Modern heat resistant ferritic-martensitic steels are of high interest as superheater materials in fossil fuel power plants or as material for interconnectors in solid oxide fuel cells. The environments of such applications contain high amounts of water vapor which is known to promote the formation of the volatile chromium species CrO2(OH)2 leading to insufficient oxidation resistance of 9%Cr- steels in such atmospheres.Results pertaining to the enrichment of manganese and chromium in metal subsurface regions without altering the bulk phase will be presented. The formation of a chromium-manganese-spinel during oxidation to suppress the evaporation of chromium in water vapor containing environments was achieved. The diffusion treatment developed was based on thermodynamic considerations for the design of the pack cementation process to reach an appropriate composition of chromium and manganese in the enriched diffusion zone. The improved oxidation behavior will be illustrated with oxidation experiments in a simulated combustion environment with water vapor at temperatures of 650 to 800°C.