This paper introduces a numerical 2.5D model of continuous casting of steel slabs. This model is based on the finite element method and it has been applied to the study of some local defects in a continuous caster, such as partial blockage of nozzles (leading to a local reduction of secondary cooling rate), locking or misalignment of rolls. The purpose of the study was the evaluation of the effect of such defects on the risk of transverse cracking during bending and unbending operations. To do so, the simulation at macro-scale of the complete process has been first performed in standard conditions to get reference values and then each defect has been introduced. Defining two indexes (indicators) of the risk of transverse cracking, it has been possible to classify the defects in terms of risk increase, helping steel producers to focus on the most critical problems.Keywords: Continuous casting; Transverse crack; Nozzle blockage; Roll locking; Misalignment; Finite element
PROCESS PRESENTATION AND CHALLENGESContinuous casting has progressively replaced ingot casting over the years 70s and 80s. Nowadays it is the most common way to produce cast steel thanks to its advantages: better quality, higher yield and lower costs (in manpower and energy). The process is schematically drawn in Fig. 1: it consists in pouring a mould with molten metal, i.e. steel in the present case, that starts solidifying in contact with the walls of the mould (primary cooling). When the process is launched, the bottom of the mould is a dummy that is moving down at a constant speed, so-called casting speed, allowing a constant supplying of the process. When the dummy reaches the exit of the mould, the solidified skin of the strand should be thick and resistant enough to avoid breaking. At this moment, the core of the strand is still liquid. To keep on cooling, the surface of the strand is then sprayed with water at each roll interval (secondary cooling), so that solidification front finally reaches the core of the strand, which can be cut and generally sent to next process (rolling). Once the process has been launched, the caster is continuously supplied in molten steel and the production does not stop until the geometry (cross section) of cast product must be changed. Obviously, this short presentation of continuous casting remains simplified and partial and it does not introduce all the complexity of such a process. For further reading, a lot of information is available in literature as well as on the internet.The quality of continuously cast products is still increasing, thanks to the development and the improvement of the technique. To do so, many studies have been conducted by different teams. Among others, Brimacombe and co-workers are recognized to have helped going ahead in understanding the keys of the process, see [4][5][6]2,3,9,30]. Meanwhile, the growth of computer's potential progressively enabled the advent of powerful numerical models. Thomas and co-workers at University of Illinois have also developed many applications i...