FE Simulation And Analysis Of Special Steel Rod And Wire Hot Continuous Rolling Process

As the biggest steel production country in the world, China is also No.1 of theproduction capability of rod and wire continuous rolling. But there are still many problems insome aspects, such as the products quality and the fabrication of high-technique products,which have big difference with developed countries. To meet the society demands and thecompetitive market, Chinese steel companies have to make continuous improvement to theprecisions of shape, dimensions and properties of strip product, meanwhile shorten the leadtime and reduce the development the production cost. Modern rolling process ismulti-parameters, strong coupled, high non-linearity and rapid forming process. Advanceddevelopment tools are needed to enable them design and analyze the steel product and rollingprocess in an efficient and productive manner. In the past without accurate and systematicstudies, traditional rolling profile and new products fabrication were relied upon theaccumulated experience of expensive and time-consuming trial and error approach.Mathematical models of controlled rolling and controlled cooling of rod and wire rollingprocess based on the fundamental principles of continuum mechanics, heat transfer and solidphase transformation can provide more scientific and effective tools for the design and controlof rolling process to obtain steel products with rolling profile, organization and mechanicalproperties. With the development of computer hardware and software, FE simulation hasgained widespread application in rod and wire rolling industry. The special steel rod and wirecontinuous rolling mill of Dongbei Special Steel Group is studied with FE simulation method.The rod and wire hot rolling process is divided into controlled rolling process andcontrolled cooling process. The controlled rolling process is studied with 3-Dthermal-mechanical coupled FE model and the controlled cooling process with 2-Dthermo-phase coupled FE model.The controlled rolling process is complex deformation process with 30 passes. Therolling processes ofΦ8mm wire of GCr15 steel andΦ5.5mm wire of 304 stainless steel aresimulated with 3-D thermal-mechanical coupled elastic-plastic FE models developed with aseries of practical rolling parameters. All the 30 passes rolling process is separated to simulatewith several FE models according to the different deformation stages. With the continuous FEmodels, the simulation results of the whole rolling process would be obtained. Based on theconceptions of FEM, interpolation function and isoperimetric exchange, data mapping methodis developed to solve and transfer the simulation results of present model to the next one asinitial condition. Data mapping method makes it possible to study the whole mill rollingprocess with FE numerical simulation. Static and dynamic models are developed separately as rolling process is a rapid formingprocess with the rolling speed changes widely. Static model is optimized with a rigid body.The rigid body is proposed to keep a force on the deformable in static model and is used toshorten the billet length, reduce the element account and achieve a satified running efficiency.Different time step methods are proposed to optimize dynamic model. In the rolling processSimulation, the deformation process is very short compared to the whole process, and the partof billet moving in the interpass causes a lot of computative time. Auto step technology takesthe place of constant step technology to change the control of time step and distribute thecomputative time in simulation, with the purposes of shortenning the running time andincreasing the efficiency. The simulation results of static and dynamic models are compared.It can be seen that both of the two algrithms can achieve satified simulation results. But thestatic model is more accurate, and the dynamic model is more efficient. The simulation resultsshow that the static model is fit for simulating the low speed rolling process, such as atroughing mill and intermediate mill, and the dynamic model is fit for the high speed rollingprocess that the effect of rolling speed cannot be ignored such as at finishing block.The results of simlation for controlled rolling process parameters such as temperature,rolling force, defomation, stress and strain are obtained timely with the developed FE models.There are good agreement between the temperatures predicited by the simulation and thoseobtained by experimentation. The simulation results of rolling speed are found to be inexcellent agreement with the settings. It's proved the accuracy and reliability of the developedmodels. Temperature is an important parameter that shows great influence on billetdeformation and mircorstructure transformation. The controlled cooling process is simulatedand the results show the temperature curves with different controlled cooling schedules. Withthe proposed thermal-phase coupled FE model, the phase transformation of billet in controlledcooling process is studied. Different temperature variations and phase transformations atdifferent cooling conditions are obtained. In controlled cooling process the temperature arecontrolled with different settings of cooling parameters, which have great influence on theending microstructure and qualities of billet.It shows that the simulation system is capable of obtaining the billet deformation, metalflow, temperature variation and rolling force of rolled billet during rod and wire rollingprocess, and predicting the rolling loads, billet dimensions and solid transformations. It can beused to design and optimize billet rolling process. Several optimizing methods are developedwith the purpose of simulation the practical rolling process. On the basic demand of studyingthe rolling process accurately, all methods are used to increase the running efficiency so as tomake it possible to simulate the whole rolling process with practical parameters under currenthardware and software conditions. The study in this paper makes a foundation of further studying the microstructure transformations in rolling process, designing new products andoptimizing rolling mill with simulation method.