Tribological performance of low-temperature plasma carburized AISI 420 martensitic stainless steel

Abstract

Plasma carburizing has emerged as a potent technique for improving the wear resistance of stainless steels, and sustaining or improving corrosion resistance through a suitable choice of process parameters. This study evaluated the impact of plasma carburizing time and temperature on the tribological behavior of AISI 420 martensitic stainless steel through dry-sliding wear tests in a ball-on-disk configuration. Two different treatment sets were conducted to assess the impact of carburizing time and temperature on the wear performance of the treated AISI 420 steel. The first group encompassed treatments at temperatures spanning from 350 to 500 °C, with fixed treatment times of 8 and 12 h. The second group involved treatments at a temperature of 400 °C for durations spanning 12 to 48 h and at temperature of 450 °C for durations between 4 and 16 h. To facilitate the discussion of wear test results, microstructural analysis was performed using metallographic analysis, X-ray diffraction, and microscale hardness measurements. Microstructural characterization results revealed that the carburized surface consists of an outer layer followed by a diffusion layer. The diffusion layer is primarily composed of the α′C phase, while the outer layer contains α′C and Fe3C (for low-temperature and short-time treatments) and Cr/Fe-carbides primarily formed due to the α′C decomposition into Fe–α phase (for the studied higher-temperature and longer-time treatments). Wear test results suggest that the surface structure and composition of the treated material exert substantial influence on its tribological behavior. Carburized layers free from Cr-carbide precipitation exhibit lower wear and friction coefficients. The decomposition of α′C into Fe-α and Cr/Fe-carbides leads to an elevation of friction and wear coefficients. Finally, carbon enrichment does not alter the wear mechanism, as both uncarburized and carburized samples exhibited microabrasion and oxidative wear.