文摘
The effect of high silicon content in steel, 1.6聽wt.%Si and 3.2聽wt.%Si, and high oxidation temperatures (850-1200聽掳C) on scale growth rate and morphology were investigated. The steels were oxidized in a 15% humid air with short isothermal oxidation times (15聽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聽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聽掳C, silica is formed. Between 950聽掳C and 1150聽掳C, fayalite (Fe2SiO4) grains appear in the w眉stite matrix close to the scale/metal interface. For temperatures higher than 1177聽掳C, a fayalite-w眉stite eutectic is formed; this molten phase favours iron diffusion leading to high scale growth. After cooling, a continuous fayalite layer with small w眉stite grains is obtained at the scale/steel interface.
