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An oscillating multi-mold simulator with embedded thermocouples was used to study the initial solidification of medium carbon steels and crystallization characteristics of the mold flux. Casting speed variations in the simulator from 0.7 m/min to 1.4 m/min at fixed oscillation frequency and stroke resulted in higher copper mold temperatures. Frequency modifications from 2.5 Hz to 5.0 Hz and stroke changes from 8.1 mm to 5.4 mm at fixed casting speeds also resulted in higher copper mold temperatures. Surface profile analysis of as-cast steel strips showed characteristic oscillation marks comparable to the narrow faces of the industrial cast slabs. The apparent effect of casting variables on the temperature and surface profiles during the solidification of the medium carbon steels could be correlated to the variations in the negative strip time and subsequent changes in the extent of mold flux infiltration. Back scattered scanning electron microscope analysis of the full length of the retrieved flux film after casting showed cuspidine crystallization ratio that increased from the upper to lower portion of the flux film. This dynamic crystallization and growth of the cuspidine phase increases as the flux is sustained at high temperatures for longer periods. Additional experiments with industrial fluxes designed for soft cooling of medium carbon steel grades showed comparable infiltration thickness of the flux, but the crystallization characteristics were significantly different, which could have a significant impact on the heat transfer rate and mechanism through the flux film.

An inverted water-cooled multi-mold continuous casting simulator was used to investigate initial solidification of low-carbon steels and crystallization of mold flux. Embedded mold thermocouples showed characteristic temperature profiles dependent on parameters including casting speed, oscillation frequency, and stroke. Higher maximum temperatures for thermocouples at higher casting speeds, higher frequencies, and lower stroke lengths were observed. The surface of the as-cast steel strips showed oscillation marks similar to those of industrially cast slabs and higher casting speeds resulted in shallower oscillation marks. The measured pitch agreed well with the theoretical pitch suggesting the multi-mold simulator to be a cost-effective alternative to pursue fundamental studies on initial solidification in the mold. Analysis of the mold flux taken between the copper mold and solidified steel shell showed highly dendritic uni-directional crystallization occurring within the flux film suggesting that the heat transfer direction is dominantly horizontal towards the water-cooled copper mold. In addition, the solidified flux located at the upper to lower part of the mold suggested morphological differences in the size and shape of the crystalline phases indicating that crystallization ratio can increase depending upon the retention in the mold and subsequently decrease radiative heat transfer as the flux traverses down the mold.

In this study, we establish a 3-D numerical analysis model to analyze the thermal behavior and to obtain the detailed heat transfer coefficient of a copper mold in a continuous casting system. This heat transfer coefficient changes according to variations in the mold geometry or cooling system. For increased flow speeds of the cooling water, the heat transfer coefficient also increases, but the rate of increase for the coefficient diminishes at higher flow speeds. As the thickness of the mold between the melt and the cooling water slots increases, the mold’s heat transfer coefficient decreases. However, the uniformity of the heat transfer coefficient improves with greater thickness. The effect of distance between cooling water slots on the mold’s heat transfer coefficient is also observed. Calculations show that greater distances between cooling water slots decrease the heat transfer coefficient.