| Solidification process of continuous casting (CC) steel liquid involves complex physical phenomena, such as liquid flow, solid movement, heat transfer in solid phase, liquid phase & mushy zone and solute transport, etc., which are important influencing factors for CC process. It has become a significant research instrument on CC process and slab quality to make study on the mentioned solidification process based on numerical simulation techniques.A hybrid numerical simulation approach has been put forward firstly in this thesis, according to the various macro-transport phenomena in CC process, in which, the whole length of caster is divided into two independent calculation domains along withdrawing direction, viz., the upper domain which is specially for the 3-D steady conjugated flow, heat transfer & solute transport mathematical model of billet CC and the lower domain which is for the 2-D unsteady heat transfer mathematical model of billet CC, and there is an organic unity of them during numerical calculation. The necessary theoretical foundation & implemental means have been provided for reasonable design of secondary cooling system, by the hybrid numerical simulation within range of whole length of caster. This method can be used in a wide range, which adapts not only to billet CC, but also to slab & thin slab CC.By consideration of fluctuations of casting temperature in tundish in actual CC process and changes of temperature of secondary cooling water in different seasons, an original frame of secondary cooling control model has been developed for the design of secondary cooling system. Besides casting speed used in normal frame of control model, two new control variable have been imported into this new model frame, as described as below: in which, refers to water flowrate, refers to casting speed, refers to superheat, , & are coefficients related to casting speed, is coefficient related to superheat, is coefficient related to temperature of cooling water.Thermal physical properties and mechanical properties of the billet samples have been measured by thermo-analyzer and thermo-simulator respectively, and scanning electron microscope analysis has also been executed for the samples, which provide the experimental gists for reasonable determining of thermo-physical properties and metallurgical rules in numerical simulation, In addition, the normal temperature performance and high temperature performance of the spraying nozzles have been tested to provide the necessary basis for accurate defining of heat transfer conditions in secondary cooling zone.Three thermo-physical properties, which are most important for accuracy of macroscale transport model, have been determined by new & more considerate methods, which include density, thermal conductivity and solute partition coefficient. Local mixing density is set to be the harmonic average of density of each phase, in which, evolution of phase density with temperature & solute concentration has been considered detailedly. Local effective thermal conductivity equals to the arithmetic average of series-wound thermal conductivity and shunt-wound thermal conductivity, in which a convection affecting coefficient is imported to depict the effect of steel liquid flow to heat transfer. For binary alloy system, in condition of equilibrium solidification, solute partition coefficient is decided directly from phase diagram, but in nonequilibrium condition, it's changing with temperature.A semi-analytic microsegreation mathematical model for binary peritectic/eutectic alloy system has been erected by strict derivation, in terms of mass balance pricinple of solute in the typical micro-solidification volume element, in which, the dilution effects of back diffusion & coarsening to solute concentration in liquid phase have been considered detailedly. For Q235 carbon steel, numerical solution of the microsegregation model will be very difficult and take a long time. A regressive analysis has been executed firstly according to two different modes (...
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