Segregation in wide-end-up ingots (Part 3)

Increasing attention is being paid to the attainment of low sulphur levels in steelmaking practice; one of the benefits that may result from lower ingot sulphur contents is a reduced driving force for macro segregation. Top end and ?-segregates have been evaluated by assessment of ingot sections and of the rolled product of two ingots from a calcium injected cast (0.004% S) and two ingots from a comparison high sulphur cast (0.025% S) of similar base composition. Although there was no reduction in the intensity of carbon and sulphur segregation in the ingot head, the ingots of lower sulphur level did contain markedly less A-segregates. A theoretical model to determine interdendritic liquid densities and hence the potential for ?-segregate formation has been developed. This predicts beneficial effects from reduced levels of silicon (in particular) followed by sulphur, phosphorus and manganese. Higher density elements such as molybdenum are anticipated to decrease ?-segregates. Other solidification features such as general ingot structure, the bottom cone and a region of surface segregation adjacent to the head tiles have also been investigated.