Process for producing gear with hard bainite structure on surface

The process of making gear with hard bainite structure has the material of aluminum-containing carburized steel in the aluminum content of 0.5-2.0 wt%. The process includes forging or rolling the gear, carburizing the surface of the gear, and final heat treatment, which comprises austenitizing at 850-920 deg.c, maintaining in medium at 180-350 deg.c for 0.1-20 hr, air cooling, and final tempering at 150-350 deg.c for 1-3 hr. The gear with martensite in the core and hard bainite structure in the surface possesses excellent use performance, less heat treatment deformation and long service life.