Improved mechanical and wear properties of H13 tool steel by nitrogen-expanded martensite using current-controlled plasma nitriding

Nitrogen-expanded martensite is a crystalline structure formed by incorporating nitrogen atoms into the interstitial sites of martensitic steels. It has recently gained significant industrial attention due to its excellent mechanical and wear-resistance properties. However, the major challenge in synthesizing nitrogen-expanded martensite is obtaining a phase free of iron or chromium nitrides precipitates. In this study, the effects of varying temperature (460, 480, and 500 degrees C) and plasma current density (0.5, 1.0, and 1.5 mA/cm2) during plasma nitriding of H13 tool steel were investigated to evaluate their influence on crystalline phases. The results of X-ray diffraction analysis indicate that expanded martensite free of nitride precipitates can be obtained at a temperature of 480 degrees C and low current density. Moreover, wear analysis using a ball-on-disk wear tester showed that the lowest wear rates were achieved under similar conditions. Grazing incidence X-ray diffraction analysis revealed that the outer region of the nitrided zone had a disordered structure, which could be attributed to a nano crystallization process. The nanoindentation analysis demonstrated that the expanded martensite phase has rigid-elastic properties characterized by high elastic energy (144.5 nJ) and high resistance to plastic deformation. (c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CCBY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).