The bearings loaded into automobile, industrial machinery, home appliances, information machines and other mechanical devices not only require light weight, compact, but also require to improve the performance of the bearings to adapt to the use of too harsh environment.To meet this demand, materials, heat treatment processes, shapes and sizes must be optimized, and the integration of the surrounding components must be sought with the user of the material.
Datong special steel has been developing bearing materials suitable for use in particularly harsh environments and heat treatment processes suitable for such materials.The following is a brief introduction to the high temperature bearing steel which is jointly developed by the company and the bearing manufacturer and has been put into practical application, as well as the foreign body resistant bearing steel which is independently developed by the company.
1. High temperature bearing steel STJ2
With the continuous improvement of the output power of automobile engines and the rapid development and sealing of industrial machinery, the ambient temperature for the use of bearings rises.It is desirable to develop bearings that maintain performance at temperatures ranging from 473 to 523K.At this temperature range, if the tempered SUJ2 is used, its hardness will be reduced and its rolling life characteristics will become worse.On the other hand, although the precipitated hardened alloy steel-m50 used in jet engines has a full rolling life in the same temperature range, the alloy contains about 10% Cr, Mo, V and other alloy elements, so the cost of the material is high, the heat treatment is complex, and the lack of universality.Therefore, it is effective to develop a high-temperature bearing with steel as the working target to increase quenching hardness, and to improve the tempering resistance and softening to prevent the softening at high temperature.
The company investigated the influence of alloy elements on quenching hardness and tempering hardness, and used element C to improve quenching hardness and element Si to improve tempering softening.Therefore, for the bearing steel SUJ2 for comparison, a material STJ2 was developed to increase the content of C and Si to prevent the hardness from decreasing at high temperature and to maintain rolling characteristics by adding Ni elements.
2. Steel DCJ2 for foreign body resistant bearings
Used in the bearings of automobile transmission and differential, because of foreign body (silt, cutting powder) mixed in the oil, once the foreign body bites into the rolling surface of the bearing, it will produce indentation and cause early spalling of the rolling surface. For this reason, foreign body resistant bearing steel is developed.
In order to improve the service life of the bearing in the mixed foreign body environment, it is effective to improve the residual austenitic volume on the surface and the surface hardness or the toughness of the matrix.
Development to add more than 2% of the Mn's resistance to foreign body bearing steel DCJ2 in quenched and tempered condition of foreign body fatigue life of rolling resistance and rolling fatigue life compared with SUJ2 clean oil, its residual austenite volume is high, under the condition of the foreign bodies with shows like in clean oil, excellent rolling fatigue life has clear DCJ2 nitrocarburizing treatment steel excellent resistance to foreign life.
Datong special steel company has carried out the research on the surface hardening treatment of two kinds of steel, STJ2 and DCJ2, which are high-temperature bearing steel and foreign body bearing steel, and jointly developed the heat-resistant carburized bearing steel with Si and Ni with NTN company.In addition, the developed surface hardening steel for foreign body resistance with Mn addition, which has better life characteristics than carburizing and nitriding treatment, has been promoted and applied to bearing manufacturers in Japan, the United States and Europe.