Effect of initial surface roughness on the cyclic oxidation behavior of an austenitic stainless steel

The cyclic oxidation behavior of TP347H ASS with different initial surface roughness at 800-30 degrees C was investigated. The R-a of samples after 180#, 180#-400# SiC grinding was 0.640 +/- 0.06 mu m and 0.352 +/- 0.05 mu m, respectively. The result shows that the oxidation resistance of the alloy can be improved with the increase of the surface roughness. A thicker deformation layer with the fine grain is present beneath the rough surface, which accelerates the diffuse of Cr to form the protective oxide film. However, a non-dense Cr2O3 layer is formed on the smooth surface, which causes the significantly outward diffusion of the Fe ions to form a thick Fe-rich layer. The rapid growth of the Fe-rich oxide with a larger expansion coefficient causes the residual strain in the oxide to accumulate during the cooling process of the thermal cycle and result in the failure of the oxide film. An internal oxidation zone with an outer layer of NiFe + FeCr2O4 particles and an inner layer of NiFe + Cr2O3 particles is formed on the substrate after the failure of the oxide film. A healing Cr2O3 layer may formed at the interface of the substrate and internal oxidation zone, which achieves the transformation from internal oxidation to external oxidation.