High-strength hydrogen-embrittlement-resistant stainless steel

Abstract

The present invention provides a high-strength hydrogen-embrittlement-resistant stainless steel, comprising, in percentage by mass: C: 0.1%-0.4%, Si: 0.2%-0.5%, Mn: 4.5%-5.5%, P≤0.01%, S≤0.002%, Cr: 0.6%-1.0%, V: 0.1%-0.2%, Nb≤0.08%, B: 0.001%-0.005%, and the balance being Fe. By adding Nb and V microalloying elements on an original stainless steel, austenite grains are refined, and a high-efficiency hydrogen trap is formed in a matrix, thereby improving the resistance of the steel to hydrogen-induced delayed fracture. The stainless steel is processed by means of a hot forming process. Once a steel plate has undergone isothermal annealing, a tempering process is added, the temperature and time of the tempering process are controlled, and finally quenching is performed. Brittle intergranular fracture in the obtained stainless steel is significantly reduced, and the hydrogen embrittlement susceptibility of the stainless steel is effectively decreased.

Description

A high-strength, hydrogen-embrittlement-resistant stainless steel Technical Field

[0001] This invention relates to the field of stainless steel production and manufacturing, and more particularly to a high-strength, hydrogen-embrittlement-resistant stainless steel. Background Technology

[0002] With the continuous development of my country's high-end industries, advanced high-strength steel is being used more and more. However, as the strength increases, the steel's susceptibility to delayed fracture also gradually increases, especially for hot-formed steel. The deformation during the hot forming process leads to strong residual stress in the steel matrix, which easily causes hydrogen-induced delayed fracture in a hydrogen-containing environment, seriously affecting safety in use. Therefore, it is necessary to improve existing high-strength steel to reduce its susceptibility to hydrogen-induced fracture and enhance its safety in use.

[0003] Current research on hydrogen embrittlement resistance of stainless steel mainly focuses on adding specific trace elements or refining the grain size of stainless steel through heat treatment processes. However, in the research and development of stainless steel, any change in the ratio of elements and manufacturing process will cause a series of interconnected effects and changes. Through experiments, our company has obtained a high-strength hydrogen embrittlement resistant stainless steel. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by proposing a high-strength, hydrogen-embrittlement-resistant stainless steel.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A high-strength, hydrogen-embrittlement-resistant stainless steel, comprising, by mass%, C: 0.1%-0.4%, Si: 0.2%-0.5%, Mn: 4.5%-5.5%, P≤0.01%, S≤0.002%, Cr: 0.6%-1.0%, V: 0.1%-0.2%, Nb≤0.08%, B: 0.001%-0.005%, with the balance being Fe.

[0007] The preparation process of the stainless steel includes the following steps:

[0008] S1. Melt and cast the billet according to the set composition;

[0009] S2. After heating the billet at 1200℃ for 1.5-2 hours, rolling begins, with a final rolling temperature of 900℃, and finally rolled into a steel plate with a thickness of 6mm.

[0010] S3. Isothermal anneal the hot-rolled steel plate in the two-phase region at 650℃ for 6 hours;

[0011] S4. After pickling the steel plate, it is rolled in 4-5 passes, and the final rolled steel plate thickness is 2mm.

[0012] S5. Cool the steel plate to room temperature;

[0013] S6. Heat the steel plate to 480-520℃ for tempering treatment and hold for 1 hour.

[0014] S7. Take out the heat-treated stainless steel plate and immediately transfer it to the thermoforming mold, then quench it to 150°C.

[0015] S8. Remove the stainless steel sheet from the thermoforming mold and cool it to room temperature.

[0016] Preferably, the stainless steel contains ≤0.2% (Nb+V) by mass%.

[0017] Preferably, the stainless steel contains 0.14% V by mass%.

[0018] Preferably, the stainless steel contains 1.0% Cr by mass%.

[0019] Preferably, the average grain size of the stainless steel is 5 μm.

[0020] Preferably, in the stainless steel, the average size of the fine carbide precipitates with a size greater than 10 nm is 16 nm, and the average size of the fine carbide precipitates with a size less than 10 nm is 5.5 nm.

[0021] Furthermore, in S4, the steel plate is pickled using 18% hydrochloric acid and then rolled in 4-5 passes on a 450 type rolling mill.

[0022] Furthermore, in S7, the quenching method is water-cooled quenching.

[0023] Furthermore, in S5 and S8, the cooling method is air cooling.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. By adding Nb and V microalloying elements to the original stainless steel, the austenite grains are refined, and high-efficiency hydrogen traps are formed in the matrix, thereby improving the steel's resistance to hydrogen-induced delayed fracture and its resistance to hydrogen embrittlement.

[0026] 2. By controlling the Nb and V content, the resistance of stainless steel to hydrogen embrittlement can be effectively improved while ensuring the ductility and other properties of stainless steel.

[0027] 3. In the preparation process of the high-strength hydrogen embrittlement resistant stainless steel of the present invention, the isothermal annealing time of the steel plate is set to 6 hours, and a tempering process is added. The temperature and time of the tempering process are controlled, and finally quenching is performed. The resulting stainless steel exhibits significantly reduced intergranular brittle fracture and effectively reduced hydrogen embrittlement sensitivity. Attached Figure Description

[0028] none Detailed Implementation

[0029] To provide a further understanding of the purpose, structure, features, and functions of the present invention, detailed descriptions are provided below with reference to specific embodiments.

[0030] A high-strength, hydrogen-embrittlement-resistant stainless steel, comprising, by mass%, C: 0.1%-0.4%, Si: 0.2%-0.5%, Mn: 4.5%-5.5%, P≤0.01%, S≤0.002%, Cr: 0.6%-1.0%, V: 0.1%-0.2%, Nb≤0.08%, B: 0.001%-0.005%, with the balance being Fe.

[0031] The preparation process of the stainless steel includes the following steps:

[0032] S1. Melt and cast the billet according to the set composition;

[0033] S2. After heating the billet at 1200℃ for 1.5-2 hours, rolling begins, with a final rolling temperature of 900℃, and finally rolled into a steel plate with a thickness of 6mm.

[0034] S3. Isothermal anneal the hot-rolled steel plate in the two-phase region at 650℃ for 6 hours;

[0035] S4. After pickling the steel plate, it is rolled in 4-5 passes, and the final rolled steel plate thickness is 2mm.

[0036] S5. Cool the steel plate to room temperature; preferably, air cool to room temperature;

[0037] S6. Heat the steel plate to 480-520℃ for tempering treatment and hold for 1 hour; preferably, set the tempering temperature to 500℃.

[0038] S7. Take out the heat-treated stainless steel plate and immediately transfer it to the thermoforming mold, then quench it to 150°C.

[0039] S8. Remove the stainless steel sheet from the thermoforming mold and cool it to room temperature; preferably, air cool it to room temperature.

[0040] The high-strength hydrogen-embrittlement resistant stainless steel of the present invention adds Nb and V microalloying elements to the original 22MnB5 stainless steel. Nb and V are elements that easily form carbon and nitrogen compounds, which can refine the austenite grains and form high-efficiency hydrogen traps in the matrix, thereby improving the steel's resistance to hydrogen-induced delayed fracture.

[0041] Based on 22MnB5 stainless steel, V is added: 0.1%-0.2%. V has a good effect on improving strength and grain refinement. At the same time, it can form carbonitrides with carbon (C) or nitrogen (N) and be used as a trapping point for hydrogen that invades the steel. It also plays a role in inhibiting the intrusion of hydrogen into the steel and reducing corrosion.

[0042] The addition of Nb (≤0.08%) to 22MnB5 stainless steel enhances its resistance to hydrogen embrittlement. This is primarily because Nb acts as a reversible hydrogen trap, capturing hydrogen atoms and reducing the hydrogen diffusion coefficient within the steel, thus minimizing hydrogen embrittlement. Furthermore, the addition of Nb can significantly improve the steel's resistance to hydrogen embrittlement by controlling the microstructure. However, excessive Nb content leads to the formation of coarse carbonitrides, resulting in decreased ductility of the stainless steel. Therefore, after testing, the Nb content was limited to ≤0.08%.

[0043] Compared with traditional 22MnB5 hot-formed steel, the high-strength hydrogen-embrittlement resistant stainless steel of the present invention has an average austenite size of 12μm after quenching and trial production, while the stainless steel of the present invention has an average austenite size of 8μm. The microalloying elements Nb and V segregate at the austenite grain boundaries, which hinders the grain growth of austenite in hot-formed steel and plays a role in refining the grains.

[0044] Compared with traditional 22MnB5 hot-formed steel, the high-strength hydrogen embrittlement resistant stainless steel of the present invention has a smaller overall grain size, more small-angle grain boundaries, and more uniform grain size, resulting in lower hydrogen embrittlement sensitivity.

[0045] Hydrogen embrittlement resistant stainless steel of the present invention and traditional 22MnB5 hot-formed steel were compared under the same conditions in hydrogen embrittlement sensitivity tests. The time to delayed fracture of the high-strength hydrogen embrittlement resistant stainless steel of the present invention was significantly longer than that of the traditional 22MnB5 hot-formed steel. The analysis is as follows: The stainless steel of the present invention utilizes the combination of Nb, V and C to create a large number of hydrogen traps within the material. The accumulation regions of C, Nb, V and H are basically overlapping, which greatly reduces the concentration of hydrogen that can accumulate along the direction of maximum stress gradient, effectively inhibiting hydrogen diffusion and thus delaying the time to delayed fracture. In contrast, the distribution of hydrogen and C elements within the traditional 22MnB5 steel is not correlated, and hydrogen diffusion cannot be inhibited, resulting in a relatively higher hydrogen embrittlement sensitivity.

[0046] In the stainless steel preparation process of this invention, a large amount of reverse-transformed austenite and ferrite are formed in the initial stage of the stainless steel plate annealing process, along with a small amount of cementite. As the annealing time increases to 6 hours, the content of reverse-transformed austenite increases to approximately 18% and its size increases, while carbides disappear. After tempering the stainless steel plate, the brittle intergranular fracture of the stainless steel is significantly reduced, and the hydrogen embrittlement susceptibility of the stainless steel is effectively decreased.

[0047] In one embodiment, the stainless steel contains ≤0.2% (Nb+V) by mass. Excessive content will reduce the ductility of the stainless steel and increase costs.

[0048] In one embodiment, the stainless steel contains 0.14% V by mass. Further, the stainless steel contains 1.0% Cr by mass. While VC precipitates improve material strength, they can effectively suppress hydrogen embrittlement. As the V content increases, the size and quantity of VC precipitates increase. However, when the mass fraction of V exceeds 1%, large-sized undissolved VC precipitates appear, easily leading to hydrogen embrittlement. Multi-microalloying with 0.14% V and 1% Cr achieves optimal resistance to hydrogen embrittlement and work hardening ability.

[0049] In a preferred embodiment, a high-strength, hydrogen-embrittlement-resistant stainless steel comprises, by mass%, C: 0.2%, Si: 0.3%, Mn: 5%, P ≤ 0.01%, S ≤ 0.002%, Cr: 0.7%, V: 0.1%, Nb: 0.06%, B: 0.002%, with the balance being Fe.

[0050] In this embodiment, the stainless steel has an average grain size of 5μm, which is smaller and more uniform than that of traditional 22MnB5 hot-formed steel, resulting in better resistance to hydrogen embrittlement.

[0051] In this embodiment, the average size of fine carbide precipitates with a size greater than 10 nm in stainless steel is 16 nm, and the average size of fine carbide precipitates with a size less than 10 nm is 5.5 nm.

[0052] The high-strength, hydrogen-embrittlement-resistant stainless steel of this invention has smaller and more uniform grain size, more small-angle boundaries, and smaller average size of fine carbide precipitates, thus exhibiting better resistance to hydrogen embrittlement.

[0053] The high-strength hydrogen embrittlement resistant stainless steel of this invention was subjected to hydrogen embrittlement sensitivity test under bending loading conditions. When the span reached 70 mm and the stress reached 1622 MPa, it could still remain crack-free for 300 hours under hydrogen environment solution conditions.

[0054] In the description of this invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0055] The present invention has been described in the above-described embodiments; however, these embodiments are merely examples for implementing the present invention. It must be noted that the disclosed embodiments do not limit the scope of the present invention. Conversely, any modifications and refinements made without departing from the spirit and scope of the present invention are within the scope of patent protection of the present invention.

Claims

1. A high-strength, hydrogen-embrittlement-resistant stainless steel, characterized in that, The composition by mass% includes C: 0.1%-0.4%, Si: 0.2%-0.5%, Mn: 4.5%-5.5%, P≤0.01%, S≤0.002%, Cr: 0.6%-1.0%, V: 0.1%-0.2%, Nb≤0.08%, B: 0.001%-0.005%, with the balance being Fe. The preparation process of the stainless steel includes the following steps: S1. Melt and cast the billet according to the set composition; S2. After heating the billet at 1200℃ for 1.5-2 hours, rolling begins, with a final rolling temperature of 900℃, and finally rolled into a steel plate with a thickness of 6mm. S3. Isothermal anneal the hot-rolled steel plate in the two-phase region at 650℃ for 6 hours; S4. After pickling the steel plate, it is rolled in 4-5 passes, and the final rolled steel plate thickness is 2mm. S5. Cool the steel plate to room temperature; S6. Heat the steel plate to 480-520℃ for tempering treatment and hold for 1 hour. S7. Take out the heat-treated stainless steel plate and immediately transfer it to the thermoforming mold, then quench it to 150°C. S8. Remove the stainless steel sheet from the thermoforming mold and cool it to room temperature.

2. The high-strength, hydrogen-embrittlement-resistant stainless steel as described in claim 1, characterized in that: The stainless steel contains ≤0.2% (Nb+V) by mass%.

3. The high-strength, hydrogen-embrittlement-resistant stainless steel as described in claim 2, characterized in that: The stainless steel contains 0.14% V by mass%.

4. The high-strength, hydrogen-embrittlement-resistant stainless steel as described in claim 3, characterized in that: The stainless steel contains 1.0% Cr by mass%.

5. The high-strength, hydrogen-embrittlement-resistant stainless steel as described in claim 1, characterized in that: The average grain size of the stainless steel is 5 μm.

6. The high-strength, hydrogen-embrittlement-resistant stainless steel as described in claim 1, characterized in that: In the stainless steel, the average size of fine carbide precipitates with a size greater than 10 nm is 16 nm, and the average size of fine carbide precipitates with a size less than 10 nm is 5.5 nm.

7. The high-strength, hydrogen-embrittlement-resistant stainless steel as described in claim 1, characterized in that: In S4, the steel plate is pickled with 18% hydrochloric acid and then rolled in 4-5 passes on a 450 type rolling mill.

8. The high-strength, hydrogen-embrittlement-resistant stainless steel as described in claim 1, characterized in that: In S7, the quenching method is water quenching.

9. The high-strength, hydrogen-embrittlement-resistant stainless steel as described in claim 1, characterized in that: In S5 and S8, the cooling method is air cooling.