We have studied the general corrosion of 2¼ Cr— 1 Mo steel in pure superheated steam, in impure superheated and saturated steam, and under nucleate boiling conditions. The test parameters were selected to provide information relevant to the use of this steel for the Clinch River Breeder Reactor superheaters and evaporators. The oxidation rate of 2¼ Cr—1 Mo steel in superheated steam was measured under heat transfer conditions at 510 to 540°C (950 to 1005°F), and was times that measured under iso thermal conditions. Extensive general attack of stressed 2¼ Cr—1 Mo steel specimens occurred in cyclic tests in superheated and saturated steam with chloride and oxygen additions, although no cracking or localized attack was observed. Considerably less attack occurred under superheat conditions or in the absence of oxygen. Tests under nucleate boiling conditions were operated to evaluate crevice effects associated with porous films on heat transfer surfaces. Significant crevice corrosion was produced in water containing 10 ppm chloride; a heavier but more general attack occurred in treated cooling tower water.