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

Abstract

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.