Abstract:Liquid nitriding of 17-4 PH martensitic precipitation hardening stainless steels was conducted at 430 °C for different time using a complex chemical heat-treatment, and the erosion corrosion resistance of the nitrided samples was evaluated. Experimental results revealed that the main phase of the nitrided layer was expanded austenite (S), CrN、Fe4N and Fe2N， when 17-4PH stainless steel was subjected to complex salt bathing nitriding,. The nitrided layer depth thickened intensively with the increasing nitrding temperature. The salt bath nitriding can effectively improve the surface hardness. The maximum values measured from the treated surface are observed to be approximate 1100 HV0.1 for 40 hours from the untreated material (309 HV0.1). Low temperature nitriding can improve the erosion corrosion resistance against two phases flow. After nitrided for 4 hours, the sample has the best corrosion resistance than others.