Research On Comprehensive Metallurgical Behavior Of Large Bloom Alloy Steel Vertical Continuous Casting

With the rapid development of various major projects,the demand for large specification,low cost and high-end special steel is more and more intense.The round billet cast by vertical bending or arc continuous casting machine needs to go through bending and straightening process,and the larger the diameter of round billet,the more difficult the steel grade development will be.In order to meet the production of large size alloy steel,vertical continuous casting form is re-adopted,but the research on vertical continuous casting technology is rarely reported.This paper takes ?800mm alloy steel round billet vertical continuous caster as the research object,establishes the magnetic fluid-thermal mathematical model,carries on the systematic research and optimization to the continuous casting technology.The vertical continuous casting technology of large size alloy steel round billet is used to control solidification quality of large size alloy steel round billet by using slow drawing speed and narrow interval secondary cooling to reduce metallurgical length,combined with R-EMS and MARI.The large size round billet is difficult to penetrate into the round billet due to the cooling strength of water mist.In the final solidification period,the feeding time left for the liquid core is short,and the dendrite is easy to grow simultaneously,which interrupts the feeding channel,resulting in shrinkage cavity and crack defects.At the same time,solute elements are easy to concentrate in the front of solidification,forming local segregation of large round billet.Research aimed at slow speed under M-EMS and R-EMS of circulation control system,narrow range of secondary cooling and MARI of heat coagulation system,comprehensive analysis of the system of process parameters on the distribution of magnetic field in the round billet,scope of circulation flow,liquid level fluctuation,temperature range,the influence of solidified structure.The optimization and coordination of each system are good,the solidification process of vertical continuous casting is controlled,and the feeding defect and local segregation degree of large size round billet are improved.By the researches above,the following conclusions has been provided:(1)The simulation results of the heat transfer solidification model and the time-varying electromagnetic model are in good agreement with the experimental measurements.The temperature deviations of comparison points are 0.08%,0.15%,0.11%,0.12%,and the thickness deviations of billet shells are 1.38% and 0.41%,respectively.(2)When the M-EMS parameter is 380 A,3Hz;R-EMS parameter is 200 A,6Hz.The round billet has a wide range of uniform agitation,which can disperse the concentrated solute in the front area of solidification in the round billet and improve the partial degree analysis.At the same time,the hot zone is concentrated in the upper part of the mold.Reasonable liquid level temperature is beneficial to protect the melting and flow of slag and improve the quality of round billet.(3)Increasing the amount of water in the single secondary cooling zone in the narrow interval can reduce the temperature return range at the exit of the first zone,but increase the temperature return range in the zone and its subsequent zones.If the water quantity in the second cooling 1 zone increases from 10L/min to 16L/min,the temperature return range at the outlet of the mold decreases from 4.43? to 0.35?,but the temperature return range at the outlet of the second cooling zone 1 increases from 0.13? to 8.49?.(4)When the average blackness of the MARI decreases from 0.85 to 0.55,the return temperature of radiation section I increases from 10.49? to 12.98?,and the return temperature rate has little change.The temperature recovery rate at the exit of the second cooling zone 3 increases from 62.77?/m to 82.08?/m,and the over-strong insulation ability is not conducive to the temperature control of the round billet surface.(5)When the water quantity in the second cooling 1 zone is 14L/min,the water quantity in the second cooling 2 zone is 17L/min,and the water quantity in the second cooling 3 zone is 9L/min,the average blackness of MARI is optimized to 0.8.The surface return temperature of the round billet is 29?,the length and width of CET region are moderate,and the height from the beginning of CET to the meniscus is5.53 m,which is in the influence range of R-EMS.