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 has been investigated by means of isothermal heating at temperatures up to 1 273 K in air and, the structures of the scale and 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. The Si addition of about 0.1% improved the limit temperature of the oxidation resistance more than 100 K. The presence of an amorphous SiO2 layer was found in the interface 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 the Cr2O3 scale, and the Fe2Nb- free region formed beneath 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.