مدل انتقال حرارت سردشدن ورق نورد گرم بين نورد نهايي تا كلاف پيچي براي انواع مختلف و چيدمان هاي متنوع نازل ها

چكيده انگليسي :

Heat Transfer Modeling of Hot Rolled Strip Cooling between Finishing and Coiling for Different Nozzle Types and Different Nozzle Arrangements Sheila Edalatpour s edalatpour@me iut ac ir May 22 2010 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Dr Ahmad Saboonchi ahmadsab@cc iut ac ir AbstractRun out table ROT is located between last finishing stand and down coiler in a hot strip mill As the hot steel strippasses from ROT water jets impact on it from top and bottom and strip temperature decreases approximately from800 950 C to 500 750 C The temperature history that strip experience while passing through ROT affectssignificantly the metallurgical and mechanical properties such as strength stiffness weldability fatigue resistance flexibility and the flatness of the final product Consequently the mill engineers and researchers are much interestedin attaining desired mechanical and metallurgical properties of the product through controlling the cooling rate andtemperature history and even with reducing amount of carbon contents Reducing carbon content considerablyimproves the weldability due to reducing hardenability of the steel In achieving this aim it is vital to developphysical models which are capable of precisely predicting the temperature history and phase transformation kineticthrough ROT The heat transfer mechanisms in ROT are heat conduction in steel strip natural and force convection with air radiation and forced convection boiling heat transfer due to impacting subcooled water jets It is also coupled withphase transformation phenomenon because of the heat released during decomposition of austenite into ferrite pearliteand bainite during strip cooling In addition to these complexities other effects such as strip movement changing ofthermo physical properties with steel phase mixture and temperature the water stream on the plate and its temperatureincrement have been redoubled the difficulties of developing a precise model for prediction of such behaviors As aresult most of the developed models consider either heat transfer characteristics of impacting water jets and local heattransfer phenomenon or predicting phase transformation kinetics during strip cooling Recently researchers began toconsider the strong interaction between the heat transfer and phase evolution In this thesis a numerical model was developed to predict the temperature and phase transformation of strip on a run out table ROT in hot strip mill Furthermore this model could predict final phases produced during cooling in theterm of nozzles arrangement in ROT With this feature the mill engineers would be able to arrange nozzleconfiguration in order to obtain desired steel final phases Alternating direction implicit ADI method was used to solve the heat conduction equation in both thickness andwidth direction in the strip The kinetics of the diffusional transformation of austenite to ferrite had been calculated forthe isothermal condition by Avrami equation and additivity rule The specific heat thermal conductivity and densityof steel had been determined in the term of phase fraction and temperature Accuracy of the phase transformation model was examined through comparing the results with the results presented inthe literature and the accuracy of the proposed coupled complete model was examined through comparison of coilingtemperatures obtained from the model with the actual data ones from Hot Strip Mill in Mobarake Steel Complex Theerror of the model for predicting coiling temperature is less than 3 that indicates the capability of the model inpredicting temperature and phase transformation in ROT Keywords Hot Strip Mill Strip Cooling Run Out Table Phase Transformation ADI method Avrami Equation

عدالت پور، شيلا

مدل انتقال حرارت سردشدن ورق نورد گرم بين نورد نهايي تا كلاف پيچي براي انواع مختلف و چيدمان هاي متنوع نازل ها

نورد گرم ورق , خنك كاري ورق , ميز خروجي نورد گرم , تغيير فاز , روش ADI , معادله آورامي