Research On Mechanics Characteristics Of Dynamic Soft Reduction In Continuous Casting Slabs

Internal defect restricts the development of slab continuous casting with highefficiency, and central crack is especially induced by central segregation and centralporosity in slab, which deteriorates mechanical properties of plates seriously. Dynamicsoft reduction is the effective way to decrease the central segregation and centralporosity by giving some reduction amount on the end position of solidification in slab,and it is widely used in production of casting slabs. Research shows that processparameters such as the casting temperature and the casting speed often change in theprocess of continuous casting, so the solidification and heat transfer model is difficultto predict the end position of liquid core accurately, and reduction position deviatesfrom the best position and unreasonable reduction amount applied to produce thecasting slabs. Therefore, to research the key technology parameters of dynamic softreduction in slabs, and to set reasonable reduction rules and to develop a dynamicprediction model for the end position of liquid core are benefit to accurately setreduction amount at optimum position. It is significant for improving quality ofcasting slabs, and decreasing unqualified product and shorting the development periodof new steel grades.A two dimensional solidification and heat transfer model was established. Thevariation laws of broad surface temperature, center temperature field of slab, length ofmushy zone, length of reduction zone and heat shrinkage of solidification wereresearched as the changing of the casting speed, and superheat degree, and slabthickness and steel grade respectively, and the research results provide foundation forthe setting of basic roll gaps in produce of casting slabs.A thermal elastic-plastic FEM was established in soft reduction process of castingslabs. Deformation in process of soft reduction and the varying laws of reductionefficiency with shell thickness, and reduction amount, and slab thickness and steelgrades were researched. Furthermore, stress distribution and reduction force of thepinch roll in different solid fractions in process of soft reduction were analyzed. The research provided theoretical basis for setting the optimum roll gaps and reasonablereduction zone of soft reduction.The mechanical behavior characteristics of the slab solidification shell with liquidcore during soft reduction was researched. A dynamic forecast mathematical modelwas built based on force feedback in order to predict the end position of liquid coreduring the soft reduction, and the variable laws of reaction force on pinch rolls andtotal pressure of segment with the changing of the end position of liquid core werecalculated by the mathematical model. In addition, two normal methods for judgingthe end position of liquid core was presented based on force feedback model.The existed problems of the dynamic soft reduction technology in productionprocess were analyzed, and the reasonable process regulation for the dynamic softreduction was presented. The end position of liquid core in different workingconditions was judged, and experiments in different working conditions wereconducted in order to analyze the internal quality of slab. The experiment resultsshows that the end position of liquid core judged with the force feedback model isaccuracy. It is significant to guide the engineering application for establishingreasonable dynamic soft reduction parameters and it provides theoretical basis for softreduction technology using in new steel.