Effect of high-temperature oxidation on the subsurface microstructure and magnetic property of medium manganese austenitic steel

The oxidation behavior of Fe-Mn-Cr-Al-Si medium manganese austenitic steel and the effect of high-temperature oxidation on the subsurface microstructure and magnetic properties were studied. When the oxidation temperature is relatively low (800 °C and 900 °C), the oxide layer is mainly composed of Mn oxides, Fe oxides, and Mn-Cr spinel. On the other hand, at the oxidation temperature of 1000 °C, the outer oxide layer consists of Fe2O3, Mn2O3, Fe3O4, and Mn3O4, while the inner oxide layer is composed of Mn-Cr, Fe-Cr, Mn-Al, and Fe-Si spinel. A thin ferrite layer (less than 6 µm) is formed in the subsurface of the samples oxidized at 800 °C and 900 °C. However, in the subsurface of the sample oxidized at 1000 °C, a thicker martensite layer (over 100 µm) is also observed besides the ferrite layer with thickness of about 10 µm. VSM results show that the samples oxidized at 800 °C and 900 °C exhibit paramagnetic behavior attribute to the relatively thin oxide and ferrite layer. However, the sample oxidized at 1000 °C exhibits soft magnetic property due to the much thicker oxide and BCC layer.