Effect of Solute Content on Plasma Nitriding Behavior of Fe-Cr Alloys

Abstract

Fe-Cr alloys with 3.0 to 18.6wt%Cr were plasma-nitrided at 650°C for 16h in a mixed gas of N2:H2=1:3. A nitriding layer, which is so called "internal nitriding layer", was formed parallel to the specimen surface, but the formation of a surface nitriding layer of γ'-Fe₄N was not observed. The Cr nitride formed in the nitriding layer was determined by XRD experiments to be CrN, not Cr₂N. The hardness Hv of the nitriding layer increased as the Cr content increased. The hardness increase is due to the dispersion of fine CrN particles in α-Fe matrix. The thickness of the nitriding layer decreased linearly as the Cr content increased.