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In continuous casting of steel, prevention of surface cracks on the slab is an important issue. For quantitative evaluation of cracks that occur in the continuous casting machine, the critical strain for crack generation was analyzed by a high-temperature tensile test and FEM simulation. Based on obtained material property values, a model for crack generation by tensile strain was constructed. The local strain at the notch relative to the strain in the whole specimen was determined by a simulation of the tensile test, and the critical strain for crack generation ε c was calculated. The results of a crack simulation by FEM using ε c showed that the average strain until crack initiation was small under deep notch conditions. The average strain for crack generation calculated by the simulation model was in good agreement with the value measured in the tensile test. As a result of the simulation applying temperature distribution to the slab, the depth change of the oscillation mark was more influential to crack formation than the change of the width. The effect of the shape of the oscillation mark on the crack cannot be organized only by the stress concentration factor. Simulation analysis that includes the shape of the oscillation mark is considered to be effective. Using this simulation model, it is possible to predict the generation of cracking when the temperature distribution or the oscillation mark shape in actual operation changes.

Synopsis : Controlofsolidificationmicrostructureisnecessarybecausethemicrostructureaffectsmaterialcharacters.Inordertopredictsolidification microstructure, effect of fragmentation was indirectly introduced to the cellular automaton method using V crit , which is threshold of molten steelflow.CalculationswerecarriedoutwithvariousV crit (200μms-1 V crit 1 mms-1)andtheresultswerecomparedwiththeresultsof castingexperimentusinghighcarbonsteel.Observedspecimenswereextractedfromupperpartandlowerpartofcasting.Equiaxedgrains andbranchedcolumnargrainswereobservedinthemicrostructureofupperspecimenandjustcolumnargrainswereobservedinthemicrostructureoflowerspecimen.CalculationresultswithV crit whichisgreaterthan400μms-1 show good agreement with microstructure of both observedspecimensqualitatively.Themicrostructureswerecalculatedbecauseflowvelocityofmoltensteelaroundupperspecimenwas muchgreaterthanflowvelocityaroundlowerspecimen.Thereisapossibilitythatsolutetransportationwhichinducesthefragmentationoc-cursevenifvelocityofmoltensteelflowwasintheorderof10-4 ms-1 .

In continuous casting of steel, prevention of surface cracks on the slab is an important issue. For quantitative evaluation of cracks that occur in the continuous casting machine, the critical strain for crack generation was analyzed by a high-temperature tensile test and FEM simulation. Based on obtained material property values, a model for crack generation by tensile strain was constructed. The local strain at the notch relative to the strain in the whole specimen was determined by a simulation of the tensile test, and the critical strain for crack generation ε c was calculated. The results of a crack simulation by FEM using ε c showed that the average strain until crack initiation was small under deep notch conditions. The average strain at crack generation calculated by the simulation model was in good agreement with the value measured in the tensile test. As a result of the simulation applying temperature distribution to the slab, the depth change of the oscillation mark was more influential to crack formation than the change of the width. The effect of the shape of the oscillation mark on the crack cannot be organized only by the stress concentration factor. Simulation analysis that includes the shape of the oscillation mark is considered to be effective. Using this simulation model, it is possible to predict the generation of cracking when the temperature distribution or the oscillation mark shape in actual operation changes.