Oxidation behavior of 9Cr-RAFM steel at high temperature

The effect of yttrium on the mechanism of oxidation film formation of the 9Cr reduced activation ferritic/martensitic (9Cr-RAFM) steel was investigated. Four alloys yttrium contents ranging from 0 to 0.065% were melted in a vacuum induction furnace and subjected to continuous isothermal oxidation experiments. The alloys were oxidized in air at 600, 700, 800 and 900 °C for 100 h. Oxidation kinetic curves were obtained and analyzed to study the effect of yttrium on the oxidation resistance of the alloys at high temperatures. The oxide films formed on the alloys were observed and analyzed by X-ray diffractometry, scanning electron microscopy and electron probe X-ray microanalysis. The results indicated that the oxidation weight gain of the samples varied with the yttrium content, with the highest gain observed in the yttrium-free alloy sample, and the least in those containing 0.065% yttrium. Adding yttrium significantly enhanced the high temperature oxidation resistance of 9Cr-RAFM alloy by promoting the formation of a selective Cr 2 O 3 oxide film. The film improved the adhesion of the oxide layer to the base metal, reduced the oxidation rate, and thereby enhanced the high-temperature oxidation resistance of the alloy.