Scratch resistance of low-temperature plasma nitrided and carburized martensitic stainless steel

Martensitic stainless steel is a potential material class for selection in some tribological systems, particularly those subjected to wear by hard particles and corrosion. To improve its mechanical resistance, without loss of corrosion performance, surface treatments such as low-temperature nitriding and carburizing have been systematically employed. In this context, this paper studied martensitic stainless steel samples subjected to different plasma-assisted treatments, in the case the plasma nitriding and plasma carburizing. The treatments were carried out at temperatures of 300, 350 or 400 °C, for different times, aiming to compare the scratch resistance of the treated surfaces. Specimens were initially characterized using X-Ray diffractometry, micro and nanohardness measurements. Scratch resistance was performed using the constant load mode for two levels, 8 and 15 N. All worn tracks were evaluated using optical interferometry, to get information about the widths and depths of track profiles. Worn surfaces were analysed using scanning electron microscope, revealing tensile cracks on the surface of nitrided samples. The friction coefficient and the wear resistance were analysed and related to the geometry of scratches, which was associated to the micro-mechanism of wear. Despite the high hardness and low friction coefficient achieved using nitriding treatment, the global performance of carburized samples could be considered as more suitable, because the carburized case significantly minimized the cracks formation. Therefore, plasma carburized martensitic stainless steel can be considered an adequate combination for corrosion environments subjected to wear.