Research status and progress on cleanliness of high-fatigue-life bearing steels

Bearing steel is a significant material for producing basic components in many industrial sectors, such as automotive, high-speed trains, and aerospace. In most cases, the bearings belong to the safety-relevant parts of these structures, so that extensive quality control measures are applied to ensure the entire assembly’s reliability and safety. In the last century, the precise instruments’ bearings were almost dependent on imports, which cost a large fortune. In recent years, the production technique and the production quality of domestic bearing steels keep improving, and the cleanliness keeps increasing. The qualities of some superior domestic bearing steels have become close to foreign bearing steels with high quality. However, the stability still needs to be improved, especially in the aspects of calcium aluminate inclusions and the titanium content in steels. To understand the gaps between domestic and foreign bearing steels, the differences in metallurgical properties of high-fatigue-life bearing steels, such as the main impurity elements and the characteristics of main inclusions, were compared in this paper. Fatigue properties of bearing steels and factors that cause fatigue fracture under various metallurgical properties were also compared. The cleanliness status of domestic bearing steels and the gap with foreign high-quality bearing steels were summarized. There are two types of controlling strategies of the cleanliness for bearing steels: 1) controlling the total oxygen content strictly to get an extremely low total oxygen content; 2) controlling the size and type of oxide inclusions with a relatively low total oxygen content. On this basis, in order to further improve the efficiency of domestic steel bearings, the development of the smelting technology and the integration control system for domestic steel bearings were analyzed and sorted out. Besides, the development direction of further improving the quality and fatigue life of domestic bearing steel was discussed.