Scale formation and adhesion to mild steels during reheating for hot working.

The literature relating to scale formation and adhesion has been reviewed, with particular reference to the factors which have been found to influence the adherence of scales formed on mild steels during reheating. The methods used to assess scale adhesion and the current thoughts on the mechanism of adherence are also outlined. In addition the practical importance of scale pitting problems and current methods of' scale removal are considered.Laboratory oxidation and scale adhesion tests have been carried out on silicon killed, rimming, semi-killed and a silicon-killed aluminium treated steel under simulated reheating conditions. Temperatures in the range 950°C-1350°C were studied for times of up to three hours in atmospheres simulating the products of combustion of uncleaned coke-oven gas burnt to give 6% free oxygen in the furnace atmosphere.The oxidation behaviour was studied by metallographic examination of the scale and scale/metal interface and by thermo-gravimetric techniques.The amount of oxidation was found to increase rapidly with temperature and only approximately parabolically with time. Deviations' from classic oxidation theory are discussed with reference to the structure and composition of the scale and metal/scale interface. Although the amount of oxidation was similar for each steel studied, marked differences were found.