A differential-scanning-calorimetry (DSC) technique was employed to measure the melting point of fayalite formed on a steel containing 0.81% Si at elevated temperatures. Effects of heating temperature and atmosphere in the laboratory and actual mill of the heating furnace on the high temperature scale adherence were investigated. The evaluation of adherence was based on the amounts of the residual scale after the oxidation followed by water quench. The results showed that the scale adherence increased significantly above 1179 ℃ when the fayalite started to melt. Increase of contents of oxidizing atmospheres (H2O, CO2) slightly enhanced the scale adherence due to the increase of cross-sectional distribution of fayalite. It was found that the scale adherence in the mill was smaller than that in the laboratory, because of the slower cooling rate and larger thermal stress in the mill.