Oxidation Resistance of Plasma Nitride Valve Steel

The aim of this study is to investigate the oxidation behavior of DIN 1.4871 austenitic valve steel after plasma nitriding. For this, plasma nitriding treatment was carried out by entering nitrogen and hydrogen with a ratio ofN2IH2: 1/3 and maintaining pressure to about 10 Torr. Nitriding cycles were performed at 450,500 and 550DC respectively, for 7 hours each. For removing the oxide layer and. better diffusion, sputtering treatment was applied for 60 minutes. The structure and property of the samples were examined by metallographic, micro hardness, XRD and SEM tests. The cyclic oxidation tests were used to evaluate the oxidation characteristics of samples that consisted of 50 cycles in 750°C for 30 min. It was concluded that, the layer plasma nitrided at 450°C lacked the CrN phase, but for higher temperature nitriding it contained CrN. X-ray diffraction and scanning electron microscopy studies indicated that oxide scale of 450°C and 550°C nitrided samples was mainly Cr203 and FC203 respectively. Our results show that nitridation at 450DC increases the high temperature oxidation resistance of Din 1.4871 valve austenitic steel at 750°C.

کلیدواژه ها:

Valve austenitic stee~ Plasma nitriding ، Cyclic oxidation