RI 9236 Structural Stability and Oxidation Resistance of Substitute Alloys With Various Cr and Mn Levels

The U.S. Bureau of Mines is conducting research on the oxidation resistance and structural stability of Fe-(0-8)Cr-(0-16)Ni-(0-16)Mn-3.5Si-lAl alloys as potential substitutes for high-Cr stainless steels. Oxidation tests were conducted in air over the temperature range of 6000 to 9000 C for up to 1,000 h. Microstructures were analyzed at room temperature after hot rolling. The oxidation properties and the structural stability were found to be greatly affected by the Cr and Mn levels. Although substitution of Mn for Ni increased the oxidation rate, the Mn helped to stabilize the austenitic microstructure. Decreasing the Cr content or increasing the Mn content produced higher oxidation rates and earlier oxide spalling. In this study, reaction kinetics, oxide morphologies, and microstructure of the alloys were investigated using scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, and electron microprobe analysis.