Shape of slab solidification end under non-uniform cooling and its influence on the central segregation with mechanical soft reduction

In order to study the effect of continuous casting process parameters on the shape of slab solidification end under non-uniform cooling,a solidification model of a continuous-cast slab with non-uniform cooling condition was established with ProCAST software.The model was verified by the results of nail shooting tests and the infrared temperature measurement equipment.Four characteristic parameters were defined to evaluate the uniformity of the shape of slab solidification end.The results showed that the nonuniformity at the beginning and end of solidification,the solidification end length,and the solidification unevenness increased with the rise of casting speed.For each 10°C increase of superheat,the solidification unevenness increased by about 0.022.However,the effect of superheat on the solidification end length can be ignored.The secondary cooling strength showed minimal effect on the nonuniformity at the beginning and end of solidification.With the increase in secondary cooling intensity,the solidification end length decreased,but the solidification unevenness increased.In addition,the central segregation of the slab produced with and without the mechanical soft reduction(MSR)process was investigated.The transverse flow of molten steel with low solid fraction influenced the central segregation morphology under MSR.

Mathematical model of solidification for round CC billets

A coupled mathematical model was established to simulate the whole solidification process of round billet continuous casting for wheel steel using piecewise linear functions of heat flux density in the mold, the secondary cooling zone and the with- drawing-straightening zone. The calculated results were consistent with the measured data showing that the model accords with the practice. The surface temperature and the solidified shell thickness of round billets are more strongly influenced by casting speed than by casting temperature. The holding zones have effect on surface temperature, which is more obvious for the 450 mm round billet. The relation between casting temperature/speed and solidification end is expressed as a linear function. The solidification end is located after straightening machine.

Microstructure evolution and its influence on thermoplasticity of wide and thick continuous casting slab with heavy reduction

After the heavy reduction(HR)process was carried out at the solidification end of the continuous casting slab,the austenite grains were refined by recrystallization,which improved the thermoplasticity of the slab.However,the reduction in deformation during the HR process initiated stress concentration at the slab surface,and the crack risk increased.To effectively evaluate the risk of slab surface cracks under these complex conditions,the effect of the HR on the austenite recrystallization and thermoplasticity of a microalloyed slab surface was investigated by 15-pass reduction thermal simulation according to the wide and thick slab continuous casting process.The softening fraction was introduced as a global internal variable to quantitatively analyze various recrystallized re-refined grains.After the critical strain reaches the critical strain of dynamic recrystallization,a variety of recrystallization modes alternately occur.Among them,the contribution rate of dynamic crystallization to the later refinement reaches more than 50%.The contribution rates of static recrystallization and metadynamic recrystallization to grain refinement are almost the same.The thermoplasticity of the slab surface first increases and then decreases with increasing reduction pass.It was verified by transmission electron microscopy that the main reason for the decrease in thermoplasticity is that the dislocation multiplication rate increases,resulting in a sharp increase in stress and a decrease in thermoplasticity.