EFFECTS OF NITRIDING TEMPERATURE ON GAS N ITRIDING PROPERTY OF STEELSFOR NITRIDING

Effects of nitriding temperature on gas nitriding property of SACM645 stocks were investigated in order to develop a new nitriding process. In this investigation, TEM observation was performed to study surfaces hardening mechanism in gas nitriding. Effective case depth increased with nitriding temperature was raised. On the other hand, surface hard ness decreased as nitriding temperature increased. Precipitation of co mplex nitride (Al, Cr) N which has f.c.c structure was observed in the nitrided layer. It is proved that, surface hardness increased at lowe r nitriding temperature because procipirates became fine and were incl uding large coherent strain on matrix. In examining a few patterns of temperature profiles in nitriding, it is concluded that the nitriding process with continous heating, showed better nitriding property than other ordinary nitriding processes. The reasons for this are as follow s: i) high surface hardness obtained at lower temperature in the early nitriding stage is maintained in higher temperature, ii) enough amoun t of nitrogen diffuse into the steel during continous heating.