8Cr4Mo4V steel is a kind of high-temperature bearing steel widely used in my country, mainly used in the manufacture of aero-engine spindle bearings. With the increasingly severe service conditions of engine main shaft bearings, the requirements for material properties are getting higher and higher, domestic and foreign scholars have carried out a lot of research work on the performance improvement of 8Cr4Mo4V steel. The author introduces the research progress of chemical composition optimization of 8Cr4Mo4V steel; focuses on analyzing the development of heat treatment technology for 8Cr4Mo4V steel, including traditional quenching and tempering, bainite isothermal quenching and dimensional stabilization and other heat treatment processes; introduces the research progress of surface strengthening technology for 8Cr4Mo4V steel And related achievements, involving surface alloying, coating deposition, shot peening and composite strengthening technologies; finally, combined with the service requirements of 8Cr4Mo4V steel and the research status of related technologies, its follow-up research directions are prospected. 3. 8Cr4Mo4V steel surface modification technology The failure of aero-engine bearings generally occurs on the surface of the material, such as friction and wear, corrosion, surface fatigue, etc. It is of great significance to improve the surface properties of the material to prolong the life of the bearing. In view of this, scholars at home and abroad have carried out a lot of research on the surface modification technology of 8Cr4Mo4V steel, mainly including surface alloying, coating and mechanical strengthening. 3.1 Surface alloying technology 3.1.1 Ion nitriding technology Ion nitriding technology can achieve the purpose of improving material properties by changing the chemical composition and structure of the material surface. As early as the 1990s, the research on the surface nitriding technology of 8Cr4Mo4V steel has been carried out abroad, and the results show that the life and reliability of the parts can be greatly improved. Literature [27] carried out research on ion nitriding of 8Cr4Mo4V steel, using anode layer ion source-assisted nitriding technology to carry out nitriding treatment of 8Cr4Mo4V steel at different temperatures, the surface hardness gradient of the material and the depth of nitriding layer are shown in Figure 7a and Figure 7b. Show. It can be seen from Figure 7 that with the increase of nitriding temperature, the surface hardness of the nitriding sample increases slightly, and the highest surface hardness reaches 1 100 HV0.1; The depth of the infiltration layer is nearly double that of 430 °C. However, the shallow depth of nitrided layer of 8Cr4Mo4V steel cannot meet the performance improvement requirements of 8Cr4Mo4V steel; after process improvement, the depth of nitrided layer of 8Cr4Mo4V steel reaches 120 μum, which will greatly improve the fatigue resistance of 8Cr4Mo4V steel. Fig.7 Depth and hardness of nitriding layer of 8Cr4Mo4V steel after ion nitriding . After nitriding, its microstructure, morphology and hardness gradient are shown in Figure 8. Although the surface hardness of 8Cr4Mo4V steel has been greatly improved, the nitriding method makes the surface have a brittle 'white light layer' and vein-like structure, which is not suitable for the material. performance may be adversely affected. Fig. 8 Microstructure and properties of 8Cr4Mo4V steel after salt bath nitriding It can be seen from Fig. 7 and Fig. 8 that vacuum ion nitriding of 8Cr4Mo4V steel has more significant advantages than salt bath nitriding. 3.1.2 Electron beam alloying technology High-current pulsed electron beam surface alloying technology usually includes two processes: first, coating the surface of the material, and then bombarding the surface of the material with high-energy electron beams, thereby changing the molten layer on the surface of the material, producing composition and The microstructure changes, and the mechanical properties and corrosion resistance of the material surface are improved [29]. References [30-33] used electron beam alloying technology to prepare Cr and Ta alloyed layers on the surface of 8Cr4Mo4V steel, respectively. After surface alloying and subsequent tempering, the microstructure and surface hardness of the alloyed layer are shown in Figure 9: a large number of particles with a size of only a few nanometers are precipitated on the surface of 8Cr4Mo4V steel. The maximum hardness of the alloyed layer and the Cr alloy reached 17.3 and 18.2 GPa, respectively, which were increased by 57% and 65% compared with the 11 GPa of the matrix. Some research results show that the surface alloying technology of high-current pulsed electron beam can effectively improve the friction, wear and corrosion resistance of 8Cr4Mo4V steel surface.