Study On Magnetoelectricity And Heat Transfer Behavior Of Continuous Casting Slab And High Temperature Mechanical Properties During Tensile Test

The crack defect of continuous casting slab is the main defect that affects the quality of slab,and its internal cause is determined by the high temperature mechanical properties of the slab.At present,the measurement of high temperature mechanical properties is mainly achieved through hot tensile test of the Gleeble thermal simulator.However,during the tensile experiment,the uneven temperature distribution of tensile specimen will affect the measured accuracy of mechanical properties obtained from hot tensile.Therefore,building magnetoelectric and thermal model for the high temperature tensile test process to study the temperature distribution of the sample and optimize the final test temperature to improve the measurement accuracy of high temperature mechanical properties is significant.In this paper,X70 steel slab is chosen as research object,through numericalsimulation method,three-dimensional mathematical model coupled electric field and magnetic field is established for copper grips and tensile sample under the alternative current input.By calculating the model,magnetic field distribution and current transmission behavior of the specimen at the typical test temperature was studied.Based on the current distribution obtained by the electric and magnetic coupling model,three-dimensional Joule thermal model coupled electric field and heat transfer for copper grips and specimen is constructed,the relationship between the input current and the stretching temperature is quantified,and the temperature distribution of the specimen at different test temperature is discussed.Based on the temperature field information,the average absolute difference method is used to optimize the test temperature during hot tensile test;finally,based on the uniaxial hot tensile test,the difference of mechanical properties data between optimized test temperature and traditional test temperature is compared and analyzed.The detailed conclusions are as follows:(1)Three-dimensional mathematical model coupled electric field and magnetic field was established for copper grips and tensile sample under the alternative current input,and magnetic field and current distribution of specimen at two typical temperature was studied.It was found that distribution of the magnetic field of sample was similar at both high and room test temperature,the value of magnetic induction intensity at surface layer was maximal and attenuated toward the center.However,the magnetic induction intensity varies greatly with temperature,at room test temperature,magnetic induction intensity is relatively large,and skin effect of current is also relatively obvious and concentrated on the surface of the sample by about 2 mm;at high temperature,the magnetic induction intensity is small.The resulting skin effect could be almost disregarded.(2)Based on the current distribution calculated by magnetic and electoral model,a three-dimensional Joule thermal model coupling electricity and heat transfer for copper grips and specimen is established.The relationship between the input current and the test temperature was quantified by a bisection method.The law of temperature distribution of sample at different test temperature is studied.Results shows that as the input current increases,the temperature first increases slowly,and then when the input current density reaches 4.5×10~5 A/m~2,the temperature increases sharply with the increase of the current.And at this current,the temperature and current almost show linear relationship;At different tensile temperature,temperature distribution in the cross section of sample is distributed symmetrically about the center and decreases from center to edge.In addition,as the test temperature increases,the temperature difference between center and surface of sample increases,in other words,the temperature gradient increases.(3)Based on the temperature information calculated by electoral and thermal coupling model in the cross-section of the specimen at different test temperature,the degree of temperature difference is defined in the form of average absolute difference,test temperature is optimized on the premise that the total value of difference is minimized.The difference between the modified test temperature and the traditional test temperature increases with the increase of the test temperature and shows a linear relationship.(4)Based on the uniaxial hot tensile test,the difference of mechanical properties between the optimized temperature and traditional temperature was compared.With the increase of the test temperature,the degree of temperature correction increases,but the difference of the ultimate strength and the yield strength between the optimized and the traditional test decreases.