Adhesion of thermal oxide scale formed on silicon-containing hot-rolled steel oxidised in oxygen

Abstract

Defects can be caused by the thermal oxide scale that forms on the surface of steel during the hot rolling process. The oxidation and adhesion of scale on silicon-containing hot-rolled steel were investigated in a flowing 20% O2-N2 gas mixture at 900°C. Scale spallation was observed using a tensile testing machine equipped with a CCD camera. The thickness of the scale was 3.45 μm for the higher silicon steel and 4.86 μm for the lower silicon steel. The oxide scale consists of hematite, magnetite, wustite, and iron. The strain that caused the first spallation was used to calculate the mechanical adhesion energy, which indicated the behaviour of the scale adhesion on a steel substrate. The strain initiation of the first spallation of scale on higher silicon steel was 5.57% which was higher than 4.57% for lower silicon hot-rolled steel. The calculated adhesion energy on the studied steel was shown to be in the range of 281 J.m-2 to 334 J.m-2. It can be noted that the higher amounts of silicon content in hot-rolled steel increased steel-scale interface adherence. This was due to the precipitated silicon oxide near steel-scale interface might be exhibited as a reinforcing phase.