Mold behavior, heat transfer and quality of billets cast with in mold electromagnetic stirring

Mold behavior, mold-related quality and the columnar-to-equiaxed transition influenced by in-mold EMS were examined by performing trials at two steel companies, metallurgical examination of the billet samples and mathematical modelling. The effect of electro-magnetic stirring on mold heat extraction was found to be negligible. The mold temperatures and cooling water temperatures are strongly dependent on the mold/billet gap which is affected by dynamic distortion of the mold tube. In a rectangular mold, differential expansion of the wide and narrow faces of the mold led to periodic wall movement at the midface causing cycling in the mold and water temperature. Time-dependent mold distortion also resulted from boiling adjacent to the cold face due to low water velocity and poor water quality. Cooling water velocity and mold temperature profile were input to a two-dimensional transient heat-flow model to establish heat-flux profiles. A steep taper of 2.6%/m in the Mpper regions of the mold increased the heat extraction compared to previously published heat-flux data in 0.8%/m tapered-molds. However, due to the periodic wall movement in the rectangular mold, the heat-flux declines to lower values periodically.; The influence of superheat, carbon content and the radius of the machine on the columnar-to-equiaxed transition in stirred and unstirred billets was explicated based on the predictions from a one-dimensional transient heat flow/solidification model and classical solidification theories. The major heat flow effect of in-mold EMS was inferred to be one of increasing the convective heat flow at the solidification front leading to earlier superheat extraction from the liquid steel.; Electro-magnetic stirring appears not to affect either the average depth and the variation of depth of oscillation marks across a given face. No influence of EMS was found on the formation of hooks or the chill zone. Rhomboidity and off-corner crack formation were found to depend, as reported by previous researchers, on mold distortion and its dynamic nature. The absence of any effect of EMS on these defects is due to its lack of effect on mold heat transfer and thus mold distortion.