Microstructure and wear resistance of plasma nitrocarburized high deformed and controlled hot rolled low carbon bainitic steel

Abstract

Despite the growing industrial relevance of continuously cooled bainitic steels, the combination of plasma nitrocarburizing and HSX 130HD remains unexplored. Furthermore, no prior studies have investigated plasma treatments applied to HSX 130HD XTP® steel, which undergoes microstructural refinement through thermomechanical post-processing. This study evaluates the effects of plasma nitriding and nitrocarburizing on two bainitic steels, HSX 130HD and HSX 130HD XTP® (Xtreme Performance Technology®), with a focus on microstructural evolution, microhardness, phase formation, and wear resistance. Although both steels share the same chemical composition, the HSX 130HD XTP® variant exhibits a finer microstructure due to its thermomechanical processing. Plasma treatments were conducted using different gas mixtures, specifically N₂ (fixed at 75 vol%), H₂ (balance), and CH₄ (3 vol% and 5 vol%), at 500 °C for 6 h. The resulting microstructure, roughness, surface and profile microhardness, phase composition (determined via X-ray diffraction), friction coefficient under dry sliding, and wear resistance (evaluated through reciprocating sliding wear tests) were analyzed. The results indicate that increasing CH₄ concentration led to a reduction in white layer thickness, an increase in surface microhardness and roughness, and enhanced Fe₂-₃N phase formation for both substrates. Fe₃C formation was also observed in HSX 130HD XTP® samples treated with 5 vol% CH₄, while a lower friction coefficient was recorded for the same steel treated with 3 vol% CH₄. Although plasma nitrocarburizing proved to be effective for both steels, plasma-nitrided HSX 130HD XTP® exhibited the lowest worn volume, highlighting its superior wear resistance.