研究主要探討9Cr-1Mo鍋爐用鋼（T91）在650～850℃含水汽下之空氣氧化行為。研究結果顯示，T91在650～850℃含水汽下之氧化動力學皆遵守拋物線律，其氧化速率隨著溫度增加而增加，主要形成外層Fe2O3與Fe3O4以及內層（Fe，Cr）3O4，而當在850℃氧化峙，更有少量的FeO生成。此外，SEM亦觀察到在氧化層（Fe3O4/（Fe，Cr）3O4）中會有裂縫產生，其主要原因可能為水分子進入氧化層後轉換成氣相導致氧化層裂開，而使合金的氧化速率比乾空氣下的氧化速率更快。

The high-temperature oxidation behavior of the 9Cr-1Mo steel (T91) was studied over the temperature range of 650~850℃ in wet air. The results showed that the oxidation kinetics of T91 followed the parabolic-rate law at 650~850℃, and the oxidation-rate constants (K(subscript p) values) increased with increasing temperature. Duplex scales formed on the steel consisted of an outer layer of Fe2O3 and Fe3O4 and an inner layer of (Fe, Cr)3O4. In addition, minor amounts of FeO were also detected in the inner-layer at 850℃. On the other hand, numerous cracks were observed in the scales of Fe3O4/(Fe,Cr)3O4, and this phenomenon has never been observed for this steel in dry air. It was very likely that water molecules penetrated into the scales, formed water vapor, and resulted in the severe cracks, thereby leading to greater oxidation rates of the steel.