Abstract
The rate and extent of formation of crystalline phases in the slag film that develops between the mold and the strand in steel continuous casting determine heat transfer and lubrication between them and therefore play crucial roles in shell integrity. In this work, a commercial mold powder for casting medium carbon (MC) thin steel slabs is selected for carrying out detailed comparisons between predicted and experimental results of the rates of isothermal crystallization and devitrification of liquid and glassy slag, respectively. Predictions are obtained with a kinetic model that combines the induction period (of Simon and Kolman) and the Kissinger methods to evaluate time–temperature–transformation (TTT) diagrams for the devitrification and crystallization reactions associated with the peaks appearing in non-isothermal thermo-analysis traces. To obtain experimental validation of the diagram, a high-temperature confocal laser scanning microscope (HT-CLSM) is used to rapidly heat or cool a sample, ~ 140 mg, of glassy powder or liquid slag, respectively, to selected isothermal conditions, where it is held for a prescribed length of time before quenching. Identification and quantification of the phases present in the quenched samples are done by a quantitative X-ray powder diffraction analysis (QXRPDA) method that uses a PONKCS (partial or not known crystal structure) procedure based on Le Bail and Rietveld strategies for refinement of diffraction patterns. The many experimental results indicate that the predicted TTT diagrams for devitrification and crystallization of the mold slag give a good estimation of the rate of the transformations that take place at different temperatures and reveal the differences in the reactions that occur along both paths.
Published Version
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