In the actual work process, there are often large differences in the requirements for the state, structure and performance of the surface and center of the bearing parts. The overall heat treatment process of the bearing cannot take into account these requirements. The surface strengthening technology of materials can well solve this differential demand, so that the bearing surface can obtain special working performance and meet the performance requirements of bearings under specific conditions. The surface strengthening technology of bearing materials is generally divided into five categories: surface deformation strengthening, surface heat treatment strengthening, chemical heat treatment strengthening, surface metallurgy strengthening, and surface film strengthening.
1. Chemical heat treatment strengthening
Through solid infiltration of specific elements, the composition of its surface layer is adjusted to achieve surface strengthening, also known as heat dissipation treatment. The types of chemical heat treatment strengthening usually include boronizing, carburizing and carbonitriding, nitriding and nitrocarburizing, chromizing, etc. The elements infiltrated can change the composition of the surface layer and obtain different phase structures.
2. Surface deformation strengthening
The metal surface layer is mechanically hardened to form a hard layer with high hardness and strength. This method is also called work hardening. The common types include shot peening, sand blasting, cold extrusion, rolling, etc. In this way, the strengthened layer with higher dislocation density and refined sub-crystal structure can be obtained, the surface hardness and strength can be improved, the surface roughness value can be reduced, and the fatigue strength of the part surface can be improved.
3. Surface heat treatment strengthening
Based on the principle of solid phase transformation, the surface layer of parts is quenched by rapid heating. The types of heat treatment methods usually include flame quenching, high and medium frequency induction quenching, laser or electron beam quenching, etc. This heat treatment method is fast and efficient by local heating and quenching the bearing surface, and the deformation of the workpiece is small; The surface oxidation decarburization is very slight. It can improve the wear resistance and fatigue strength of large or extra-large bearings bearing large impact loads.
4. Surface metallurgical strengthening
The expected composition or structure is obtained by melting and solidification of surface layer materials.
Classification usually includes: surface self-soluble alloy, surface melting crystallization treatment, surface alloying and other methods. Rapid heating with high energy density can melt the metal surface layer or alloying material again, and obtain the strengthening layer with special structure or performance after cooling and solidification. Through research and practice; The surface layer of micro bearing can be strengthened by laser heating.
5. Surface film strengthening
The metal surface of the bearing is coated with a strengthening film of the base material. In terms of subdivision, the methods usually include electroplating, chemical plating and composite plating, etc. In recent years, there have also appeared such as CVD, PVD, P-CVD and other vapor deposition film strengthening methods and ion implantation surface strengthening technology. It can form a film on the surface layer to effectively strengthen its wear resistance, fatigue resistance, corrosion resistance and self-lubrication.