Preventing convexity at the narrow faces of continuous-cast billet

Abstract

At OAO Ural’skaya Stal’, there is great interest in determining the best length of the supporting system in the mold in order to prevent convexity at the narrow faces of 270 × 1200 mm slabs. To this end, the strength of the solidifying crust at the narrow face is compared with the calculated expansion pressure of the liquid metal on the crust at various points over the length of the billet. Where plastic deformation of the shell is possible, the strength of the crust may be characterized by the conditional yield point of the cast steel. The conditional yield point of 09Г2С, 15ХСНД, and Ст3сп steel is determined experimentally on a Zwick/Roell Z1600H instrument at 900–1400°C. The expansion pressure of the liquid metal on the crust is calculated by a method in which the specific casting conditions for the continuous-casting machine are taken into account. Comparison of the experimental and calculated results indicates that the crust on the narrow face of the slab (thickness 270 mm) begins to withstand the expansion pressure of the liquid metal at a distance of 1610 mm from the metal meniscus. Given that the height of the metal in the mold is around 800 mm, the length of the supporting system at the narrow faces of the billet should be 810 mm. That is possible if the number of supporting rollers (diameter 130 mm) on each side of the billet is increased from four to five. The results permit determination of the optimal length of the supporting system in the mold to prevent convexity of the narrow faces of 270 × 1200 mm slabs at OAO Ural’skaya Stal’.