Improvement of corrosion and wear resistances of AISI 420 martensitic stainless steel using plasma nitriding at low temperature

The influence of low temperature plasma nitriding on the wear and corrosion resistance of AISI 420 martensitic stainless steel was investigated. Plasma nitriding experiments were carried out with DC-pulsed plasma in 25% N-2+75% H-2 atmosphere at 350 degrees C, 450 degrees C and 550 degrees C for 15 h. The composition, microstructure and hardness of the nitrided samples were examined. The wear resistances of plasma nitrided samples were determined with a ball-on-disc wear tester. The corrosion behaviors of plasma nitrided AISI420 stainless steel were evaluated using anodic polarization tests and salt fog spray tests in the simulated industrial environment. The results show that plasma nitriding produces a relatively thick nitrided layer consisting of a compound layer and an adjacent nitrogen diffusion layer on the AISI 420 stainless steel surface. Plasma nitriding not only increases the surface hardness but also improves the wear resistance of the martensitic stainless steel. Furthermore, the anti-wear property of the steel nitrided at 350 degrees C is much more excellent than that at 550 degrees C. In addition, the corrosion resistance of ATS1420 martensitic stainless steel is considerably improved by 350 degrees C low temperature plasma nitriding. The improved corrosion resistance is considered to be related to the combined effect of the solid solution of Cr and the high chemical stable phases of epsilon-Fe3N and alpha(N) formed on the martensitic stainless steel surface during 350 degrees C low temperature plasma nitriding. However, plasma nitriding carried out at 450 degrees C or 550 degrees C reduces the corrosion resistance of samples, because of the formation of CrN and leading to the depletion of Cr in the solid solution phase of the nitrided layer. (c) 2007 Elsevier B.V. All rights reserved.