Comparative Study of the Microstructure, Mechanical and Thermal Properties of Nitrided and Base Ferritic SS439 Stainless Steel Rod

A thick hydrogen coating layer and dark colour of SS439 were obtained when it is nitrided at high temperature (1100 Celsius). A thin hydrogen coating layer and brighter colour (blue) of SS439 were obtained when it is nitrided at low temperature (500 Celsius). Most of ferrite phase is present based on the microstructure of base SS439 at 100x and 500x magnification. Martensite phase is present in the high temperature nitrided microstructure of the SS439 as well as the ferrite phase. This is due to the heat applied and the penetration of hydrogen into the SS439. Hardness test on the three different samples are done using the Rockwell hardness machine at scale B. The load is set to a constant of 100kgf and 1/16’’ steel ball is used. Result shows that different samples nitrided at different temperature yield different hardness value. The samples are heated up to 100 Celsius to determine the length of its expansion and to calculate the thermal coefficient of the samples. Three different samples are tested using three point bending test to investigate its stiffness. High temperature nitrided sample shows a 59% of increase in stiffness value.