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Research On Solidification Structure And Continuous Casting Process Simulation Of Oil Casting Steel

Posted on:2018-04-30Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y Y ZhaiFull Text:PDF
GTID:1361330572464588Subject:Metallurgical physical chemistry
Abstract/Summary:PDF Full Text Request
Oil casing steel is the most important metal consumables during the process of oil exploration,whose quality is closely related to mining safety and transportation.With strategic shift of our oil drilling industry from eastern to western and the coastal area and the deeper depth of the reservoir,the higher and newer quality and property requirements are proposed.It plays an important role to oil casing steel billet quality,for too many alloy elements and the continuous casting process as the basic sector of production of oil casing steel billet.It is frequently seen that unstable alloy composition,composition segregation and lower equiaxial crystal during the continuous oil casing steel process.In order to get the high quality oil casting,it is studied solidification characteristic and microstructure using high-temperature experiment,SEM and numerical simulation.The main technological processes such as electromagnetic stirring in-mold,optimization of water distribution of secondary cooling are simulated to get the optimum parameters of the stirring and the optimized water distribution of secondary cooling.It is significant to improve the quality of oil casting iron and save production cost.The macro solidification and heat transfer model of the continuous billet casting is built for analyzing the problems in the continuous casting,which is simulated by moving phase boundary method and changeable space finite difference method.The error is less than 2%compared to the measured temperature,because of the model with higher precision.The cellular automaton-finite difference model is built coupled with the macro solidification and heat transfer model,considering the nucleation,growth,curvature effects.The error is very little compared the simulated structure to the macrostructure.It is analyzed the technological parameters influence on the structure.It can be increasing the numbers of gains,reducing the mean radius and improving the equiaxial crystal ratio to reduce superheat.The equiaxial crystal ratio can be improved by reducing the water distribution of secondary cooling.Drawing speed has little effect on equiaxial crystal rate.It is optimized water distribution of mold and secondary cooling zone.The improved adaptive genetic algorithm is discussed to improve optimization efficiency,which is used to optimize water distribution of secondary cooling zone.The value function has been considered metallurgical criteria such as temperature limitation,drum belly limitation,heating rate,cooling rate,target temperature and cooling water consumption.During the optimization process of the oil casing steel billet,the water consumption is saved 10%,the surface temperature after optimization is more reasonable,temperature returning rate and cooling rate are very gentle.All conditions are satisfied metallurgical criteria,and reached the requirement of saving energy and reducing consumption.The electromagnetic model coupled with flow field,temperature field of M-EMS and F-EMS.The electromagnetic fields of M-EMS and F-EMS are rotating.The current intensity is increased by 250A to 400A,the maximum central magnetic induction of M-EMS is increased by 40mT to 70mT.The magnetic induction becomes smaller with the inceasing current frequency.The maximum central magnetic induction of M-EMS is 55mT with the current frequency 3Hz,reduced to 36mT with the current frequency 6Hz.The maximum tangential velocity of edge is 0.12m/s with current intensity 250A,increased to 0.18m/s with the current intensity 400A.Electromagnetic force in the radial direction of F-EMS presents the rule "small at both ends but big in the middle".When the current intensity is inceased 50A,the magnetic induction is inceased 11mT with the current frequency of F-EMS 9Hz.When the current intensity incease by 450A to 600A,electromagnetic force is increased by 3010N/m3 to 3916N/m3,max stirring rate is increased by 0.12m/s to 0.18m/s.Based on these above numerical simulation results and experiment results,the best electromagnetic optimization parameters of M-EMS and F-EMS are 300A,4Hz and 550A,8Hz.The biller quality has been improved obviously,the equiaxial crystal ratio of the billet is over 50%,most of the billet defect has disappeared,and the uniformity and compactness of billet structure has been significantly enhanced.The distribution range of C and Mo segregation after optimization becomes lower,fluctuates smaller,and composition distribution becomes more uniform.
Keywords/Search Tags:continuous casting, heat transfer of solidification, microstructure, electromagnetic stirring, water distribution of secondary cooling
PDF Full Text Request
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