| Nitriding with plasma nitriding technique was performed with various holding time and temperature, to provide minimum surface hardness of AISI 4140 Alloy Steel for automotive industrial gearing purpose, i.e. 505 HV. Plasma nitriding is a thermal diffusion of nitrogen atoms on the surface of the substrate, which is intended to improve the surface quality of metal especially its hardness. To achieve optimum hardness condition, the plasma nitriding process was carried out with temperature variations at 400°C, 450oC, 500oC, with variations in holding time of 2, 3, and 4 hours. Metallographic and micro hardness tests conducted in research to investigate the relationship between microstucture and improvement of the surface hardness,and to calculate the case depth that occurs.Result of the test indicates that: AISI 4140 steel surface hardness meets minimum values for automotive industrial gearing purpose after undergoing plasma nitriding process with temperatures of 450oC and 500oC for all holding times. |