B. Widell’s research while affiliated with KTH Royal Institute of Technology and other places

Centreline segregation in continuously cast billets has been decreased using thermal soft reduction (TSR) at the end of solidification in the caster. Full scale experiments have shown that it is possible to decrease the segregation ratio in steel with 0.51%C from 1·23 to 1·10. The segregation ratio is calculated as the mean value plus two standard deviations from 30 samples divided by the ladle composition. Multivariate data analysis (MDA) has been used to find the relationship between observed segregation and registered process variables. The MDA model's ability for explanation is sufficiently high to be used as a model for segregation prediction. The influence of different variables according to the MDA model agrees well with that determined by traditional methods of evaluation. The short range variation of segregation along the centreline can not be explained by the variables in the MDA model. Electromagnetic stirring in the mould alters the best position of the TSR cooling zone in the caster.

Various methods have been proposed to decrease centreline segregation in continuously cast billets. One method often used is electromagnetic stirring (EMS). In this study, mould EMS has been combined with thermal soft reduction (TSR) at the end of solidification in the caster. Full scale experiments have shown that it is possible to decrease the segregation ratio from 1·18 to 1·10. Multivariate data analysis (MDA) has been used to find the relationship between segregation and saved process variables. It has been found that the explanation ability of MDA is sufficiently high to be used as a tool for segregation prediction. MDA has shown that unavoidable fluctuations of variables during 'steady state' operation of the machine are of great importance for segregation. The relationship between casting variables and centreline segregation has also been obtained. It is concluded that further investigations are needed to optimise the relationship between EMS and TSR.