Ways of improving steel quality in the tundish

Abstract

The role of the tundish in the continuous casting process has evolved from that of abuffer between the ladle and mold to being a grade separator, an inclusion removal deviceand a metallurgical reactor. For both grade separation and inclusion removal, the flowpatterns inside the tundish play an important role. The separation of non-metallicinclusions at the interface between the steel and the slag in the tundish is to a greatextent controlled by interfacial phenomena in the steel-slag-inclusion system. Oneconstant in the world of high-purity, low-residual and clean steels is the continual driveto reduce and control the frequency of the inclusions. For example, there are high-purity,low-residual clean steels such as IF- steel sheets for automobiles which require theabsence of oxide inclusions with diameters larger than 100 micrometers. Great efforts havebeen made to optimize the flow and turbulence in the tundish through weirs, dams or othersystems. Furthermore, a new system, the porous annular well block for injecting argon, hasbeen developed to optimize the bubble size and distribution and hence to achieve a highefficiency in trapping inclusions and in decreasing the hydrogen content in steel.Consequently, the steel quality is further improved in the tundish. Tested with success ina seamless steel shop, the new system gives results in agreement with the water models.