Structural, tribological and corrosion properties of plasma nitrided-chromized-316L stainless steel in air and artificial seawater

Abstract

To improve the protective performance of 316L stainless steel surface in seawater, a series of modified layers on the 316L stainless steel were fabricated by plasma nitriding, vacuum solid powder chromizing and duplex surface treatment of nitriding-chromizing, respectively. The microstructure, mechanical properties, tribological properties and corrosion resistance of different modified layers were contrastively investigated. The results of x-ray diffraction (XRD) and transmission electron microscope (TEM) showed that the nitrided layer was mainly CrN and Fe4N phases, and the chromized layer was mainly Fe-Cr and Cr23C6 phases. The surface hardness of 316L stainless steel was improved to varying degrees by nitriding and chromizing due to the formation of hard phases such as CrN and Cr23C6 on the surface of 316L. The friction coefficient and wear rate can be obviously reduced by nitriding treatment. However, the nitriding treatment can cause the precipitation of Cr from the solid solution of 316L to form CrN, resulting in the decrease of corrosion resistance in seawater. In contrast, chromizing treatment can significantly improve the corrosion resistance of 316L by increasing the chromium content of stainless steel surface. The duplex surface treatment of nitriding and chromizing made the 316L stainless steel had the highest surface hardness and plastic deformation resistance and showed the excellent tribological properties in both atmosphere and seawater.