Technical note Roles of silicon and aluminium in high temperature oxidation behaviour of low alloy steel ingots in a simulated combustion atmosphere

Abstract

The effects of (0·5-2%)Si and (0 or ∼0·4%)Al contents in a low alloy steel ingot on high temperature oxidation in a simulated combustion atmosphere (N₂-6·55CO₂-18·84H₂O-3·75O₂) at 1050°C have been investigated. The experimental methods include thermogravimetric tests and analyses of oxidation products. The results indicate that the major oxidation kinetics obeyed a parabolic rate law, and diffusion of Fe²+ in the FeO layer was the rate controlling step. Increase in Si content decreased oxidation, because the FeO + Fe₂SiO₄ layer between the scale and the substrate became more compact or thicker. The effect of Al depended upon the Si content. At 0·5%Si, alloying with Al reduced the oxidation due to the segregation of FeAl₂O₄ at the scale/base metal interface. At 1%Si, Al promoted oxidation due to the doping effect of p type semiconducting oxide by small amounts of Al³⁺. At 1·5 and 2%Si, Al did not affect oxidation.