Method for improving strength and hydrogen brittleness resistance of austenitic stainless steel material

Abstract

The invention provides a method for improving the strength and hydrogen brittleness resistance of an austenitic stainless steel material, which comprises the following steps: under the protection of argon, depositing thin austenitic stainless steel powder by using a powder spreading device to form an austenitic stainless steel powder thin layer, and simultaneously continuously applying ultrasonic waves to the austenitic stainless steel powder thin layer; a laser beam is incident in a scanning mode to melt the austenitic stainless steel powder thin layer, so that the melted austenitic stainless steel powder thin layer is bonded with the part in the solidified area; then, the thickness of one austenitic stainless steel powder thin layer is reduced for the part, and deposition and laser beam melting of the next austenitic stainless steel powder thin layer are carried out; and by repeating the steps, the sample is constructed layer by layer until the 3D printing sample with the preset shape is obtained. Additive manufacturing is carried out by adopting selective laser melting and applying ultrasonic waves at the same time, and the problem that under the hydrogen pre-charging condition, the higher the strength is, the poorer the hydrogen embrittlement resistance is existing in traditional machined structure state austenitic stainless steel is solved.

Description

Technical Field

[0002] This application relates to the field of high austenitic stainless steel material processing technology, and in particular to a method for improving the strength and resistance to hydrogen embrittlement of austenitic stainless steel materials. Background Technology

[0004] Austenitic stainless steel is widely used in petrochemical, marine engineering, hydrogen storage and transportation fields due to its relatively low cost and excellent corrosion resistance. However, hydrogen is inevitably introduced during processing and use, leading to hydrogen embrittlement cracking. Simultaneously, as load-bearing structural components, it often requires sufficient strength. However, the higher the strength of a metallic material, the worse its resistance to hydrogen embrittlement. Therefore, how to improve the hydrogen embrittlement resistance of austenitic stainless steel while maintaining its strength is a challenging problem.

[0005] Patent application CN117987749A discloses an ultra-high strength, hydrogen-embrittlement-resistant austenitic stainless steel and its preparation method. The austenitic stainless steel is composed of the following mass fraction: 14% Cr ≤ 20%, 23% ≤ Ni ≤ 26%, 3.0% ≤ Al ≤ 5.0%, 2.0% ≤ Ti ≤ 4.0%, 0% ≤ N ≤ 1.0%, with the balance being Fe and unavoidable impurities. While this method employs laser additive manufacturing, which can improve the hydrogen embrittlement resistance of the austenitic stainless steel to some extent, its mechanical properties and resistance to hydrogen embrittlement remain relatively poor.

[0006] Patent application CN117144117A discloses a deep nano-gradient structure anti-hydrogen embrittlement material and its preparation method and apparatus. It employs both laser shock peening and ultrasonic shock peening to simultaneously strengthen the surface of a stainless steel sheet. During laser shock peening, ultrasonic shock peening is applied using ultrasonic impactors. The interaction between multiple uniform ultrasonic impacts and single or multiple high-strain-rate laser impacts creates a deep gradient nano-heterogeneous structure and residual compressive stress distribution on the stainless steel sheet surface. At the microscale, the refined nanolayers hinder hydrogen atom intrusion, and the hydrogen trapping effect of fine grain boundaries and dislocations suppresses hydrogen atom diffusion, preventing hydrogen-induced plasticity loss and hydrogen-induced cracking caused by localized hydrogen atom enrichment. This patent improves the hydrogen embrittlement resistance of stainless steel through post-processing of the finished stainless steel sheet, but the improvement in strength and hydrogen embrittlement resistance is relatively small. Summary of the Invention

[0008] The technical problem this application aims to solve is that, in the prior art, the higher the strength of austenitic stainless steel, the worse its resistance to hydrogen embrittlement.

[0009] To address the aforementioned problems, this application provides a method for improving the strength and hydrogen embrittlement resistance of austenitic stainless steel materials, comprising:

[0010] Thin-layer deposition: A thin layer of austenitic stainless steel powder is deposited using a powder spreader to form a thin layer of austenitic stainless steel powder, while ultrasound is continuously applied to the thin layer of austenitic stainless steel powder.

[0011] Laser melting: The austenitic stainless steel powder thin layer is melted by scanning the austenitic stainless steel powder thin layer, so that the melted austenitic stainless steel powder thin layer is bonded to the component in the solidified austenitic stainless steel region.

[0012] The thickness of the component is reduced by one layer of austenitic stainless steel powder, and then the next layer of austenitic stainless steel powder is deposited and melted by laser beam.

[0013] Specimen construction: By repeating the above steps, the specimen is constructed layer by layer until a 3D printed specimen of the preset shape is obtained.

[0014] The entire process described above was carried out under an argon protective atmosphere.

[0015] According to the method described in this application, the thickness of the powder layer is 30 μm.

[0016] To reduce residual stress between the material and the substrate at the start of printing, according to the method described above in this application, the substrate preheating temperature for the thin-layer deposition is 80°C.

[0017] According to the method described above in this application, the particle size of the austenitic stainless steel powder is 25–30 μm.

[0018] To avoid anisotropy of the printing material in the two-dimensional direction of the horizontal plane and to ensure a high powder bed packing density, the laser melting scanning strategy described in the above method of this application is a checkerboard pattern.

[0019] According to the method described above in this application, the scanning rate of the incident laser beam is 1000 mm / s; the scanning power is 180W; and the deflection angle of the laser beam per layer is 67°.

[0020] According to the method described above in this application, the frequency of the applied ultrasonic wave is 5kHz to 20kHz, and the amplitude is 5 to 15μm.

[0021] According to the method described in this application, the direction of the applied ultrasonic wave is from bottom to top.

[0022] According to the method described above in this application, the construction direction of the 3D printed sample is 0°~45°.

[0023] According to the method described above in this application, after the construction of the specimen is completed, the method further includes an annealing process: annealing the 3D printed specimen.

[0024] The annealing process is as follows: stress-relief annealing at 300℃~1000℃ for 2 hours, followed by air cooling to room temperature.

[0025] The technical advantages of this application are as follows:

[0026] The laser selective melting additive manufacturing method employed in this application effectively addresses the problem of "higher strength, lower resistance to hydrogen embrittlement" in traditionally processed austenitic stainless steels under pre-hydrogen-charged conditions. Furthermore, the material exhibits excellent resistance to hydrogen embrittlement even under in-situ dynamic hydrogen-charged tensile conditions. The 3D-printed specimens in this application are constructed at angles ranging from 0° to 45°, resulting in specimens with high strength and plasticity, and good resistance to hydrogen embrittlement. This application also incorporates an annealing process; stress annealing reduces hydrogen embrittlement sensitivity and increases resistance to hydrogen embrittlement.

[0027] Unlike existing technologies (such as CN117144117A) that subject stainless steel test products to ultrasonic impact treatment, this application applies ultrasonic waves to the metal powder simultaneously during laser melting. Through the action of ultrasound, the internal microstructure of the 3D-printed alloy becomes more refined and uniform, thereby improving the material's strength and resistance to hydrogen embrittlement. When ultrasound acts on the molten metal, the molten metal generates strong vibrations, promoting the formation of high-density dislocation cell structures in selective laser melting additive manufacturing, thus achieving excellent hydrogen embrittlement resistance in the sample. On the other hand, during ultrasonic vibration, cavitation and vibration effects are generated on the surface of the metal powder, which can remove gases adhering to the metal surface, thereby avoiding the generation of excessive gas channels in the molten metal during laser melting and preventing hydrogen from entering the metal interior. Attached Figure Description

[0029] Figure 1 This is a scanned image of the austenitic stainless steel powder used in the embodiments.

[0030] Figure 2 These are schematic diagrams of samples with different printing orientations.

[0031] Figure 3 This is a schematic diagram of the tensile test specimen dimensions used in each embodiment and comparative example.

[0032] Figure 4 This is a schematic diagram of an in-situ dynamic hydrogen charging tensile test.

[0033] Figures 5-7 These are the stress-displacement curves of the tensile specimens obtained in various embodiments and comparative examples under air tension and in-situ dynamic hydrogen-filled tension.

[0034] Figure 8 These are bar charts showing the tensile hydrogen embrittlement sensitivity obtained from various embodiments and comparative examples. Detailed Implementation

[0036] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0037] One embodiment of the method for improving the strength and hydrogen embrittlement resistance of austenitic stainless steel provided in this application specifically includes:

[0038] Thin-layer deposition: A thin layer of austenitic stainless steel powder is deposited using a powder spreader to form a thin layer of austenitic stainless steel powder, while ultrasound is continuously applied to the thin layer of austenitic stainless steel powder.

[0039] Laser melting: The austenitic stainless steel powder thin layer is melted by scanning the austenitic stainless steel powder thin layer, so that the melted austenitic stainless steel powder thin layer is bonded to the component in the solidified austenitic stainless steel region.

[0040] The thickness of the component is reduced by one layer of austenitic stainless steel powder, and then the next layer of austenitic stainless steel powder is deposited and melted by laser beam.

[0041] Specimen construction: By repeating the above steps, the specimen is constructed layer by layer until a 3D printed specimen of the preset shape is obtained.

[0042] The entire process described above was carried out under an argon protective atmosphere.

[0043] In the following specific embodiments of this application, the laser selective melting process uses a 3D printer (FF-M140-H) manufactured by Dalian Meiguang Speed ​​Manufacturing Technology Co., Ltd.

[0044] This application employs a checkerboard pattern laser melting scanning strategy in selective laser melting (SLM) technology. This avoids the anisotropy of the printing material in the two-dimensional direction of the horizontal plane, ensuring a high powder bed packing density. The scanning rate is 1000 mm / s, and the scanning power is 180 W.

[0045] like Figure 1 The following is a scanned image of the austenitic stainless steel powder used in the specific embodiments below. The mass fraction chemical composition of the austenitic stainless steel powder is: C 0.04%, Si 0.75%, Mn 1.25%, P 0.045%, S 0.03%, Cr 18%~20%, Ni 8%~10.5%, N 0.1%.

[0046] In the following specific embodiments, the average diameter of the austenitic stainless steel powder spheres is 25 μm to 30 μm. Preferably, the powder layer thickness is 30 μm, and the laser beam deflection angle per layer is 67°. The sample printing substrate size is 125 mm × 125 mm, and to reduce the residual stress between the material and the substrate at the start of printing, the substrate preheating temperature for the thin layer deposition is 80°C.

[0047] In the specific embodiments and comparative examples described below, cuboid test blocks were printed in construction directions with angles of 0°, 45°, and 90° to the horizontal plane, respectively. The ultrasonic treatment direction during thin-layer deposition was vertically upward or vertically downward, with a frequency of 5 kHz or 15 kHz and an amplitude of 5 μm, as detailed in Table 1.

[0048] In the specific embodiments and comparative examples described below, after the specimen is constructed, an annealing process is also included: annealing the 3D printed specimen; annealing the 3D-0° specimen at different temperatures, with the annealing process selected as: stress-relief annealing at 300 ℃ for 2 h, followed by air cooling to room temperature; or, high-temperature annealing at 1000 ℃ for 2 h, followed by air cooling to room temperature; or, high-temperature annealing at 1200 ℃ for 2 h, followed by air cooling to room temperature, as detailed in Table 1.

[0049] Table 1. Scale control conditions for each embodiment

[0050]

[0051] like Figure 2 As shown, plane 1 represents the major axis plane of each specimen construction direction, and planes 2 and 3 represent the other two side planes, respectively. Shapes and dimensions are cut from plane 1 as shown. Figure 3 Tensile specimens, Figure 3 The units of the dimensions marked in the figure are mm. The thickness of all samples is 2 mm. The laser selective melting samples with different construction directions are marked as 3D-0°, 3D-45° and 3D-90° respectively.

[0052] Test example: The samples obtained from the above embodiments and comparative examples were tested.

[0053] Hydrogen embrittlement sensitivity test: All tensile samples were processed according to GB / T228.1-2010 "Metallic materials, tensile testing—Part 1: Test methods at room temperature". Slow strain tensile tests were conducted at room temperature using a general-purpose testing machine (DNS 200). The gauge length of the samples was 25 mm. After grinding and polishing, the samples were pre-charged with hydrogen in a 1 mol / L NaOH + 1 g thiourea solution for 48 h, with a current density of 50 mA / cm². The tensile speed was 0.5 mm / min. All tests on the hydrogen-charged samples began within 5 minutes after the hydrogen charging was completed. Figure 4 This is a schematic diagram of dynamic hydrogen charging and stretching.

[0054] Figures 5-7 The figures show the stress-displacement curves of the samples obtained in each embodiment and comparative example under air tension and in-situ dynamic hydrogen-filled tension. In the figures, "Example x-empty" represents the stress-displacement curve of the sample under air tension, and "Example xH" represents the stress-displacement curve of the sample under in-situ dynamic hydrogen-filled tension.

[0055] Figure 5 These are the stress-displacement curves of the samples obtained in Examples 1, 2, and 1 under air tension and in-situ dynamic hydrogen-filled tension.

[0056] Figure 6 These are the stress-displacement curves of the samples obtained in Examples 1, 3, 4, and Comparative Example 3 under air tension and in-situ dynamic hydrogen-filled tension.

[0057] Figure 7 These are the stress-displacement curves of the samples obtained in Examples 1, 5, 6, and Comparative Example 2 under air tension and in-situ dynamic hydrogen-filled tension.

[0058] Figure 8 The bar charts show the tensile hydrogen embrittlement sensitivity obtained from each embodiment and comparative example.

[0059] Table 2 shows the mechanical properties of the samples from each embodiment and comparative example under air tension and in-situ dynamic hydrogen-charged tension.

[0060] Table 2. Mechanical property test results of samples obtained before and after hydrogen charging in each embodiment and comparative example.

[0061]

[0062] pass Figure 5 , Figure 8 As shown in Table 2, different construction orientations affect the mechanical properties and hydrogen embrittlement susceptibility of the stainless steel samples obtained by the method of this application. Figure 5 As can be seen, after dynamic hydrogen charging and tensile testing, the plasticity of the 3D-0° specimen in Example 1 and the 3D-45° specimen in Example 2 both decreased to varying degrees, while the 3D-90° specimen in Comparative Example 1 underwent severe damage under tension in both air and hydrogen environments. Figure 8Based on the displacement change rate, the hydrogen embrittlement susceptibility of the 3D-0° specimen in Example 1 and the 3D-45° specimen in Example 2 were 11.5% and 37.7%, respectively, while the 3D-90° specimen fractured immediately upon being stretched. The 3D-0° specimen in Example 1 had slightly lower strength and plasticity, but also lower hydrogen embrittlement susceptibility and better resistance to hydrogen embrittlement. The 3D-45° specimen in Example 2 had higher strength and plasticity than the 3D-0° specimen in Example 1, but higher hydrogen embrittlement susceptibility and worse resistance to hydrogen embrittlement. The specimen in Comparative Example 1 had extremely poor mechanical properties.

[0063] like Figure 6 The stress-displacement curves of the samples after different ultrasonic treatments under air tension and in-situ dynamic hydrogen-filled tension are shown.

[0064] In Example 1, the applied ultrasonic frequency was 15 kHz and the direction was vertically upward; in Example 3, the applied ultrasonic frequency was 5 kHz and the direction was vertically upward; in Example 4, the applied ultrasonic frequency was 15 kHz and the direction was vertically downward; and in Comparative Example 3, no ultrasonic wave was applied.

[0065] like Figure 6 , Figure 8 Table 2 shows that a comparison between Examples 1 and 3 reveals that the ultrasonic frequency has a slight impact on the sample performance, with higher frequencies being beneficial for improving the overall performance. A comparison between Examples 1 and 4 shows that the direction of ultrasonic waves applied to the metal powder during laser melting also affects the sample performance; an upward ultrasonic wave direction is beneficial for improving the overall performance. A comparison between Example 1 and Comparative Example 3 shows that applying ultrasonic waves to the metal powder during laser melting can significantly improve the mechanical strength and resistance to hydrogen embrittlement of the sample. Figure 8 Based on the displacement change rate before and after hydrogen charging, the hydrogen embrittlement susceptibility of the four samples (Example 1, Example 3, Example 4, and Comparative Example 3) was found to be 11.5%, 12.9%, 12.0%, and 13.5%, respectively. It can be inferred that when ultrasound acts on the molten metal, the molten metal generates strong vibrations, thereby promoting the formation of high-density dislocation cell structures in laser selective melting additive manufacturing, thus improving the mechanical strength and hydrogen embrittlement resistance of the samples. On the other hand, during ultrasonic vibration, cavitation and vibration effects are generated on the surface of the metal powder, which can remove gases adhering to the metal surface, thereby avoiding the generation of excessive gas channels in the molten metal during laser melting and preventing hydrogen from entering the metal.

[0066] Figure 7 The stress-displacement curves of specimens annealed at different temperatures under air tension and in-situ dynamic hydrogen-charged tension are obtained from... Figure 7As can be seen, Example 1 was not returned; Example 5 was a sample stress-relief annealed at 300 °C for 2 h; Example 6 was a sample annealed at 1000 °C for 2 h; and Comparative Example 2 was a sample annealed at 1200 °C for 2 h. Figure 7 Table 2 shows the stress-displacement curves for Examples 1, 5, 6, and Comparative Example 2. It can be seen that the strength of the annealed material is lower than that of the unannealed material, while the plasticity is slightly increased. Figure 8 Based on the displacement change rate before and after hydrogen charging, the hydrogen embrittlement sensitivities of the four samples (Example 1, Example 5, Example 6, and Comparative Example 2) were 11.5%, 9.3%, 22.0%, and 29.8%, respectively. The sample with the lowest hydrogen embrittlement sensitivities was obtained after stress-relief annealing at 300 °C for 2 h. The hydrogen embrittlement sensitivities increased again after high-temperature annealing at 1000 °C. In Example 5, the sample with the lowest hydrogen embrittlement sensitivities was obtained after stress-relief annealing at 300 °C for 2 h.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for improving the strength and hydrogen embrittlement resistance of austenitic stainless steel, characterized in that, include: Thin-layer deposition: A thin layer of austenitic stainless steel powder is deposited using a powder spreader to form a thin layer of austenitic stainless steel powder, while ultrasound is continuously applied to the thin layer of austenitic stainless steel powder. Laser melting: The austenitic stainless steel powder thin layer is melted by scanning the austenitic stainless steel powder thin layer, so that the melted austenitic stainless steel powder thin layer is bonded to the component in the solidified austenitic stainless steel region. The thickness of the component is reduced by one layer of austenitic stainless steel powder, and then the next layer of austenitic stainless steel powder is deposited and melted by laser beam. Specimen construction: By repeating the above steps, the specimen is constructed layer by layer until a 3D printed specimen of the preset shape is obtained. The entire process described above was carried out under an argon protective atmosphere.

2. The method according to claim 1, characterized in that, The powder layer is 30 μm thick.

3. The method according to claim 1, characterized in that, The substrate preheating temperature for the thin-layer deposition is 80°C.

4. The method according to claim 1, characterized in that, The austenitic stainless steel powder has a particle size of 25μm~30μm.

5. The method according to claim 1, characterized in that, The laser fusion scanning strategy is a checkerboard pattern.

6. The method according to claim 1, characterized in that, The incident laser beam has a scanning rate of 1000 mm / s, a scanning power of 180 W, and a deflection angle of 67° per layer.

7. The method according to claim 1, characterized in that, The applied ultrasound has a frequency of 5 kHz to 20 kHz and an amplitude of 5 to 15 μm.

8. The method according to claim 1, characterized in that, The direction of the applied ultrasonic wave is from bottom to top.

9. The method according to claim 1, characterized in that, In the constructed specimen, the construction direction of the 3D printed specimen is 0°~45°.

10. The method according to claim 1, characterized in that, After the specimen is constructed, the process also includes annealing: annealing the 3D printed specimen. The annealing process is as follows: stress-relief annealing at 300℃~1000℃ for 2 hours, followed by air cooling to room temperature.

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