The Effect of S and Mn on the High-temperature Oxidation and Scale Spallation Behavior of Low-carbon Steels

Abstract

Early-stage oxidation behavior in air of low-carbon steels with and without S and Mn additions was investigated in terms of oxidation kinetics and scale spallation in a temperature range of 900 to 1 150°C. S and Mn did not appear to affect the growth rate of oxide scales within the given oxidation time, ~30 min, however it was found that S significantly enhanced oxide scale spallation. Scale spallation occurred only on the S doped steels oxidized at temperatures more than 1 000°C when the thickness of oxide scale exceeded about 120,um. This scale spallation was confirmed to occur during cooling after the given oxidation time. GD-OES analysis revealed that a significant amount of S enrichment occurred at the oxide/steel interface, which was around 1 mass% on 100 ppm S steel after 120 s of oxidation at 1 150°C. Such sulfur enrichment was speculated to be due to accumulation of rejected S from surface recession during the high-temperature oxidation. Observation of the steel surface after complete removal of the oxide scale by quenching the steels into liquid nitrogen clearly indicates the formation of eutectic Fe-FeS structure at scale/steel interface, resulting from a liquid phase formation above 1 000°C. Formation of sulfide, and therefore a liquid phase at higher temperature, greatly affected oxide scale spallation.