Oxidation Behavior of Stainless Steel 441 and 430 in Dual Atmosphere: Effects of Alloy Grain Boundaries

The effects of alloy grain boundaries on the oxidation behaviors of alloys 430 and 441 in dual atmospheres (35 mL/min wet Ar-5vol% H-2 vertical bar 5 mL/min dry air) at 800 degrees C for 100, 200 and 400 hours were investigated. The samples with large grain size (430: 50 mu m and 441: 150 mu m) were tested. For alloy 430, the surface of the scale formed on the dual-atmosphere samples after 100 and 200 hours oxidation contained many Fe-rich nodules along alloy grain boundaries. For alloy 441, all the oxide scales were composed mainly of a surface (Mn,Cr,Fe)(3)O-4 spinel layer and a Cr2O3 sublayer. Only some isolated areas contained Fe-rich nodules on the dual-atmosphere samples. Based on the dual atmosphere oxidation results, a model was created to describe the growth of oxide scale for samples with large alloy grain size during dual atmosphere oxidation. (C) 2013 The Electrochemical Society.