Low Temperature Plasma Nitriding Characteristics of Precipitation Hardening Stainless Steel

Abstract

The low temperature plasma nitriding behaviour of 17-4PH type precipitation hardening stainless steel was investigated in the present work. The morphology, thickness, hardness and X-ray diffraction characteristics of the nitrided layers produced at temperatures between 350 ° C and 450 ° C were studied. It was found that, at temperatures lower than 425 ° C, a thin, hard nitrided layer exhibiting a 'white' and featureless morphology could be produced on the steel investigated. X-ray diffraction analysis revealed that this layer was X-ray amorphous, as derived from its lack of Bragg reflection peaks in the diffraction pattern. At higher nitriding temperatures, chromium and iron nitrides began to form in the nitrided layer, leading to a transition in nitriding kinetics and a decrease in hardness. The possible mechanisms relating to the formation of the amorphous-like nitrided layer at sufficiently low temperatures are discussed in terms of the theory of solid state diffusion reaction for amorphous alloy formation.