Surface strengthening method of bearing steel and bearing steel

Abstract

The application provides a surface strengthening method of bearing steel and bearing steel, and comprises the following steps: step (1): performing surface gradient micro-nanometer treatment on the bearing steel to form a nano-micron gradient structure on the surface of the bearing steel; and the nano-micron gradient structure forms a gradient strengthening layer on the surface of the bearing steel. According to the surface strengthening method of bearing steel and the bearing steel, the surface of the bearing steel can be effectively strengthened.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material processing, and particularly relates to a surface strengthening method of bearing steel and bearing steel. BACKGROUND

[0002] A large number of examples show that the main forms of failure of aero bearings are surface contact fatigue failure and friction and wear failure, and the core is generally kept intact, so that a suitable surface treatment process of bearing steel is crucial to the reliability of the bearing. The high-temperature steel currently used most widely for aero bearings is M50 steel; compared with the traditional bearing steel GCr15, the steel has better dimensional stability and higher hardness under high-temperature conditions. Therefore, the M50 steel has been widely applied in high-end equipment fields such as aero engines, spacecraft, and warships which often bear high temperature, high speed, and heavy load. The most prominent advantage of the M50 steel is that it can serve for a long time below 315 DEG C, can maintain good dimensional stability and contact fatigue performance under high temperature, and has sufficiently high hardness and strength, and the strengthened layer prepared on the surface of the M50 steel for aero bearings must have good thermal stability.

[0003] At present, the main methods and ways to improve the surface performance of the M50 steel include:

[0004] (1) A hard and wear-resistant coating or a coating with a low friction coefficient is deposited on the substrate through surface coating technology, beam ion implantation technology, and ion beam assisted deposition technology.

[0005] (2) A high-hardness, wear-reducing, and wear-resistant modified permeation layer is prepared through nitriding, carburizing, and plasma carburizing methods.

[0006] (3) A strengthened layer with high residual stress is prepared through high-current pulsed electron beam irradiation, shot peening treatment, laser shock peening strengthening, deep rolling treatment, and surface mechanical grinding technology.

[0007] However, the above methods have certain problems in actual production and service practice, and the specific reflection conditions are as follows:

[0008] (1) The surface coating technology is simple to operate, low in cost, and can obtain a relatively thick strengthened layer, but the film-substrate adhesion is poor, and the film layer is easy to fall off. The beam ion implantation modification layer has strong adhesion between the substrate, but the beam ion implantation technology has the limitation of directivity, resulting in poor uniformity of the injection dose, low processing efficiency, and high cost, which is difficult to be applied in the bearing production industry. The ion beam assisted deposition technology combines surface coating and beam ion implantation, which can obtain a relatively thick deposition layer on the material surface, has strong film-substrate adhesion, and can obtain more significant strengthening effect than single surface coating and single ion implantation, but it still has the limitation of directivity of ion beam technology, is not suitable for processing parts with complex shapes, and has high processing cost.

[0009] (2) Nitriding, carburizing process is more complex and has a certain pollution; the high temperature environment of the nitriding, carburizing process thickens the permeation layer, but softens the matrix, and the grains grow, damaging the service performance of the bearing; the uniformity, depth and organization consistency of the permeation layer are also the short board that restricts its wide application.

[0010] (3) Strong current pulse electron beam irradiation is easy to produce large size crater defects (about 70 μm). Shot peening, laser shock peening and surface mechanical grinding technology can all prepare gradient strengthening layers. However, the disadvantages of shot peening, laser shock peening and surface mechanical grinding are that the surface roughness of the prepared sample is high, and the subsequent ultra-precision process has a large removal amount, which is not conducive to bearing production. Deep rolling treatment can reduce the surface roughness of the workpiece. However, the traditional deep rolling treatment has a short tool life, high comprehensive use cost, and causes great damage to the precision and service life of the machine tool.

[0011] Therefore, how to provide a bearing steel surface strengthening method and bearing steel capable of effectively strengthening the surface of bearing steel has become a problem that those skilled in the art urgently need to solve. SUMMARY

[0012] Therefore, the technical problem to be solved by the present application is to provide a bearing steel surface strengthening method and bearing steel capable of effectively strengthening the surface of bearing steel.

[0013] In order to solve the above problems, the present application provides a bearing steel surface strengthening method, comprising the following steps:

[0014] Step (1): surface gradient micro-nano treatment is performed on the bearing steel to form a nano-micron gradient structure on the surface of the bearing steel; the nano-micron gradient structure forms a gradient strengthening layer on the surface of the bearing steel.

[0015] Further, in step (1), the equipment used for surface gradient micro-nano treatment of the bearing steel is a micro-nano machining equipment; the micro-nano machining equipment includes a machining tool; the machining tool can roll / roll on the surface of the bearing steel to cause plastic deformation of the surface of the bearing steel to obtain a nano-micron gradient structure.

[0016] Further, the surface gradient micro-nano treatment of the bearing steel comprises the following steps:

[0017] First pass treatment: the tool bit of the machining tool is pressed into the rotating bearing steel surface for the first time, and at the same time, the tool bit of the machining tool is fed along the axial direction of the bearing steel or the direction perpendicular to the bearing steel rotation surface;

[0018] Further, according to the surface area of the bearing steel and the machining efficiency of the machining tool, the peripheral linear speed v1 and the feed speed v2 of the bearing steel rotation are controlled;

[0019] Further, in the first pass processing, the bearing steel rotates at a peripheral linear speed v1 = 50-800 mm / s; and / or, the first pressing depth a p = 20-100 μm; and / or, the feeding speed v2 = 1 x 10 -3 -2 x 10 -1 mm / r.

[0020] Further, the surface gradient micro-nano processing of the bearing steel further comprises the following steps:

[0021] The nth pass processing: the tool head of the machining tool is pressed into the surface of the rotating bearing steel for the nth time, and the tool head of the machining tool is fed along the axial direction of the bearing steel or the direction perpendicular to the bearing steel surface; wherein n = 1-8;

[0022] Further, in the nth pass processing, the bearing steel rotates at a peripheral linear speed v1 = 50-800 mm / s; and / or, the nth pressing depth a p *n; and / or, the feeding speed v2 = 1 x 10 -3 -2 x 10 -1 mm / r.

[0023] And / or, according to the surface strengthening requirements of the bearing steel and the principle of non-damage to the processed surface, the pressing depth and the pressing pass of the first pressing are controlled; and / or, according to the surface strengthening requirements of the bearing steel and the principle of non-damage to the processed surface, the pressing depth a p and the pressing pass n of the first pressing are controlled.

[0024] Further, the micro-nano processing equipment comprises a surface mechanical rolling processing device, and the surface mechanical rolling processing device comprises a rolling ball which can freely roll and forms a machining tool; further, the material of the rolling ball is WC-Co cemented carbide; and / or, the diameter of the rolling ball is 4-10 mm.

[0025] Alternatively, the micro-nano processing equipment comprises a surface mechanical rolling processing device, and the surface mechanical rolling processing device comprises a fixed ball which forms a machining tool; further, the material of the fixed ball is WC-Co cemented carbide; and / or, the diameter of the fixed ball is 4-10 mm.

[0026] Further, the micro-nano processing equipment comprises an oily lubrication cooling system; the oily lubrication cooling system can provide oily cooling liquid; in the process of the surface gradient micro-nano processing of the bearing steel in step (1), the oily lubrication cooling system can lubricate and cool the bearing steel.

[0027] Further, the following steps are further included:

[0028] Step (2): heat treating the bearing steel after step (1) to relax the martensite substructure interface on the nano-micro gradient structure, and then form a stable strengthening layer;

[0029] Further, the temperature of the heat treatment is 300-550℃; and / or, the time of the heat treatment is 1-20h.

[0030] Further, the thickness of the gradient strengthening layer is 150-1000μm; and / or, the microhardness peak value of the gradient strengthening layer exceeds 9GPa; and / or, the surface residual compressive stress of the gradient strengthening layer is greater than 500MPa.

[0031] And / or, the bearing steel comprises M50 steel.

[0032] Further, before step (1), further comprising the following steps:

[0033] Grinding the surface of the bearing steel.

[0034] According to still another aspect of the present application, a bearing steel is provided, which is obtained after the bearing steel is treated by the surface strengthening method of the bearing steel described above.

[0035] The surface strengthening method of the bearing steel and the bearing steel provided by the present application have the following advantages: the surface strengthening method of the bearing steel is simple to implement, and during the process of gradient micro-nano treatment of the surface of the bearing steel, local high-speed deformation is generated on the surface of the bearing steel, dislocations are generated in the martensite of the surface layer and subsurface layer of the bearing steel and are entangled, thereby strengthening the surface of the bearing steel and enhancing the surface strength of the bearing steel; after the surface of the bearing steel is treated by the surface gradient micro-nano treatment, the surface roughness of the M50 steel is lower than that in the rough grinding and fine grinding states, the Ra value is less than 0.2μm, the thickness of the gradient strengthening layer on the surface of the M50 steel is 150-1000μm, the microhardness peak value of the surface layer is more than 9GPa, the surface residual compressive stress is greater than 500MPa, and the M50 steel has excellent thermal stability at 400℃; the surface of the bearing steel can be effectively strengthened. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The structural schematic diagram of the surface gradient micro-nano treatment in the embodiments;

[0037] Figure 2 The organizational structure diagram of the M50 steel;

[0038] Figure 3 The organizational structure diagram of the M50 steel after the SMRT and 400℃ heat treatment for 2h;

[0039] Figure 4 The nano-micro gradient structure characteristic size diagram of the M50 steel after the SMRT and 400℃ heat treatment for 2h

[0040] Figure 5 Surface forming photo of M50 steel after SMRT treatment in the example;

[0041] Figure 6 Microhardness distribution of gradient strengthening layer of SMGT treated M50 steel for aviation bearing in the example;

[0042] Figure 7 Microhardness distribution of gradient strengthening layer of SMRT treated M50 steel for aviation bearing after 300℃ heat treatment for 2h in the example;

[0043] Figure 8 Microhardness distribution of gradient strengthening layer of SMRT treated M50 steel for aviation bearing after 400℃ heat treatment for 2h in the example;

[0044] Figure 9 Rolling contact fatigue performance comparison of M50 steel with gradient strengthening layer and original sample in the example. DETAILED DESCRIPTION

[0045] In connection with Figures 1-9 As shown in the figure, a surface strengthening method of bearing steel comprises the following steps:

[0046] Step (1): surface gradient micro-nano treatment is performed on the bearing steel to form a nano-micro gradient structure on the surface of the bearing steel; the nano-micro gradient structure forms a gradient strengthening layer on the surface of the bearing steel. The bearing steel in the present application is M50 steel for aviation bearing.

[0047] The surface strengthening method of the bearing steel in the present application is simple in implementation. During the surface gradient micro-nano treatment of the bearing steel, local high-speed deformation is generated on the surface of the bearing steel, dislocations are generated and entangled in the martensite of the surface layer and subsurface layer of the bearing steel, and the surface of the bearing steel is thus strengthened, thereby enhancing the surface strength of the bearing steel. After the surface gradient micro-nano treatment of the bearing steel, the surface roughness of the M50 steel is lower than that in the rough grinding and fine grinding states, the Ra value is less than 0.2m, the thickness of the gradient strengthening layer on the surface of the M50 steel reaches 150-1000m, the peak microhardness of the surface layer exceeds 9GPa, the surface residual compressive stress is greater than 500MPa, and the M50 steel has excellent thermal stability at 400℃.

[0048] The application also discloses some embodiments, wherein the equipment for performing the surface gradient micro-nano processing on the bearing steel in step (1) is a micro-nano processing equipment; the micro-nano processing equipment comprises a processing tool; the processing tool can be rolled / rolled on the surface of the bearing steel to make the surface of the bearing steel plastically deform to obtain a nano-micro gradient structure, and the nano-micro gradient structure forms a mechanical strengthening layer. The surface strengthening method of the bearing steel is simple and can strengthen the bearing steel rotary part. During the surface gradient micro-nano processing, the bearing steel rotary part rotates at a high speed, the tool head of the gradient micro-nano processing tool is pressed into the surface of the bearing steel to produce local high-speed deformation, a large number of dislocations are generated in the local high-speed deformation area of the bearing steel and are intertwined with each other, the lath martensite in the original structure is refined, the original nano lath martensite is refined into nanocrystalline, the nano-micro gradient structure is obtained, and then the surface strengthening layer is generated. The bearing steel can be M50 steel, the M50 steel rotary part rotates at a high speed, the tool head of the gradient micro-nano processing tool is pressed into the surface of the M50 steel to produce local high-speed deformation, a large number of dislocations are generated in the local high-speed deformation area of the M50 steel and are intertwined with each other, the lath martensite in the original structure is refined, the original nano lath martensite is refined into nanocrystalline, and then the surface strengthening layer is generated. The surface layer is generally referred to as the surface layer at a depth of 0-50 microns; the subsurface layer is 50-300 microns. Here, the surface layer and the subsurface layer refer to the stress loading area of the tool head, that is, the local stress area, which is in a range of about several hundred microns (and the effect is obvious in this range). Under the action of stress, new dislocations are generated, and the dislocations are prone to entanglement after increasing. The dislocations are difficult to move, and thus the strengthening is generated.

[0049] The application also discloses some embodiments, wherein the surface gradient micro-nano processing on the bearing steel comprises the following steps:

[0050] The first pass processing: the tool head of the processing tool is pressed into the surface of the rotating bearing steel for the first time, and the tool head of the processing tool is fed along the axial direction of the bearing steel or the direction perpendicular to the rotary surface of the bearing steel;

[0051] The application also discloses some embodiments, wherein the peripheral linear speed v1 of the rotating bearing steel and the feeding speed v2 are controlled according to the surface area of the bearing steel and the processing efficiency of the processing tool.

[0052] The application also discloses some embodiments, wherein the peripheral linear speed v1 of the rotating bearing steel is 50-800 mm / s during the first pass processing; and / or the pressing depth a of the first pressing is 20-100 microns; and / or the feeding speed v2 is 1x10 p -2x10 -3 -2x10 -1mm / r. The method of the application can obtain a high-depth strengthened layer with good thermal stability, and effectively improve the service life of the aviation bearing. The above processing parameters can make the processing uniform and ensure a certain processing efficiency.

[0053] The application also discloses some embodiments, and the surface gradient micro-nano treatment of the bearing steel further comprises the following steps.

[0054] The n-th processing: the tool head of the processing tool is pressed into the rotating bearing steel surface for the n-th time, and the tool head of the processing tool is fed along the axial direction of the bearing steel or the direction perpendicular to the rotating surface of the bearing steel; wherein n = 1-8; the surface strengthening effect can be further improved, and the more the processing passes are, the more significant the hardened layer is under the premise of no damage.

[0055] The application also discloses some embodiments, and in the n-th processing, the peripheral linear speed v1 of the rotating bearing steel is 50-800 mm / s; and / or the pressing depth of the n-th pressing is a p *n; and / or the feeding speed v2 is 1*10 -3 -2*10 -1 mm / r.

[0056] The application also discloses some embodiments, and according to the surface strengthening requirement of the bearing steel and the principle of no damage to the processed surface, the pressing depth and the pressing pass of the first pressing are controlled; and / or according to the surface strengthening requirement of the bearing steel and the principle of no damage to the processed surface, the pressing depth a p and the pressing pass n of the first pressing are controlled.

[0057] The application also discloses some embodiments, and the micro-nano processing device comprises a surface mechanical rolling treatment device, the surface mechanical rolling treatment device comprises a rolling ball, the rolling ball can freely roll, and the rolling ball forms a processing tool; the application also discloses some embodiments, and the material of the rolling ball is WC-Co cemented carbide; and / or the diameter of the rolling ball is 4-10 mm; the rolling ball of the above-mentioned type of cemented carbide is hard and low in price, and the tool is not easy to damage in use.

[0058] Alternatively, the micro-nano processing device comprises a surface mechanical rolling treatment device, the surface mechanical rolling treatment device comprises a fixed ball, and the fixed ball forms a processing tool; the application also discloses some embodiments, and the material of the fixed ball is WC-Co cemented carbide; and / or the diameter of the fixed ball is 4-10 mm. The fixed ball is directly pressed down on the surface of the bearing steel, and the diameter is in the above-mentioned range, so that the surface strengthening effect is better and the hardness is improved by a large margin.

[0059] The surface gradient micro-nanocrystallization adopted includes surface mechanical rolling treatment (SMRT) and surface mechanical grinding treatment (SMGT). The surface gradient micro-nanocrystallization treatment is performed on a special numerical control surface nanocrystallization processing equipment, which includes an SMRT / SMGT processing tool and an oil lubrication cooling system.

[0060] The application also discloses some embodiments, wherein the micro-nanocrystallization processing equipment comprises an oil lubrication cooling system; the oil lubrication cooling system can provide oil cooling liquid; and in step (1), the oil lubrication cooling system can lubricate and cool the bearing steel during the surface gradient micro-nanocrystallization treatment of the bearing steel.

[0061] The application also discloses some embodiments, which further comprise the following steps.

[0062] Step (2): performing heat treatment on the bearing steel treated in step (1) to relax the martensite substructure interface on the nano-micrometer gradient structure, and then form a stable strengthening layer; the application can further stabilize the strengthening layer and improve the strength by inducing grain boundary relaxation through heat treatment.

[0063] The application also discloses some embodiments, wherein the heat treatment temperature is 300-550 ℃; and / or, the heat treatment time is 1-20 h. In this way, the hardness can be further improved.

[0064] The application also discloses some embodiments, wherein the thickness of the gradient strengthening layer is 150-1000 μm; and / or, the microhardness peak value of the gradient strengthening layer is greater than 9 GPa; and / or, the surface residual compressive stress of the gradient strengthening layer is greater than 500 MPa; the microhardness peak value in the application refers to the maximum hardness in the gradient strengthening layer.

[0065] And / or, the bearing steel comprises M50 steel.

[0066] The application also discloses some embodiments, which further comprise the following steps before step (1):

[0067] Grinding treatment is performed on the surface of the bearing steel. The grinding treatment can process the bearing steel workpiece to the required shape, remove the large surface shape defects, and ensure uniform treatment of the surface gradient micro-nanocrystallization processing.

[0068] The specific method comprises: treating the surface of the M50 steel rotary part for aviation bearings by surface gradient micro-nano treatment. The surface gradient micro-nano machining system comprises a surface gradient micro-nano machining tool and an oily lubrication cooling system, and the surface gradient micro-nano machining system can be embedded in a numerical control machine tool. The front end of the machining tool is a hard ball (the material is a WC-Co hard alloy ball), and the diameter is 4-10 mm. The surface gradient micro-nano machining tool is pressed into the surface of the M50 steel rotating at high speed (the outer circle linear speed v1=50-800 mm / s) (the pressing depth ap=20-100 μm), and at the same time, the machining tool is fed along the axial direction of the M50 steel (or the direction perpendicular to the surface of the M50 steel rotary part) (the speed v2=1×10 -3 -2×10 -1 mm / r). The oily cooling liquid is used for lubrication and cooling during the treatment process of the M50 steel for aviation bearings, so as to ensure the stability and uniformity of the treatment process. After single-pass machining is completed, the M50 steel rotary part is treated in the same step according to the preset pressing depth ap*n for n (1-8) passes. The M50 steel rotary part treated by the surface gradient micro-nano treatment is subjected to heat treatment at 300-550 ℃ for 1-20 h, under the action of the internal stress field and heat, dislocations are rearranged, the nano-plate martensite in the M50 steel is refined into nanocrystalline and further strengthened Figure 3 , the surface martensite substructure interface of the workpiece is relaxed, and a gradient strengthening layer with good thermal stability, strength and higher surface residual stress is obtained. Under the action of the internal stress field and heat, dislocations are rearranged, the grain boundary strengthening effect of the sub-surface layer of the M50 steel is further improved and more stable.

[0069] Compared with the existing method for improving the surface performance of the M50 steel for aviation bearings, the present application has the following advantages:

[0070] 1. The process is simple, the cost is low, and industrialized production and machining can be realized. There is no noise pollution in the SMRT / SMGT treatment process, and no dust and cutting chips are generated during the machining process. The method is green and environmentally friendly. The surface gradient micro-nano machining system can be embedded in a numerical control machine tool. The process treatment mode is similar to the turning process mode, and only the surface gradient micro-nano machining program instruction needs to be added and the surface gradient micro-nano machining tool with an oily lubrication cooling system needs to be assembled. Therefore, the present application can realize industrialized production and machining.

[0071] 2. The surface quality of the M50 steel after surface gradient micro-nano machining is good. The machining mode produces a burnishing effect on the surface of the workpiece, ensuring good surface quality of the workpiece.

[0072] 3. The thickness of the gradient strengthening layer obtained by the surface gradient micro-nano processing and heat treatment composite process can reach 150-1000 μm, the strengthening layer has a larger thickness and higher thermal stability. The maximum shear stress of the aviation bearing is distributed at a distance of 100-500 μm from the surface of the bearing. Therefore, the effective strengthening layer is the key to ensure the service life of the aviation bearing; moreover, the aviation bearing has a higher service temperature, and requires higher organizational stability. The method provided by the application has a higher strengthening layer depth and good thermal stability, and can effectively improve the service life of the aviation bearing.

[0073] The embodiment of the application provides a method for generating a stable gradient strengthening layer on the surface of M50 steel for aviation bearings, and the specific implementation process of the method is as follows:

[0074] (1) The M50 steel for aviation bearings is made into a rotary piece, and the surface is subjected to grinding treatment. The grinding treatment can process the M50 workpiece to the required shape, remove the surface defects of a larger shape, and ensure uniform treatment of the surface gradient micro-nano processing.

[0075] (2) The surface of the rotary piece made of the M50 steel for aviation bearings is subjected to surface gradient micro-nano processing. The speed of the rotary piece, the feed rate and the penetration depth of the tool head are determined according to the actual product industrial demand; and the size of the tool head is selected according to the size of the actual workpiece. If the gradient residual stress layer is formed on the surface of the rotary piece, in one embodiment, the SMRT tool head is preferably selected, the rotating speed is between 300-800 mm / s, the feed speed is v2=1×10 -3 -2×10 -1 mm / r, the penetration depth is 20-40 μm, and 1-3 passes are processed; if the gradient strengthening layer with the highest surface hardness is formed on the rotary piece, in one embodiment, the SMGT tool head is preferably selected, the rotating speed is between 50-400 mm / s, the feed speed is v2=1×10 -3 -3×10 -2 mm / r, the penetration depth is 20-50 μm, and 1-3 passes are processed. If the gradient strengthening layer with a higher peak hardness and a deeper hardening is formed on the rotary piece, the SMRT tool head can also be used, the rotating linear speed is between 50-800 mm / s, the feed speed is v2=1×10 -3 -3×10 -2 mm / r, the penetration depth is 20-50 μm, and 3-8 passes are processed.

[0076] (3) In the heat treatment process of the M50 steel for aviation bearings, the heat treatment system is 300-550 ℃ for 1-20 h. The heat treatment temperature is preferably 300-480 ℃, and the heat treatment time is 1-3 h. Such heat treatment can effectively prevent the M50 steel matrix from being excessively tempered and softened, so as to further form a stable gradient strengthening layer.

[0077] Embodiment

[0078] Embodiment 1

[0079] A quenched and tempered M50 steel cylindrical test bar with a diameter of 10 mm is treated by the SMRT surface micro-nano processing system of the present application, and the main technical parameters are as follows:

[0080] The SMRT processing tool head has a diameter of 6 mm;

[0081] The linear speed v1 of the outer circle rotation of the M50 steel test bar is 320 mm / s;

[0082] The SMRT processing tool feed speed v2 is 2x10 -2 mm / r;

[0083] The processing pass n is 3 times;

[0084] The single processing pass indentation depths are ap(1)=40 μm, ap(2)=80 μm, and ap(3)=120 μm, respectively.

[0085] The test shows that the surface of the M50 steel for aviation bearings after SMRT treatment is smooth and has a higher surface roughness. Figure 5 The surface residual compressive stress after SMRT treatment can reach-1003 MPa, the matrix residual stress is close to 0, and a gradient strengthening layer with gradient residual stress is formed.

[0086] Embodiment 2

[0087] A quenched and tempered M50 steel cylindrical test bar with a diameter of 10 mm is treated by the SMGT surface micro-nano processing and heat treatment composite process of the present application, and the main technical parameters are as follows:

[0088] The SMGT processing tool head has a diameter of 8 mm;

[0089] The linear speed v1 of the outer circle rotation of the M50 steel test bar is 320 mm / s;

[0090] The SMGT processing tool feed speed v2 is 1x10 -2 mm / r;

[0091] The processing pass n is 2 times;

[0092] The single processing pass indentation depths are ap(1)=40 μm and ap(2)=80 μm, respectively.

[0093] The heat treatment temperature is 400℃, and the holding time is 2h.

[0094] After SMGT treatment, the surface hardness of the M50 steel for aviation bearings is the highest, and the hardness value can reach 11 GPa, and after heat treatment, the surface hardness is further increased, and the hardness value can reach 11.4 GPa.

[0095] Example 3

[0096] The quenched + tempered M50 steel cylindrical test bar with a diameter of 10 mm is treated by the SMRT surface micro-nano processing and heat treatment composite process of the present application, and the main technical parameters are as follows:

[0097] The SMRT processing tool bit has a diameter of 6 mm;

[0098] The linear speed v1 of the outer circle rotation of the M50 steel test bar is 400 mm / s;

[0099] The SMRT processing tool feed speed v2 is 2*10 -2 mm / r;

[0100] The processing pass n is 4 times;

[0101] The single processing pass indentation depths are respectively ap(1)=40 μm, ap(2)=80 μm, ap(3)=120 μm, and ap(4)=160 μm;

[0102] The heat treatment temperature is 300℃ and 400℃, and the holding time is 2h.

[0103] The gradient strengthening layer of the M50 steel for aviation bearings after SMRT treatment can reach 600 μm; the peak hardness of the M50 steel after heat treatment is further increased Figure 7 and Figure 8 ).

[0104] The M50 steel with a gradient strengthening layer is subjected to a rolling contact fatigue test, and the contact stress is 6.5 GPa. The test shows that the rolling contact fatigue life of the M50 steel for aviation bearings with a gradient strengthening layer after the treatment of the present application is significantly improved Figure 9 . Among them, the L 10 of the M50 steel with a gradient strengthening layer is 4 times that of the original sample, and the L 50 is improved by about 3 times. The surface nano layer and the higher residual compressive stress of the M50 steel with a gradient strengthening layer effectively inhibit the initiation of surface cracks, and thus significantly improve the ability of the M50 steel to resist rolling contact fatigue.

[0105] Example 4

[0106] The quenched + tempered M50 steel cylindrical test bar with a diameter of 4 mm is treated by the SMRT surface micro-nano processing and heat treatment composite process of the present application, and the main technical parameters are as follows:

[0107] The SMRT machining tool head diameter is 4mm;

[0108] The linear speed v1 of the outer circle rotation of the M50 steel test bar is 800mm / s;

[0109] The SMRT machining tool feed speed v2 is 1x10 -3 mm / r;

[0110] The machining pass n is 8 times;

[0111] The single machining pass indentation depths are respectively ap(1)=20μm, ap(2)=40μm, ap(3)=60μm, ap(4)=80μm, ap(5)=100μm, ap(6)=120μm, ap(7)=140μm, and ap(8)=160μm;

[0112] The heat treatment temperature is 300℃, and the holding time is 1h.

[0113] After the SMRT treatment, a gradient strengthening layer is formed on the surface of the M50 steel for aviation bearings; and after the heat treatment, the peak hardness of the M50 steel is further increased.

[0114] Example 5:

[0115] The quenched and tempered M50 steel cylindrical test bar with a diameter of 130mm is treated by the SMGT surface micro-nano machining and heat treatment composite process of the present application, and the main technical parameters are as follows:

[0116] The SMGT machining tool head diameter is 10mm;

[0117] The linear speed v1 of the outer circle rotation of the M50 steel test bar is 50mm / s;

[0118] The SMRT machining tool feed speed v2 is 2x10 -1 mm / r;

[0119] The machining pass n is 3 times;

[0120] The single machining pass indentation depths are respectively ap(1)=40μm, ap(2)=80μm, and ap(3)=120μm;

[0121] The heat treatment temperature is 300℃, and the holding time is 1h.

[0122] After the SMRT treatment, a gradient strengthening layer is formed on the surface of the M50 steel for aviation bearings.

[0123] Example 6:

[0124] A quenched and tempered M50 steel cylindrical test bar with a diameter of 60 mm is treated by the SMRT surface micro-nano processing and heat treatment composite process of the application, and the main technical parameters are as follows:

[0125] The SMRT processing tool bit has a diameter of 8 mm.

[0126] The linear speed v1 of the outer circle rotation of the M50 steel test bar is 600 mm / s.

[0127] The SMRT processing tool feed speed v2 is 2*10 -2 mm / r.

[0128] The processing pass n is 2 times.

[0129] The single processing pass indentation depths are ap(1)=100 μm and ap(2)=200 μm, respectively.

[0130] The heat treatment temperature is 300 ℃, and the holding time is 1 h.

[0131] After the SMRT treatment, a gradient strengthening layer is formed on the surface of the M50 steel for aviation bearings.

[0132] Comparative Example 1

[0133] The preparation method is basically the same as that of Example 1, except that the third pass is processed by using an SMGT tool bit, and the sample surface is worn during the processing process due to severe heat generation.

[0134] Comparative Example 2

[0135] The preparation method is basically the same as that of Example 2, except that the sample surface hardness before and after processing is 8 GPa, and there is no obvious change after processing by using an SMRT tool bit.

[0136] Comparative Example 3

[0137] The preparation method is basically the same as that of Example 3, except that the indentation depth exceeds 400 μm (50 μm*8). The sample surface is worn during the processing process due to severe heat generation.

[0138] Comparative Example 4

[0139] The preparation method is basically the same as that of Example 3, except that the sample substrate is reduced from 8 GPa to 7.5 GPa after heat treatment at 550 ℃ for 20 h, and is significantly softened.

[0140] The application also discloses a bearing steel obtained by the above bearing steel surface strengthening method.

[0141] Those skilled in the art can easily understand that the above-mentioned advantageous modes can be freely combined and superimposed without conflict.

[0142] The above merely describes the preferred embodiments of the present application, but should not be used to limit the present application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application. The above merely describes the preferred embodiments of the present application, but should not be used to limit the present application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A surface strengthening method of a bearing steel, characterized by, The method comprises the following steps: Step (1): surface gradient micro-nano processing of bearing steel is performed by using a micro-nano processing device to form a nano-micro gradient structure on the surface of the bearing steel; the nano-micro gradient structure forms a gradient strengthening layer on the surface of the bearing steel; The micro-nano processing device comprises a processing tool; the bearing steel is M50 steel; The surface gradient micro-nano processing of the bearing steel comprises the following steps: First pass processing: the cutting head of the processing tool is pressed into the rotating surface of the bearing steel for the first time, and the cutting head of the processing tool is fed along the axial direction of the bearing steel or the direction perpendicular to the bearing steel; According to the surface area of the bearing steel and the processing efficiency of the processing tool, the peripheral linear velocity v1 and the feed speed v2 of the rotating bearing steel are controlled; The n-th pass processing: the cutting head of the processing tool is pressed into the rotating surface of the bearing steel for the n-th time, and the cutting head of the processing tool is fed along the axial direction of the bearing steel or the direction perpendicular to the bearing steel; n = 1-8; During the nth processing step, the outer circular linear velocity of the bearing steel is v1 = 50-800 mm / s; the indentation depth of the nth pressing step is a. p *n; The feed rate v2 = 1 × 10 -3 -2×10 -1 mm / r; where a p a is the initial insertion depth. p =20-100μm; Step (2): the bearing steel processed in step (1) is subjected to heat treatment to relax the martensite substructure interface on the nano-micro gradient structure, thereby forming a high-temperature stable strengthening layer; The temperature of the heat treatment is 300-480℃; the time of the heat treatment is 1-3h.

2. The surface hardening method of a bearing steel according to claim 1, characterized by, In step (1), the processing tool can roll or roll on the surface of the bearing steel, so that the surface of the bearing steel is plastically deformed to obtain the nano-micro gradient structure.

3. The surface hardening method of a bearing steel as set forth in claim 1, characterized by According to the surface strengthening requirement of the bearing steel and the principle of non-damage processing of the surface, the pressing depth and pressing pass of the first pass are controlled.

4. The surface hardening method of a bearing steel according to claim 1, characterized by, The micro-nano processing device comprises a surface mechanical rolling treatment device, the surface mechanical rolling treatment device comprises a rolling ball, the rolling ball can freely roll, and the rolling ball forms the processing tool; the material of the rolling ball is WC-Co cemented carbide; and / or, the diameter of the rolling ball is 4-10mm; Alternatively, the micro-nano processing device comprises a surface mechanical rolling treatment device, the surface mechanical rolling treatment device comprises a fixed ball, the fixed ball forms the processing tool; the material of the fixed ball is WC-Co cemented carbide; and / or, the diameter of the fixed ball is 4-10mm.

5. The surface hardening method of a bearing steel as set forth in claim 1, characterized by The micro-nano processing device comprises an oil lubrication cooling system; the oil lubrication cooling system can provide oil cooling liquid; during the surface gradient micro-nano processing of the bearing steel in step (1), the oil lubrication cooling system can lubricate and cool the bearing steel.

6. The surface hardening method of a bearing steel as set forth in claim 1, characterized by The thickness of the gradient strengthening layer is 150-1000μm; and / or, the peak microhardness of the gradient strengthening layer is more than 9GPa; and / or, the surface residual compressive stress of the gradient strengthening layer is greater than 500MPa.

7. The surface hardening method of a bearing steel as set forth in claim 1, characterized by Before step (1), the following steps are further included: Grinding treatment is performed on the surface of the bearing steel.

8. A bearing steel, characterized in that, The bearing steel is obtained after the bearing steel is treated by the surface strengthening method of any one of claims 1-7. The bearing steel is obtained after the bearing steel is treated by the surface strengthening method of any one of claims 1-7.

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