Using a Two-Phase Columnar Solidification Model to Study the Principle of Mechanical Soft Reduction in Slab Casting

Abstract

A two-phase columnar solidification model is used to study the principle of mechanical soft reduction (MSR) for the reduction of centerline segregation in slab casting. The two phases treated in the model are the bulk/interdendritic melt and the columnar dendrite trunk. The morphology of the columnar dendrite trunk is simplified as stepwise growing cylinders, with growth kinetics governed by the solute diffusion in the interdendritic melt around the growing cylindrical columnar trunk. The solidifying strand shell moves with a predefined velocity and the shell deforms as a result of bulging and MSR. The motion and deformation of the columnar trunks in response to bulging and MSR is modeled following the work of Miyazawa and Schwerdtfeger from the 1980s. Melt flow, driven by feeding of solidification shrinkage and by deformation of the strand shell and columnar trunks, as well as the induced macrosegregation are solved in the Eulerian frame of reference. A benchmark slab casting (9-m long, 0.215-m thick) of plain carbon steel is simulated. The MSR parameters influencing the centerline segregation are studied to gain a better understanding of the MSR process. Two mechanisms in MSR modify the centerline segregation in a slab casting: one establishes a favorable interdendritic flow field, whereas the other creates a non-divergence-free deformation of the solid dendritic skeleton in the mushy region. The MSR efficiency depends not only on the reduction amount in the slab thickness direction but also strongly on the deformation behavior in the longitudinal (casting) direction. With enhanced computation power the current model can be applied for a parameter study on the MSR efficiency of realistic continuous casting processes.

Analysis and Application of Soft Reduction Amount for Bloom Continuous Casting Process

“…3 is another important factor which influences the SR effect, because most of SR amount is consumed on the bloom deformation process. 15,18,19) The SR efficiency η i is defined to characterize the relationship between SR amount on the strand surface and the required SR amount of the shrinkage volume. 18,20) According to the authors' previous work, 19,21) Where, R i is the surface SR amount in i th SR point shown in Fig.…”

“…[12][13][14][15][16] Recently, Menghuai Wu and et al 15,16) developed a two-phase columnar solidification model to describe the effect of shell deformation, melt flow, dendrite growth on the macro-segregation behavior, and revealed more detailed mechanism and principles of SR. However, due to the complicated coupled macro and micro factors and variable industrial process, it is still difficult to precisely quantify the SR amount, and more studies were carried out with industrial trial method.…”

Dilatancy in semi-solid steels at high solid fraction

“…On the other hand, external deformation can be beneficial such as the application of a 'soft reduction', a small rolling reduction (e.g. a few % strain) near to the end of the sump to compensate for solidification shrinkage and reduce centreline segregation and porosity [6][7][8]. Despite this importance, there remains only limited understanding of the mechanical behaviour of the mushy-zone in steels and, in particular, of their microstructural response to load and how this leads to defects.…”

Numerical Modeling of Macrosegregation in Round Billet with Different Microsegregation Models

“…Favourable results have been obtained by applying the described models to quantitatively predict macrosegregation in cast alloys. [12][13][14][15][16] Solute redistribution occurring at a moving solid-liquid interface, calculated by the microsegregation model, is known to play a significant role in the modeling of mac-rosegregation. A few microsegregation models, including the Lever rule, Gulliver-Scheil equation (Scheil), Brody-Flemings (BF) model, Ohnaka model, Clyne-Kurz (CK) model and Voller-Beckermann (VB) model, are reported in previous works.…”