High Temperature Oxidation of Si Containing Steel

Abstract

Red-scale is caused by the residual primary scale prior to hot rolling. In silicon- containing steel, during reheating, liquid fayalite (Fe2SiO4) forms and makes descaling difficult, thus it produces the red-scale. The aim of this study is to predict the formation of oxides so as to reduce red-scale formation and optimize the silicon concentration in steel. The formation of oxides on Fe ？C 0.1 C ？C (0 ~ 13) Si wt% steel at high temperature in air has been studied. In air, the formation energies of FeO, Fe2SiO4 and SiO2 are negative, thus those oxides can in practice form spontaneously. The most stable phase is SiO2 in air. However, FeO, SiO2 and Fe2SiO4 cannot exist in equilibrium at the single oxygen pressure at high temperatures because Fe2SiO4 is more stable than SiO2 for the given condition. The mechanism for SiO2 and Fe2SiO4 growth based on the diffusion of silicon in steel is suggested and the growth rates of SiO2, Fe2SiO4 have been calculated according to that mechanism. The calculated growth rates of SiO2, Fe2SiO4 and FeO at 1000 ▲C are, 1.62 ≠ 10-7┢m2 s-1, 2.269 ≠ 10-6 ┢m2 s-1 and 0.12 ┢m2 s-1, respectively for the relevant conditions. FeO grows much faster than Fe2SiO4 and Fe2SiO4 grow faster than SiO2. The volume fraction of each phase has been predicted according to the calculated growth rate.The oxides on Fe ？C 0.1 C ？C 1 Si wt% steel at 1000 ▲C and 1250 ▲C in air have been investigated with microscopy. Also, the effects of nickel and aluminum are investigated. The addition of nickel in Si-containing steel makes the steel/oxide interface uneven. However, no significant effect was found with the addition of aluminum.