The Effect of Time and Temperature of Nitridation-Oxidation Process on Properties and Corrosion Resistance of AISI 316L Steel

Abstract

In this research, AISI 316L austenitic stainless steel has been subjected to plasma nitriding and oxidation- nitridation heat treatment at several temperatures for different times. Plasma nitriding of the samples was performed in N₂/H₂ = 1/3 atmosphere at temperatures of 425, 450, and 475°C for 5 h. To study the effects of the combined nitridation-oxidation process on mechanical and physical properties, the samples have been exposed in O₂/H₂ = 1/5 oxidating atmosphere at 425, 450, and 500°C for 15, 30, and 60 min, respectively. The mechanical and physical properties of the samples were studied after nitridation-oxidation heat treatment. The microstructural properties were examined by optical microscopy and scanning electron microscopy; the phases were analyzed by X-ray diffraction. The wear behavior of the oxidized-nitrided samples was studied using pin-on-disk tribotesting. The hardness and depth of the nitrided layer were measured by a Vickers hardness tester. The corrosion resistance of both untreated and treated samples was tested by the Tafel polarization and potentiodynamic polarization in 3.5% NaCl solution at ambient temperature. The results indicate that the combined nitridation-oxidation heat treatment improves both the pitting corrosion and wear resistances of AISI 316L steel and further increases its hardness.