Elevated Temperature Plasma Nitriding of CrMoV Tool Steel for the Enhancement of Hardness and Wear Resistance

Abstract

Elevated temperature plasma nitriding of Cr-Mo-V based tool steel was performed by varying the treatment time to enhance hardness and wear resistance. Steel samples after metallographic polishing were placed on the conducting substrate holder in the nitriding reactor and evacuated to 0.5 Pa pressure. The sample holder was then negatively biased at 250 V to accelerate the ions toward the surface of the samples. A gas mixture of N2 and H2 was then passed into the vacuum chamber to generate the plasma. After plasma generation nitriding was performed at variable temperatures 500oC and 550oC for 6 and 10 hrs. Then X-ray diffraction (XRD) and Scanning Electron Microscope/Electron Dispersive Spectroscopic (SEM/EDS) studies were followed to understand the structural modifications. XRD analysis predicted the presence of iron nitrides whereas SEM/EDS had shown the presence of N availability from the surface to the core of the steels. Following the structural characterization hardness and wear resistance were measured by using Vicker’s microhardness tester and ball-on-plate method respectively. It was found that the hardness, case depth, and wear resistance of the steel were significantly enhanced mainly due to nitrogen solid solnution and nitride formation. Thus, it has been proved that a longer time or higher temperature of nitriding may be beneficial for such improvement.