can also promote the formation of fine and dispersed carbide particles in the steel, and these carbide particles can hinder dislocation movement, thereby improving the strength and toughness of the steel.

[0033] Positive effects of limiting the mass fraction of Al to 0.025% - 0.065%: Al is a commonly used deoxidizing element in steel. The acid - soluble Al in steel can precipitate during rolling to fix free N elements, reduce the work - hardening rate, and improve the cold - working performance of the steel. When the mass fraction of Al is less than 0.025%, it cannot play the role of fixing N. When the mass fraction of Al is higher than 0.065%, problems such as nozzle blockage and straightening cracks are likely to occur during the tundish casting of small billets.

[0034] Positive effects of limiting P ≤ 0.015%: P is prone to segregation in steel, especially at grain boundaries, which will increase the brittleness tendency of steel during tempering. Limiting the content of P can significantly reduce the risk of temper brittleness and ensure that the steel has good toughness and plasticity after heat treatment.

[0035] Positive effects of limiting S ≤ 0.010%: S is prone to forming sulfide inclusions in steel. These inclusions will significantly reduce the plasticity of the steel when the steel is heated to high temperatures, resulting in easy cracking of the steel during hot working. This phenomenon is called hot brittleness. Limiting the content of S can significantly reduce the hot brittleness of the steel and improve its hot - working performance.

[0036] In some embodiments, in terms of mass fraction, the chemical composition of the high-strength and high-toughness steel further adds at least one of Nb: 0.05% to 0.15%, V: 0.06% to 0.30%, and Ti: 0.030% to 0.085%.

[0037] Positive effects of limiting the mass fraction of Nb to 0.05% to 0.15%: As an important microalloying element, Nb can combine with carbon and nitrogen in the steel to form Nb(C,N) precipitates, pin the austenite grain boundaries, and inhibit grain growth during high-temperature heating and rolling. The fine and dispersed carbides or carbonitrides precipitated under high-temperature conditions can serve as hydrogen traps to greatly improve the H capture ability, refine the grains, strengthen the grain boundaries to hinder the propagation of intergranular cracks, and improve the hydrogen-induced delayed fracture resistance of the steel. When the mass fraction of Nb is less than 0.05%, it is difficult to achieve a hydrogen content of 3 ppm in the material; when the mass fraction of Nb is greater than 0.15%, the cost is high and the slab cracks are difficult to control during the production process.

[0038] Positive effects of limiting the mass fraction of V to 0.06% to 0.30%: V can form fine and dispersed carbonitride precipitation phases in the steel. These precipitation phases can significantly improve the strength of the steel because they can hinder the movement of dislocations, thereby enhancing the deformation resistance of the material; V can inhibit grain growth during hot working and heat treatment of the steel, contributing to obtaining a fine grain structure. The refined grains can improve the strength and toughness of the steel, and also contribute to improving the plasticity and toughness of the steel; in a harsh hydrogen environment with high humidity and heat, hydrogen-induced delayed fracture of the steel is an important issue. The carbonitride precipitation phases formed by V can serve as hydrogen traps to capture hydrogen atoms in the steel, reduce the diffusion and aggregation of hydrogen atoms in the steel, and thus improve the hydrogen-induced delayed fracture resistance of the steel. When the mass fraction of V is less than 0.06%, it is difficult to achieve a hydrogen content of 3 ppm in the material; when the mass fraction of V is greater than 0.3%, the production cost is high and the contribution of V is economically poor.

[0039] Positive effects of limiting the mass fraction of Ti to 0.030% to 0.085%: Ti is relatively active in the steel and has a strong binding ability with element N, playing a role in fixing nitrogen atoms and improving the cold working ability of the material. When the mass fraction of Ti is less than 0.03%, it is difficult to fix the N content in the steel; when the mass fraction of Ti is higher than 0.085%, the large-sized TiN in the steel can significantly reduce the low-temperature impact performance of the steel.

[0040] In some embodiments, the chemical composition of the high-strength and high-toughness steel satisfies: 0.15 ≤ (1.2[Nb] + 1.48[V] + 0.48[Ti])·[C] ≤ 0.30, where [Nb], [V], [Ti], and [C] represent the mass fractions of Nb, V, Ti, and C, respectively.

[0041] The elements Nb, V, and Ti also need to satisfy the relationship: when 0.15 ≤ (1.2[Nb] + 1.48[V] + 0.48[Ti])·[C] ≤ 0.30, excellent strength and toughness and hydrogen-induced delayed fracture performance in a harsh hydrogen environment can be obtained.

[0042] In some embodiments, by volume fraction, the microstructure of the high-strength and tough steel is: lower bainite: 70% - 75%, martensite 10% - 15%, austenite 10% - 15%.

[0043] This specific microstructure ratio has the following positive effects:

[0044] 1. Balance between high strength and toughness:

[0045] Lower bainite has a good balance of strength and toughness. Its lath structure can effectively disperse stress and prevent crack propagation. It accounts for 70% - 75% in the total volume, providing the main strength source for the steel.

[0046] Martensite is famous for its high strength. Appropriate addition of martensite can further improve the overall strength of the steel, but excessive martensite will reduce toughness. Therefore, controlling martensite within the range of 10% - 15% ensures both strength and toughness.

[0047] Austenite can undergo a phase transformation when subjected to external forces, absorbing energy, thereby improving the toughness of the steel. Appropriate amount of austenite (10% - 15%) helps to enhance the impact resistance and delayed fracture resistance of the steel in a harsh environment.

[0048] 2. Excellent resistance to delayed fracture:

[0049] Retained austenite plays the role of a "hydrogen trap" in the steel, capable of capturing and fixing hydrogen atoms, reducing the number of diffusible hydrogen, and thus reducing the risk of hydrogen-induced delayed fracture.

[0050] The mixed microstructure of lower bainite and martensite can also effectively hinder the diffusion and aggregation of hydrogen atoms through its complex interfaces and phase transformation behaviors, further improving the resistance of the steel to delayed fracture.

[0051] In some embodiments, the grain size of the austenite is 0.05 μm - 0.50 μm, and the austenite is in the form of thin films and / or blocks.

[0052] The refinement of austenite grain size (0.05μm - 0.50μm) helps to improve the toughness of steel. Fine austenite grains can more effectively disperse and absorb stress, thus delaying the initiation and propagation of cracks. Fine austenite grains and complex morphology can act as effective "hydrogen traps" to capture and fix hydrogen atoms in the steel, reducing the amount of diffusible hydrogen, which helps to reduce the risk of hydrogen-induced delayed fracture and improve the service life of steel in harsh environments.

[0053] Film-like and massive austenite morphologies can form complex interface structures in the steel. These interfaces can absorb more energy when stressed, further improving the toughness of the steel. This morphology and size design of austenite also helps to hinder the diffusion path of hydrogen atoms, making it more difficult for hydrogen atoms to move and aggregate freely in the steel, thus further reducing the possibility of delayed fracture.

[0054] In some embodiments, when the hydrogen content of the high-strength and high-toughness steel is greater than 3 ppm, under a constant load of 0.8 Rp 0.2 , the delayed fracture time > 100 h.

[0055] In an environment with a high hydrogen content, ordinary steel is prone to hydrogen-induced delayed fracture, resulting in the sudden failure of equipment or structures. In this embodiment, the high-strength and high-toughness steel can resist hydrogen-induced delayed fracture for more than 100 hours in a hydrogen-containing environment (hydrogen concentration > 3 ppm) and at a relatively high stress level (0.8 times the yield strength).

[0056] In some embodiments, the tensile strength of the high-strength and high-toughness steel is 1200 Mpa - 1400 Mpa.

[0057] The tensile strength of the high-strength and high-toughness steel being between 1200 Mpa and 1400 Mpa means that it can withstand a relatively high tensile load without fracture.

[0058] Figure 1 It is a schematic flow chart of a preparation method of a high-strength and high-toughness steel adapted to a harsh hydrogen environment with high humidity and heat for the embodiments of this application.

[0059] Please refer to Figure 1 , Second, this application provides a preparation method of the high-strength and high-toughness steel described in the first aspect, and the method includes:

[0060] S1. Obtain a billet with the described chemical composition;

[0061] S2. Heat, roll, perform a first isothermal heat treatment, and a second isothermal heat treatment on the billet in sequence to obtain the finished high-strength and high-toughness steel.

[0062] In some embodiments, the temperature of the first isothermal heat treatment is (Ms + 10°C) to (Ms + 15°C), and the time of the first isothermal heat treatment is 10 min to 30 min.

[0063] In the embodiments of the present application, the first isothermal heat treatment and the second isothermal heat treatment can be carried out in a molten salt bath, and the molten salt bath can provide a stable heat treatment environment, which helps to reduce temperature fluctuations and microstructural inhomogeneity during the heat treatment process, and improve the stability and repeatability of the process.

[0064] The temperature of the first isothermal heat treatment is precisely set between (Ms + 10°C) and (Ms + 15°C). Here, Ms represents the martensite start temperature, which is the temperature point at which martensite begins to form during the cooling process of the steel. By performing isothermal heat treatment within this temperature range, the phase transformation process of the steel can be precisely controlled, promoting the formation of lower bainite and retained austenite.

[0065] The time of the first isothermal heat treatment is controlled between 10 min and 30 min. This time range ensures that the steel can fully undergo phase transformation reactions at the set temperature, achieving the desired microstructure transformation effect, while avoiding unnecessary phase transformations or microstructural changes that may be caused by too long a time.

[0066] In some embodiments, the temperature of the second isothermal heat treatment is (Ms (剩余奥氏体) + 5°C) to (Ms (剩余奥氏体) + 10°C), and the time of the second isothermal heat treatment is 30 min to 60 min.

[0067] The temperature of the second isothermal heat treatment is set between (Ms (retained austenite) + 5°C) and (Ms (retained austenite) + 10°C), where Ms (retained austenite) refers to the start transformation temperature of the retained austenite after the first isothermal heat treatment. By performing the second-stage isothermal heat treatment within this temperature range, the microstructure of the steel can be further optimized, especially the morphology and distribution of the retained austenite. The time of the second isothermal heat treatment is controlled between 30 min and 60 min, and this time range ensures that the steel can further complete the optimization of the microstructure during the second-stage isothermal heat treatment process, improving the comprehensive properties of the steel.

[0068] In summary, the embodiments of the present application significantly improve the strength, toughness, and hydrogen-induced cracking resistance of the steel by optimizing the alloy element ratio and synergistic effect, enabling it to meet the long-term service requirements in a harsh hydrogen environment at a strength level of 1200 Mpa to 1400 MPa. Specifically:

[0069] By precisely controlling the contents of Ni (nickel), Cr (chromium), and Mo (molybdenum) elements, the following functions are achieved: regulating the phase transformation thermodynamics (critical temperature range) and kinetics (phase transformation rate) of carbide-free bainite to form a uniform and fine bainite / martensite duplex structure; stabilizing the retained austenite content (5% - 15%), using its high hydrogen solubility to buffer the local hydrogen concentration and inhibit the initiation of hydrogen-induced cracks; avoiding the precipitation of carbides along grain boundaries and reducing hydrogen diffusion channels.

[0070] Adding Nb (niobium), V (vanadium), and Ti (titanium) elements to form, through hot rolling and heat treatment processes, dispersion-precipitated phases of carbonitrides (such as NbC, TiN, VC) as efficient hydrogen traps to fix diffused hydrogen and reduce hydrogen activity; refining the original austenite grains, increasing the grain boundary density, and hindering the propagation of intergranular cracks; strengthening the bonding strength between grain boundaries and phase boundaries and enhancing the crack propagation resistance.

[0071] The prepared product of the preparation method of the high-strength and high-toughness steel adapted to a harsh hydrogen environment with high humidity and heat is the above-mentioned high-strength and high-toughness steel adapted to a harsh hydrogen environment with high humidity and heat. Since the preparation method of the high-strength and high-toughness steel adapted to a harsh hydrogen environment with high humidity and heat adopts some or all of the technical solutions of the embodiments of the high-strength and high-toughness steel adapted to a harsh hydrogen environment with high humidity and heat, it thus has at least all the beneficial effects brought by the technical solutions of the embodiments of the high-strength and high-toughness steel adapted to a harsh hydrogen environment with high humidity and heat, which will not be elaborated one by one here.

[0072] The following will further elaborate on this application in combination with specific embodiments. For the experimental methods without specifying specific conditions in the following embodiments, they are usually determined according to national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0073] The chemical composition (wt%) of the continuous casting billet of the high-strength and high-toughness steel is shown in Table 1.

[0074] Table 1

[0075]

[0076]

[0077] Both the examples and the comparative examples adopt the preparation method provided in this application to obtain the finished high-strength and high-toughness steel.

[0078] Perform performance tests on the prepared finished high-strength and high-toughness steel. The specific performance parameters are shown in Table 2. Among them, the finished high-strength and high-toughness steel of the application examples and the comparative examples is in an aqueous solution of 0.25 mol / L H2SO4 + 0.5 g / L thiourea, and the current density is J = 1.0 mA / cm 2Under the given conditions, electrochemically charge hydrogen for 2 - 4 hours. Immediately after the electrochemical hydrogen charging, conduct a TDS experiment on a hydrogen thermal analyzer (G4 PHOENIX DH). Heat the specimen in a vacuum to 800 °C at a rate of 10 °C / s and hold for 20 min to obtain the hydrogen content.

[0079] Table 2

[0080]

[0081]

[0082] As can be seen from Tables 1 - 2, compared with the comparative examples, the chemical compositions of the examples of the present application are all within the required ranges of the present invention, and the tensile strength is stably within 1200 - 1400 Mpa. In a 0.25 mol / L H2SO4 + 0.5 g / L thiourea aqueous solution, with a current density of J = 1.0 mA / cm 2 Under the given conditions, electrochemically charge hydrogen for 2 - 4 hours. The hydrogen content in the material can reach the level of 3.02 - 4.66 ppm, and it can maintain without fracture under a 0.8 Rp0.2 loading stress for 110 - 168 h, enabling long-term service in a harsh hydrogen environment with high humidity and heat.

[0083] One or more technical solutions in the embodiments of the present invention at least further have the following technical effects or advantages:

[0084] High strength and high toughness: The tensile strength of the prepared high-strength and high-toughness steel is stably within 1200 - 1400 Mpa, with good strength and toughness matching.

[0085] Excellent resistance to hydrogen-induced cracking: In a harsh hydrogen environment with a hydrogen content greater than 3 ppm, under a constant load of 0.8 Rp0.2 for 100 hours without fracture, significantly improving the hydrogen-induced cracking resistance of the material.

[0086] Meet the requirements of special environments: This high-strength and high-toughness steel is particularly suitable for harsh environments with high humidity and heat, strong radiation, and high chloride ion concentration, such as offshore wind power infrastructure, etc., ensuring the safe, reliable, and long-term service performance of the material in these environments.

[0087] Broad prospects for popularization and application: This technical solution is of great significance in the field of new material development and has long-term value in future market competition and the popularization and application in China's marine environment.

[0088] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but rather to the broadest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A high-strength and tough steel adapted to a harsh hydrogen environment with high humidity and high temperature. By mass fraction, the chemical composition of the high-strength and tough steel is as follows: C: 0.40% - 0.55%, Si: 0.20% - 1.50%, Mn: 0.55% - 1.50%, Cr: 0.70% - 1.50%, Ni: 0.50% - 1.50%, Mo: 0.15% - 0.35%, Al: 0.025% - 0.065%, P ≤ 0.015%, S ≤ 0.010%, and the balance is Fe and unavoidable impurities.

2. The high-strength and tough steel according to claim 1, wherein By mass fraction, the chemical composition of the high-strength and tough steel further adds at least one of Nb: 0.05% - 0.15%, V: 0.06% - 0.30%, and Ti: 0.030% - 0.085%.

3. The high-strength and tough steel according to claim 2, wherein The chemical composition of the high-strength and tough steel satisfies: 0.15 ≤ (1.2[Nb] + 1.48[V] + 0.48[Ti])·[C] ≤ 0.30, where [Nb], [V], [Ti], and [C] respectively represent the mass fractions of Nb, V, Ti, and C.

4. The high-strength and tough steel according to claim 1, characterized in that, By volume fraction, the microstructure of the high-strength and tough steel is as follows: lower bainite: 70% - 75%, martensite 10% - 15%, and austenite 10% - 15%.

5. The high-strength and tough steel according to claim 4, characterized in that, The grain size of the austenite is 0.05μm - 0.50μm, and the austenite is in the form of thin films and / or blocks.

6. The high-strength and tough steel according to claim 1, characterized in that, When the hydrogen content of the high-strength and tough steel is greater than 3 ppm, under a constant load of 0.8 Rp 0.2 , the delayed fracture time > 100 h.

7. The high-strength and tough steel according to claim 1, characterized in that, The tensile strength of the high-strength and tough steel is 1200 Mpa - 1400 Mpa.

8. A preparation method of the high-strength and tough steel according to any one of claims 1 to 7, the method comprising: Obtaining a continuous casting billet with the above chemical composition; Successively heating, rolling, performing a first isothermal heat treatment, and a second isothermal heat treatment on the continuous casting billet to obtain a finished high-strength and tough steel.

9. The method according to claim 8, characterized in that The temperature of the first isothermal heat treatment is (Ms + 10°C) - (Ms + 15°C), and the time of the first isothermal heat treatment is 10 min - 30 min.

10. The method according to claim 8, wherein The temperature of the second isothermal heat treatment is (Ms ( retained austenite ) + 5 °C) to (Ms ( retained austenite ) + 10 °C), and the time of the second isothermal heat treatment is 30 min to 60 min.

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