Method for improving residual compressive stress on surface of high-carbon chromium steel and distribution of residual compressive stress

Abstract

The invention belongs to the technical field of steel smelting and processing technologies, and particularly relates to a method for improving residual compressive stress and distribution on the surface of high-carbon chromium steel. The method comprises the steps of annealing treatment, ultrasonic cleaning, assembling, pressing, pressure relief, tempering treatment and the like, specific process parameters are adjusted, pressing methods with different pressures and temperatures are adopted, and then tempering process parameters are adjusted, so that the residual compressive stress on the surface of the high-carbon chromium steel and the distribution condition are improved, and the surface quality of the high-carbon chromium steel is improved. The service life is prolonged; and the usability of parts is improved. Compared with shot blasting treatment in the prior art, the process method disclosed by the invention has the advantages of simple steps, short processing time and high processing efficiency; compared with normal-pressure heat treatment, the method provided by the invention can effectively improve the residual compressive stress, the compressive stress is improved by 104.2% compared with the normal-pressure heat treatment, the distribution is more uniform, and the method has positive significance for prolonging the service life of the workpiece.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting and processing technology, and specifically relates to a method for improving the residual compressive stress on the surface of high-carbon chromium steel and its distribution. Background Art

[0002] Mechanical effects, thermal effects, phase change effects, etc. during material processing will cause residual stress in the workpiece, which can be divided into residual tensile stress and residual compressive stress. Residual stress has a very important influence on the shape, size and performance of the workpiece. Residual stress can be divided into residual tensile stress and residual compressive stress. When the residual stress is tensile stress, the workpiece is prone to cracks, reducing its fatigue life.

[0003] There are many studies on residual compressive stress in the prior art. For example, in 2006, Hyukjae Lee ab, Shankar Mall et al. found that residual compressive stress can inhibit the formation of microcracks or close existing microcracks, thereby improving the fatigue resistance of the sample (see BHLA, ASM, AWY A. Fretting fatigue behavior of shot-peened Ti-6Al-4V under seawater environment [J]. Materials Science & Engineering A, 2006, 420 (1-2): 72-78. DOI: 10.1016 / j.msea.2006.01.031.). For example, in 2020, Yanfei Wang, Honglin Xie and others found that the residual compressive stress caused by shot peening can effectively reduce the apparent hydrogen diffusion coefficient (see Wang Y, Xie H, Zhou Z, et al. Effect of shot peening coverage on hydrogen embrittlement of a ferrite-pearlite steel [J]. International Journal of Hydrogen Energy, 2020, 45 (11). DOI: 10.1016 / j.ijhydene.2020.01.021.). In addition, other studies have also shown that introducing an appropriate amount of residual compressive stress into a workpiece can extend its fatigue life, increase the tensile yield limit, reduce brittle failure, prevent and reduce stress corrosion cracking, etc. Therefore, under certain conditions, controlling the stress to make the residual compressive stress reasonably distributed can improve the mechanical properties and service life of the parts.

[0004] There are also some studies on this prior art. For example, the Chinese patent with publication number CN110257757A discloses a high-carbon chromium bearing steel part and a processing method for heat treatment thereof. By controlling the heat treatment process of the high-carbon chromium bearing steel part, the surface stress control of the high-carbon chromium bearing steel part after heat treatment is achieved. However, the maximum surface compressive stress value of the high-carbon chromium bearing steel obtained by the patent is only -60MPa, and there is still a tensile stress of +80MPa, which cannot well meet the high pressure stress requirements required by high-end bearings.

[0005] In addition, in order to obtain an ideal surface compressive stress distribution and improve the fatigue life of parts, mechanical methods such as rolling, extrusion, shot peening, etc. can also be used to produce cold deformation and hardened layers, or high-energy beam processing methods can be used. For example, the Chinese patent with publication number CN101135344A discloses a composite processing technology for high-carbon chromium steel of rocker arm bearings. The patent obtains a residual compressive stress of 400-1000MPa through preliminary heat treatment and rough grinding and shot peening process after heat treatment. However, this method has the problems of low processing efficiency, uneven surface of the shot peening workpiece due to the impact of the projectile, increased roughness, increased stress concentration effect or generation of surface microcracks, and the expansion of the residual compressive stress field distribution and surface thickness requires a very high steel shot impact speed.

[0006] Therefore, exploring new processing methods to increase the residual compressive stress of materials has far-reaching practical significance for improving the service life of parts and has important application prospects in the engineering field. Summary of the invention

[0007] The purpose of the present invention is to provide a method for improving the residual compressive stress and its distribution on the surface of high carbon chromium steel. By adjusting the specific process parameters in the process method, adopting a pressing method with different pressures and temperatures, and then adjusting the tempering process parameters, the residual compressive stress and its distribution on the surface of high carbon chromium steel are improved, thereby improving its service life and the performance of parts.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for improving residual compressive stress and its distribution on the surface of high carbon chromium steel comprises the following steps:

[0010] (1) Annealing treatment: The high carbon chromium steel raw material bar is forged, cut into cylindrical billets, and then kept at 850-900°C for 1-2 hours, and then furnace cooled for stress relief annealing;

[0011] (2) Ultrasonic cleaning: The high carbon chromium bearing steel blank in step (1) is processed into a sample and ultrasonically cleaned;

[0012] (3) Assembling: assembling the high carbon chromium bearing steel sample obtained in step (2) using a high pressure assembly structure to obtain a high pressure assembly block;

[0013] (4) Pressing: Pressing the high-pressure assembly block in step (3) at high temperature and high pressure;

[0014] (5) Pressure relief: After the pressing is completed, the pressure is naturally reduced to room temperature, and then the pressure is relieved to normal pressure at a pressure relief rate of 100 to 200 MPa / min;

[0015] (6) Tempering treatment: The high carbon chromium bearing steel sample obtained in step (5) is tempered to obtain a tempered high carbon chromium steel product.

[0016] Specifically, the chemical composition (wt%) of the high carbon chromium bearing steel raw material bar in step (1) is shown in the following table:

[0017] C Si Mn P S Cr Cu 0.95-1.05 0.15-0.35 0.2-0.4 ≤0.027 ≤0.02 1.30-1.65 ≤0.25

[0018] Specifically, the forging process described in step (1) is shown in the following table:

[0019] Billet outer diameter / mm Heating temperature / ℃ Repeated upsetting (min / mm) Direct forming (min / mm) ≤80 1130～1180 0.40～0.60 0.60～0.80

[0020] Specifically, in step (1) of the present invention, the reason for adding forging and controlling its process is that there is carbide segregation in the raw material. Adding the forging process can reduce the unevenness of carbides and make the carbide distribution more uniform to meet the needs of the heat treatment process; at the same time, the fiber direction of the material is reasonably distributed to increase the service life of the tool.

[0021] Furthermore, the assembly method in step (3) is to first cover the front, back, top, bottom, left and right sides of the sample with ZrO2 insulation material, then add graphite tubes and MgO on the front, back, left and right sides in turn, and add Ti metal sheets and ZrO2 insulation plugs on the upper and lower sides in turn, and finally add talc on the outside.

[0022] Furthermore, the high temperature and high pressure pressing process in step (4) is to first pressurize to 3-7 GPa at a pressure increase rate of 1.0-1.5 GPa / min, and maintain this pressure for 30-150 minutes; at the same time, heating is performed 2 minutes after the start of the pressure increase, and the heating procedure is to heat to 600-1500°C at a rate of 50-300°C / min. Finally, when the pressure is increased to 3-7 GPa and the temperature is increased to 600-1500°C, it is maintained for 10-60 minutes.

[0023] Furthermore, during the pressing process in step (4), the final pressure error should not exceed ±0.1 GPa.

[0024] Furthermore, the time to reach the final temperature in step (4) should not be less than the time to reach the final pressure.

[0025] Furthermore, during the pressing process in step (4), the error of the final temperature should not exceed ±30°C.

[0026] Furthermore, in step (6), the tempering treatment process parameters are as follows: controlling the furnace temperature to ≤100°C, and performing tempering at a heating rate of 10 to 15°C / min. When the temperature is heated to 550 to 1000°C, the temperature is kept at that for 1 to 5 hours, and then air-cooled to room temperature.

[0027] Specifically, in step (4) of the present invention, the pressure is controlled to increase to a final pressure of 3 to 7 GPa at a rate of 1.0 to 1.5 GPa / min and this pressure is maintained for 30 to 150 minutes because too short a holding time is difficult to achieve the purpose of improving the residual stress distribution, while too long a holding time is not only time-consuming but also has little effect on improving the residual stress.

[0028] Specifically, in step (4) of the present invention, the temperature range is controlled to be 600-1500°C because lower temperatures make it difficult to achieve the effect of heat treatment, resulting in lower hardness of the workpiece; while higher temperatures will reduce the surface quality of the workpiece and damage the microstructure of the workpiece, making it difficult to meet practical requirements.

[0029] Specifically, in step (5) of the present invention, the pressure relief rate is controlled within the range of 0 to 300 MPa / min because too fast a pressure relief rate will make it difficult to release the residual stress on the surface of the workpiece to achieve uniformity. At the same time, too fast a pressure relief rate may cause "explosion", thereby damaging the equipment and possibly endangering the safety of personnel.

[0030] Furthermore, the present invention also provides a high-carbon chromium steel product prepared by the above-mentioned method, specifically a high-carbon chromium bearing steel product. The high-carbon chromium steel processed by the method of the present invention has a more uniform distribution of residual compressive stress and has a good service life.

[0031] Furthermore, based on a general inventive concept, the present invention also provides the use of the processed high-carbon chromium steel product as an equipment component.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] Compared with the shot peening treatment in the prior art, the process method of the present invention has the advantages of simple steps, short processing time and high processing efficiency; compared with the normal pressure heat treatment, the method provided by the present invention can effectively increase the residual compressive stress, and the compressive stress is increased by 104.2% compared with the normal pressure heat treatment, and the distribution is more uniform, which has a positive significance for extending the service life of the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the high-pressure structure of the process method of the present invention during assembly;

[0035] Figure 2 This is the stress magnitude and distribution diagram of the high carbon chromium steel after normal pressure heat treatment obtained in Example 1, in which the compressive stress is concentrated and is only 452MPa;

[0036] Figure 3 is the stress magnitude and distribution diagram of the high carbon chromium steel after high pressure heat treatment obtained in Example 1, wherein the compressive stress is evenly distributed and is 848 MPa;

[0037] Figure 4 This is the stress magnitude and distribution diagram of the high carbon chromium steel after high pressure heat treatment obtained in Example 2, in which the compressive stress is evenly distributed and has a magnitude of 923 MPa. DETAILED DESCRIPTION

[0038] The technical solution of the present application is described clearly and completely below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0039] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change of the proportion relationship or adjustment of the size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical content disclosed by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description, and are not used to limit the scope of the implementation of the present invention. The change or adjustment of their relative relationship should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0040] Comparative Example 1

[0041] Comparative Example 1 provides a treatment method in the prior art. The chemical composition of the high carbon chromium bearing steel targeted by Comparative Example 1 is shown in Table 1.

[0042] Table 1 is the chemical composition table (wt%) of high carbon chromium bearing steel of comparative example 1

[0043] C Si Mn P S Cr Cu 0.95-1.05 0.15-0.35 0.2-0.4 ≤0.027 ≤0.02 1.30-1.65 ≤0.25

[0044] The method comprises the following specific steps:

[0045] (1) Annealing treatment: The high carbon chromium steel raw material bar is forged and cut into cylindrical billets, then kept at 880°C for 2 h, and then furnace cooled for stress relief annealing. The forging process is shown in Table 2.

[0046] Table 2 shows the forging process of comparative example 1

[0047] Billet outer diameter / mm Heating temperature / ℃ Repeated upsetting (min / mm) Direct forming (min / mm) 60 1130 0.4 0.6

[0048] (2) Quenching treatment: the annealed billet is heated to 850°C and preheated for 45 min, then heated to 1260°C and kept at this temperature for 27 min for quenching;

[0049] (3) Tempering treatment: The quenched billet is cooled to 550°C and kept at this temperature for 2.5 hours, and then tempered.

[0050] Example 1

[0051] Example 1 provides a method for improving residual compressive stress and distribution on the surface of high-carbon chromium steel. The chemical composition of the high-carbon chromium bearing steel targeted by Example 1 is shown in Table 3.

[0052] Table 3 is the chemical composition table (wt%) of high carbon chromium bearing steel of Example 1

[0053] C Si Mn P S Cr Cu 0.95-1.05 0.15-0.35 0.2-0.4 ≤0.027 ≤0.02 1.30-1.65 ≤0.25

[0054] The method comprises the following specific steps:

[0055] (1) Annealing treatment: The high carbon chromium bearing steel raw material bar is forged and cut into cylindrical billets, then kept at 880°C for 2 h, and then furnace cooled for stress relief annealing. The forging process is shown in Table 4;

[0056] Table 4 shows the specific process of forging high carbon chromium bearing steel raw materials in Example 1

[0057] Billet outer diameter / mm Heating temperature / ℃ Repeated upsetting (min / mm) Direct forming (min / mm) 60 1130 0.4 0.6

[0058] (2) Ultrasonic cleaning: The high carbon chromium bearing steel blank in step (1) was processed into a sample of φ8*13 mm, and ultrasonically cleaned in anhydrous ethanol for 30 minutes;

[0059] (3) Assembly: The high carbon chromium bearing steel sample obtained in step (2) is assembled as follows: Figure 1 The high-pressure assembly structure in the test tube is assembled, specifically, the ZrO2 insulation material is firstly covered on the front, back, top, bottom, left, and right sides of the test specimen, and then graphite tubes and MgO are sequentially added on the front, back, left, and right sides, and Ti metal sheets and ZrO2 insulation plugs are sequentially added on the upper and lower sides, and finally pyrophyllite is added on the outside;

[0060] (4) Pressing: The high-pressure assembly block in step (3) is placed in a hinged six-sided top press for pressing. The specific pressing process is to first pressurize to 5.5 GPa at a pressure increase rate of 1.5 GPa / min; and then heat the block 2 minutes after the pressure increase. The heating procedure is to heat the block to 1000°C at a rate of about 300°C / min. Finally, when the pressure is increased to 5.5 GPa and the temperature is increased to 1000°C, the pressure is maintained at 5.5 GPa and the temperature is maintained at 1000°C for 30 minutes.

[0061] (5) Pressure relief: After the pressing is completed, the pressure is naturally reduced to room temperature, and then the pressure is relieved to normal pressure at a pressure relief rate of 200 MPa / min;

[0062] (6) Tempering treatment: The high carbon chromium bearing steel sample obtained in step (5) is tempered. The specific process parameters are: controlling the furnace temperature to ≤100°C, and tempering at a heating rate of 15°C / min. When the temperature is heated to 550°C, the temperature is kept for 2 hours, and then air-cooled to room temperature to obtain a high carbon chromium bearing steel product after tempering treatment.

[0063] Example 2

[0064] Example 2 provides a method for improving the residual compressive stress and distribution on the surface of high carbon chromium steel. The chemical composition of the high carbon chromium bearing steel targeted by Example 1 is shown in Table 5:

[0065] Table 5 is the chemical composition table (wt%) of high carbon chromium bearing steel of Example 2

[0066] C Si Mn P S Cr Cu 0.95-1.05 0.15-0.35 0.2-0.4 ≤0.027 ≤0.02 1.30-1.65 ≤0.25

[0067] The method comprises the following specific steps:

[0068] (1) Annealing treatment: The high carbon chromium bearing steel raw material bar is forged and cut into cylindrical billets, then kept at 880°C for 2 h, and then furnace cooled for stress relief annealing. The forging process is shown in Table 6;

[0069] Table 6 shows the specific process of forging high carbon chromium bearing steel raw materials in Example 2:

[0070] Billet outer diameter / mm Heating temperature / ℃ Repeated upsetting (min / mm) Direct forming (min / mm) 60 1130 0.4 0.6

[0071] (2) Ultrasonic cleaning: The high carbon chromium bearing steel blank in step (1) was processed into a sample of φ8*13 mm, and ultrasonically cleaned in anhydrous ethanol for 30 minutes;

[0072] (3) Assembly: The high carbon chromium bearing steel sample obtained in step (2) is assembled using the same high pressure assembly structure as in Example 1;

[0073] (4) Pressing: The high-pressure assembly block in step (3) is placed in a hinged six-sided top press for pressing. The specific pressing process is to first pressurize to 7.0 GPa at a pressure increase rate of 1.0 GPa / min; and then heat the block 3 minutes after the pressure increase. The heating procedure is to heat the block to 800°C at a rate of about 200°C / min. Finally, when the pressure is increased to 7.0 GPa and the temperature is increased to 800°C, the pressure is maintained at 60 minutes.

[0074] (5) Pressure relief: After the pressing is completed, the pressure is naturally reduced to room temperature, and then the pressure is relieved to normal pressure at a pressure relief rate of 100 MPa / min;

[0075] (6) Tempering treatment: The high carbon chromium bearing steel sample obtained in step (5) is tempered. The specific process parameters are as follows: the furnace temperature is controlled to be ≤100°C, the heating rate is 10°C / min for tempering, and when the temperature is heated to 550°C, it is kept warm for 2.5 hours, and then air-cooled to room temperature to obtain a high carbon chromium bearing steel product after tempering treatment.

[0076] The results obtained in Comparative Example 1, Example 1 and Example 2 are as follows Figure 2 , 3 , 4, from Figure 2 , 3 4. It can be seen that, compared with the high carbon chromium steel after atmospheric pressure heat treatment, the residual compressive stress of the high carbon chromium steel treated by Example 1 of the present application is increased from -452MPa to -848MPa, an increase of 87.61%; the residual compressive stress of the high carbon chromium steel treated by Example 2 is increased to -923MPa, an increase of 104.2%. At the same time, the high carbon chromium steel after atmospheric pressure heat treatment has poor distribution uniformity; the high carbon chromium steel treated by the method of the present invention has a more uniform distribution of residual compressive stress.

[0077] Performance Testing

[0078] The products in Examples 1 and 2 and Comparative Example 1 were subjected to low-cycle fatigue performance tests, and fatigue performance tests were performed using an American INSTRON electro-hydraulic servo fatigue testing machine. The samples were tested according to the method in the standard "GBT 3075-2008 Axial Force Control Method for Fatigue Test of Metallic Materials". In order to ensure that the roughness of the sample surface reaches 0.32 μm, and that there are no circumferential scratches on the parallel section and the transition arc part, the machined sample surface was axially ground using diamond sandpaper with a particle size ranging from 150 to 2000, and the standard for judging fatigue cycle failure is sample fracture.

[0079] Table 7 is the fatigue life comparison results of Examples 1 and 2 and Comparative Example 1.

[0080]

[0081] By conducting rolling contact fatigue life tests on high carbon chromium bearing steels with different treatment processes, it can be seen from Table 7 that under the current experimental conditions, the endurance times of the embodiment are increased by 71.18% and 195.39% compared with the control example, that is, the service life of the high carbon chromium steel treated by the method of the present invention is greatly improved.

[0082] The above embodiments are examples of the implementation methods of the present invention, and the implementation methods of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for improving the residual compressive stress and distribution on the surface of high carbon chromium steel. It is characterized in that The method comprises the following steps: (1) Annealing treatment: The high carbon chromium steel raw material bar is forged, cut into cylindrical billets, and then kept at 850-900°C for 1-2 hours, and then furnace cooled for stress relief annealing; (2) Ultrasonic cleaning: The high carbon chromium bearing steel blank in step (1) is processed into a sample and ultrasonically cleaned; (3) Assembling: assembling the high carbon chromium bearing steel sample obtained in step (2) using a high pressure assembly structure to obtain a high pressure assembly block; (4) Pressing: Pressing the high-pressure assembly block in step (3) at high temperature and high pressure; (5) Pressure relief: After the pressing is completed, the pressure naturally drops to room temperature, and then the pressure is relieved to normal pressure; (6) Tempering treatment: The high carbon chromium bearing steel sample obtained in step (5) is tempered to obtain a tempered high carbon chromium steel product.

2. The method according to claim 1, It is characterized in that The mass percentages of the chemical components of the high carbon chromium bearing steel raw material bar in step (1) are shown in the following table: 。 3. The method according to claim 1, It is characterized in that The assembly method in step (3) is to first cover the sample with ZrO 2 Insulation material, then add graphite tubes and MgO on the front, back, left, and right sides in turn, and add Ti metal sheets and ZrO on the upper and lower sides in turn. 2 Insulation plug, and finally add talc on the outside.

4. The method according to claim 1, It is characterized in that The high temperature and high pressure pressing process in step (4) is to first pressurize to 3-7 GPa at a pressure increase rate of 1.0-1.5 GPa / min, and maintain this pressure for 30-150 minutes; at the same time, heating is performed 2 minutes after the start of the pressure increase, and the heating procedure is to heat to 600-1500°C at a rate of 50-300°C / min, and finally, when the pressure is increased to 3-7 GPa and the temperature is increased to 600-1500°C, it is maintained for 10-60 minutes.

5. The method according to claim 1, It is characterized in that In step (4), during the pressing process, the final pressure error should not exceed ±0.1 GPa.

6. The method according to claim 1, It is characterized in that During the pressing process of step (4), the error of the final temperature should not exceed ±30°C.

7. The method according to claim 1, It is characterized in that In step (6), the tempering treatment process parameters are: controlling the furnace temperature ≤ 100°C, and tempering at a heating rate of 10 to 15°C / min. When the temperature is heated to 550 to 1000°C, the temperature is kept for 1 to 5 hours, and then air-cooled to room temperature.

8. A high carbon chromium steel product produced by the method according to any one of claims 1 to 7.

9. Use of the high carbon chromium steel product according to claim 8 as equipment parts.

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