Effect of Si Addition on Oxidation Behavior of Nb containing Ferritic Stainless Steel

The effect of Si on the oxidation resistance of high purity Nb containing 19% Cr ferritic stainless steels have been investigated by means of isothermal heating at temperatures up to 1273 K in air and, the structures of scale and the scale/metal interface were investigated with FE-SEM and FE-TEM. The results are as follows: Si improved the oxidation resistance, as reported in previous studies. Si addition of about 0.1% improved the limit of the oxidation resistance more than 100 K. The presence of an amorphous SiO2 layer was found between the Cr2O3 scale and the metal. This layer might act as an oxidation resistance barrier. In the Si-free steel, a NbO2 layer formed under Cr2O3 scale, and the Fe2Nb- free region formed in the vicinity of the surface. On the other hand, when Si was added, the formation of NbO2 layer was suppressed. In case of 1%Si, no NbO2 layer formed and the Fe2Nb-free region was eliminated. In addition, Fe particles were present in the Cr2O3 scale in the Si-added steel.