Study On The Thermal-mechanical Coupling Behaviors Of Ultra-Heavy Slab Continuous Casting Under Heavy Reduction

Due to the characteristics of large cross-section size and long solidification time in the production of ultra-heavy slab,the defects of center segregation,looseness and shrinkage of the slabs are more serious than those of conventional slabs.These defects are often difficult to effectively eliminate through subsequent processing,which will seriously affect the quality of the final product.At present,the heavy reduction process can effectively reduce the center looseness and shrinkage defects of large-section slabs,significantly increase the density of the slab center,and is an important technical means to improve the quality of the ultra-heavy slab center.In order to obtain a good reduction effect during heavy reduction,it is necessary to determine key parameters such as a reasonable reduction amount and reduction position.Therefore,in this paper,the numerical simulation of the heavy reduction process is carried out,and the influence of the reduction parameters on the reduction force,the resistance of the slab and the stress,strain and temperature field of the slab is studied,which has a guiding significance for the design and optimization of the heavy reduction process.In this paper,the ultra-heavy slab is taken as the research object,and the heat transfer model of the continuous casting solidification of the ultra-heavy slab is established through numerical simulation,and the internal temperature distribution of the slab at different positions is obtained;through the hot compression experiment,Q345 is obtained Stress-strain relationship curve of steel in compression process;based on the above simulation and experimental data,a three-dimensional thermal-mechanical coupling model of heavy plate single-roll heavy reduction process was established,and comparative analysis of the slab under different reduction parameters.The situation of stress and strain and the change of pressing force and resistance provide an important basis for the design of the process under heavy pressure and the quality control of the slab.The detailed research contents are as follows:(1)The solid heat transfer model for continuous casting of ultra-heavy slab is established,and the temperature field information inside the slab is calculated,which provides a more accurate initial temperature field of the slab for the thermomechanical coupling model under heavy pressure.(2)The compression stress-strain curve of Q345 steel at a strain rate of 0.01 s^-1 in the range of 973?1673 K was measured by hot compression experiments.The results show that the maximum plastic deformation resistance of Q345 steel during compression decreases significantly with the increase of compression temperature.From 973 to 1173 K,the compressive stress increases rapidly at the beginning,and the strain reaches a peak value when the strain reaches about 0.3,and then the stress no longer increases with the increase of strain;when the temperature is higher than 1273 K,the stress curve is 0.1 The peak value is reached when the dependent variable is about.(3)Based on the calculated slab temperature field and the high-temperature mechanical performance parameters measured by the hot compression experiment,the thermal-mechanical coupling mathematical model of the slab and the roller during the single-roll heavy reduction process is established,and the different reductions and pressures are calculated.The temperature,stress,and strain of the cast slab at the lower position and the radius of the pressing roller,as well as the roller pressing force and the resistance to drawing.The results show that the area of temperature reduction of the slab caused by the interaction with the rollers is mainly concentrated at the position of 0?20 mm from the upper and lower surfaces of the slab during heavy pressing,and the temperature change decreases sharply as it goes deeper into the slab.The stress and strain of the slab increase with the reduction.When the reduction is increased from 5mm to 30 mm,the maximum stress of the slab increases from 84 Mpa to 170 Mpa.The equivalent plastic strain in the central area of the slab increases by 0.013 on average.The reduction force and blank resistance increase rapidly with the increase of the reduction.When the reduction is 30 mm,they are 13.5 MN and 5.6 MN,respectively.The solid phase ratio of the cast slab at the reduction position increased from 0.8 to 1.0,and the stress at the center of the slab,the rolling force of the roller and the resistance to the drawing increased slightly.Increasing the radius of the reduction roll can effectively reduce the maximum stress and strain of the slab,and basically has no effect on the stress and strain in the center area of the slab;at the same time,the increase of the radius of the reduction roll will also cause the reduction force and the resistance of the slab to pull.Certain increase.