OXIDATION BEHAVIOR OF 2.25CR-1MO STEEL WITH PRIOR TEMPERING AT DIFFERENT TEMPERATURES

The oxidation behavior of a normalized 2.25Cr-1 Mo steel tempered prev iously for 10 hr at different temperatures between 873 and 1023 K has been studied up to a maximum duration of 1000 hr in air at 773-973 K. The oxidation resistance of the steel was found to decrease significan tly with the temperature of tempering. Tempering of this steel is repo rted to cause microstructural changes involving precipitation of Cr as carbides and a decrease in the effective (free) Cr contents, that cou ld influence the oxidation resistance of the Cr-containing alloys. Rel ative compositions across the thickness of the oxide scales, as analyz ed by SEM/EDX and SIMS, suggest that a less Cr-rich (and less protecti ve) and thicker scale on the steel formed because previous tempering c aused extensive depletion of free Cr.