Metallographic investigation of the diffusion zone of 31CrMoV9 steel after gas nitriding

Gas nitriding is a process of thermal treatment of steels, which is carried out at temperatures higher than 5000C. During this process, the peripheral layer of the steel is enriched with nitrogen and thus changes its physical properties. The layer enriched with nitrogen consists of two zones: compound and diffusions or precipitates zone. The thicknesses of the zones depend on nitriding parameters: temperature, duration of nitriding and nitriding parameter. For research we had the chromium-enriched steel 31CrMoV9. Nitriding of this steel was done at three different temperatures 5100C, 5500C and 5900C. For each temperature, there were four different durations of stay of the samples in the furnace where nitriding was performed. Then, the samples were investigated by various experimental methods. In this contribution, we will present the results of metallographic research, namely optical microscopy. With the help of the optical microscope, we found the thicknesses of the diffusions zones from which we calculated the growth kinetics of these zones