Development Of Bearing Materials

1. High carbon chromium bearing steel
All countries in the world use the steel equivalent to GCr15 as the basis for bearing steel, and develop in the direction of improving hardenability to meet the needs of thick-walled bearing parts. The method is to appropriately increase the mass fraction of molybdenum in the composition (0.1%, 0.2%, …, 0.6%), the mass fraction of chromium is slightly adjusted or unchanged, thus developing a series of high-hardenability high-carbon chromium bearing steels. These steel grades are not only suitable for martensitic quenching, but also for bainitic quenching of thick-walled bearing parts.
Another development of high-carbon chromium bearing steel is to properly reduce the hardenability and apply medium-frequency induction heating. The hardenability is limited and the overall quenching is only surface hardened. It not only has the superior performance of carburizing and quenching carburizing steel, but also saves the steel cost of alloy carburizing steel and the high cost of carburizing heat treatment. Good results have been obtained with this steel for railway bearings.

2. Chromium-free bearing steel
Chromium-free bearing steel is a new type of steel developed by my country to replace chromium bearing steel based on the characteristics of domestic resources, including six steel grades: GSiMnV, GSiMnMoV, GSiMnMoV, GSiMnMoVR, GMnMoV, and GMnMoVR. They have good hardenability, hardenability, contact fatigue resistance and wear resistance. Compared with chromium bearing steel, its surface decarburization sensitivity is slightly greater, and its corrosion inhibition performance and machining performance are slightly inferior. However, it is completely feasible to use this kind of steel instead of chromium bearing steel to produce bearings by taking appropriate measures.

3. Carbon bearing steel
Foreign bearing steel academic circles believe that the main function of alloy elements in bearing steel is to improve hardenability, and the main properties such as high strength, high hardness, wear resistance and fatigue resistance are the function of carbon elements. With the development of vacuum degassing technology, the purity of carbon steel can also be greatly improved. For bearings with small wall thickness, vacuum degassed high-carbon steel can fully meet the requirements. At present, there is a tendency to further expand the scope of use of carbon steel.

4. Carburized bearing steel
With the development of high-speed aero-engines, the fracture toughness of fully hardened steel can no longer meet the requirements. For this reason, the United States has developed high-temperature-resistant carburized bearing steel M50NiL, which has particularly good fracture toughness, high-temperature performance, high-speed performance, impact toughness, wear resistance and fatigue resistance. At present, it is studying the carburizing steel of super M50NiL.

5. Stainless bearing steel
Coarse carbides in 9Gr18 stainless steel are harmful. Foreign countries are committed to research to reduce the carbon mass fraction to 0.5-0.7, which improves the comprehensive performance of 9Gr18 steel. At present, some countries are investing more power in the research of nitrogen-containing stainless steel. The United States and Germany jointly developed a Cronidur30 nitrogen-containing stainless bearing steel, Germany developed a low-nitrogen steel LNS for aeroengines and aerospace bearings, France developed a XD15N high-nitrogen martensitic stainless steel for aerospace bearings, and the United States developed a A high-performance carburized stainless steel CSS-42L is also successfully used in aerospace bearings.

6. Ceramic materials
The ceramic materials used in bearings are mainly Si3N4 and ZrO2 and their series combination products. It has the advantages of low density, small friction factor, extremely high hardness, high temperature resistance, strong corrosion resistance, moderate impact toughness, and high fatigue life under medium contact stress. For bearings working under strong friction, it is better to use ceramic materials. The types of ceramic bearings currently mainly include deep groove ball bearings, angular contact ball bearings and cylindrical roller bearings. There are two types in terms of whether ceramic materials are completely used: one is the inner and outer rings made of steel plus ceramic rolling elements, which is called composite type; the other is that both rings and rolling elements are made of ceramics, which is called full ceramic type . The difficulty in the application of all-ceramic bearings is that they are broken due to the different expansion coefficients of the materials when mating with the shaft.