ROLE OF SILICON IN DETERMINING OXIDATION RESISTANCE OF AN AUSTENITIC STEEL

The effect of varying the silicon content of a manganese-free 20% Cr/25% Ni/Nb-steel has been studied. Alloys containing 0.3-1.6 wt.% silicon have been examined after oxidation in CO2 at 750° and 850° C for 0.1-1000 h. In addition, removal of silicon from the steel has been evaluated by comparison with the standard steel. Development of a Cr2O3-rich surface oxide layer is dependent on the silicon level in the alloy to the extent that complete removal of silicon results in the appearance of a solid solution phase (α-Fe2O3/Cr2O3) and a spinel of variable composition. On the manganese-free alloys, growth of the oxide is largely sustained by cation diffusion in Cr2O3. Adhesion of the oxide scale can be correlated with the silicon content of the alloy; poor adhesion of the oxide formed on the 1.6 wt.% Si alloy is linked with the rapid development of a very thick Cr2O3 layer, and possibly with enhanced chromium diffusion in the alloy. © 1969.