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 t echnique over the range of test parameters near to the hot rolling conditio ns at entry into the roll gap. Temperature, strain and strain rates were 78 3 - 1200 degreesC, 2.0 - 5.0 % and 0.2 - 4.0 s(-1), respectively. The scale thickness was maintained within 5 - 250 mum. Mild steel has the highest ox idation rate throughout the temperature range. A slightly thicker scale for the Mn-Mo steel compared with Si-Mn steel was observed. The stainless stee l 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 cr acking or were delaminated over the whole temperature range 783 - 1200 degr eesC. Modelling based on the finite-element method was applied for better u nderstanding of the micro-events both during uni-axial tension and just bef ore contact with the rolls. The part of the model related to oxide scale fa ilure has been upgraded taking into account experimental evidence concernin g differences in scale failure, due to the steel chemical content, which we re observed in the hot tensile tests.