Improvement of the surface layer of steel using microwave plasma nitriding

Abstract

Microwave plasma was employed for the nitriding of SCM445 steel and characteristics of the steel obtained by this process were compared with those of steel treated by conventional ion nitriding. The latter showed a large amount of globular shaped nitride compounds around 1-2 μm size precipitated on the steel surface and surface coarsening after ion nitriding. However, microwave plasma nitriding successfully produced a nitrided steel without a compound layer and a diffusion layer thickness of more than 0.5 mm was achieved at gas composition of 30%N2-70%H2 (500°C, 2 h). Also, a smooth surface was also achieved. Microwave plasma nitriding was capable of producing just the diffusion layer with a good surface condition for subsequent deposition of a protective coating.