On the Ion-Nitriding of Nitriding Steel

Metals are nitrided by glow discharge in the low pressure atmosphere involving nitrogen. The ion-nitriding process using this phenomenon has many advantages over the conventional nitriding process and has become the subject of increasing concern. The basic research of ion-nitriding has been reported by some workers, but there are very few systematical investigations on it.In this experiment, the nature of the surface layer of SACM-1 steel produced by ion-nitriding under various conditions has been investigated by means of micro-vickers hardness testing, X-ray diffraction and wear testing, compared with that by the conventional nitriding with ammonia gas. The following results are obtained.(1) The thickness of the compound layer is notably affected by such factors as the nitrogen gas ratio in the atmosphere, the processing temperature and time, and the gas pressure. However, the depth of the nitriding layer is affected only by the processing temperature and time. The hardness of the nitriding layer is influenced considerably by the processing temperature, and the highest hardness is obtained at 500°C.(2) Within the range of this experiment, the ε-Fe2−3N and γ′-Fe4N phases are found to be formed on the surface of SACM-1 steel even if the N2 gas ratio in the atmosphere is small.(3) The ion-nitriding process has higher rate of nitriding than the conventional nitriding process using ammonia gas.(4) The ion-nitrided and the ammonia gas nitrided specimens showed a considerably improved wear resistance at a sliding speed of 1.37 m/sec, at which the amount of wear in the untreated specimen is maximum, and at a higher sliding speed producing scuffing, showing better wear resistance than the untreated specimen.