Growth of nitrided layers on Fe-Cr alloys

Chromium is an important alloying element present in numerous commercial st eels. A systematic study on the nitriding behavior of Fe-Cr alloys is helpf ul in predicting the properties of nitrided Cr-alloyed steels. Aspects such as microstructural evolution, growth kinetics, and mechanical properties s hould be particularly emphasized. Fe-Cr alloys containing 5, 10, and 20 wt. % Cr have been are melted and subsequently plasma nitrided under a N-2-80% H-2 atmosphere. The microstructure of the resulting nitrided layers was cha racterized and the microhardness profiles evaluated. Thicker layers develop ed on low chromium alloys. Differences in hardness profiles were also obser ved as a function of chromium contents. Nitriding Fe-5% Cr alloys resulted in two discrete fronts, refereed to as the diffusion front and the transfor mation front. Transformed regions sustained a decrease in hardness from 100 0 down to 600 HV, associated with the conversion of homogeneously dispersed fine precipitates into coarser needle like particles immersed in the ferri tic matrix. Similar behavior was not observed for the other alloys, where b oth fronts developed simultaneously. (C) 2000 Elsevier Science S.A. All rig hts reserved.