Defect Formation Processes and Mechanisms during Twin Roll Strip Casting of Steel
【摘要】：Twin roll strip casting is a net-shape low carbon emission frontier technology for fast, efficient and direct casting of molten steel(and other alloys) into final products in the form of 1~2 mm thick strip. Due to its high cooling rate(up to 2000℃/s) and complex process during solidification, surface defects such as cracks and dents may form on the surface of the strip during casting. Therefore, their formation mechanisms need to be understood so as to eliminate these defects and generate high quality commercial steel strip products by the optimization of the production process. In this work, defect formation in low carbon steel strip produced in a twin roll strip casting pilot plant were examined by cross sectioning through the strip thickness, with the microstructure and crystallography of each cross section studied using optical microscopy, SEM and EBSD techniques. The microstructure and crystallography of the defects on the strip surface change significantly during sectioning from surface to the strip centre. In this way, the microstructures and their crystallography of the defects were successfully revealed in 3D. It was found that the atmosphere, surface texture and temperature profile of the mould(twin rollers) in the casting compartment play an important role in defect formation. Accordingly, their mechanisms of formation and relationship with key processing variables have been revealed and discussed herein. These results lay a solid foundation for the elimination of these defects in the future production of strip-cast steel products.