Research On The Shape Evolution Of The Hot Rolled Steel Strip After Finish Mill

In the production of hot rolled strips,there is a situation that they are good flatness in the exit of the finishing rolling,but the wave shape and the cross bow are found after cooling.This situation is more prominent in the hot rolled high strength steel strip produced by the rapid cooling technology,and the mechanism and evolution law are lack of a unified understanding.This problem involves the process of laminar cooling,coiling and uncoiling.It involves not only the macroscopic deformation,but also the microscopic phase transformation.In addition,there is no flatness detector after finish rolling,which makes it more difficult to research on the problem.In this paper,aimed at the wave shape and cross bow,the causes and evolution of the plate shape defects are studied hot.The main contents and results are as follows:(1)According to the equipment parameters,cooling process,experiment of isothermal transformation expansion and dynamic CCT,a multi physical field coupled three dimensional finite element model is established through the further development of the finite element software ABAQUS.The factors such as the initial temperature distribution,the thermal physical parameters,the heat exchange boundary conditions,the phase transition and the latent heat of the phase change are considered in the model.The model is based on the laminar cooling process of a 700 MPa high strength hot rolled strip and involves temperature field,phase transformation and strain/stress.The evolution of temperature,phase transformation and stress are obtained.(2)Based on the model of laminar cooling,an integrated model of the hot rolled strip after rolling was established,and the cooling process after coiling was considered.The temperature,phase transformation,strain and stress of hot rolled strip in the process from cooling to room temperature are solved.The results show that the cooling process after coiling has a great influence on the strip shape.The effects of the edge masking,sparse cooling and micro wave rolling on the strip shape are analyzed and compared with the integration model and the most effective shape optimization process is obtained.(3)Considering the effects of temperature and phase transformation,a multi field coupled finite element model for the asymmetric cooling of the upper and lower surfaces of hot rolled strip was established.The evolution law of strip transverse bending during laminar cooling is obtained,and the effects of different cooling processes and parameters on the cross bow are analyzed systematically.The viewpoint that the cross bow is caused by the asymmetry cooling of the upper and the lower surfaces during laminar cooling is changed.Based on that,an analytical model of elastic mechanics and a finite element model of the strip rolling process are established.The mechanical deformation behavior of steel strip during uncoiling is analyzed.Combined with the measurement during industrial production,the reason and main influence factors of the cross bow in the uncoiling process are obtained.