Effect of Si-Addition in Stainless Steel on Surface Oxidation in Alkaline High Temperature Water

Abstract

Model alloys 9Cr-25Ni-1.5Mo-5Si and 9Cr-25Ni-1.5Mo-3Si with lower Cr and higher Ni and Si contents than 316L SS were to simulate the grain boundary chemical compositions resulting from irradiation induced segregation in irradiated austenitic stainless steels. The effect of Si-addition in the model alloys on the oxide film formed in alkaline high temperature water at 290 o C was investigated by Raman spectroscopy, scanning electron microscopy and XPS. Compact layer was observed on all the alloys after exposure for 24h or longer. The outer layer oxides on model alloys were larger than that on 316L SS after the same immersion period. The oxide films formed on 316L SS and 9Cr-26Ni-5Si after exposure to the alkaline water at 290 o C for 120 h had a duplex structure. The oxide film formed on 316L SS was thicker than that on 9Cr-25Ni-1.5Mo-5Si alloy. Oxides of silicon was identified in the inner oxide layer 9Cr-25Ni-1.5Mo-5Si alloy but not significant on 316L SS.