Oxidation Rate of Advanced Heat-Resistant Steels for Ultra-Supercritical Boilers in Pressurized Superheated Steam

Abstract

Oxidation kinetics of recently developed ferritic heat-resistant steels, HCM12A, NF616, and HCM2S, were investigated in a superheated steam to evaluate the effects of chemical composition of the steels, testing temperature (560–700°C), steam pressure (1–10 MPa), and degrees of microstructural evolution by aging on oxidation. The contribution of alloyed Cr to oxidation resistance was pronounced above 600°C, while no material dependency was found at 600°C or lower. The apparent activation energy of the oxidation rate clearly changed at around 600°C for NF616 and HCM12A. In contrast, HCM2S showed single activation energy over the range of temperatures. Although temperature and chemical composition were the major factors, steam pressure also showed a clear negative effect on the oxidation rate in the lower temperature range, 570–600°C.