9th ECCC European Continuous Casting Conference – ECCC 2017

Micro alloy steels are an important product within the automotive, energy, pipeline and structural segments. Superior continuous cast bloom quality is critical in order to achieve the high quality strength and toughness balance required for today’s demanding bar, plate and sheet applications. Continuous casting parameters, such as super heat, mold level fluctuation, heat transfer, fine grain chill zone depth and other process performance parameters directly influence solidification behavior and hence the surface and internal quality of the steel strand. This research identifies that the traditional hot ductility as measured via the percent reduction in area (%RA) at elevated temperature grossly overstates the minimum ductility required to assure crack-free casting of micro alloyed steels. Strain energy measured from industrial heat sample stress and strain curves are a better measure of the hot ductility behavior than %RA. This research describes the poor relationship between %RA prediction and the propensity for slab cracking during the industrial casting of micro alloyed steels. The strain at the ultimate tensile strength exhibits a very high correlation coefficient with strain energy and extremely low correlation coefficient with %RA. The carbon content, fine grain chill zone depth and strain energy directly govern hot ductility behavior and the propensity for crack formation during the unbending phase of the continuous casting process. Elements other than carbon and micro alloys exhibit secondary or tertiary root causes for crack formation.