Mechanical Properties of Oxide Scales on Mild Steel at 800 to 1000°C

Abstract

In the hot-rolling process of steels the oxide scales play a key role with regard to surface quality of the sheet. Therefore, a quantitative knowledge of the mechanical properties of oxide scales at rolling temperature can provide a significant improvement of sheet quality. In the present paper the mechanical properties of the oxide scales formed on mild steel were investigated in 4-point bend tests at 800, 900, and 1000°C in dry air, humid air (7–19.5 vol.% H₂O) and laboratory air at different deformation rates. It turns out that the environment has a significant influence on scale thickness and structure as well as on adhesion of the oxide scales. The mechanical measurements show plastic-creep deformation of the oxide scales. Water vapor did not have any significant effect on the creep properties of the oxide scales. In the measurements the secondary-creep-stress values of the oxide were determined as a function of the strain rate and plotted into an Ashby map for FeO. This plot can serve for an extrapolation of the data for even higher strain rates as relevant for the hot-rolling process.