Method for improving surface hardness and wear resistance of G13Cr4Mo4Ni4V steel through ion nitriding

Abstract

The invention belongs to the technical field of metal materials, and relates to a method for improving the surface hardness and wear resistance of a G13Cr4Mo4Ni4V steel bearing ring through ion nitriding. The method comprises the following steps: step 1, carrying out vacuum quenching and tempering on a G13Cr4Mo4Ni4V bearing steel ferrule which is subjected to carburizing treatment and rough machining; secondly, the bearing steel ferrule subjected to quenching and tempering heat treatment in the first step is ground, and the requirement for part grinding smoothness is met; and thirdly, the ground bearing steel ring is subjected to surface ion nitriding treatment, and the final G13Cr4Mo4Ni4V steel bearing ring is obtained. After the bearing steel ferrule is subjected to carburizing treatment and rough machining, a good matrix structure is obtained through vacuum quenching and tempering, and after rough grinding, ion nitriding treatment is conducted to obtain a high-hardness nitriding layer, so that the hardness and wear resistance of a material surface layer are improved, and the surface hardness and wear resistance of the bearing are improved; therefore, the service life of the machine tool spindle bearing is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of metal materials, and in particular relates to a method for improving the surface hardness and wear resistance of a G13Cr4Mo4Ni4V steel bearing ring by ion nitriding. Background Art

[0002] my country's mid- and low-end CNC machine tools have achieved good substitution for imports, but the poor high-precision retention of domestic high-end CNC machine tools is still the main problem. Among them, the spindle bearings of machine tools work in a high-speed and high-load environment for a long time, and their performance and life seriously affect the accuracy of the whole machine. Regarding improving the comprehensive mechanical properties of G13Cr4Mo4Ni4V bearing steel, there have been a lot of studies on carburizing treatment processes, mainly through the diffusion properties of carbon elements, so that the elements penetrate into the metal surface layer of parts, thereby changing the composition, organization and properties of the surface layer, to improve the strength, hardness and wear resistance of the material. Nitriding treatment is a chemical heat treatment method that can significantly improve the surface hardness, wear resistance and fatigue resistance of bearing rings.

[0003] Conventional atmosphere nitriding and liquid nitriding methods usually require higher temperatures and longer processing times, which not only increases energy consumption, but also reduces production efficiency and even affects the overall production plan. In addition, due to the different shapes, sizes and placement of workpieces, the surface uniformity after nitriding is poor, which may cause significant differences in the thickness and performance of the nitrided layer, leading to product failure in actual use. At the same time, surface brittleness is another key issue. Although the nitriding process can increase the surface hardness, the accompanying brittleness will reduce the toughness and ductility of the material. In some applications, brittleness may cause the material to crack when it is impacted or deformed, thereby affecting the reliability of the product. In addition, workpieces manufactured by conventional nitriding processes will undergo dimensional changes during the nitriding process, which will affect the subsequent processing accuracy. For precision parts with strict requirements such as aviation bearings, such slight changes in size may be enough to affect their normal use.

[0004] Compared with this, ion nitriding technology has shown obvious advantages. Ion nitriding has the characteristics of short processing time, small deformation of workpiece, high uniformity of nitriding layer, etc. At the same time, this process can effectively reduce surface brittleness, improve the toughness and wear resistance of materials, and is suitable for applications requiring high wear resistance. Therefore, a specific ion nitriding method is needed to improve the surface hardness and wear resistance of G13Cr4Mo4Ni4V steel bearing rings. Summary of the invention

[0005] In view of the problems of low surface hardness and poor wear resistance of domestic machine tool spindle bearings, the present invention provides a method for improving the surface hardness and wear resistance of G13Cr4Mo4Ni4V steel bearing rings by ion nitriding. The G13Cr4Mo4Ni4V bearing steel rings in the present invention are subjected to carburizing treatment and rough machining, and then vacuum quenching and tempering are performed to obtain a good matrix structure. After rough grinding, ion nitriding treatment is performed to obtain a high-hardness nitrided layer, thereby improving the hardness and wear resistance of the material surface layer, and improving the surface hardness and wear resistance of the bearing, thereby extending the service life of the machine tool spindle bearings. The present invention is suitable for the preparation of machine tool spindle bearings.

[0006] In order to achieve the above object, the present invention provides the following technical solutions.

[0007] A method for improving the surface hardness and wear resistance of a G13Cr4Mo4Ni4V steel bearing ring by ion nitriding, comprising the following steps: Step 1: vacuum quenching and tempering the G13Cr4Mo4Ni4V bearing steel ring that has been carburized and rough-machined; Step 2: Grind the bearing steel ring that has been quenched and tempered in step 1 to meet the grinding finish requirements of the parts; Step 3: Perform surface ion nitriding treatment on the grinding bearing steel ring to obtain the final G13Cr4Mo4Ni4V steel bearing ring.

[0008] Furthermore, in step one, the temperature of vacuum quenching is 1060-1110°C.

[0009] Furthermore, in step 1, vacuum quenching + tempering is specifically as follows: the bearing steel is placed in a vacuum quenching furnace, and the furnace temperature is required to be less than 200°C before loading the furnace. The quenching furnace is first evacuated and then heated up. When the vacuum degree reaches 5×10 -1 -5×10 -2Pa starts to heat up, the temperature is first raised to 1000-1050℃ at a heating rate of 5-8℃ / min, kept at this temperature for 10-20min, and then raised to 60-90℃ at a rate of 3-5℃ / min. When the temperature reaches 1060-1110℃, it is kept for 0.3-1.5h; after the insulation, high-purity nitrogen is used for cooling, and the nitrogen filling pressure is required to be 0.3~0.6MPa in the high-temperature stage of 1110℃~550℃. The fan is used to stir the gas for cooling, and the cooling capacity is sufficient to cool the surface temperature of the bearing ring to less than or equal to 550℃ within 1-10min, and then the filling pressure is adjusted to 0.1~0.2MPa, and the bearing ring is cooled to below 200℃ within 5min, and then the filling pressure is adjusted to <0.1MPa, and the bearing The ferrule is slowly cooled to less than or equal to 40°C, and the slow cooling time is controlled at 25-35min; after cooling to a temperature of less than 40°C, the time interval is less than 2h, and cold treatment is carried out, the cooling rate of the cold treatment is 2-3°C / min, the cold treatment temperature is -65°C~-75°C, and the insulation time is 2h~3h. After the insulation is completed, it is heated to room temperature at a rate of 2-3°C / min, and then heated to 80°C at a rate of 3-5°C / min; after the cold treatment, the time interval is less than 4h, and tempering treatment is carried out, the tempering treatment heating rate is 5-8°C / min, heated to 520-560°C, and the insulation time is 1.5-3h. After the insulation is completed, it is cooled with nitrogen at a pressure of 0.15~0.2MPa, cooled to a temperature of less than 40°C and taken out of the furnace; cold treatment and tempering treatment are then carried out, and a total of three cold treatments and three tempering treatments are carried out.

[0010] Furthermore, in step 2, the bearing ring is rough ground with a grinding wheel, and the surface residue after rough grinding is less than 0.1 mm.

[0011] Further, in step 3, the furnace is loaded at room temperature, then evacuated to 300 Pa, and then filled with NH 3 The gas flow rate of ammonia is 1200~1500mL / min, and then the temperature is raised to the ion nitriding temperature at a rate of 120℃ / h. The nitriding temperature is 450~550℃, the nitriding holding time is 20~30h, the current during nitriding is 60~70A, the nitriding voltage is 650~700V, the duty cycle is 40~45%, and it is cooled to below 80℃ and taken out of the furnace.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows.

[0013] In step one, vacuum quenching and tempering of the workpiece before nitriding can enhance the thermal stability of the material, reduce deformation during the nitriding process, and optimize the microstructure of the material so that it can obtain a more ideal nitriding layer structure during the subsequent nitriding process.

[0014] In step 2, grinding the workpiece and leaving a margin of less than 0.1 mm can improve the nitriding efficiency and reduce the impact of brittleness on the performance of the workpiece.

[0015] In step three, the nitriding temperature is 450~550℃, which is lower than the tempering temperature of the workpiece. The lower nitriding temperature can control the diffusion rate of nitrogen during the nitriding process, prevent the excessively fast nitriding rate from causing the accumulation of nitrogen in areas such as grain boundaries, forming vein-like structures, and reducing the diffusion capacity of nitrogen. At the same time, the lower nitriding temperature can ensure that a large amount of austenite structure is not formed on the surface during the nitriding process, thereby affecting the hardness and wear resistance of the steel and the dimensional stability of the steel. The nitriding temperature between 450℃ and 550℃ ensures a high nitriding efficiency while effectively alleviating the decrease in the hardness of the matrix structure caused by the excessively high insulation temperature. Ion nitriding treatment of the workpiece can obtain a uniform nitriding layer. The nitriding temperature of 450-550℃ can effectively reduce the thermal deformation of the material during the nitriding treatment and ensure the dimensional accuracy of the workpiece. At the same time, the nitriding time is short, which can improve production efficiency compared to traditional nitriding methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a comparison chart of Rockwell hardness of G13Cr4Mo4Ni4V bearing steel rings before and after nitriding.

[0017] Figure 2 The Vickers hardness comparison diagram of the G13Cr4Mo4Ni4V bearing steel ring before and after nitriding (a, without nitriding, b, Example 1, c, Example 2, d, Example 3).

[0018] Figure 3 This is a comparison chart of the friction coefficient of the G13Cr4Mo4Ni4V bearing steel ring before and after nitriding in Example 1.

[0019] Figure 4 This is a comparison chart of the wear amount and average friction coefficient of the G13Cr4Mo4Ni4V bearing steel ring before and after nitriding.

[0020] Figure 5 Comparison of the three-dimensional morphology of the wear marks on the G13Cr4Mo4Ni4V bearing steel ring before and after nitriding in Example 1 (a, without nitriding, b, Example 1).

[0021] Figure 6 This is a two-dimensional cross-sectional comparison diagram of the wear scar of the G13Cr4Mo4Ni4V bearing steel ring before and after nitriding in Example 1 (a, without nitriding, b, Example 1).

[0022] Figure 7 This is an electron microscope comparison of the wear scar surface of the G13Cr4Mo4Ni4V bearing steel ring before and after nitriding in Example 1. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] A method for improving the surface hardness and wear resistance of a G13Cr4Mo4Ni4V steel bearing ring by ion nitriding, comprising the following steps: Step 1: Vacuum quenching and tempering of the G13Cr4Mo4Ni4V bearing steel rings that have been carburized and rough-machined; quenching is carried out under vacuum conditions, and the vacuum quenching temperature is 1060-1110°C. Put the bearing steel into a vacuum quenching furnace. Before loading the furnace, the furnace temperature is required to be less than 200°C. First, evacuate the quenching furnace and then increase the temperature. When the vacuum degree reaches 5×10 -1 -5×10 -2 Pa starts to heat up. The heating is that the furnace temperature is first heated to 1000-1050℃ at a heating rate of 5-8℃ / min, and kept at this temperature for 10-20min, and then heated to 60-90℃ at a rate of 3-5℃ / min. When the temperature reaches 1060-1110℃, it is kept for 0.3-1.5h. The specific holding time is determined according to the wall thickness of the part; after the insulation, high-purity nitrogen is used for cooling. The nitrogen filling pressure is required to be 0.3~0.6MPa in the high temperature stage of 1110℃~550℃. The fan is used to stir the gas to circulate the gas to take away the heat. The gas circulation mode is from top to bottom, and it quickly passes through the horizontally placed bearing rings, so that the bearing rings have the same cooling rate in the circumferential direction. The cooling capacity is sufficient to cool the surface temperature of the bearing ring to less than or equal to 550℃ within 1-10min, and then the filling pressure is adjusted to 0.1~0.2MPa. min, then adjust the inflation pressure to <0.1MPa, slowly cool the bearing ring to less than or equal to 40℃, and control the slow cooling time to 25-35min; after cooling to a temperature of <40℃, the time interval is <2h, and cold treatment is carried out, the cooling rate of cold treatment is 2-3℃ / min, the cold treatment temperature is -65℃~-75℃, and the insulation time is 2h~3h. After the insulation is completed, the temperature is raised to room temperature at a rate of 2-3℃ / min, and then raised to 80℃ at a rate of 3-5℃ / min to prevent rust caused by condensation of water vapor; after the cold treatment, the time interval is <4h, and tempering treatment is carried out, the tempering treatment heating rate is 5-8℃ / min, heated to 520-560℃, and the insulation time is 1.5-3h. After the insulation is completed, the nitrogen pressure is 0.15~0.2MPa for cooling, and it is cooled to a temperature of <40℃ and taken out of the furnace. Then cold treatment and tempering treatment are carried out, a total of three cold treatments and three tempering treatments are carried out.

[0025] Step 2: Grind the bearing steel ring that has completed quenching + tempering heat treatment in step 1 to meet the grinding finish requirements of the parts; use a grinding wheel to rough grind the bearing ring, and the surface retention after rough grinding is less than 0.1mm, which is used for the grinding removal amount of the surface after nitriding treatment to prevent grinding burns and tempering on the grinding surface.

[0026] Step 3: Perform surface ion nitriding treatment on the grinding bearing steel ring; load the furnace at room temperature, evacuate to 300Pa, and then fill with NH 3 The gas flow rate of ammonia is 1200~1500mL / min, and then the temperature is raised to the ion nitriding temperature at a rate of 120℃ / h, the nitriding temperature is 450~550℃, the nitriding holding time is 20~30h, the current during nitriding is 60~70A, the nitriding voltage is 650~700V, the duty cycle is 40~45%, and it is cooled to below 80℃ and taken out of the furnace to obtain the final G13Cr4Mo4Ni4V steel bearing ring.

[0027] Example 1.

[0028] A method for improving the surface hardness and wear resistance of a G13Cr4Mo4Ni4V steel bearing ring by ion nitriding, comprising the following steps: Step 1: Vacuum quenching and tempering of the G13Cr4Mo4Ni4V bearing steel rings that have been carburized and rough-machined; quenching is carried out under vacuum conditions, and the vacuum quenching temperature is 1090°C. Put the bearing steel into a vacuum quenching furnace. Before loading the furnace, the furnace temperature is required to be 180°C. First, evacuate the quenching furnace and then increase the temperature. When the vacuum degree reaches 5×10 -2Pa starts to heat up. The temperature is first raised to 1020℃ at a heating rate of 8℃ / min, kept at this temperature for 20min, and then raised to 70℃ at a rate of 5℃ / min. When the temperature reaches 1090℃, it is kept for 1.0h. After the insulation, high-purity nitrogen is used for cooling. The nitrogen filling pressure is 0.4MPa in the high-temperature stage of 1110℃~550℃. The fan is used to stir the gas so that the gas circulates and takes away the heat. The gas circulates from top to bottom and quickly passes through the horizontally placed bearing rings, so that the bearing rings have the same cooling rate in the circumferential direction. The surface temperature of the bearing rings is cooled to 545℃ within 5min, and then the filling pressure is adjusted to 0.2MPa. The bearing rings are cooled to 190℃ within 5min, and then the filling pressure is adjusted to 0.05MPa. The bearing rings are slowly cooled to 39℃, and the slow cooling time is controlled at 30min. After cooling to 39°C, the temperature is cooled at a time interval of 1.5 hours. The cooling rate of the cold treatment is 3°C / min, the cold treatment temperature is -70°C, and the insulation time is 2.5 hours. After the insulation is completed, the temperature is raised to room temperature at a rate of 3°C / min, and then raised to 80°C at a rate of 5°C / min to prevent rust problems caused by condensation of water vapor. After the cold treatment, the tempering treatment is carried out at a time interval of 2 hours. The tempering treatment heating rate is 8°C / min, heated to 545°C, and the insulation time is 2.5 hours. After the insulation is completed, the nitrogen pressure is 0.15MPa for cooling, and it is cooled to 38°C and taken out of the furnace. Cold treatment and tempering treatment are carried out again, and a total of three cold treatments and three tempering treatments are carried out.

[0029] Step 2: Grind the bearing steel ring that has been quenched and tempered in step 1 to meet the grinding finish requirements of the parts; use a grinding wheel to rough grind the bearing ring, leaving 0.08mm on the surface after rough grinding, which is used to remove the surface after nitriding treatment. Prevent grinding burns and tempering on the grinding surface.

[0030] Step 3: Perform surface ion nitriding treatment on the grinding bearing steel ring; load the furnace at room temperature, evacuate to 300Pa, and then fill with NH 3 The gas was heated at a rate of 120 °C / h to an ion nitriding temperature of 470 °C, a nitriding holding time of 25 h, a current of 65 A, a nitriding voltage of 700 V, a duty cycle of 44%, and then cooled to 75 °C before being taken out of the furnace to obtain the final G13Cr4Mo4Ni4V steel bearing ring.

[0031] After nitriding treatment, the Rockwell hardness and Vickers hardness of the surface of the unnitrided and nitrided samples were tested, and the hardness values ​​were recorded and compared. The samples were weighed before the friction and wear test, first cleaned with ultrasonic waves, then sprayed with alcohol, and blown dry with a hair dryer. The samples were weighed 5-10 times, and the initial weight of the samples was recorded (retaining four significant digits). Then the samples were installed on the fixture of the reciprocating friction and wear tester, and the vertical test force was set to 0.5kN, the number of reciprocating times: 7200 times, the time: 7200s, the frequency: 1Hz, the amplitude: 8mm, and the special oil for aviation bearings was used for lubrication. After the friction and wear test, the samples were cleaned again with ultrasonic waves, sprayed with alcohol, and blown dry with a hair dryer. They were weighed again 5-10 times, and the experimental data were recorded for comparison. The three-dimensional morphology and two-dimensional cross-sectional profile morphology of the wear scars were recorded with an ultra-depth of field microscope, and finally the wear scar morphology was observed with a scanning electron microscope.

[0032] Determination of the surface Rockwell hardness of G13Cr4Mo4Ni4V steel after tempering and nitriding, such as Figure 1 As shown in the figure, the surface hardness of G13Cr4Mo4Ni4V steel after tempering reaches 61.58HRC, and the surface hardness of nitrided G13Cr4Mo4Ni4V steel reaches 63.78HRC. Surface Vickers hardness measurement, such as Figure 2 As shown in (a), it can be seen that the surface Vickers hardness of G13Cr4Mo4Ni4V steel before nitriding is as high as 773.6HV1. Figure 2 As shown in (b), the maximum Vickers hardness of the surface after nitriding can reach 1006.5HV1, and the effective nitrided layer thickness is 0.137mm. The nitrided G13Cr4Mo4Ni4V steel was subjected to a reciprocating friction and wear test, and the friction coefficient was recorded, such as Figure 3 As shown in the figure, the friction coefficient of G13Cr4Mo4Ni4V steel has an overall trend of first rising, then falling and finally stabilizing. It can be clearly seen that the friction coefficient of nitrided G13Cr4Mo4Ni4V steel is significantly lower than that of unnitrided G13Cr4Mo4Ni4V steel. The smaller the friction coefficient, the better the wear resistance. Record the wear amount and average friction coefficient, such as Figure 4 As shown in the figure, it can be seen that the wear volume has decreased significantly after nitriding, and the average friction coefficient has also decreased slightly. The three-dimensional wear scar morphology and wear scar width of the reciprocating friction and wear test are shown in the figure. Figure 5 As shown in the figure, the maximum depth of the wear scar after nitriding is much smaller than that of the non-nitrided sample. Figure 6 As shown in the figure, the width of the wear scar after nitriding becomes much narrower. In the reciprocating friction and wear test, the wear scar image under the scanning electron microscope is recorded after wear, as shown in the figure. Figure 7As shown in the figure, the wear scars without nitriding have a lot of plowing grooves and fewer spalling pits, which are mainly caused by abrasive wear. However, the wear scars after nitriding have fewer plowing grooves and more spalling pits, which are typical adhesive wear types.

[0033] Example 2.

[0034] A method for improving the surface hardness and wear resistance of a G13Cr4Mo4Ni4V steel bearing ring by ion nitriding, comprising the following steps: Step 1: Vacuum quenching and tempering of the G13Cr4Mo4Ni4V bearing steel rings that have been carburized and rough-machined; quenching is carried out under vacuum conditions, and the vacuum quenching temperature is 1090°C. Put the bearing steel into a vacuum quenching furnace. Before loading the furnace, the furnace temperature is required to be 100°C. First, evacuate the quenching furnace and then increase the temperature. When the vacuum degree reaches 5×10 -2 Pa starts to heat up. The temperature is first raised to 1020℃ at a heating rate of 8℃ / min, kept at this temperature for 20min, and then raised by 70℃ at a rate of 5℃ / min. When the temperature reaches 1090℃, it is kept for 1.0h. After the insulation, high-purity nitrogen is used for cooling. The nitrogen filling pressure is required to be 0.4MPa in the high-temperature stage of 1110℃~550℃. The fan is used to stir the gas so that the gas circulates and takes away the heat. The gas circulates from top to bottom and quickly passes through the horizontally placed bearing rings to make the bearing rings cool at the same speed in the circumferential direction. The surface temperature of the bearing rings is cooled to 550℃ within 5min, and then the filling pressure is adjusted to 0.2MPa. The bearing rings are cooled within 5min. Cool to 198℃, then adjust the inflation pressure to 0.05MPa, and slowly cool the bearing ring to 37℃, and the slow cooling time is controlled at 32min; after cooling to 37℃, the time interval is 1.5h, and cold treatment is carried out, the cooling rate of cold treatment is 3℃ / min, the cold treatment temperature is -70℃, and the insulation time is 2.5h. After the insulation is completed, the temperature is raised to room temperature at a rate of 3℃ / min, and then raised to 80℃ at a rate of 5℃ / min to prevent rust caused by water vapor condensation; after cold treatment, the time interval is 3h, and tempering treatment is carried out, the tempering treatment heating rate is 8℃ / min, heated to 545℃, and the insulation time is 2.5h. After the insulation is completed, the nitrogen pressure is 0.15MPa for cooling, and it is cooled to 35℃ and taken out of the furnace. Cold treatment and tempering treatment are carried out again, and a total of three cold treatments and three tempering treatments are carried out.

[0035] Step 2: Grind the bearing steel ring that has completed quenching + tempering heat treatment in step 1 to meet the grinding finish requirements of the parts; use a grinding wheel to rough-grind the bearing ring, leaving 0.07mm on the surface after rough grinding, which is used to grind and remove the surface after nitriding treatment to prevent grinding burns and tempering on the grinding surface.

[0036] Step 3: Perform surface ion nitriding treatment on the grinding bearing steel ring; load the furnace at room temperature, evacuate to 300Pa, and then fill with NH 3 The gas was heated at a rate of 120 °C / h to an ion nitriding temperature of 540 °C, a nitriding holding time of 25 h, a current of 66 A, a nitriding voltage of 700 V, a duty cycle of 45%, and then cooled to 60 °C before being taken out of the furnace to obtain the final G13Cr4Mo4Ni4V steel bearing ring.

[0037] After nitriding treatment, the Rockwell hardness and Vickers hardness of the surface of the sample were tested, and the hardness values ​​were recorded and compared. The sample was weighed before the friction and wear test, first cleaned with ultrasonic waves, then sprayed with alcohol, and blown dry with a hair dryer. The sample was weighed 5-10 times, and the initial weight of the sample was recorded (retain four significant digits), and then the sample was installed on the fixture of the reciprocating friction and wear tester, and the vertical test force was set to 0.5kN, the number of reciprocating times: 7200 times, the time: 7200s, the frequency: 1Hz, the amplitude: 8mm, and the special oil for aviation bearings was used for lubrication. After the friction and wear test, the sample was cleaned again with ultrasonic waves, sprayed with alcohol, and blown dry with a hair dryer, and weighed again 5-10 times, and the experimental data was recorded for comparison.

[0038] The surface hardness of nitrided G13Cr4Mo4Ni4V steel is as follows: Figure 1 As shown, it reached 63.55HRC; the surface Vickers hardness measurement results, such as Figure 2 As shown in (c), the maximum Vickers hardness of the surface can reach 983.3HV1, and the effective nitrided layer thickness is 0.158mm. The wear loss of nitrided G13Cr4Mo4Ni4V steel is 4.98mg, and the average friction coefficient is 0.1807. Figure 4 shown.

[0039] Example 3.

[0040] A method for improving the surface hardness and wear resistance of a G13Cr4Mo4Ni4V steel bearing ring by ion nitriding, comprising the following steps: Step 1: Vacuum quenching and tempering of the G13Cr4Mo4Ni4V bearing steel rings that have been carburized and rough-machined; quenching is carried out under vacuum conditions, and the vacuum quenching temperature is 1090°C. Put the bearing steel into a vacuum quenching furnace. Before loading the furnace, the furnace temperature is required to be 50°C. First, evacuate the quenching furnace and then increase the temperature. When the vacuum degree reaches 5×10 -2Pa starts to heat up. The temperature is first raised to 1020℃ at a heating rate of 8℃ / min, kept at this temperature for 20min, and then raised by 70℃ at a rate of 5℃ / min. When the temperature reaches 1090℃, it is kept for 1.5h. After the insulation, high-purity nitrogen is used for cooling. The nitrogen filling pressure is required to be 0.45MPa in the high-temperature stage of 1110℃~550℃. The fan is used to stir the gas so that the gas circulates to take away the heat. The gas circulates from top to bottom and quickly passes through the horizontally placed bearing rings to make the bearing rings have the same cooling rate in the circumferential direction. The surface temperature of the bearing rings is cooled to 548℃ within 5min, and then the filling pressure is adjusted to 0.2MPa. The bearing rings are cooled within 5min. To 195℃, then adjust the inflation pressure to 0.05MPa, slowly cool the bearing ring to 38℃, and control the slow cooling time to 31min; after cooling to 38℃, the time interval is 1.7h, cold treatment is carried out, the cooling rate of cold treatment is 3℃ / min, the cold treatment temperature is -70℃, and the insulation time is 2.5h. After the insulation is completed, the temperature is raised to room temperature at a rate of 3℃ / min, and then raised to 80℃ at a rate of 5℃ / min to prevent rust caused by water vapor condensation; after the cold treatment, the time interval is 1.5h, tempering treatment is carried out, the tempering treatment heating rate is 8℃ / min, heated to 545℃, and the insulation time is 2.5h. After the insulation is completed, the nitrogen pressure is 0.15MPa for cooling, and it is cooled to a temperature of 37℃ and taken out of the furnace. Cold treatment and tempering treatment are carried out again, and a total of three cold treatments and three tempering treatments are carried out.

[0041] Step 2: Grind the bearing steel ring that has completed quenching + tempering heat treatment in step 1 to meet the grinding finish requirements of the parts; use a grinding wheel to rough grind the bearing ring, leaving 0.06mm on the surface after rough grinding, which is used to grind and remove the surface after nitriding treatment to prevent grinding burns and tempering on the grinding surface.

[0042] Step 3: Perform surface ion nitriding treatment on the grinding bearing steel ring; load the furnace at room temperature, evacuate to 300Pa, and then fill with NH 3 The gas was heated at a rate of 120 °C / h to an ion nitriding temperature of 520 °C, a nitriding holding time of 25 h, a current of 65 A, a nitriding voltage of 700 V, a duty cycle of 42%, and then cooled to 50 °C and taken out of the furnace to obtain the final G13Cr4Mo4Ni4V steel bearing ring.

[0043] After nitriding treatment, the Rockwell hardness and Vickers hardness of the surface of the sample were tested, and the hardness values ​​were recorded and compared. The sample was weighed before the friction and wear test, first cleaned with ultrasonic waves, then sprayed with alcohol, and blown dry with a hair dryer. The sample was weighed 5-10 times, and the initial weight of the sample was recorded (retain four significant digits), and then the sample was installed on the fixture of the reciprocating friction and wear tester, and the vertical test force was set to 0.5kN, the number of reciprocating times: 7200 times, the time: 7200s, the frequency: 1Hz, the amplitude: 8mm, and the special oil for aviation bearings was used for lubrication. After the friction and wear test, the sample was cleaned again with ultrasonic waves, sprayed with alcohol, and blown dry with a hair dryer, and weighed again 5-10 times, and the experimental data was recorded for comparison.

[0044] The surface hardness of nitrided G13Cr4Mo4Ni4V steel is as follows: Figure 1 As shown, it reached 63.4HRC; the surface Vickers hardness measurement results, such as Figure 2 As shown in (d), the maximum Vickers hardness of the surface can reach 1089.0HV1, and the effective nitrided layer thickness is 0.30mm. The wear loss of nitrided G13Cr4Mo4Ni4V steel is 4.35mg, and the average friction coefficient is 0.1805. Figure 4 shown.

Claims

1. A method for improving the surface hardness and wear resistance of a G13Cr4Mo4Ni4V steel bearing ring by ion nitriding, characterized in that: The following steps are involved: Step 1: vacuum quenching and tempering the G13Cr4Mo4Ni4V bearing steel ring that has been carburized and rough-machined; Step 2: Grind the bearing steel ring that has been quenched and tempered in step 1 to meet the grinding finish requirements of the parts; Step 3: Perform surface ion nitriding treatment on the grinding bearing steel ring to obtain the final G13Cr4Mo4Ni4V steel bearing ring.

2. The method for improving the surface hardness and wear resistance of a G13Cr4Mo4Ni4V steel bearing ring by ion nitriding according to claim 1, characterized in that: In the step 1, the temperature of vacuum quenching is 1060-1110°C.

3. The method for improving the surface hardness and wear resistance of a G13Cr4Mo4Ni4V steel bearing ring by ion nitriding according to claim 1, characterized in that: In step 1, vacuum quenching + tempering is specifically as follows: the bearing steel is placed in a vacuum quenching furnace, and the furnace temperature is required to be less than 200°C before loading the furnace. The quenching furnace is first evacuated and then heated up. When the vacuum degree reaches 5×10 -1 -5×10 -2 Pa starts to heat up, the temperature is first raised to 1000-1050℃ at a heating rate of 5-8℃ / min, kept at this temperature for 10-20min, and then raised to 60-90℃ at a rate of 3-5℃ / min. When the temperature reaches 1060-1110℃, it is kept for 0.3-1.5h; after the insulation, high-purity nitrogen is used for cooling, and the nitrogen filling pressure is required to be 0.3~0.6MPa in the high temperature stage of 1110℃~550℃. The fan is used to stir the gas for cooling, and the cooling capacity is sufficient to cool the surface temperature of the bearing ring to less than or equal to 550℃ within 1-3min, and then the filling pressure is adjusted to 0.1~0.2MPa, and the bearing ring is cooled to below 200℃ within 5min, and then the filling pressure is adjusted to <0.1MPa, and the bearing The ferrule is slowly cooled to less than or equal to 40°C, and the slow cooling time is controlled at 25-35min; after cooling to a temperature of less than 40°C, the time interval is less than 2h, and cold treatment is carried out, the cooling rate of the cold treatment is 2-3°C / min, the cold treatment temperature is -65°C~-75°C, and the insulation time is 2h~3h. After the insulation is completed, it is heated to room temperature at a rate of 2-3°C / min, and then heated to 80°C at a rate of 3-5°C / min; after the cold treatment, the time interval is less than 4h, and tempering treatment is carried out, the tempering treatment heating rate is 5-8°C / min, heated to 520-560°C, and the insulation time is 1.5-3h. After the insulation is completed, it is cooled with nitrogen at a pressure of 0.15~0.2MPa, cooled to a temperature of less than 40°C and taken out of the furnace; cold treatment and tempering treatment are then carried out, and a total of three cold treatments and three tempering treatments are carried out.

4. The method for improving the surface hardness and wear resistance of a G13Cr4Mo4Ni4V steel bearing ring by ion nitriding according to claim 1, characterized in that: In the step 2, the bearing ring is roughly ground with a grinding wheel, and the surface residue after rough grinding is less than 0.1 mm.

5. The method for improving the surface hardness and wear resistance of G13Cr4Mo4Ni4V steel bearing rings by ion nitriding according to claim 1, characterized in that: In the step three, the furnace is loaded at room temperature, then evacuated to 300Pa, and then filled with NH3 gas from which water vapor has been removed, with an ammonia flow rate of 1200-1500mL / min, and then heated to the ion nitriding temperature at a rate of 120°C / h, the nitriding temperature is 450-550°C, the nitriding holding time is 20-30h, the current during nitriding is 60-70A, the nitriding voltage is 650-700V, the duty cycle is 40-45%, and the furnace is cooled to below 80°C and taken out of the furnace.

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