Bearings have higher requirements for their materials, and must have high hardness, resistance, contact fatigue strength, elastic limit, good impact toughness, fracture toughness, dimensional stability, rust resistance and cold and hot processing

Equal performance. In order to ensure these performance requirements, the gold quality of bearing steel must ensure its strict chemical composition and chemical composition uniformity, especially high purity, very low oxygen content and residual element content, strict low-power structure and high-power structure, strict carbide uniformity, strict surface decarburization layer and internal porosity, segregation, microscopic pores, etc. Surface and internal defects such as cracks, slag inclusion, burrs, folds, scarring, oxidation, shrinkage, bubbles, white spots and overburning are not allowed.

At present, there are five main categories of bearing steel used in the world, namely, high-carbon chromium bearing steel, carburized bearing steel, stainless bearing steel, high-temperature bearing steel, and medium-carbon bearing steel.

1) High carbon chromium bearing steel. High-carbon chromium bearing steel is a high-carbon alloy steel containing 0.6%~1.5% chromium. At present, five grades are used in the Chinese standard, GCr15, GCr6, GCr9, GCr9SiMn, Gcr15SiMn. High-carbon chromium bearing steel can basically meet the bearing requirements of general working conditions, has good wear resistance and contact fatigue resistance, has ideal corrosion resistance and a certain degree of elasticity, toughness, processing performance is better, the price is also cheaper, so the most widely used. Due to the difference in hardenability, the largest amount of GCr15 and GCr15SiMn, GCr6 and GCr9 have been rarely used.

2) Carburized bearing steel. Carburized bearing steel is in essence a high-quality carburized structural steel, the current Chinese standard uses 6 grades G20CrMo, G20CrNiM0, G20Cr2Ni4, G20CrNi2Mo, G10CrNi3Mo, G20Cr2Mn2Mo. This kind of steel after carburizing, quenching, tempering and other heat treatment processes, the surface has a high hardness and certain wear resistance and high contact fatigue strength, and its heart has good toughness, a certain strength and hardness. It is mainly used for bearing and oversized bearing under impact load, such as railway and rolling mill bearings.

3) Stainless bearing steel. There are martensitic stainless steel and austenitic stainless steel, the current Chinese standard uses 3 grades,9Cr18, 9Cr18Mo, Cr14Mo4. Among them, martensitic stainless steel 9Cr18 is the most used. This kind of steel can get all or most of the martensitic structure after heat treatment, with high strength, good wear resistance and toughness, especially in seawater, acid, organic brine solution has strong corrosion resistance. The disadvantage of these bearing steels is that the carbon content is high, and the carbon and chromium form coarse primary carbides, which reduces the mechanical properties of the material and reduces the contribution of the chromium element against corrosion. Austenitic stainless steel such as 1Cr18Ni9Ti can obtain a single austenitic structure after heat treatment, which has good toughness and good corrosion resistance. However, because the strength and hardness are not high, it is only suitable for manufacturing low-load and low-speed bearings.

4) High temperature bearing steel. High temperature bearing steel has certain high temperature hardness and high temperature wear resistance. High temperature contact fatigue strength, oxidation resistance, impact resistance, high temperature dimensional stability, etc. This type of steel uses some steel grades of high speed steel and high chromium martensitic stainless steel. China's current use of high temperature bearing steel are mainly :9Cr18Mo(260℃), Cr4M04V(315℃), Cr14Mo4(480C), W6M5Cr4V2(480C), W18Cr4V(560C), W12Cr4V5Co5(590℃) The most commonly used is Cr4M4V. The tempering temperature of high-carbon chromium bearing steel is 160~180 ° C, so the use temperature generally does not exceed 120 ° C, if the use temperature exceeds 120 ° C, the strength of the steel drops sharply, the size is unstable and leads to the fatigue strength of the bearing is reduced. Therefore, can only use high temperature bearing steel and can not use high carbon chromium bearing steel, such as aircraft turbojet engine power is increasing, compressor and turbine main shaft bearing requirements of high temperature, the working temperature is generally 55~260 ° C, the highest can reach 370 ° C, in this working condition, can only use high temperature bearing steel.

5) Medium carbon bearing steel. Medium carbon bearing steel is medium carbon alloy steel, China is currently mainly :55, 50MnA, 70Mn, 5CrMnMlo, 60CrMnMOA, 55SiMOVA, 50SiM, the last two steel numbers are the impact bearing steel developed in China. This type of steel is suitable for making oversized bearings for heavy equipment such as driving, lifting, and large machine tools. The general speed is not high, but it bears large axial and radial loads and bending stresses.