Simulation Of Hot Tandem Rolling Of Medium Plate By Using FEM And Prediction Of Its Phase Transformation In Cooling Process

Medium plate is one of the important steel products to the national economic construction.It concerns the development of many fields such as construction,transportation,national defense and pipeline transportation,etc.With the need of the transportation of oil and natural gas,the requirements on the performance of pipeline steel become higher and higher.Although medium plate can be efficiently produced by hot tandem rolling in many iron and steel company,there still exist many difficulties in the prediction and control of the microstructures and properties of it by means of the traditional experimental method,which affects the development of new products.In this thesis,the finite element method was used to simulate the hot tandem rolling of the plate.The thermal mechanical coupling finite element model was established for the simulation.The changes of temperature field,strain field and stress field during the rolling process were studied with respect to the pipeline steel X100.The influence of rolling temperature,reduction and speed on deformation behavior was analyzed.According to the characteristics of the cooling process,the FEM model for the cooling process was established.It was analyzed the influence of cooling rates on temperature field.The evolution of microstructures was also predicted on the basis of the phase transformation theory.In order to reduce the computational cost,the solid roll is viewed as a composite with rigid body in interior and elastic in exterior,which can be further simplified as a hollow cylinder.Another technique is using a model ratio to make the simulated object smaller.Considering the symmetry of the system,only a quarter of the entire model is considered for the finite element analysis.By FEM analysis,the influence of different parameters on the rolling process was obtained.With the reduction 30%and the rotate speed of the main work roll 27 rpm,the residual stress on the rolling surface reaches the largest when the rolling temperature is 1100?.While the residual stress in the central part changes little with the rolling temperature.The strain reaches the largest at rolling temperature 1100?.Under the condition of rolling temperature 1000? and the rotate speed 27 rpm,the finishing temperature is the most uniform when the rolling reduction is larger.Under the start rolling temperature of 1000 ? and reduction of 30%,when the rotate speed is larger,the final rolling temperature is more evenly distributed.The residual stress and the strain changes little with the rotate speed.In this thesis,the influence of different cooling parameters on the phase transition was studied,and the microstructure of X100 pipeline steel after cooling was predicted.When the convection coefficient is 2000 w/(m2·?),the microstructure is granular bainite and polygonal ferrite(GB+QF),which is uniformly distributed on the surface and at the center.When the coefficient is 3000 w/(m2·?),microstructures at the center is granular bainite and polygonal ferrite(GB+QF).Microstructure on the surface is mostly granular bainite and polygonal ferrite(GB+QF)and a small amount of bainitic ferrite precipitated(BF).When the convection coefficient is 4000 w/(m2·?),microstructures at the center is granular bainite and polygonal ferrite(GB+QF).Microstructure on the surface is the combination of granular bainite,polygonal ferrite(GB+QF),martensite(M)and bainitic ferrite(BF).The work of this thesis is of good value to the optimization of the plate rolling and the prediction of the microstructures,which provides a effective way to the new product development for pipeline steel.