Study On Wide Scale Constitutive Relationship Of Continuous Casting Bloom In The Heavy Reduction Process

Heavy reduction technology of Continuous casting is a important method to improve the bloom center segregation,porosity and shrinkage.Deformation during the casting process is extremely important.The constitutive relationship of metal,as the basic information of the mechanical properties of bloom material and a key model of the process of bloom deformation by Finite Element Method(FEM),has widely used to describ the deformation behavior,center shrinkage welding,crack evolution law of bloom.The accuracy of the constitutive relationship directly affects the accuracy of FEM.In this paper,the FEM was used to establish a three-dimensional thermo-mechanical coupling model,the strain rate range of GCr15 bearing steel bloom under heavy reduction condition was studied.Using the method of high temperature thermal simulation,the flow stress of GCr15 bearing steel under the conditions of heavy deformation was studied.Establishing a wide-scale constitutive relationship(750-1300?)suitable for deformation under heavy pressure,the approximate treatment of stress in the high temperature zone(T>1300?)is also made.The content of this paper and the results obtained are as follows:(1)The strain rate of heavy reduction of bloom under 10-3-10-1 s-1,it was significantly higher than that of the conventional continuous casting(10-6-10-3 s-1)and below the strain rate during hot rolling(10-1-10 s-1).(2)In the process of high temperature compression,GCr15 bearing steel shows typical dynamic recrystallization characteristics at 750-1300? and 10-3-10-1 s-1.The microstructure of the samples was analyzed at high temperature,and the two temperature range,750-850?and 900-1300?,were divided to establish constitutive models.(3)The Johnson-Cook constitutive model and Arrhenius constitutive model were established under the conditions of heavy reduction deformation.The results show that the Johnson-Cook constitutive model is not applicable to the deformation under heavy reduction and Arrhenius constitutive model is suitable for deformation under heavy reduction pressure with the least error.(4)Simplifying the complicated calculation process of conventional Arrhenius constitutive model,the computational efficiency is greatly improved,and the calculation results can satisfy the calculation of FEM.(5)Based on the physical meaning of the Arrhenius constitutive model,the model parameters were calculated.The results show that the predicted values of the model have large deviations in the temperature range of 750-850?,which can not accurately describe the flow stress changes in the cementite-austenite two-phase region of GCrl5 bearing steel.The model accuracy is better than the conventional Arrhenius constitutive model in the strain rate range of 900-1300? under heavy reduction comdition,which can meet the needs of finite element simulation.A method of approximate stress treatment in the high temperature region of T>1300? is proposed,which can be used in the finite element simulation calculation.