ON THE MECHANISM OF HALFWAY CRACKS AND MACROSEGREGATION IN CONTINUOUSLY CAST STEEL SLABS .1. HALFWAY CRACKS

Background/aims: Continuous casting machines must be operated under co ntrolled cooling conditions to avoid development of high thermo-mechan ical stresses in the solid shell. These stresses have a considerable i nfluence on internal quality in continuous slab casting, particularly internal cracks and macrosegregation. One form of cracks is midway cra cks or halfway cracks that appear at the various positions between the surface and the centre of the strand. In the present investigation, a mathematical model was extended to involve the effect of various cool ing conditions in which governing equations for heat transfer and soli dification were combined with a thermo-mechanical strain model to pred ict the formation mechanism of halfway cracks. Methods: The investigat ion combined industrial measurements, metallographic examination of ca st slab samples and mathamatical modelling. Results and conclusions: G ood agreements are obtained between the predicted and measured surface temperature profiles and between the predicted and observed zone of h alfway cracks under various cooling conditions. The model shows that h alfway cracks form due to a combined effect of the slab surface reheat ing and solid shell thickness on the continuous variation of load dist ribution between the rolls; the minor effect of peritectic phase trans formation on the crack morphology is also discussed. The model predict ions are the input to a coupled solidification model which is describe d as part II in a later paper.