Effects of Nitrocarburization on the Surface Morphology and Tribology of SKH51 High-Speed Tool Steel

This research focused on investigating the impact of nitrocarburization on the surface characteristics and tribological properties of SKH51 high-speed tool steels. We performed various heat treatment procedures, including single tempering quenching (QT1), double tempering quenching (QT2), triple tempering quenching (QT3), and a combination of double tempering quenching followed by nitrocarburization (QT2N). We evaluated attributes such as 3D surface morphology, tribological attributes, surface roughness, and hardness. The results revealed that the QT2N resulted in samples with a rougher surface and approximately 4.4 times harder than the untreated specimen (AR). Moreover, these samples were approximately 1.4 times harder than those subjected to QT3. Surface roughness was observed to increase after quenching and multiple tempering processes. However, the surface roughness of the QT2N specimen was reduced due to the formation of a compound layer following the nitrocarburizing process. The retained austenite of QT3 and QT2N demonstrated a lower standard deviation than those of AQ, QT1, and QT2, owing to the transformation of retained austenite into tempered martensite and precipitated carbide. The compound layer formed during nitrocarburization enhanced surface hardness, improved surface roughness, and reduced the coefficient of friction. Consequently, the QT2N process demonstrated greater efficiency than QT3, suggesting that nitrocarburization can effectively replace the final tempering process. This adaptation could result in a simplified heat treatment procedure and lower production costs.