Oxidation of 21Cr-6Ni-9Mn Stainless Steel in Molten Lead Oxide and Static Air^★

The effects of silicon content on the oxidation behavior of 21Cr-6Ni-9Mn stainless steel in static air and in molten lead oxide were investigated. It is concluded that the kinetics of external scale formation on air oxidized alloys are affected by silicon content. The low silicon alloys oxidize faster and exhibit a greater tendency to form a cubic internal oxide phase than high silicon alloys. Also a two-phase cubic and/or tetragonal external scale which is contrary to Beaubien et al⁴  predictions is formed. The kinetics of metal dissolution of alloys immersed in molten lead oxide also are affected by silicon content. However, the high silicon alloys dissolve faster, and all alloys exhibit a tendency to form an internal phase. The lead oxide is found to preferentially dissolve the iron and manganese of any alloy. The dissolution rate of these elements is dependent upon the availability of oxygen at the metal/scale interface and the solubility of the protective metal oxides in the molten lead oxide.