Tertiary Scale Behaviour during Finishing Hot Rolling of Steel Flat Products
Steel strip surface oxidation during hot mill processing represents an industrial and environmental problem: secondary oxide is removed after roughing, but tertiary oxide scales already start to form before entering the finishing stands. Their properties affect the final steel surface quality and its response to further processing. Controlling the oxide layer growth kinetics and mechanical properties can make pickling easier and improve downstream behaviour. A thin wustite-dominated scale layer (<20 μm) is created under controlled conditions in an original laboratory device adequately positioned in a compression test machine to investigate plane strain compression. A first series of oxidation tests were performed on a ULC steel grade to measure the kinetics of oxide scale growth. The samples were first heated up under a protective atmosphere (nitrogen), before being oxidised in air at different temperatures for various oxidation times. These experiments can be considered fair quantitative and qualitative simulations of scale growth as it occurs in a hot strip mill, insofar as the results thus obtained are in good agreement with the literature. After the oxide growth, plane strain compression (PSC) was performed immediately to simulate the hot rolling process. The oxide layers were characterised before and after compression tests by optical and secondary electron microscopy. As expected, the oxide is seen to deform during compression. The obtained oxide layers exhibit good adhesion to the substrate and homogeneity over the thickness, even after compression.
T. Chandra, K. Tsuzaki, M. Militzer and C. Ravindran
L. Suárez et al., "Tertiary Scale Behaviour during Finishing Hot Rolling of Steel Flat Products", Advanced Materials Research, Vols. 15-17, pp. 732-737, 2007