Development And Application Of Cr-Mo Gear Steel For Automobile

Gear steel is one of key materials in automobile. Cr-Mo Gear steel is top grade steel imported from Japanese standard JIS for development of automobiles in our country. This kind of gear steel has refined grain size with high mechanical strength and good service performance such as high rigidity, high abrasion resistance, good hardenability and tenacity. In order to develop new Cr-Mo gear steel for automobiles, the demands on gear steel composition, micro structural states and mechanical properties have been decided on at first. Then this paper brings out a systematic study on Cr-Mo Gear steel by using featuring advanced equipments and processes, such as 30t EBT arc furnace and 40t LFV vacuum refining furnace, optimization of inner composition control, rolling process. The proper processes of melting, refining and rolling for Cr-Mo Gear steel are given with particular testing results and production characteristics. Cr-Mo Gear steel for automobile has been produced with good quality. The experiment results show that the developed Cr-Mo Gear steels have high purity and low oxygen content (14~20ppm). The microstructure and zonal structure have been improved. The grade of zonal structure is smaller than grade 2 and grain size is smaller than grade 6. At the end of the sample, the rigidity can also catch up to the technique standard. In the production, the hardenability can be controlled in a narrow band. In the second part, the critical point, density, continues cooling curve of Cr-Mo gear steel have been measured and the effects of heat~treatment processes on grain size, microstructure and properties have been investigated. These results can be used to improve and optimize the production process in future. Finally, the SCM822H(22CrMoH) gear steel are put into practice in automobile. The results indicated that the hardenability of SCM822H(22CrMoH) gear steel is better than that of 20CrMnTi gear steel. The hardness of J15 can be controlled at 36~42HRC or 35~41HRC.Other properties of this gear steel are also the same as or better than those imported from Japan. This gear steel can be used for automobiles.