Evaluation of solidified shell thickness by thermocouple in mold

High speed continuous casting technology has been developed to improve productivity. In this study, the method of real-time calculation of the solidified shell thickness by using multiple thermocouples embedded in the mold copper plates was tested at JFE Steel Kurashiki No. 4CCM, and the possibility of detecting various types of breakouts in high-speed casting was demonstrated. The main results are summarized as follows. (1) Real-time calculation of the solidified shell thickness at the mold outlet position was successfully achieved on the basis of the local heat flux calculated by two thermocouples installed 5 mm apart in the copper plate depth direction. (2) The calculated solidified shell thickness was in good agreement with that observed by FeS addition. (3) Retardation of solidification was evaluated by a calculation in consideration of the heat input caused by the impingement of the steel stream from the submerged entry nozzle. The index on the narrow face increased under the condition of high speed casting of narrow width slabs. (4) An instantaneous local heat flux drop in the thermocouple measurements was observed when slag rim or scum entrapment in the solidified shell occurred. The calculated solidified shell thickness at the mold outlet position was reduced to about 2/3 in this case.