The Effect of Shot Peening on the Oxidation Resistance of Super304H Steels in Water Vapor

Oxidation of shot-peened Super304H and Non Shot-Peened Super304H austenitic stainless steel were investigated at 650 degrees C/27MPa in water vapor. After oxidation for 1000 and 2000 hours, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and optical microscopy(OM) were employed to determine the morphology, chemical composition and microstructure of the oxide films, respectively. It was observed that the oxidation resistance of the Super304H steels was effectively improved by shot peening. Furthermore, spallation was only observed on the Non Shot-Peened Super304H specimens after oxidation for 2000 hours. The improvement of oxidation resistance could be attributed to the fact that the shot peening process produced an ultra-fine grain surface microstructure and plenty of grain boundaries, sub-grain boundaries and dislocations, which enhanced the diffusion of Cr to form a layer of high density of Cr-rich oxides on the surface. The shot peening processing is an effective approach, which not only improved steam oxidation resistance, but also mitigated oxide exfoliation on Super304H steel.