Water Vapor Oxidation Behavior under High-Temperature and Pressure Conditions of the Nitrided Alloys for Steam Turbine Valve System Parts

Abstract

Mechanical and corrosion properties were evaluated in the nitrided and non-nitrided specimens of ASTM 355 and SUS422 steels. The oxides formed on the specimen were analyzed using by XRD and the weight change was measured after oxidation test at high temperature, high pressure, and steam conditions. The oxidation behaviors and rates between two alloys and nitrided/non-nitrided specimens were clearly different. XRD analysis showed that the nitrides formed on the nitrided specimen were composed of CrN, Fe4N, and Fe2-3N. Also, it was found that the hardness on the nitrided specimen at 283°C decreased from Hv 1150 of room temperature to Hv 425.