Also known as gas nitriding. Nitrocarburizing is a kind of chemical heat treatment process in which two kinds of active atoms of nitrogen and carbon penetrate into the surface of the workpiece at the same time. Generally, this process is adopted for the workpieces with less thickness and strict deformation. In particular, this process can improve the anti bite and corrosion resistance. The effect of rack and ring gear after treatment is very obvious. The treatment temperature is about 570c.