Effects of Initial Microstructure on the Low-Temperature Plasma Nitriding of Ferritic Stainless Steel.

AISI 430 ferritic stainless steel with different initial microstructures was low-temperature plasma nitrided to improve its hardness and wear resistance in the present investigation. The microstructure and properties of the low-temperature nitrided layers on stainless steel with different initial microstructures were studied by an optical microscope, X-ray diffractometer, scanning electron microscope, microhardness tester, pin-on-disk tribometer, and electrochemical workstation. The results show that the low-temperature nitrided layer characteristics of ferritic stainless steel are highly initial-microstructure dependent. For the ferritic stainless steel with a solid solution and annealing treatment, it had the best performance after low-temperature plasma nitriding when compared with the stainless steel with other initial microstructures. The nitrided layer thickness reached 34 μm after nitriding at 450 °C for 8 h. The phase composition of the low-temperature-nitrided layer consisted mainly of a nitrogen "expanded" α phase (α_N) and iron nitrides (Fe₄N and Fe_2–3N). The hardness of the nitrided layer could reach up to 1832 HV_0.1. Moreover, the wear and corrosion resistance of the nitrided layer on the solution and annealing treated ferritic stainless steel could be improved at the same time. [ABSTRACT FROM AUTHOR]