Steel with high strength and toughness and high hydrogen embrittlement resistance and preparation method thereof

Abstract

The invention provides high-toughness and high-hydrogen-embrittlement-resistance steel and a preparation method thereof. The preparation method comprises the steps that firstly, a steel plate is subjected to cold deformation treatment under the condition that the temperature ranges from the room temperature to 250 DEG C, and the true strain ranges from 0.05 to 0.30; then austenitizing heating is carried out under the condition of 850-1000 DEG C, and the heat preservation time is 1-15 min; carrying out thermal deformation treatment at the temperature of more than or equal to 850 DEG C, wherein the total true strain is more than or equal to 0.1; after thermal deformation is completed, the steel plate is subjected to slow cooling or heat preservation treatment, and nanoscale carbide is separated out in situ; and finally, quenching treatment is conducted, and the martensite structure high-toughness high-hydrogen-embrittlement-resistance steel is obtained. According to the invention, a synergistic process of'precooling deformation-slow cooling after thermal deformation 'is adopted, and a harmful coarse precipitated phase is converted into a beneficial nano precipitated phase through a'deconstruction-reconstruction' mechanism, so that the plasticity and hydrogen embrittlement resistance of the hot-formed steel are greatly improved while the ultrahigh strength is maintained.

Description

Technical Field

[0001] This invention relates to the field of high-strength steel material preparation technology, specifically to a high-strength, high-toughness, and high-resistance to hydrogen embrittlement steel and its preparation method. Background Technology

[0002] Steel is a cornerstone material for global infrastructure, with a massive annual production. Its microstructure can be extensively controlled through adjusting chemical composition and complex thermomechanical processing, resulting in diverse mechanical properties. However, hydrogen embrittlement is a common challenge faced by various high-strength steels, particularly hot-formed martensitic steels. This is mainly attributed to their high strength (typically exceeding 1500 MPa) and the high-density dislocations, grain boundaries, and other multi-level interface structures within martensite, which provide pathways for hydrogen capture and diffusion, leading to a significantly increased risk of brittle fracture.

[0003] To improve resistance to hydrogen embrittlement, microalloying is a common technique used in hot-formed martensitic steels. By adding alloying elements such as Mo, Nb, and V, carbides and nitrides are formed in the steel, acting as "deep hydrogen traps" to fix hydrogen atoms and inhibit their diffusion to stress concentration areas, thereby reducing hydrogen embrittlement sensitivity. However, in actual industrial production, steel undergoes multiple processes such as hot rolling, cold rolling, and annealing. During this process, the size distribution of the precipitates formed by the aforementioned microalloying elements is difficult to control precisely, often resulting in a large number of large precipitates (diameter > 100 nm). The interface between these large precipitates and the martensitic matrix is ​​often weak, becoming a strong irreversible hydrogen trap. Once hydrogen atoms are trapped, they are difficult to desorb, leading to abnormal local enrichment of hydrogen around the precipitates. When the local hydrogen concentration reaches a critical value, microcracks easily initiate at the interface, becoming the origin of hydrogen-induced cracking and severely deteriorating the steel's resistance to hydrogen embrittlement.

[0004] Furthermore, hot-formed martensitic steel components require austenitizing heating before final use. However, to prevent austenite grain coarsening from impairing toughness, the austenitizing temperature and holding time are typically low, far below the complete dissolution temperature of these large-sized precipitates. Therefore, the possibility of eliminating these harmful precipitates through subsequent heat treatment is extremely low. This means that harmful large-sized precipitates formed during the initial thermomechanical processing will be inherited by the final product, posing a persistent safety hazard.

[0005] The original intention of microalloying was to introduce beneficial deep hydrogen traps to resist hydrogen embrittlement. However, due to insufficient control of traditional processes, large-sized precipitates with harmful interfacial properties are easily generated. These precipitates, on the contrary, become hydrogen enrichment points and crack sources, offsetting the positive effects of alloying and limiting the further improvement of the hydrogen embrittlement resistance of hot-formed martensitic steel.

[0006] Therefore, how to effectively eliminate harmful large-size precipitates inherited from previous processing and transform them into high-density, beneficial nano-precipitates that are well-bonded with the matrix within the conventional hot forming process window without causing austenite grain coarsening has become an urgent technical problem to be solved. Summary of the Invention

[0007] In view of the technical problems existing in the background art, the present invention provides a high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel and its preparation method, aiming to solve the technical problem of poor hydrogen embrittlement resistance caused by the presence of coarse and harmful precipitates in traditional hot-formed steel.

[0008] In a first aspect, the present invention provides a method for preparing high-strength, high-toughness, and high-resistance to hydrogen embrittlement steel, comprising the following steps: S1. The steel plate is subjected to cold deformation treatment at room temperature to 250°C, and the true strain of the cold deformation treatment is 0.05~0.30. S2. The cold-deformed steel plate is subjected to austenitizing heating at 850℃~1000℃ for 1~15 minutes. S3. Quickly transfer the austenitized steel plate into a mold and perform hot deformation treatment at a temperature of ≥850℃; the total true strain of the hot deformation treatment is ≥0.1. S4. After hot deformation is completed, the steel plate is subjected to slow cooling or heat preservation treatment to precipitate nano-scale carbides in situ. S5. The steel plate is quenched to obtain a high-strength, high-toughness, and high-hydrogen-brittleness-resistant steel with a martensitic structure.

[0009] Preferably, in step S1, the steel plate is in the state after hot rolling, pickling, and cold rolling annealing.

[0010] Preferably, in step S1, the chemical element composition of the steel plate, by mass percentage, includes: C 0.20%~0.35%, Si 0.10%~0.50%, Mn 1.0%~2.5%, P≤0.02%, S≤0.005%, Mo 0.10%~0.50%, Nb 0.02%~0.10%, V 0.05%~0.20%, Ti 0.01%~0.05%, Al 0.02%~0.06%, B 0.001%~0.005%, and the balance Fe.

[0011] Preferably, in step S1, the cold deformation treatment method includes any one of cold rolling, cold stretching or cold stamping preforming; the true strain of the cold deformation treatment is 0.10~0.20.

[0012] Preferably, in step S2, the austenitizing heating temperature is 900~950℃, and the holding time is 3~5min.

[0013] Preferably, in step S3, the true strain rate of the heat deformation treatment is ≥0.1 s⁻¹. -1 The hot deformation treatment methods include any one of hot stamping, rapid flattening, and micro forging.

[0014] Preferably, in step S4, the heat preservation treatment specifically includes: quickly transferring the steel plate to a heat preservation device with a temperature maintained at 700~850℃ and heat preservation for 5~300 seconds.

[0015] Preferably, in step S4, the slow cooling treatment specifically includes: cooling the steel plate from the end temperature of hot deformation to 700~750°C at a cooling rate of 1~10°C / s.

[0016] Preferably, in step S5, the cooling rate of the quenching process is ≥30℃ / s.

[0017] Secondly, the present invention provides a high-strength, high-toughness, and high-resistance to hydrogen embrittlement steel, which is prepared by the preparation method described in the first aspect.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The preparation method of high strength, toughness and high resistance to hydrogen embrittlement steel provided by the present invention adopts the "pre-cooling deformation-slow cooling after hot deformation" synergistic process. Through the "deconstruction-reconstruction" mechanism, harmful coarse precipitates are transformed into beneficial nano precipitates, giving full play to the role of microalloying design elements and greatly improving the resistance to hydrogen embrittlement of hot-formed steel.

[0019] (2) The high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel prepared by the present invention maintains an ultra-high strength of over 2000 MPa while enhancing its plasticity and improving its hydrogen embrittlement resistance by over 40%, thus solving the industry problem of the difficulty in achieving a balance between high strength, plasticity, and high hydrogen embrittlement sensitivity.

[0020] (3) The technology of this invention has strong compatibility. It can achieve mass production simply by adding a pre-deformation process and optimizing the cooling path in the existing production line, providing an efficient and low-cost solution for the safe application of ultra-high strength steel. Attached Figure Description

[0021] Figure 1 This is a technical roadmap of the preparation method of the high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel of the present invention; Figure 2 This is a TEM image of the high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel sample prepared in Example 1 of the present invention. Figure 3 This is a TEM image of the hot-formed steel sample prepared in Comparative Example 1 of the present invention. Figure 4 This is a TEM image of the hot-formed steel sample prepared in Comparative Example 2 of this invention. Detailed Implementation

[0022] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0023] To address the technical problem of poor hydrogen embrittlement resistance caused by the presence of coarse and harmful precipitates in traditional hot-formed steel, this invention provides a high-strength, high-toughness, and high-hydrogen-embrittlement-resistance steel and its preparation method. The method involves actively weakening and breaking down harmful precipitates through cold deformation pretreatment to promote their solidification (deconstruction) during subsequent austenitization. Then, through hot deformation and controlled slow cooling, the dissolved microalloying elements are induced to precipitate in situ at dislocations and other defects, forming a high-density beneficial nanophase (reconstruction). This allows the microalloying elements to enhance hydrogen embrittlement resistance, thereby transforming process defects into performance advantages.

[0024] In a first aspect, embodiments of the present invention provide a method for preparing high-strength, high-toughness, and high-resistance to hydrogen embrittlement steel, comprising the following steps: S1. The steel plate is subjected to cold deformation treatment at room temperature to 250°C, and the true strain of the cold deformation treatment is 0.05~0.30. S2. The cold-deformed steel plate is subjected to austenitizing heating at 850℃~1000℃ for 1~15 minutes. S3. Quickly transfer the austenitized steel plate into a mold and perform hot deformation treatment at a temperature of ≥850℃; the total true strain of the hot deformation treatment is ≥0.1. S4. After hot deformation is completed, the steel plate is subjected to slow cooling or heat preservation treatment to precipitate nano-scale carbides in situ. S5. The steel plate is quenched to obtain a high-strength, high-toughness, and high-hydrogen-brittleness-resistant steel with a martensitic structure.

[0025] In the technical solution of this invention embodiment, firstly, cold deformation is used to induce plastic deformation and introduce high-density dislocations, which cut and peel off the coarse precipitates, weakening and fragmenting them. During the subsequent austenitizing heating process, the weakened large-sized precipitates are fully dissolved, while austenite grain growth is effectively suppressed. Then, hot deformation is performed to introduce high-density crystal defects, providing excellent nucleation sites for subsequent strain-induced precipitation. Next, slow cooling or heat preservation treatment provides the necessary thermodynamic and kinetic conditions for strain-induced precipitation. During this process, microalloying elements dissolved in austenite... Elements such as Mo, Nb, and V will rapidly nucleate at defects such as dislocations introduced by hot deformation, precipitating in situ to form a large number of nanoscale carbides. During the quenching process, the temperature drops below the martensitic transformation point, thereby obtaining a fully martensitic structure and giving the steel ultra-high strength. The formed nanoprecipitates are "frozen" in the martensitic matrix. These nanoprecipitates have a good interfacial bond with the martensitic matrix and can act as efficient deep hydrogen traps, stably capturing hydrogen atoms and preventing them from migrating and accumulating to stress concentration areas, thereby significantly reducing hydrogen embrittlement sensitivity and ultimately achieving a good match between high strength, plasticity, and high resistance to hydrogen embrittlement.

[0026] Furthermore, in some embodiments, in step S1, the steel plate is in a state after hot rolling, pickling, and cold rolling annealing.

[0027] In the technical solution of this invention embodiment, after hot rolling, pickling, and cold rolling annealing, the steel plate has initially formed a certain microstructure and carbide precipitate distribution. The cold rolling annealing process aims to eliminate the work hardening generated during cold rolling, restore the material's plasticity, and make it suitable for subsequent processing. As described in the background art, the precipitates formed at this stage are often large in size and unevenly distributed, becoming potentially harmful phases in subsequent hot forming processes. Therefore, this invention chooses to perform cold deformation pretreatment in this state to actively intervene in these existing coarse precipitates, laying the foundation for the subsequent "deconstruction-reconstruction" mechanism.

[0028] This invention does not strictly limit the specific process parameters for hot rolling, pickling, and cold rolling annealing; conventional process conditions in the art can be used. For example, hot rolling can employ conventional heating temperatures, rolling passes, and reduction amounts to obtain suitable billet thickness and preliminary microstructure; pickling is used to remove iron oxide scale from the surface of the hot-rolled steel sheet to ensure the smooth progress of subsequent cold rolling; the annealing temperature is typically between 650 and 800°C, and the holding time is adjusted according to the steel sheet thickness and performance requirements to achieve preliminary control of recrystallization and precipitated phases. The steel sheet obtained after these conventional processes meets the basic requirements for material plasticity in subsequent cold deformation treatment.

[0029] Further, in some embodiments, in step S1, the chemical element composition of the steel plate, by mass percentage, includes: C 0.20%~0.35%, Si 0.10%~0.50%, Mn 1.0%~2.5%, P≤0.02%, S≤0.005%, Mo 0.10%~0.50%, Nb 0.02%~0.10%, V 0.05%~0.20%, Ti 0.01%~0.05%, Al 0.02%~0.06%, B 0.001%~0.005%, and the balance Fe.

[0030] In the technical solution of this invention embodiment, the initial state of the steel plate composed of the above elements after hot rolling, pickling and cold rolling annealing is ferrite + pearlite, and there are (Mo, Nb, V, Ti) carbide precipitates with a size of 20~300nm inside. These carbides act as strong hydrogen traps, which can firmly capture hydrogen atoms and greatly reduce the concentration of "free hydrogen" that can cause embrittlement; at the same time, they also provide precipitation strengthening to ensure strength.

[0031] Furthermore, in some embodiments, in step S1, the cold deformation process includes any one of cold rolling, cold stretching, or cold stamping preforming.

[0032] Furthermore, in some embodiments, in step S1, the true strain of the cold deformation treatment is 0.10~0.20.

[0033] Furthermore, in some embodiments, in step S2, the austenitizing heating temperature is 900~950℃, and the holding time is 3~5min.

[0034] Furthermore, in some embodiments, in step S3, the true strain rate of the heat deformation treatment is ≥0.1 s⁻¹. -1 .

[0035] Furthermore, in some embodiments, in step S3, the hot deformation treatment method includes any one of hot stamping, rapid flattening, and micro forging.

[0036] Furthermore, in some embodiments, step S4 specifically includes: rapidly transferring the steel plate to a heat preservation device with a temperature maintained at 700~850℃ and heat preservation for 5~300 seconds.

[0037] Furthermore, in some embodiments, the temperature of the heat preservation treatment is 730~800°C, and the heat preservation treatment time is 20~120 seconds.

[0038] Furthermore, in some embodiments, step S4 specifically includes: cooling the steel plate from the end temperature of hot deformation to 700-750°C at a cooling rate of 1-10°C / s.

[0039] Furthermore, in some embodiments, the cooling rate is 1~5°C / s.

[0040] Furthermore, in some embodiments, in step S5, the cooling rate of the quenching process is ≥30℃ / s.

[0041] Furthermore, in some embodiments, in step S5, the quenching process includes water cooling of the mold or transferring the workpiece to a quenching medium for cooling.

[0042] Secondly, embodiments of the present invention provide a high-strength, high-toughness, and high-resistance to hydrogen embrittlement steel, which is prepared by the preparation method described in the first aspect.

[0043] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0044] The raw material test steel in Examples 1-5 was B1800HS steel plate produced by Baosteel, with the following chemical composition (mass percentage, wt%): C 0.35 wt.%, Si 0.26 wt.%, Mn 1.3 wt.%, P 0.015 wt.%, S 0.003 wt.%, Mo 0.2 wt.%, Ti 0.05 wt.%, Nb 0.05 wt.%, V 0.1 wt.%, Al 0.04 wt.%, B 0.03 wt.%, Fe balance.

[0045] Initial state of the steel plate: The steel plate was subjected to conventional hot rolling, pickling, cold rolling, and annealing at 720℃ for 5 hours before being air-cooled. Its room temperature microstructure consisted of ferrite and pearlite. Observation by transmission electron microscopy (TEM) confirmed the presence of a large number of coarse (Nb, Ti) composite carbide precipitates with sizes ranging from 80 nm to 300 nm in the initial steel plate.

[0046] In Examples 1-5, all experimental samples were cut from adjacent positions of the steel plate to ensure that the chemical composition was completely consistent with the initial microstructure.

[0047] Example 1 A method for preparing high-strength, high-toughness, and high-resistance to hydrogen embrittlement steel, comprising the following specific steps: (1) Blanking and pre-stretching: Cut tensile specimen blanks with gauge length of 80mm × 20mm from uniform raw materials. At room temperature, use a universal testing machine to perform unidirectional pre-stretching deformation on the blanks so that their true strain reaches 0.10 (corresponding to an engineering strain of about 10.5%). Then unload the blanks to obtain the pre-stretched specimen blanks. (2) Austenitization: The pre-stretched sample blank is placed in a box-type resistance furnace, heated to 930℃ and held for 5 minutes; (3) Hot deformation: The austenitized sample was quickly transferred to a mold preheated to 200°C and subjected to rapid flattening / micro-forging (simulating the deformation effect of hot stamping). The deformation temperature was about 850°C and the strain rate was about 1s. -1 The total true strain is 0.3; (4) Heat preservation treatment: After the hot deformation is completed, do not quench immediately. Quickly transfer the sample to a preheating and heat preservation furnace with a set temperature of 760℃ and heat preservation for 20 seconds. (5) Quenching: After the heat preservation is completed, the sample is quickly immersed in room temperature water for quenching to obtain high strength, toughness and high resistance to hydrogen embrittlement steel.

[0048] Example 2 A method for preparing high-strength, high-toughness, and high-resistance to hydrogen embrittlement steel, comprising the following specific steps: (1) Blanking and pre-stretching: Cut tensile specimen blanks with gauge length of 80mm × 20mm from uniform raw materials. At room temperature, use a universal testing machine to perform unidirectional pre-stretching deformation on the blanks so that their true strain reaches 0.15 (corresponding to an engineering strain of about 16.2%). Then unload the blanks to obtain the pre-stretched specimen blanks. (2) Austenitization: The pre-stretched sample blank is placed in a box-type resistance furnace, heated to 930℃ and held for 5 minutes; (3) Hot deformation: The austenitized sample was quickly transferred to a mold preheated to 200°C and subjected to rapid flattening / micro-forging (simulating the deformation effect of hot stamping). The deformation temperature was about 850°C and the strain rate was about 1s. -1 The total true strain is 0.3; (4) Heat preservation treatment: After the hot deformation is completed, do not quench immediately. Quickly transfer the sample to a preheating and heat preservation furnace with a set temperature of 780℃ and heat preservation for 40 seconds. (5) Quenching: After the heat preservation is completed, the sample is quickly immersed in room temperature water for quenching to obtain high strength, toughness and high resistance to hydrogen embrittlement steel.

[0049] Example 3 Please see Figure 1 This is a technical roadmap for the preparation method of high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel in this embodiment. The specific steps are as follows: (1) Blanking and pre-stretching: Cut tensile specimen blanks with gauge length of 80mm × 20mm from uniform raw materials. At room temperature, use a universal testing machine to perform unidirectional pre-stretching deformation on the blanks so that their true strain reaches 0.10 (corresponding to an engineering strain of about 10.5%). Then unload the blanks to obtain the pre-stretched specimen blanks. (2) Austenitization: The pre-stretched sample blank is placed in a box-type resistance furnace, heated to 930℃ and held for 5 minutes; (3) Hot deformation: The austenitized sample was quickly transferred to a mold preheated to 200°C and subjected to rapid flattening / micro-forging (simulating the deformation effect of hot stamping). The deformation temperature was about 850°C and the strain rate was about 1s. -1 The total true strain is 0.3; (4) Slow cooling treatment: After the hot deformation is completed, the high temperature sample is quickly placed on a stationary refractory brick platform for air cooling. The infrared thermometer is used to monitor the cooling. The sample is cooled to 730℃ at an average rate of about 5-8℃ / s. (5) Quenching: When the temperature drops to 730℃, the sample is immediately immersed in room temperature water for quenching to obtain high strength, toughness and high resistance to hydrogen embrittlement steel.

[0050] Example 4 A method for preparing high-strength, high-toughness, and high-resistance to hydrogen embrittlement steel, comprising the following specific steps: (1) Blanking and pre-stretching: Cut tensile specimen blanks with gauge length of 80mm × 20mm from uniform raw materials. At room temperature, use a universal testing machine to perform unidirectional pre-stretching deformation on the blanks so that their true strain reaches 0.10 (corresponding to an engineering strain of about 10.5%). Then unload the blanks to obtain the pre-stretched specimen blanks. (2) Austenitization: The pre-stretched sample blank is placed in a box-type resistance furnace, heated to 930℃ and held for 5 minutes; (3) Hot deformation: The austenitized sample was quickly transferred to a mold preheated to 200°C and subjected to rapid flattening / micro-forging (simulating the deformation effect of hot stamping). The deformation temperature was about 850°C and the strain rate was about 1s. -1 The total true strain is 0.3; (4) Heat preservation treatment: After the hot deformation is completed, do not quench immediately. Quickly transfer the sample to a preheating and heat preservation furnace with a set temperature of 700℃ and heat preservation for 60 seconds. (5) Quenching: After the heat preservation is completed, the sample is quickly immersed in room temperature water for quenching to obtain high strength, toughness and high resistance to hydrogen embrittlement steel.

[0051] Example 5 A method for preparing high-strength, high-toughness, and high-resistance to hydrogen embrittlement steel, comprising the following specific steps: (1) Blanking and pre-stretching: Cut tensile specimen blanks with gauge length of 80mm × 20mm from uniform raw materials. At room temperature, use a universal testing machine to perform unidirectional pre-stretching deformation on the blanks so that their true strain reaches 0.10 (corresponding to an engineering strain of about 10.5%). Then unload the blanks to obtain the pre-stretched specimen blanks. (2) Austenitization: The pre-stretched sample blank is placed in a box-type resistance furnace, heated to 930℃ and held for 5 minutes; (3) Hot deformation: The austenitized sample was quickly transferred to a mold preheated to 200°C and subjected to rapid flattening / micro-forging (simulating the deformation effect of hot stamping). The deformation temperature was about 850°C and the strain rate was about 1s. -1 The total true strain is 0.3; (4) Heat preservation treatment: After the hot deformation is completed, do not quench immediately. Quickly transfer the sample to a preheating and heat preservation furnace with a set temperature of 850℃ and heat preservation for 10 seconds. (5) Quenching: After the heat preservation is completed, the sample is quickly immersed in room temperature water for quenching to obtain high strength, toughness and high resistance to hydrogen embrittlement steel.

[0052] Comparative Example 1 The difference between this comparative example and Example 1 is that no cold deformation (pre-stretching pretreatment) was performed, and the sample was immediately quenched after hot deformation without any heat preservation or slow cooling steps. The specific steps are as follows: (1) Cutting: Cut a sample blank with a gauge length of 80mm × 20mm from a uniform raw material; (2) Austenitization: Place the sample blank in a box-type resistance furnace, heat it to 930℃ and hold it for 5 minutes; (3) Hot deformation: The austenitized sample was quickly transferred to a mold preheated to 200°C and subjected to rapid flattening / micro-forging (simulating the deformation effect of hot stamping). The deformation temperature was about 850°C and the strain rate was about 1s. -1 The total true strain is 0.3; (4) Quenching: After the hot deformation is completed, the sample is quickly immersed in room temperature water for quenching.

[0053] Comparative Example 2 The difference between this comparative example and Example 1 is that the sample was quenched immediately after hot deformation, without any heat preservation or slow cooling steps. The specific steps are as follows: (1) Blanking and pre-stretching: Cut tensile specimen blanks with gauge length of 80mm × 20mm from uniform raw materials. At room temperature, use a universal testing machine to perform unidirectional pre-stretching deformation on the blanks so that their true strain reaches 0.10 (corresponding to an engineering strain of about 10.5%). Then unload the blanks to obtain the pre-stretched specimen blanks. (2) Austenitization: The pre-stretched sample blank is placed in a box-type resistance furnace, heated to 930℃ and held for 5 minutes; (3) Hot deformation: The austenitized sample was quickly transferred to a mold preheated to 200°C and subjected to rapid flattening / micro-forging (simulating the deformation effect of hot stamping). The deformation temperature was about 850°C and the strain rate was about 1s. -1 The total true strain is 0.3; (4) Quenching: After the hot deformation is completed, the sample is quickly immersed in room temperature water for quenching.

[0054] Example 6 The raw material for the test was B1500HS steel plate produced by Baosteel, with the following chemical composition (mass percentage, wt%): C 0.2wt.%, Si 0.1wt.%, Mn 1.0wt.%, Mo 0.1wt.%, Ti 0.01wt.%, Nb 0.02wt.%, V 0.05wt.%, Al 0.02wt.%, B 0.001wt.%, Fe balance.

[0055] Initial state of the steel plate: The steel plate is subjected to conventional hot rolling, pickling, cold rolling, and annealing at 720℃ for 5 hours before being air-cooled. Its room temperature microstructure consists of ferrite + pearlite + composite carbide precipitates.

[0056] The preparation method of high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel is exactly the same as that in Example 1.

[0057] Comparative Example 3 The difference between this comparative example and Example 6 is that no cold deformation (pre-stretching pretreatment) was performed, and the sample was quenched immediately after hot deformation without any heat preservation or slow cooling steps.

[0058] Example 7 The chemical composition of the raw material test steel plate is (mass percentage, wt%): C 0.35 wt.%, Si 0.05 wt.%, Mn 2.5 wt.%, P 0.02 wt.%, S 0.005 wt.%, Mo 0.5 wt.%, Nb 0.1 wt.%, V 0.2 wt.%, Ti 0.05 wt.%, Al 0.06 wt.%, B 0.005 wt.%, Fe balance.

[0059] Initial state of the steel plate: The steel plate is subjected to conventional hot rolling, pickling, cold rolling, and annealing at 720℃ for 5 hours before being air-cooled. Its room temperature microstructure consists of ferrite + pearlite + composite carbide precipitates.

[0060] The preparation method of high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel is exactly the same as that in Example 1.

[0061] Comparative Example 4 The difference between this comparative example and Example 7 is that no cold deformation (pre-stretching pretreatment) was performed, and the sample was quenched immediately after hot deformation without any heat preservation or slow cooling steps.

[0062] Performance testing The room temperature tensile properties of the hot-formed steel specimens prepared in Examples 1-7 and Comparative Examples 1-4 were tested. The test methods were in accordance with GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Room temperature test method". The test results are shown in Table 1 below.

[0063] Table 1

[0064] Table 1 shows that the high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steels prepared in Examples 1-7 of this invention, compared with Comparative Examples 1, 3, and 4 (which did not undergo pre-stretching pretreatment and were immediately quenched after hot deformation), significantly improved elongation after fracture while maintaining ultra-high strength, achieving a simultaneous improvement in strength and plasticity. Comparative Example 2, although undergoing pre-stretching pretreatment, was immediately quenched after hot deformation, resulting in increased yield strength but decreased elongation after fracture. This indicates that pre-stretching pretreatment alone, without subsequent heat preservation or slow cooling, leads to an imbalance in the strength-plasticity match of the material and a decrease in toughness. The test results show that, through the preparation method provided by this invention, for base steel plates with different elemental compositions and strength levels, pre-stretching pretreatment and heat preservation or slow cooling treatment after hot deformation can effectively improve the strength and plasticity of hot-formed steel while ensuring high strength.

[0065] The hydrogen embrittlement resistance of the hot-formed steel samples prepared in Examples 1-7 and Comparative Examples 1-4 was tested. The test method was in accordance with GB / T 34542.3-2018 "Hydrogen Storage and Transportation Systems - Part 3: Test Method for Hydrogen Embrittlement Sensitivity of Metallic Materials". The hydrogen embrittlement sensitivity index was calculated as follows: ; The test results are shown in Tables 2-1, 2-2, and 2-3 below.

[0066] Table 2-1

[0067] Table 2-2

[0068] Table 2-3

[0069] Test results show that the high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steels prepared in Examples 1-7 of this invention all have significantly lower hydrogen embrittlement sensitivity indices than their corresponding comparative examples. This fully demonstrates that the pre-stretching cold deformation treatment provided by this invention, combined with heat preservation or slow cooling treatment after hot deformation, can effectively improve the hydrogen embrittlement resistance of hot-formed steel and significantly reduce its hydrogen embrittlement sensitivity index. Although Comparative Example 2 underwent pre-stretching cold deformation treatment, it was directly quenched after hot deformation without heat preservation or slow cooling, resulting in only a slight improvement in its hydrogen embrittlement sensitivity index compared to Comparative Example 1 (an increase of only 5.5%), further confirming the crucial role of heat preservation or slow cooling steps after hot deformation in improving hydrogen embrittlement resistance.

[0070] Figure 2 TEM image of the high-strength, high-toughness, high-hydrogen-brittle-resistant steel specimen prepared in Example 1 (subjected to cold deformation-hot deformation-slow cooling); Figure 3 TEM image of the hot-formed steel specimen (hot deformation only - no cold deformation and slow cooling) prepared in Comparative Example 1; Figure 4 This is a TEM image of a hot-formed steel specimen (subjected to cold-hot deformation, but without slow cooling) prepared in Comparative Example 2. Figure 2 As can be seen, the martensite laths in the microstructure of the sample of Example 1 are uniformly distributed, and there are nanoscale carbide precipitates dispersed between the laths. These precipitates can effectively pin dislocations and, at the same time, act as irreversible hydrogen traps to capture hydrogen atoms, thereby inhibiting hydrogen diffusion and accumulation and improving the material's resistance to hydrogen embrittlement. Figure 3 The martensitic laths in Comparative Example 1 are relatively large, and there are large-sized undissolved carbides distributed between the laths. These large undissolved carbides have weak bonding with the matrix interface and are prone to becoming hydrogen trapping sites, leading to local aggregation of hydrogen atoms and thus increasing the susceptibility to hydrogen-induced cracking, resulting in a high hydrogen embrittlement susceptibility index. Figure 4 Although the pre-stretching pretreatment of the sample in Comparative Example 2 introduced a certain dislocation density, the lack of heat preservation or slow cooling after hot deformation resulted in a large number of dislocations in the matrix, but insufficient carbide precipitation, thus limiting the improvement in its hydrogen embrittlement resistance. In summary, the high-strength, high-toughness, and high-hydrogen-embrittlement-resistance steel provided by this invention, through the synergistic effect of pre-stretching pretreatment (cold deformation) and heat preservation or slow cooling after hot deformation, can refine the martensitic structure and promote the precipitation of nano-carbide, thereby achieving a balance between high strength, high plasticity, and excellent hydrogen embrittlement resistance.

[0071] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method for preparing high-strength, high-toughness, and high-resistance to hydrogen embrittlement steel, characterized in that, Includes the following steps: S1. The steel plate is subjected to cold deformation treatment at room temperature to 250°C, and the true strain of the cold deformation treatment is 0.05~0.

30. S2. The cold-deformed steel plate is subjected to austenitizing heating at 850℃~1000℃ for 1~15 minutes. S3. The austenitized steel plate is quickly transferred to a mold and subjected to hot deformation treatment at a temperature of ≥850℃; the total true strain of the hot deformation treatment is ≥0.

1. S4. After hot deformation is completed, the steel plate is subjected to slow cooling or heat preservation treatment to precipitate nano-scale carbides in situ. S5. The steel plate is quenched to obtain a high-strength, high-toughness, and high-hydrogen-brittleness-resistant steel with a martensitic structure.

2. The method for preparing a high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel according to claim 1, characterized in that, In step S1, the steel plate is in the state after hot rolling, pickling and cold rolling annealing.

3. The method for preparing a high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel according to claim 1, characterized in that, In step S1, the chemical element composition of the steel plate, by mass percentage, includes: C 0.20%~0.35%, Si 0.10%~0.50%, Mn 1.0%~2.5%, P≤0.02%, S≤0.005%, Mo 0.10%~0.50%, Nb 0.02%~0.10%, V 0.05%~0.20%, Ti 0.01%~0.05%, Al 0.02%~0.06%, B 0.001%~0.005%, and the balance Fe.

4. The method for preparing a high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel according to claim 1, characterized in that, In step S1, the cold deformation treatment method includes any one of cold rolling, cold stretching or cold stamping preforming; And / or, the true strain of the cold deformation treatment is 0.10~0.

20.

5. The method for preparing a high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel according to claim 1, characterized in that, In step S2, the austenitizing heating temperature is 900~950℃, and the holding time is 3~5min.

6. The method for preparing a high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel according to claim 1, characterized in that, In step S3, the true strain rate of the heat deformation treatment is ≥0.1 s. -1 ; And / or, the hot deformation treatment method includes any one of hot stamping, rapid flattening, and micro forging.

7. The method for preparing a high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel according to claim 1, characterized in that, In step S4, the heat preservation treatment specifically includes: quickly transferring the steel plate to a heat preservation device with a temperature maintained at 700~850℃ and keeping it warm for 5~300 seconds.

8. The method for preparing a high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel according to claim 1, characterized in that, In step S4, the slow cooling treatment specifically includes: cooling the steel plate from the end temperature of hot deformation to 700-750°C at a cooling rate of 1-10°C / s.

9. The method for preparing a high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel according to claim 1, characterized in that, In step S5, the cooling rate of the quenching process is ≥30℃ / s.

10. A high-strength, high-toughness, and high-resistance to hydrogen embrittlement steel, characterized in that, It is prepared by the method for preparing high-strength, high-toughness, and high-hydrogen-embrittlement-resistant steel according to any one of claims 1 to 9.

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