Continuous Casting of High-Carbon Alloy Steel Billets with Modulated Stirring at a Later Stage of Solidification

摘要

The profound effect of in-mold electromagnetic stirring, M-EMS, on improvement of as-cast product internal quality is a well-established fact. A wide zone of refined equiaxed crystals in the central area of the cast strand produced by M-EMS results in reduction of centerline carbon segregation and axial shrinkage porosity. However, the equiaxed solidification structure is also associated with the formation of V-segregation which is harmful in some steel grades and their applications.1,2,3 It was established that V- and centerline segregation ratios have values of the same order of magnitude.4 The size of segregate spots and channels, which are more pronounced in high carbon steels, also affects the segregation level.2,8 V-segregation can substantially increase the overall level of macrosegregation in both as-cast and rolled products.1,2,6,7, As both centerline and V-segregation start forming in the two-phase mushy zone, electromagnetic stirring (F-EMS) was introduced in this solidification zone in order to counterbalance this problem. To effectively deal with formation of centerline and V-segregation in the mushy zone, intensive mixing of the liquid-solid matrix should be achieved at a certain stage of the solidification process. F-EMS stirrers based on steady, unidirectional rotating magnetic field (RMF) in spite of early positive results9 have proven to be not effective for this purpose2,4,13. Stirring with alternating rotating direction has proven to be more effective, but only to a certain degree2. In order to improve stirring in the mushy zone the systems based on intermittent and alternating pulsating stirring cycles were introduced10. However, these stirring methods also had obvious limitations11.