Improvement of the Oxidation Resistance of FeMnSiCrNi Alloys with a Pre-Oxidation Treatment

Abstract

Shape-memory Mn-rich austenitic stainless steels have a low high-temperature oxidation resistance because Mn tends to inhibit the formation of protective oxides. Mn depletion from oxidation also creates a ferritic Mn-depleted layer. A Mn-depleted layer formed via vacuum annealing has been associated with increased oxidation resistance. Thus, in the present study, a Mn-depleted layer was created with a pre-oxidation treatment conducted at 1000 °C for 30 min. Then, pre-treated and untreated samples were oxidized at 800 °C for up to 200 h. The resulting oxide layers were analyzed, as well as the metal/oxide interface roughness and the ferritic layer thickness. After pre-treatment, a 9 μm thick ferritic layer as well as an oxide layer richer in Cr-containing oxides than those usually observed in FeMnSiCrNi alloys oxidized at 800 °C were detected. After 200 h at 800 °C, the metal/oxide interface roughness of pre-treated samples was considerably lower. The oxidation rate of pre-treated samples was one order of magnitude lower for the first 50 h, but the effect significantly decreased afterward. The pre-existing ferritic layer was unable to stop Mn-rich oxides from being incorporated into the oxide layer, making its effect short-lived.