Abstract: The heavy-duty internal gear of a reducer required carburizing and quenching treatment. Because the internal gear structure was a large thin-wall part, the tooth distortion after conventional carburizing treatment was large, and the common normal size after gear grinding could not meet the technical requirements, resulting in scrapping of the workpiece. By adding stress-relief annealing process before carburizing, increasing preheating process during carburizing, reducing both the carburizing temperature and the cooling intensity, the problem of tooth distortion deviation after carburizing of heavy-duty internal gear is solved, providing a quality guarantee for carburizing and quenching of the thin-wall and heavy-duty internal gear.

Key words: 18CrNiMo7-6 steel, internal gear, carburizing, quenching, distortion