SOLIDIFICATION MODELING OF MICROSTRUCTURES IN NEAR-NET-SHAPE CASTING OF STEELS

The relationship between heat transfer conditions and microstructure i n thin slab casting and twin-roller thin strip casting is analysed the oretically utilizing a one-dimensional solidification model. Experimen tally determined secondary dendrite arm spacing characteristics lambda (2)(x) in thin slabs and thin strips as functions of the distance x fr om the chill surface could well be approached by the model applying th e well-known empirical relations between local solidification time and lambda(2) for different steel grades. Stab-mould heat transfer coeffi cients of the order of 1.5-4.5 kW m(-2) K-1 were obtained from the bes t fits of the experimentally determined lambda(2)(x) characteristics o f thin slabs. The magnitude of heat transfer coefficients depends on t he cast steel grade and well exceeds the heat transfer in conventional continuous casting. Microsegregation between dendrite arms in thin sl abs was shown to be slightly enhanced compared with conventional slabs . Overall lambda(2)(x) characteristics of thin strips could be fitted with strip-roller heat transfer coefficients h approximate to 5-8 kW m (-2) K-1. Detailed investigation of lateral inhomogeneities of the den drite structure, however, revealed localized areas of excellent heat c ontact exceeding h approximate to 10 kW m(-2) K-1.