Influence of nitriding temperature on fatigue corrosion resistance in a saline solution of a plasma nitrided steel 316L

Abstract

In this research, the effect of the temperature of nitriding on the corrosion fatigue stress in a stainless steel AISI 316L in a solution of 3.5% of NaCl has been determined. The plasma nitriding treatment was performed at 430, 480, 530 and 580ºC, in a 25% de N2 + 75% de H2 gas mixture during 10 hours at pressure of 650 Pa, with 2 hours of previous sputtering in 50% N2 +50% H2 gas mixture at pressure of 300 Pa. The samples have been characterized through their thickness of nitrided layer, mechanical properties and corrosion fatigue resistance. The corrosion fatigue test were carried out in smooth cylindrical samples (Kt=1.05) at constant amplitude plane reversed bending (R=-1) at 47Hz. The thickness of nitrided layers and maximum hardness increased with nitriding temperature, and better tensile properties were observed. A constant cyclic stress amplitude (S), was applied to a specimen, and measuring the number of cycles (N), until the specimen failed the curve Wöhler (S-N) was determined. The S-N curves showed that the plasma nitriding improves the corrosion fatigue resistance at N<4x106 cycles and reduces it at N>8x106 cycles. This behaviour is related to the better mechanical properties and the loss in corrosion resistance generated by this treatment.