Abstract: Due to the heat treatment distortion, the parts with internal spline cannot pass the plug gauge check has been a common problem. In view of the many factors influencing the heat treatment distortion of parts with internal spline, with the help of the concept of “quenching distortion tolerance zone”, the part structure type, part size before heat treatment process, heat treatment process parameters(including austenitizing temperature, soaking time, furnace volume, cooling rate, loading method), material type and normalizing process after forging on the heat treatment distortion of the parts with internal spline were comprehensively analyzed, and a series of solutions to solve the problem of heat treatment distortion of the parts with internal spline were proposed by coupling all those various factors.

Key words: parts with internal spline, quenching distortion tolerance zone, heat treatment process, microstructure