This research shows that high carbon equivalent microalloyed steels which exhibit inherently lower hot ductility,through the hot tensile test as measured by percent reduction in area(%RA),still exhibit sufficient ductility to satisfactorily meet the unbending stress and strain gradients existing in the straightening section of most industrial casters.Operational results indicate only 10%~15%RA as measured by the hot tensile test,exhibits superior ductility and no cracks are generated through the unbending section of the caster.The published%RA data over the past several years has grossly overstated the minimum ductility required for crack-free casting of Nb-bearing steels by two to threefold,as well as other microalloyed steel grades.The research study clearly connects the relationship between the steelmaking and caster operation and carbon content as the primary drivers of the hot ductility behavior and resultant slab quality.The overall composition is not the primary driver.However,the carbon level of the steel and solidification considerations are the primary drivers affecting surface quality such as slab cracking.The location of the equiaxed-columnar grain transition zone below the surfacesignificantly affects the sub-surface residual strain gradient.This paper also introduces strain energy as a better measure of the hot ductility behavior than%RA which better explains the incongruence between%RA and propensity for slab cracking in microalloyed steels.This research is based solely upon industrial produced heats with an emphasis on the effect of process parameters on hot ductility behavior and successful production of crack-free slabs.