The effects of flow rate and humidity on the high temperature oxidation behavior of alloys 430 and 441 in dual atmospheres (wet Ar-5vol% H-2 vertical bar dry or wet air) at 800 degrees C were investigated. All the oxide scales were composed mainly of a surface (Mn,Cr,Fe)(3)O-4 spinel layer and a Cr2O3 sublayer. Comparing to the air control samples, the air sides of alloy 430 and 441 exposed to a dual atmosphere showed different microstructures in some areas. For alloy 441, the higher flow rate of Ar-5vol% H-2 resulted in thicker oxide scales and the formation of Fe-rich nodules on the air side of sample. In addition, particles with high concentrations of Ti and Nb were found near some of the Fe-rich nodules. The effects of high water vapor content in the air oxidation were different between alloys 430 and 441, which may be attributed to both differences in the alloy composition and alloy grain size. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.013203jes] All rights reserved.