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Modern EAF steelmaking employs scrap as its primary source of raw material. Different sources of scrap have varying levels of residuals, which can negatively influence product properties, performance, and surface quality. The presence of some residuals, such as Cu and Ni in controlled quantities, can also positively impact steel performance for some applications. It is also well known that interactions between residuals and alloying elements in steel can modify the structure of scale formed during slab reheating prior to hot rolling. These changes in the scale structure can influence scale removability. In this study, the effect of varying Cu concentrations in a low alloyed Mn and Si containing steel was examined to investigate its impact on scale removability. Laboratory studies were performed with simulated reheating and descaling conditions that mimic the conditions used in industrial practices. The scale structure that formed during reheating in the combustion atmosphere was investigated using SEM/EDX analysis. A special laboratory water jet descaling device was used to evaluate scale removability at three different hydraulic impact factors. The results showed that Cu at different levels significantly modified scale structure that formed, particularly the internal scale layers, which affected scale removability at different applied descaling impact factors. The effects of Cu level and descaling impact factor on scale removability is discussed.

The structure, phase, and composition of scale formed on a continuously cast steel slab during reheating depend on intrinsic factors (steel chemistry, microstructure, and as-cast surface condition) and extrinsic parameters (temperature, time, composition, and velocity of combustion gas atmosphere). The scale that forms on a slab normally has several layers with differing compositions and phases and knowledge of this scale structure is important in subsequent descaling and hot rolling processing steps. Formation of multiphase scale structures on steel during high temperature oxidation in reheat furnace proceeds according to a local thermodynamic equilibrium, while thickness of layers depends on kinetic conditions (mostly by diffusion). In this study, the local thermodynamic equilibrium conditions through the scale layer were simulated using different oxygen/steel ratios, which mimicked the conditions for scale formation at the external, internal, and sublayer oxide region at metal/scale boundary. Experiments were performed in a simulated combustion atmosphere using typical industrial reheat time/temperature conditions. The phases that developed in layered scale structure were documented using SEM/EDX and Raman spectroscopy. The predicted scale compositions and phases were in good agreement with the experimental results for studies with Mn and Si-alloyed carbon steel, Cr-alloyed ferritic, and Cr, Ni-alloyed austenitic steels.

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