MODELING THE THIN-SLAB CONTINUOUS-CASTING MOLD

A three-dimensional mathematical model has been developed to compute t he thermomechanical state in the mold of thin-slab continuous casters. The thin-slab mold differs from those used in conventional slab caste rs in that the upper portion of the broad side walls defines a funnel- shaped chamber which allows the nozzle to be submerged into the liquid metal. The chamber converges with distance down the mold, reducing to the rectangular cross section of the finished casting near the mold e xit. The new mold, along with casting speeds up to 6 m/min, allows sla bs to be cast 50-60 mm thick, compared with 150 to 350 mm in conventio nal continuous slab casting. However, the mold shape and high casting speed lead to higher mold temperatures and shorter mold life than are found in conventional slab casters. In this article, we develop mathem atical models of the process to determine the role of various process parameters in determining the mold life. Finite-element analysis is us ed to determine the temperatures in the mold and cast slab, and these data are then used in an elastic-viscoplastic analysis to investigate the deformation of the mold wall in service. Cyclic inelastic strains up to 1.75 pct are found in a region below the meniscus along the funn el edge. These large strains result from the combination of locally hi gh temperatures coupled with geometric restraint of the mold. The defo rmation leads to short mold life because of thermal fatigue cracking o f the mold. The computed locations and time to failure of the mold in fatigue agree very well with observations of the appearance of mold su rface cracks in an operating caster. The models are also used to devel op an improved mold design.