A Comprehensive Analysis of Macrosegregation Formation During Twin-Roll Casting

Metallurgical and Materials Transactions B - A two-phase Eulerian–Eulerian volume-averaged model is used to predict the formation of macrosegregation during the twin-roll casting of...     

Modeling of the Twin-Roll Casting Process: Transition from Casting to Rolling

During twin-roll casting, an alloy melt is passing the gap between two counter-rotating rolls, where cooling and solidification leads to the continuous formation of a solid strand. In order to describe this process, a two-phase Eulerian–Eulerian volume-averaging model is presented that accounts for (1) transport and growth of spherical grains within a flowing melt, (2) the formation of a coherent solid network above a specific solid fraction and (3) the viscoplastic flow of the solid network with the interstitial melt during casting and compression. For the considered case of an inoculated Al–4wt%Cu alloy, the process conditions are chosen such that two relatively thick viscoplastic semi-solid shells meet between the rolls, and thus, the material is pressed together and squeezed against the casting direction. The squeezed out material consists of segregated melt and some solid that quickly disappears after melting. It is observed during this study that macrosegregation distributions are inherently connected to the mush deformation that is enforced during the hot rolling process.     

Solidification and Particle Entrapment during Continuous Casting of Steel

Avoiding particle entrapment into the solidifying shell of a steel continuous caster is important to improve the quality of the continuous cast product. Therefore, the fluid flow dynamics in the steel melt and mushy zone, heat transfer and solidification of the steel shell, as well as the motion and entrapment of inclusion particles during the casting process were investigated using computational models. Solidification of the strand shell is modelled with an enthalpy‐formulation by assuming a columnar morphology in the mushy zone. The motion of particles is tracked with a Lagrangian approach. When the particles reach the solidification front, they can be entrapped/engulfed into the solid shell or pushed away from the solidification front, depending on the mushy zone morphology and the forces acting on them. The current paper focuses on the mould region at a steel continuous caster, including the submerged entry nozzle (SEN) and 1.2 m length of the strand. The results are validated with plant measurements and demonstrate the potential of the model to predict fluid flow, shell growth and the positions and the amount of entrapped/engulfed particles in the solidifying strand.     

On the Coupling Mechanism of Equiaxed Crystal Generation with the Liquid Flow Driven by Natural Convection During Solidification

Metallurgical and Materials Transactions A - The influence of the melt flow on the solidification structure is bilateral. The flow plays an important role in the solidification pattern, via the...     

Calculation Accuracy and Efficiency of a Transient Model for Submerged Entry Nozzle Clogging

Metallurgical and Materials Transactions B - A transient numerical model was proposed and validated by the current authors for nozzle clogging (Barati et al. in Powder Technol 329:181-98, 2018)....     

Simultaneous Observation of Melt Flow and Motion of Equiaxed Crystals During Solidification Using a Dual Phase Particle Image Velocimetry Technique. Part I: Stage Characterization of Melt Flow and Equiaxed Crystal Motion

A dual phase particle image velocimetry technique is applied to study the flow pattern during a combined equiaxed-columnar solidification process. This technique is able to measure simultaneously the liquid and the equiaxed grain velocity pattern within an academic Ammonium Chloride water ingot. After the formation of a steady convection pattern, solutal buoyancy together with falling crystals destabilize and break the steady convection flow into multiple chaotic cells. In the beginning of the solidification process, the flow transitioned from 2D to a 3D turbulent regime. The kinetic energy for the flow was calculated during the solidification process.     

Simultaneous Observation of Melt Flow and Motion of Equiaxed Crystals During Solidification Using a Dual Phase Particle Image Velocimetry Technique. Part II: Relative Velocities

A two-camera Particle Image Velocimetry (PIV) technique is applied to study the flow pattern and the equiaxed crystal motion during an equiaxed/columnar solidification process of Ammonium Chloride in a die cast cell. This technique is able to measure simultaneously the liquid and the equiaxed grain velocity pattern as already shown in Part I of this paper. The interaction between the equiaxed grains and the melt flow was explored by means of relative velocities. In single isolated configurations, the settling velocity of equiaxed crystal was found to be 41 times smaller than spheres of equivalent size. The coupling between the fluid flow and the equiaxed crystals was found to be important in areas of high crystal density. Chaotic and turbulent behaviors are found to be damped in regions of high equiaxed crystal density.     

Norton-Hoff model for deformation of growing solid shell of thin slab casting in funnel-shape mold

A funnel-type mold is commonly used to provide necessary clearance for the submerged entry nozzle in the thin slab casting(TSC).The partially solidified shell i...     

Modeling the Effects of Strand Surface Bulging and Mechanical Softreduction on the Macrosegregation Formation in Steel Continuous Casting

Positive centerline macrosegregation is an undesired casting defect that frequently occurs in the continuous casting process of steel strands. Mechanical softreduction (MSR) is a generally applied technology to avoid this casting defect in steel production. In the current paper, the mechanism of MSR is numerically examined. Therefore, two 25-m long horizontal continuous casting strand geometries of industrial scale are modeled. Both of these strand geometries have periodically bulged surfaces, but only one of them considers the cross-section reduction due to a certain MSR configuration. The macrosegregation formation inside of these strands with and without MSR is studied for a binary Fe-C-alloy based on an Eulerian multiphase model. Comparing the macrosegregation patterns obtained for different casting speed definitions allows investigating the fundamental influence of feeding, bulging and MSR mechanisms on the formation of centerline macrosegregation.