Method for improving torsion anti-fatigue performance of stainless steel shaft piece

Abstract

The invention discloses a method for improving torsion anti-fatigue performance of a stainless steel shaft piece. The method comprises the following steps that S1, the stainless steel shaft piece is pretreated; s2, the pretreated stainless steel shaft part is subjected to ultrasonic rolling treatment, so that a nanometer gradient structure with the deformation layer thickness larger than or equal to 76 microns is formed on the surface layer of the stainless steel shaft part; and S3, the stainless steel shaft part is subjected to nitriding treatment, a sample is obtained, the nitriding treatment temperature ranges from 420 DEG C to 470 DEG C, and the nitriding time ranges from 15 h to 25 h. The surface hardness and toughness of the stainless steel shaft piece can be synchronously improved, and the torsion anti-fatigue performance of the stainless steel shaft piece under alternating loads is remarkably enhanced.

Description

Technical Field

[0001] This invention relates to the field of metal materials technology, and in particular to a method for improving the torsional fatigue resistance of stainless steel shafts. Background Technology

[0002] Martensitic stainless steel is widely used in the manufacture of shaft components in aerospace, shipbuilding, and other fields. These shaft components often operate under alternating loads, making them prone to fatigue crack initiation on the surface, which can lead to spindle fracture in severe cases. Nitriding treatment can significantly improve the surface hardness of the material, thereby effectively inhibiting crack propagation. However, this process tends to form a thick and brittle white layer on martensitic stainless steels such as 0Cr17Ni4Cu4Nb. Furthermore, an effective mechanical property gradient transition is not formed between the white layer and the stainless steel substrate. Under alternating loads, the interface between the white layer and the substrate becomes a stress concentration point. Microcracks first initiate in the white layer and rapidly propagate to the interface, causing the entire nitrided layer to peel off, thus drastically reducing the torsional fatigue life of the shaft components.

[0003] In view of this, it is necessary to design a method to improve the torsional fatigue resistance of stainless steel shafts in order to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a method for improving the torsional fatigue resistance of stainless steel shafts by simultaneously increasing the surface hardness and toughness of the shafts and significantly enhancing their torsional fatigue resistance under alternating loads.

[0005] To achieve the above-mentioned objective, the present invention provides a method for improving the torsional fatigue resistance of stainless steel shaft components, comprising the following steps: S1. Pre-treatment of stainless steel shafts; S2. The pretreated stainless steel shaft is subjected to ultrasonic rolling treatment to form a nano-gradient structure with a deformation layer thickness of greater than or equal to 76μm on the surface of the stainless steel shaft. S3. Then, the stainless steel shaft is subjected to nitriding treatment to obtain a sample. The nitriding treatment temperature is 420-470℃ and the nitriding time is 15-25h.

[0006] As a further improvement of the present invention, in step S1, the pretreatment specifically involves: placing the stainless steel shaft in an ethanol solution for ultrasonic cleaning, followed by drying.

[0007] As a further improvement of the present invention, in step S2, after ultrasonic rolling treatment, the surface roughness of the stainless steel shaft is less than 0.4 μm.

[0008] As a further improvement of the present invention, in step S2, the static pressure of the ultrasonic rolling treatment is 0.15-0.25 MPa, the rotation speed is less than or equal to 30 r / min, and the number of rolling passes is 3-7.

[0009] As a further improvement of the present invention, in step S2, the ultrasonic rolling head is fed along the axis of the stainless steel shaft during the ultrasonic rolling process, the feeding speed is 0.1-0.3 mm / r, and the ultrasonic control current is 0.6-1.0 A.

[0010] As a further improvement of the present invention, in step S2, after the ultrasonic rolling process is completed, the stainless steel shaft is ultrasonically cleaned with an ethanol solution to remove the residual lubricating oil on the surface.

[0011] As a further improvement of the present invention, in step S3, the nitriding treatment specifically involves: raising the temperature inside the furnace to the treatment temperature and keeping it stable, evacuating the furnace, introducing nitriding gas, and keeping it at that temperature for 15-25 hours.

[0012] As a further improvement of the present invention, the nitriding gas is ammonia or a mixture of nitrogen and hydrogen.

[0013] As a further improvement of the present invention, after the nitriding treatment is completed, the surface of the sample is polished step by step with sandpaper of gradually increasing mesh size until the surface is restored to a bright state.

[0014] As a further improvement of the present invention, the stainless steel is martensitic stainless steel.

[0015] As a further improvement of the present invention, preferably, the nitriding treatment temperature is 420-450℃.

[0016] The beneficial effects of this invention are: 1. This invention uses ultrasonic rolling to form a nano-gradient structure with low roughness, high hardness, and suitable grain deformation layer thickness on the surface of stainless steel shafts. During further nitriding, nitrogen atoms are captured by alloying elements enriched at the grain boundaries, forming compounds that hinder the rapid diffusion of N atoms along the nanograin boundaries. This reduces the diffusion rate and fundamentally suppresses excessive nitrogen enrichment on the outermost layer of the matrix, preventing the formation of thick and brittle ε-Fe. 2-3 The N-bright layer is transformed into a nitrided layer with a gentler nitrogen concentration gradient, finer grains, and controllable thickness. This gives the substrate surface both high surface hardness and excellent toughness, significantly improving the fatigue resistance of stainless steel shafts under alternating loads and avoiding the problem of the nitrided layer easily collapsing under torsional stress due to the large hardness difference between the bright layer and the substrate. Attached Figure Description

[0017] Figure 1 A flowchart illustrating a method for improving the torsional fatigue resistance of stainless steel shaft components.

[0018] Figure 2 This is a schematic diagram of the nitrogen distribution in the sample of Example 1.

[0019] Figure 3 This is a schematic diagram of the nitrogen distribution in the sample of Example 2.

[0020] Figure 4 This is a schematic diagram of the nitrogen distribution in the sample of Example 3.

[0021] Figure 5 This is a schematic diagram of the nitrogen distribution in the sample of Example 6.

[0022] Figure 6 This is a schematic diagram of the nitrogen distribution in the sample of Example 7.

[0023] Figure 7 This is a schematic diagram of the nitrogen distribution in the sample of Comparative Example 1.

[0024] Figure 8 This is a schematic diagram of the nitrogen distribution in the sample of Comparative Example 10.

[0025] Figure 9 The images are scanning electron microscope (SEM) images of the samples from Example 1 and Comparative Example 10. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0028] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0029] Example 1 like Figure 1 As shown, this embodiment provides a method for improving the torsional fatigue resistance of stainless steel shaft components, using 0Cr17Ni4Cu4Nb stainless steel as the matrix for treatment, including the following steps: S1. Place the stainless steel shaft in an ethanol solution and remove surface contaminants by ultrasonic treatment, then place it in a drying oven for drying. S2. Next, the stainless steel shaft is clamped on a CNC machine tool. A lubricating oil mixture of hydraulic oil and kerosene in a 1:3 ratio is used to cool the rolling contact area to control the temperature rise. Then, ultrasonic rolling is performed. During the ultrasonic rolling process, the ultrasonic rolling head is fed along the axis of the stainless steel shaft. The process parameters for ultrasonic rolling are: feed speed of 0.2 mm / r, ultrasonic control current of 0.8A, static pressure of 0.2MPa, rotation speed of 30r / min, and 5 rolling passes. After ultrasonic rolling, the stainless steel shaft is ultrasonically cleaned with ethanol solution to remove residual lubricating oil from the surface, and then dried for later use. S3. The stainless steel shaft, after ultrasonic rolling and cleaning and drying, is placed in a vacuum ion nitriding furnace for nitriding treatment. The nitriding treatment is as follows: the temperature inside the furnace is raised to 450℃ and kept stable; vacuum is drawn until the pressure inside the furnace is 280Pa; ammonia gas is introduced as the nitriding atmosphere, and the temperature is maintained at 450℃ for 20 h; after the temperature maintenance is completed, heating is stopped, and the sample is taken out after cooling to room temperature with the furnace. Then, the sample surface was polished step by step using 800-grit, 1200-grit, 1500-grit, and 2000-grit sandpaper until the surface was restored to a bright state, in order to remove the surface oxide layer formed during the nitriding process.

[0030] Examples 2-7 Examples 2-7 provide a method for improving the torsional fatigue resistance of stainless steel shafts. Compared with Example 1, some parameters in the ultrasonic rolling and nitriding treatments of Examples 2-7 have been adjusted. The relevant parameters in the ultrasonic rolling and nitriding treatments of Examples 2-7 are shown in Table 1. The remaining steps are the same as in Example 1 and will not be repeated here.

[0031] Comparative Examples 1-9 Comparative Examples 1-9 provide a method for improving the torsional fatigue resistance of stainless steel shafts. Compared with Example 1, some parameters in the ultrasonic rolling and nitriding treatments of Comparative Examples 1-9 have been adjusted. The relevant parameters in the ultrasonic rolling and nitriding treatments of Comparative Examples 1-9 are shown in Table 1. The remaining steps are the same as in Example 1 and will not be repeated here.

[0032] Comparative Example 10 Comparative Example 10 provides a method for improving the torsional fatigue resistance of stainless steel shafts. In this method, only the stainless steel shafts are subjected to nitriding treatment. That is, compared with Example 1, Comparative Example 10 only performs steps S1 and S3.

[0033] Comparative Example 11 Comparative Example 11 provides a method for improving the torsional fatigue resistance of stainless steel shafts. Compared with Example 1, Comparative Example 11 adjusts the nitriding treatment time in step S3 from 20h to 30h. The remaining steps are the same as in Example 1 and will not be repeated here.

[0034] The relevant parameters of the samples prepared in Examples 1-7 and Comparative Examples 1-10 were tested, and the test results are shown in Table 2. Among them, the deformation layer thickness is the thickness of the deformation layer in the substrate after ultrasonic rolling; the roughness is the surface roughness of the substrate after ultrasonic rolling; the number of torsion cycles after ultrasonic rolling and after nitriding are respectively the number of cycles until fracture occurs in the torsion fatigue test with a torque of 180 N·m and a stress ratio R=0.1 after ultrasonic rolling and ultrasonic rolling plus nitriding treatments, respectively; the surface hardness is the surface hardness of the finally prepared sample; and the nitrided layer thickness is the thickness of the bright white layer after nitriding treatment.

[0035] Table 1. Relevant process parameters in Examples 1-7 and Comparative Examples 1-10

[0036] Table 2. Relevant test results of the samples prepared in Examples 1-7 and Comparative Examples 1-10.

[0037] As shown in Table 2, in Example 1, after ultrasonic rolling treatment, the stainless steel shaft fractured after 149,801 torsional fatigue tests. In a parallel sample that underwent both ultrasonic rolling and nitriding simultaneously, the stainless steel shaft fractured after 499,064 torsional fatigue tests. This indicates that nitriding treatment on top of ultrasonic rolling significantly improves the torsional fatigue resistance of the stainless steel shaft. Furthermore, the nitrided layer thickness of the sample in Example 1 was measured to be 23.9 μm, and the surface hardness was 1338.14 Hv. This demonstrates that the sample prepared by the method of this invention effectively reduces the thickness of the white layer, simultaneously improves surface hardness and toughness, and significantly enhances the fatigue performance of the material under alternating loads.

[0038] In addition, the samples prepared in Examples 2-7 can also significantly improve the fatigue performance of the material under alternating loads while ensuring surface hardness.

[0039] according to Figures 2-4It can be seen that when the rolling passes are 3-5 times, the thickness of the deformed layer is above 76 μm. Along the direction near the center of the substrate, the nitrogen concentration gradually decreases, resulting in a transition layer between the bright white layer and the substrate with gradually decreasing hardness along the direction near the substrate, effectively improving the torsional fatigue resistance of the sample. When the rolling passes are 2 times, the thickness of the deformed layer in Comparative Example 1 is only 68.55 μm, and the nitrogen in the substrate fails to achieve a good gradient distribution. Figure 7 This results in a high hardness difference between the white gloss layer and the substrate, which may be because an excessively thin deformable layer affects the gradient distribution of nitrogen.

[0040] In addition, when the number of rolling passes gradually increased from 2 to 8, the number of torsions after ultrasonic rolling first increased and then decreased. Specifically, the number of torsions after ultrasonic rolling was 128,879 when the number of rolling passes was 2, 149,801 when the number of rolling passes was 5, and 116,433 when the number of rolling passes was 8. This may be because the increase in the surface roughness of the substrate will cause the formation of tiny cracks on the substrate surface. Under torsional stress, the tiny cracks will become stress concentration points, thus reducing the torsional fatigue life of the sample.

[0041] In Comparative Examples 3 and 4, the roughness of the substrate increased significantly when the rotational speed was 60 and 90 r / min, respectively. In Comparative Examples 5 and 6, the thickness of the deformed layer of the substrate was relatively low when the static pressure was 0.1 MPa, but the roughness of the substrate increased significantly when the static pressure was 0.3 MPa.

[0042] like Figure 5 and Figure 6 As shown in Examples 6 and 7, when the nitriding time is 15 and 25 hours, the nitrogen element in the matrix is ​​distributed in a gradient, resulting in a transition layer with gradually decreasing hardness along the direction closer to the matrix between the bright white layer and the matrix. In Examples 6 and 7, the thickness of the nitrided layer is less than 30 μm, which can improve the toughness of the stainless steel shaft while ensuring the surface hardness, and improve the torsional fatigue resistance of the stainless steel shaft.

[0043] In Comparative Example 7, when the nitriding temperature was too high, the thickness of the nitrided layer increased significantly to 88.18 μm. Although the surface hardness of the sample was 1176 Hv, the number of torsion cycles after nitriding was only 21257 before the nitrided layer detached. This may be because although ultrasonic rolling treatment can form a deformation layer of a certain thickness in the matrix, the high nitriding temperature affected the diffusion effect of nitrogen, which in turn affected the distribution of nitrogen in the matrix. As a result, a good gradient transition could not be formed between the matrix and the white layer, leading to a significant reduction in torsional fatigue life.

[0044] In Comparative Examples 8 and 9, when the nitriding temperature was too low or the nitriding time was too short, the number of torsion cycles after nitriding was 168,888, the surface hardness was significantly reduced, and no obvious white layer was observed in the matrix. This may be because the low temperature or short nitriding time affected the diffusion of nitrogen, thus affecting the formation of the white layer, preventing the sample from simultaneously possessing superior surface hardness and torsional fatigue life. In Comparative Example 11, when the nitriding time was too long, the surface hardness of the sample was lower than that of Example 1.

[0045] Furthermore, in Comparative Example 10, when only the substrate was nitrided, the thickness of the nitrided layer was significantly greater than that in Example 1. Figure 9 The red box shows the nitrided layer of Comparative Example 10. Figure 9 b is the scanning electron microscope result from Example 1; furthermore, the nitrogen element in Comparative Example 10 failed to achieve a good gradient distribution ( Figure 8 Furthermore, the number of torsion cycles after nitriding was significantly lower than in Example 1.

[0046] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for improving the torsional fatigue resistance of a stainless steel shaft member, comprising: The method comprises the following steps: S1, pretreating the stainless steel shaft; S2, performing ultrasonic rolling treatment on the pretreated stainless steel shaft to form a nanometer gradient structure with a deformation layer thickness greater than or equal to 76 μm on the surface layer of the stainless steel shaft; S3, performing nitriding treatment on the stainless steel shaft to obtain a sample, wherein the nitriding treatment temperature is 420-470 ℃, and the nitriding treatment time is 15-25 h.

2. The method of improving torsional fatigue resistance of a stainless steel shaft according to claim 1, wherein: In step S1, the pretreatment is specifically: placing the stainless steel shaft in an ethanol solution for ultrasonic cleaning, and then drying.

3. The method of improving torsional fatigue resistance of a stainless steel shaft according to claim 1, wherein: In step S2, the surface roughness of the stainless steel shaft after the ultrasonic rolling treatment is less than 0.4 μm.

4. The method of improving torsional fatigue performance of a stainless steel shaft according to claim 1, wherein: In step S2, the static pressure of the ultrasonic rolling treatment is 0.15-0.25 MPa, the rotating speed is less than or equal to 30 r / min, and the rolling pass is 3-7 times.

5. The method of improving torsional fatigue performance of a stainless steel shaft according to claim 1, wherein: In step S2, the ultrasonic rolling head is fed along the axis of the stainless steel shaft during the ultrasonic rolling treatment, the feeding speed is 0.1-0.3 mm / r, and the ultrasonic control current is 0.6-1.0 A.

6. The method of improving torsional fatigue performance of a stainless steel shaft according to claim 1, wherein: In step S2, after completing the ultrasonic rolling treatment, the stainless steel shaft is cleaned with an ethanol solution to remove residual lubricating oil on the surface.

7. The method of improving torsional fatigue performance of a stainless steel shaft according to claim 1, wherein: In step S3, the nitriding treatment is specifically: raising the temperature in the furnace to the treatment temperature and keeping it stable, introducing the nitriding gas after vacuumizing, and keeping the temperature for 15-25 h.

8. The method of improving torsional fatigue performance of a stainless steel shaft according to claim 7, wherein: The nitriding gas is ammonia gas or a mixed gas of nitrogen and hydrogen.

9. The method of improving torsional fatigue performance of a stainless steel shaft according to claim 1, wherein: After completing the nitriding treatment, the surface of the sample is polished with sandpaper with gradually increasing mesh numbers until the surface is restored to a bright state.

10. The method of improving torsional fatigue performance of a stainless steel shaft according to claim 1, wherein: The stainless steel is a martensitic stainless steel.

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