Effect of Si content on the oxidation behavior of Cr-Mo steels in steam

The effect of Si content on the oxidation behavior and the oxide scale structure of 2.1/4-9 wt% Cr steels in steam was studied. The oxidation resistance of Cr-Mo steels in steam was improved with the increase of Si content in steels up to 0.5 wt% Si. The oxidation resistance of 0.5-1.0 wt%Si containing steels was similarly good. This beneficial effect of Si was remarkable at temperature above 600 degrees C. The growth rate of the oxide scale was reduced presumably due to the Si enrichment in the inner Cr-containing spinel-type oxide layer which retarded the ionization and diffusion of Fe. The regression analysis was carried out on the relationship between the growth of the oxide scale and the chemical composition of 2 1/4-9 wt%Cr-Mo steels containing less than 0.5 wt%Si. Si was found to be the most beneficial element and about 5.6 times more effective than Cr. The effect of the grain size of steels on the oxidation resistance was also detected.