Surface Treatment Strengthening Technology: Bearing Steel Surface Strengthening Method

The working surface and core of the bearing parts are quite different in terms of state, structure and performance requirements, and the overall heat treatment often makes it difficult to balance the two, and the potential of the material cannot be fully utilized. The application of material surface strengthening technology can not only better solve the differences in structure and requirements between the surface and the core, but also further enable the surface to obtain some special working properties to meet the performance of bearings working under specific conditions on the working surface. requirements. This is very meaningful in the development of modern science and technology.

The traditional surface strengthening method belongs to the category of heat treatment in technology. The surface strengthening methods such as laser, electron beam, and ion beam developed in modern times not only apply some high-tech to the surface strengthening of materials, but also go beyond the traditional heat treatment category in terms of technology, forming a new technical field. Therefore, the current surface strengthening technology can form a variety of classification methods from different angles. According to the physical and chemical process of surface strengthening technology, it can be roughly divided into five categories: surface deformation strengthening, surface heat treatment strengthening, chemical heat treatment strengthening, and surface metallurgy strengthening. , Surface film strengthening.

1.Surface deformation strengthening

The metal surface layer is plastically deformed by mechanical methods to form a hardened layer with high hardness and high strength. This surface strengthening method is called surface deformation strengthening, also known as work hardening. Including shot peening, sand blasting, cold extrusion, rolling, cold rolling and impact, blast impact strengthening, etc. The characteristics of these methods are: the dislocation density of the strengthening layer is increased, the subgrain structure is refined, so that the hardness and strength are increased, and the surface roughness value is reduced, which can significantly improve the surface fatigue strength of the part and reduce the sensitivity of fatigue notch. This strengthening method has a simple process and remarkable effect. There is no obvious boundary between the hardened layer and the matrix, and the structure is coherent, which is not easy to fall off during use. Most of its methods have been applied in the bearing industry: the surface impact strengthening of rolling elements is the application of such methods, and precision rolling has become a new ring processing and strengthening method.

2.Surface heat treatment strengthening

The use of solid-state phase transformation to quench the surface layer of parts by rapid heating is called surface heat treatment, commonly known as surface quenching. Including flame heating and quenching, high (medium) frequency induction heating and quenching, laser heating or electron beam heating and quenching, etc. The characteristics of these methods are: the surface is partially heated and quenched, the deformation of the workpiece is small; the heating speed is fast, the production efficiency is high; the heating time is short, and the surface oxidation and decarburization are very slight. The method is particularly effective in improving the wear resistance and fatigue strength of large and extra large bearing parts bearing a certain impact load.

3.Chemical heat treatment strengthening

The method of changing the chemical composition of the metal surface layer by solid-state diffusion and infiltration of certain elements to achieve surface strengthening is called chemical heat treatment strengthening, also known as diffusion heat treatment. Including boronizing, metallizing, carburizing and carbonitriding, nitriding and nitrocarburizing, sulfurizing and sulfurnitrocarburizing, chromizing, aluminizing and chromium aluminum silicon carburizing, graphitized carburizing layer, etc. , of various types and characteristics. Infiltrate elements or dissolve into matrix metals to form solid solutions, or combine with other metal elements to form compounds. In short, the infiltration of elements can change the chemical composition of the surface layer and obtain different phase structures. The treatment process of carburized bearing steel parts and the surface nitriding strengthening treatment of needle bearing sleeves belong to this type of strengthening method.

4.Surface metallurgical strengthening

The surface strengthening treatment technology that uses the re-melting and solidification of the metal on the surface layer of the workpiece to obtain the expected composition or organization is called surface metallurgical strengthening. Including surface self-dissolving alloy or composite powder coating, surface melting crystallization or amorphous treatment, surface alloying and other methods. It is characterized by the use of rapid heating with high energy density to melt the metal surface layer or the alloyed material coated on the metal surface, and then cool and solidify by itself to obtain a reinforced layer with a special structure or specific properties. This special structure may be a fine crystal structure, or it may be a supersaturated phase, a metastable phase, or even an amorphous structure, depending on the process parameters and methods of surface metallurgy.

5. Surface film strengthening

Applying physical or chemical methods to coat the metal surface with a strengthening film layer with different properties of the base material is called surface film strengthening. It includes electroplating, electroless plating (chrome plating, nickel plating, copper plating, silver plating, etc.), composite plating, brush plating or conversion treatment, etc., and also includes high-tech that has developed rapidly in recent years: such as CVD, PVD, P-CVD, etc. Vapor deposition film strengthening method and ion implantation surface strengthening technology (also known as atomic metallurgy technology) and so on. Their common feature is that they can form a film with specific properties on the working surface to enhance the surface’s wear resistance, fatigue resistance, corrosion resistance and self-lubricating properties. For example, ion implantation technology strengthens the working surface of the bearing, which can significantly improve the wear resistance, corrosion resistance, and contact fatigue resistance of the bearing working surface, so that the service life of the bearing can be doubled.