Abstract: Commonly used surface heat treatment processes of heavy-duty gears include carburizing and quenching, induction hardening and nitriding process. Nitriding process has great advantages and broad application prospects in industrial production because of its advantages of small distortion and simple process. By increasing the depth of the nitrided layer and the hardness of the matrix, the bearing capacity of nitrided gears can be effectively improved, so as to expand the application of nitriding treatment in heavy-duty gears. Influence of nitriding treatment on the contact fatigue strength and bending fatigue strength of gears was introduced, as well as the influence of matrix properties on nitriding process, the research progress of nitrided gears was reviewsed, such as deep controlled ion nitriding, rare earth accelerated nitriding, aging hardening nitriding steel. It was pointed out that the ways to improve the loading capacity of nitrided gears are as follows: to carry out more in-depth basic research on nitrided gear, to improve the control level of nitriding process and to develop the new technology more actively.

Key words: heavy duty gear, nitriding treatment, deep controllable ion nitriding, matrix properties