Effect of atmosphere on oxidation behavior of novel high Mn steel bearing Cr during heat treatment

Abstract

Abstract The oxidation behavior of novel high Mn steel bearing Cr under atmospheres with varying air content was explored by means of thermogravimetric analysis. The results show that the curve of oxidation weight gain with time obeys the parabolic rate law in the temperature range of 900–1200 °C under 25–100 vol.% Air–Ar atmosphere. The atmosphere plays an important role in oxide scale structure and oxidation weight gain, especially at 900 °C and 1000 °C. Under pure air, the oxidation weight gain at 900 °C is more than that at 1000 °C after 25 min holding. This is because the inner oxide scale mainly consisting of Cr oxide at 1000 °C is thicker than that at 900 °C, which hinders the mass transfer. As air content decreases to 50 %, a similar phenomenon occurs after 65 min holding. However, under 25 % Air–75 % Ar atmosphere, the oxidation weight gain at 900 °C is always less than that at 1000 °C during 90 min holding due to the decrease of air content. An Mn-depleted zone resulting from selective oxidation of Mn is formed in the steel matrix epidermis, leading to the subsurface phase transformation (γ-Fe→α-Fe). The atmosphere with lower oxygen content contributes to alleviating surface oxidation during heat treatment.