Bearing steel for special environment

Bearings installed in mechanical devices such as automobiles, industrial machinery, home appliances, and information equipment are not only required to be lightweight and compact, but also require improved bearing performance to adapt to use in harsh environments. In order to meet this demand, it is necessary to optimize the material, heat treatment process, shape and size, and also to seek the integration of surrounding parts together with the user of the material.
Japan's Daido Special Steel Co., Ltd. has been committed to the development of bearing materials suitable for use in particularly harsh environments and the heat treatment process suitable for this material. The following is a brief introduction of the high-temperature bearing steel developed jointly by the company and bearing manufacturers and put into practical use, and the foreign object-resistant bearing steel developed by the company itself.1. Steel STJ2 for high temperature bearings
With the continuous improvement of the output power of automobile engines and the high-speed and closed industrial machinery, the ambient temperature of bearings is rising. It is hoped to develop a bearing that maintains performance at a temperature of 473-523K. In this temperature range, if SUJ2 subjected to tempering treatment is used, the hardness will decrease and the rolling life characteristics will deteriorate. On the other hand, although the precipitation hardening alloy steel-M50 used for jet engines etc. has sufficient rolling life in the same temperature range, the alloy contains about 10% of alloying elements such as Cr, Mo, V, so the cost of the material is high , the heat treatment is also complicated and lacks versatility. Therefore, the development of steel for high-temperature bearings that minimizes the addition of high-priced alloy elements and considers heat treatability and processability is the work target. Increasing the quenching hardness and improving the resistance to temper softening are effective for preventing softening at high temperatures. of.
The company investigated the effect of alloying elements on quenching hardness and tempering hardness, and used C element to improve quenching hardness, and Si element to improve temper softening resistance. Therefore, for the comparative bearing steel SUJ2, the material STJ2, which increases the content of C and Si to prevent a decrease in hardness at high temperatures, and maintains rolling characteristics by adding Ni elements, was developed as a steel for high-temperature bearings.2. Steel DCJ2 for foreign object resistant bearings
For the bearings of transmissions and differentials of automobiles, since foreign matter (silt, cutting powder) is mixed into the oil, once the foreign matter bites into the rolling surface of the bearing, it will cause indentation and cause early peeling of the rolling surface. For this purpose, foreign matter-resistant bearing steel.
Through the reproduction test and discussion of rolling fatigue in the environment mixed with foreign matter, the result of the discussion is that in order to improve the service life of the bearing in the environment mixed with foreign matter, it is effective to increase the amount of retained austenite on the surface, improve the surface hardness or the toughness of the matrix.
The foreign matter-resistant bearing steel DCJ2 with more than 2% Mn added has a foreign matter-resistant rolling fatigue life in a quenched and tempered state and a clean oil rolling fatigue life. Compared with SUJ2, the amount of retained austenite is high, and the foreign matter mixed condition It shows the same excellent rolling fatigue life as in clean oil, and it has been confirmed that DCJ2 has an excellent foreign object resistance life equivalent to carburizing and nitriding steel.Datong Special Steel Co., Ltd. has launched the research work on the surface hardening treatment of high-temperature bearing steel STJ2 and foreign matter-resistant bearing steel DCJ2, and jointly developed the heat-resistant carburized bearing steel with Si and Ni added with NTN company, which has been practically applied. In addition, the developed Mn-added surface hardened steel for foreign matter resistance, which has better life characteristics than carbonitriding, has begun to be promoted and applied to bearing manufacturers in Japan, the United States, and Europe.