Effect of Nb on high-temperature oxidation of austenitic stainless steel at 850 °C

The effects of niobium on the high-temperature oxidation resistance of austenitic stainless steel were systematically investigated. Two austenitic stainless steels with different Nb contents were prepared and exposed to air at 850 degrees C for 200 h. Results show that Nb positively affects the high-temperature oxidation resistance of austenitic stainless steels. The matrix organization of austenitic stainless steels with added niobium does not change, while the austenitic grain size is significantly refined, and it also promoted the release of internal stresses in the oxide film, which in turn improved the integrity of the oxide film and adhesion to the substrate. In addition, with the addition of Nb element, a large number of Nb(C, N) particles are diffusely distributed in the matrix. Nb(C, N) phase distributed in the matrix and the niobium-rich layer formed by the diffusion of niobium into the interface between the metal matrix and the oxide film during the high-temperature oxidation process effectively prevents the diffusion of iron into the outer layer and enhances the oxidation resistance at high temperatures.