Effect of steel composition on failure of oxide scales in tension under hot rolling conditions

The differences in failure of oxide scales formed on mild, Si-Mn, Mn-Mo and stainless steels were investigated using a high-temperature tensile test technique over the range of test parameters near to the hot rolling conditions at entry into the roll gap. Temperature, strain and strain rates were 783 - 1200 °C, 2.0 - 5.0% and0.2 -4.0 s-1, respectively. The scale thickness was maintained within 5 - 250 μm. Mild steel has the highest oxidation rate throughout the temperature range. A slightly thicker scale for the Mn-Mo steel compared with Si-Mn steel was observed. The stainless steel has shown the highest resistance to oxidation. Although through-thickness cracks and sliding were competitive mechanisms for oxide scale failure for the mild steel, the other steel oxides failed only by through-thickness cracking or were delaminated over the whole temperature range 783 - 1200 °C. Modelling based on the finite-element method was applied for better understanding of the micro-events both du ring uni-axial tension and just before contact with the rolls. The part of the model related to oxide scale failure has been upgraded taking into account experimental evidence concerning differences in scale failure, due to the steel chemical content, which were observed in the hot tensile tests