The effect of high silicon content in steel, 1.6 wt%Si and 3.2 wt.%Si, and high oxidation temperatures (850 -1200 degrees C) on scale growth rate and morphology were investigated. The steels were oxidized in a 15% humid air with short isothermal oxidation times (15 min). The scale growth rate of the non-alloyed steel follows a parabolic law with time; it is an iron diffusion controlled oxidation. The presence of silicon delays scale growth by forming a silica SiO2 barrier layer at the scale/metal interface, this effect is more important for the steel containing 3.2 wt.%Si and induces a discontinuous scale. Silicon oxides are concentrated at the scale/metal interface; their morphology depends on the oxidation temperature. For temperatures lower than 950 degrees C, silica is formed. Between 950 degrees C and 1150 degrees C, fayalite (Fe2SiO4) grains appear in the wustite matrix close to the scale/metal interface. For temperatures higher than 1177 degrees C, a fayalite-wustite eutectic is formed; this molten phase favours iron diffusion leading to high scale growth. After cooling, a continuous fayalite layer with small wustite grains is obtained at the scale/steel interface. (C) 2013 Elsevier B.V. All rights reserved.