Thermo-mechanical behaviour of the solidified shell in a “funnel-shaped” mold for continuous casting of thin slabs

Abstract

Starting from a structural analysis of a solidified shell in a continuous casting conventional mold, the author developed a model that has now been adapted to simulate the solidification process also in the case of a funnel-shaped mold proposed for continuous casting of thin slabs. A rating of possible critical conditions in the stress level, suitable for producing cracks in longitudinal or transverse directions, is given by means of two separate cracking indices: L.C.1. (longitudinal cracking index) and T.C.1. (transverse cracking index). An analysis of the effect of a few variables on the basis of a total of 9 simulation runnings in different conditions, gave for the funnel-shaped mold the following summarized results: In comparison with a prismatic mold, casting at the same casting rate (2 m/min) and for the same product dimensions (50 mm x 1000 mm), the funnel-shaped mold behaves similarly in the corner area but less well in the center of the broad face where longitudinal cracking susceptibility is concerned. However, no significant differences result concerning transversal cracking susceptibility. Cracking risk, both transversal and longitudinal, diminishes tremendously with increasing casting rate. Cracking susceptibility when employing the funnel-shaped mold is very sensitive to small variations in the "shape" of the curved mold walls, particularly for longitudinal cracking. The effect of changing taper is not large as the gap on the short side of the mold is preserved. When the gap, on the short side, as a consequence of an excessive taper, almost disappears, in some part of the mold a great pressure concentration on the same side in the corner region is produced. The drawing action, arising on the shell because of friction, results in high shear stresses and possible cracks at the corner. Limits and reliability of the model, which depend on knowledge of high temperature steel properties, are discussed. Thermomechanisches Verhalten der erstarrten Strangschale in einer trlchterfbrmlqen Kokille zum StranggieBen dunner Brammen. Ausgehend von der Strukturanalyse einer in einer konventionellen StranggieBkokilie erstarrten Schale hat der Autor ein Modell entwickelt, das jetzt angewendet wurde, um den ErstarrungsprozeB auch fur trlchtertorrniqe Kokillen zu simulieren, die zum StranggieBen dOnner Brammen vorgeschlagen werden. Eine Bewertung rnoqlicher krltischer Bedingungen in der Spannungsebene, die Ursache fOr die Entstehung von Rissen in t.anqsund Querrichtungen sein konnen, wird durch zwei verschiedene RiBindices dargestellt: L.C.1. (LangsriB), T.C.1. (QuerriB). Eine Analyse des Einflusses einiger Variablen, auf der Basis von 9 Simulationsdurchlauten unter verschiedenen Bedingungen, ergab fur die trichtertorrniqe Kokille die folgenden zusammengefaBten Ergebnisse: 1m Vergleich mit einer prtsrnenformiqen Kokille verhalt sich die trtchtertorrnlqe -bei gleicher GieBgeschwindigkeit (2 m/min) und gleichen Produktabmessungen (50 x 1 000 mm) -in den Eckenbereichen ahnllch, in der MiUe des aufgeweiteten Bereichs aber ...

Thermomechanical finite-element model of shell behavior in continuous casting of steel

“…[14]). [31] (4) Expand this scalar stress estimate into vector form:* [32] (5) Calculate from and using the appropriate F values for the local material phase. Overall, this alternating implicit-explicit scheme with the bounded Newton-Raphson iteration gives the best robustness and efficiency of several alternative finite-element method time-integration approaches evaluated.…”

“…[32,33,34] Brimacombe, Grill, and co-workers first applied computational thermalstress models of a two-dimensional (2-D) billet section under plane stress [13,14] as it moved down the caster. These and similar early models [21,22,23] revealed important insights into crack formation, such as the need to avoid reheating.…”

Characteristics of Inclusion Motion and Accumulation in CSP Mold

“…Changping NIE, 1) Xiaofeng ZHANG, 1) Bao WANG, 1) Yuhu SUN 2) and Qing LIU 1) * The accumulation of inclusions in the initial solidified shell, which may cause longitudinal cracks, is studied in this paper. The composition, morphology and distribution of large inclusions in thin slab are investigated by inclusion measurements.…”

“…14) Specifically, the amount of simulated inclusions is determined by experimental data rather than that assumed in previous studies. [2][3][4][5][6][7] Firstly, the exact number of large inclusions in each sample was determined by SEM analysis. Then, the total amount of different-sized inclusions that enter the two-meter-long calculation domain can be calculated by Eq.…”

“…Due to the characteristics of CSP mold shape, thin slab is prone to longitudinal surface cracks. 1) Ramacciotti et al 2) found that solidifying shell in the transition region between funnel and parallel part of the funnel-shaped mold bore larger stress than that in other areas. Sun et al 3) also observed that longitudinal surface cracks mainly appeared in the 1/4 region of the broad face.…”