Abstract
Cast stainless steel CF8C-Plus (19wt%Cr/12%Ni) has excellent creep properties, but
limited oxidation resistance above 700°C in environments containing H2O. One strategy
to improve the alloy oxidation performance is to increase the Cr and Ni concentration.
Two new alloys, with, respectively, 21wt%Cr–15wt%Ni and 22wt%Cr–17.5wt%Ni were
therefore developed and their long-term oxidation behaviors in humid air were compared
with the oxidation behavior of five other cast alloys. At 650°C and 700°C, all the alloys
formed internal Cr-rich nodules, and outer nodules or layers rich in Fe and Ni, but they
grew a protective Cr-rich inner layer over time. At 750°C, the lower alloyed steels such as
CF8C-Plus showed large metal losses, but the two new alloys still exhibited a protective
oxidation behavior. The 21Cr–15Ni alloy was severely oxidized in locations at 800°C,
but that was not the case for the 22Cr–17.5Ni alloy. Therefore, the two new modified
alloys represent a potential operating temperature gain of, respectively, 50°C and 100°C
in aggressive environments compared with the CF8C-Plus alloy.
