FeMnSiCrNi Oxidation at 800 °C: Mechanism and Characterization of Improved Oxidation Resistance Generated by Vacuum Annealing Treatment

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

“…Furthermore, the formation of Mn 2 O 3 during a short period (30 to 90 min) of exposure to 1000 • C was previously observed in a similar alloy [19]. In general, it appears that the pre-treatment was successful in generating the (Mn, Cr) 3 O 4 spinels and Cr 2 O 3 oxides (the second being in very small quantities, as indicated by the low diffraction intensity), which have protective capabilities [21][22][23]. However, even with the presence of these oxides, the layer formed during the pre-treatment is not highly protective by itself, as the EDS maps do not show the presence of any continuous pure Cr oxide layer.…”

“…Both Mn and Cr contents were lower than in the unoxidized alloy, which is expected, as both Mn and Cr are consumed during oxidation. For this reason, the Cr-to-Mn ratio after pre-treatment is not as favorable for chromia formation as that previously reported and achieved via vacuum annealing [21], in which only Mn was volatilized. The EDS analysis of a pre-treated sample in Figure 2a shows the Mn-depleted region and the Mn-rich oxide layer.…”

“…This allowed the desired pre-oxidation to occur in a shorter timeframe. Also, higher temperatures favor Mn-Cr-O spinel formation in the Mn-Cr-O system [28], which is more protective than pure Mn oxides [21,23]. The samples were weighed before the pre-treatment, after the pre-treatment, and after exposure.…”

“…Despite their novelty and promising characteristics, as well as some studies interested in investigating their high-temperature properties [17,18], the usability of FeMnSiCrNi alloys at high temperatures is limited. High-temperature oxidation tests performed on FeMnSiCrNi alloys showed that their innate oxidation resistance is low when compared to conventional stainless steels [19][20][21][22][23]. This is not limited to FeMnSiCrNi alloys, as many of the recently developed multicomponent alloys present poor oxidation resistance due to the formation of complex multi-oxide layers or undesirable oxides that negatively affect protective oxide formation [24].…”

“…Among the previously attempted strategies for increasing the oxidation resistance of these alloys, pre-heat-treatment appears to be one of the most successful, as it promotes an appreciable reduction in oxidation rate and does not require compositional changes. A study on the effects of a vacuum pre-heat-treatment on an Fe-17Mn-5Si-10Cr-4Ni-VC alloy showed that pre-treated samples had a significantly lower mass gain rate than untreated ones [21]. This treatment promoted the volatilization of Mn, which is the main austenitestabilizing element in these alloys.…”