Effect of Cr and Ni contents on the oxidation behavior of ferritic and austenitic model alloys in air with water vapor

Ferritic and austenitic model alloys with various contents of Cr and Ni ranging between 10 - 20 % and 0 - 30 %, respectively, were oxidized in air+ 10 % water vapor during 1 hr cyclic oxidation at 650degreesC and 800degreesC. Depending on the alloy composition and temperature, either a thin protective oxide scale was observed or accelerated attack occurred which sometimes included spallation. For austenitic model alloys, increasing either the Cr or Ni contents delayed the accelerated attack. For lower Cr and Ni contents at 800degreesC, accelerated attack, including spallation, occurred at short exposure times. No spallation was observed for the ferritic model alloys. However, accelerated attack can occur quickly with low Cr contents. Increasing the temperature delayed the breakaway observed on ferritic alloys whereas it reduced the protective-oxide-growth stage for austenitic alloys.