Effect of rf plasma nitriding power density on microhardness, structure, and magnetic properties of 304 austenite stainless steel

Abstract

Structural phases, microhardness, and magnetic properties of nitrided 304 austenite stainless steel prepared using different rf plasma power densities ranging from 78·5 to 138 W cm^-2 torr^-1 have been investigated. The results of X-ray diffraction revealed that the structural phases of the nitrided layers are strongly dependent on the nitriding plasma power density. Fe_2–3 N, Fe₄ N, CrN, and α ferrite are the main phases formed in the treated layers which can be easily identified. The hysteresis loops of the samples were measured using a vibrating sample magnetometer, from which the saturation magnetisation M_s , remnant magnetisation B_r , coercive field H_c , and magnetic susceptibility χ, were evaluated. The highest values of M_s , B_r , H_c , and χ were obtained when the samples were nitrided at around 106 W cm^-2 torr^-1. This behaviour can be explained in terms of the high precipitation of CrN and Fe₄ N at this nitriding plasma power density.