Investigation of Active Screen Plasma Nitriding Properties of a Low Alloy Steel (DIN 1.6580)

摘要

Active screen plasma nitriding (ASPN) is a novel surface modification technique that has many capabilities and advantages over the conventional plasma nitriding (CPN).This paper considers the effects of some active screen plasma nitriding parameters such as; temperature and also active screen set-up parameters including top lid type (screen or iron plate (simple)) and screen hole size, on the surface behavior of a low alloy steel, VCN Mo 200 which is used in manufacture of structural components for heavy demands in wire industry. Plasma nitriding process was carried out at 520, 550 and 580 C for 5 hrs in atmospheres having nitrogen and hydrogen gas with volume ratio (N_2/H_2) of 3/1. The ntrided samples were characterized using metallugraphic techniques, XRD, SEM and micro-hardness measurement. X-ray diffraction analysis confirmed the development of- Fe_4N and ε- Fe_(2-3)N phases during the nitriding process. Obtained resultsindicated that compound layer thickness increase with temperature. The results also showed that increasing diameter size of the screen hole didn't influence on the compound layer thickness (with using screen top lid) and in condition of using iron plate top lid, increasing screen hole diameter in a fixed temperature, caused an increase in compound layer thickness. The micro-hardness measurement results, indicate surface hardness rise with increasing temperature. It was also indicated that hardness values obtained with using screen top lid were little more than those obtained when using iron plate top lid.