Corrosion Resistance of Ferritic Stainless Steel X12Cr13 After Application of Low-Temperature and High-Temperature Plasma Nitriding

Abstract

The impact of plasma nitriding process on corrosion resistance of ferritic stainless steel (FSS) was evaluated in this study. The FSS X12Cr13 (AISI 410) was subjected to low-temperature plasma nitriding (LTPN) treatment at a temperature of 400°C in 3H2:1N2 (l/h) and in 1H2:3N2 (l/h) reverse working atmosphere (LTPN-R) and to high-temperature plasma nitriding (HTPN) treatment at 550 °C for 15 h. The microstructure and microhardness of the untreated and nitrided stainless steel were evaluated. The corrosion properties of the untreated and plasma nitrided steel samples were evaluated using the anodic potentiodynamic polarization tests in neutral 2.5% NaCl deaerated solution. The phase analysis showed that LTPN and LTPN-R treatment on the AISI 410 steel led to the formation of N layer (nitrogen expanded ferrite) accompanied by Fe3C and Fe4N iron nitrides and CrN. The HTPN technique led additionally to the formation of an increased volume of Cr4N4 chromium nitrides and Cr15Fe7C6 chromium iron carbide. The plasma nitriding process significantly increased the microhardness of the ferritic stainless steel. The pitting was evaluated, and the pitting coefficient was calculated. The electrochemical corrosion tests showed the best corrosion resistance of the untreated X12Cr13 stainless steel, only slightly increased corrosion rates of LTPN and LTPN-R techniques, and extreme corrosion rates after application of the HTPN technique, causing Cr depletion and thereby suppressing the ability to passivation.