The deformation-induced macrosegregation in continuous casting of steel has been simulated using a finite-volume scheme. For that purpose, a two-dimensional heat-flow computation was first performed in a Eulerian reference frame attached to the mold, assuming a unique solidification path, i.e., a unique relationship between temperature and enthalpy. This gave the stationary enthalpy field in the longitudinal section of the slab. On the other hand, bulging of the slab between two rolls was calculated in the same section, assuming plane-strain deformation and using the ABAQUS code. The Lagrangian reference frame was attached to the slab, and the rolls were moved at the surface until a stationary, bulging deformation profile was reached. The bulging of the surface was then used as an input condition for the calculation of the velocity and pressure fields in the interdendritic liquid. Using a fairly simple hypothesis for the deformation of the solid skeleton, the mass conservation and Darcy equations were solved in a Eulerian reference frame. This calculation was performed in an iterative loop, within which the solute conservation equation was also solved. At convergence and using the enthalpy field, this calculation allowed to obtain the temperature, the volume fraction of solid, and the average concentration fields, in addition to the fluid velocity and pressure. It is shown that the positive centerline segregation of carbon in the slab is well reproduced with this model. The effects of shrinkage and soft reduction were also investigated.

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Mechanism of surface crack formation of steel induced by residual copper (Cu) is investigated using a new technique of Greeble test. Two kinds of experiments were carried out, to clarify the effect of temperature and to understand the behavior of crack growth. Crack is caused by liquid Cu, which precipitates at steel-scale interface during oxidation. However, no crack formed at higher temperature. Micro analysis indicates that it is due to the formation of liquid scale above eutectic temperature of FeO-2FeO¥SiO2. Liquid Cu-precipitates are trapped in the liquid scale area, and they cannot penetrate into austenite grain boundaries. The fact that silicon addition reduces the crack formation also supports this mechanism. Deformation test with various strains reveals that there exist two stages in the behavior of crack growth. At the first stage, crack grows deeper, because liquid Cu penetrates into the boundary. The crack stops growing along the depth direction and opens its width in the second stage, because of the lack of liquid Cu. That means the amount of Cuprecipitates decides the crack depth.

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