Effect of Surface Preparation on the Air Oxidation Behaviour of Modified 9Cr–1Mo Steel

Air oxidation behaviour of modified 9Cr–1Mo steel with different surface treatments is evaluated at 650 °C for about 100 h. Modified 9Cr–1Mo steel with four different surface treatments, i.e. grit blasting, grinding (120 grit finish and 600 grit finish) and diamond finish (mirror polishing), was studied to ascertain the effect of surface preparation on oxidation behaviour. The grit-blasted sample exhibited more weight gain compared to other samples, and the weight gain was higher during the initial oxidation. The nature and formation of oxide crystals/oxide layer across the surface were visualized by SEM analysis. The formation of Cr- and Fe-rich oxides on the surface, and Cr-based oxides at the interface were confirmed by the Raman spectroscopy and GDOES analysis. The formation of MnCr2O4 was also evidenced. The oxide layer thickness was measured using GDOES-DiP technique.