Abstract: In the process of ion nitriding of small modulus spline parts, the tooth root or node circle position is often difficult to be nitrided or their nitrided layer is too shallow. Aiming at this problem, ion nitriding test was carried out on the internal spline of typical rotor parts under the vacuum pressure of 300, 400, 500, 600 and 700 Pa. The results show that when argon gas is injected into the furnace and the vacuum pressure is 600 and 700 Pa, the nitrided layer deviation of tooth top, joint circle and tooth root of the internal spline can be controlled within 0.02 mm and meet the technical design requirement, at the same time, the microstructure and surface hardness also meet the process requirements.

Key words: ion nitriding, vacuum pressure, surface hardness, microstructure, infiltrated layer depth