Study On Key Technology For Inner Quality Control Of Continuous Casting Billet With Hard-line Steel

Continuous casting hard-line steel billet serve as basic material used to high strength pressing line and steel strand,their inner quality directly affect the yield and quality of final products.Therefore,this paper chooses the inner quality control of continuous casting hard-line steel billet as main contents.During the continuous casting process of billet with a cross section of 150mm×150mm in a steel plant,the eight-strand mode makes the residence time of molten steel in tun-dish of each strand differ greatly causing large difference of super heat and inclusion level among them;moreover,because of intrinsic solidification characteristics,the high carbon steel billet suffers from central segregation much.It is known to all the those potential quality problem do much harm to high inner quality of high carbon steel billet.Therefore,the present work focus on the improvement of flow characteristic of molten steel and the control of central segregation of billet,in order to improve inner quality of billet.Firstly,flow characterization of tun-dish in different control devices was studied by physical simulation method,and optional solution was presented.Secondly,combining with a pratical process parameter of billet and the result of pin shooting test,a heat transfer model for continuously cast billet was built,the change law of surface temperature、thickness of shell、liquid core length and the solidus and liquid-us line was studied in different process conditions,and installation location of F-EMS was predicted in different casting conditions.At last,the mathematical model of M-EMS was built,the change law of electromagnetic field was studied,and process parameters of M-EMS was optimized.The main conclusions are summarized as follows:(1)The results of physical simulation on the flow field of the tun-dish with original control devices show that the response time is longer,dead volume is larger of first flow and eighth flow,the response time is shorter of third flow and sixth flow,flow synchronization of each flow is poor.The flow characteristics of original control devices has a shortcomings.According to the study on present author’s laboratory,combined with real practice,turbulence suppressor and high and low dam are designed,and a new slag was established with changing original direction of tapping hole,physical simulation of different control program were studied.By thinking about average residence time、dead volume and piston flow volume and flowsynchronization of each flow of fluid have an effect on flow characteristics,for eight-strand tun-dish,the control flow effect of new slag+turbulence suppressor+double low dam has an optional selection.From eight-stand change to six-strand tun-dish,the control flow effect of new slag +turbulence suppressor has an optional selection.(2)When mold water quantity is 120m3/ h,casting speed is 1.8m/min,spray water intensity of secondary cooling zone is 0.6L/kg,when super heat from 20 ℃ to40℃,the change of the liquid is core length is from 9.50 m to 10.13 m,the distance from meniscus to installation location of F-EMS is from 6.39-7.74 m change to7.14-8.46m;when super heat is 30℃,spray water intensity of secondary cooling zone is 0.6L/kg,the change of the liquid is core length is from 9.23 m to 10.44 m,the distance from meniscus to installation location of F-EMS is from 6.29-7.57 m change to 7.18-8.60m;when super heat is 30 ℃,casting speed is 1.8m/min,basic water quantity is 0.6L/kg,basic water quantity is from 0.8 times to 1.2 times,the change of the liquid is core length is from 9.89 m to 9.77 m,the distance from meniscus to installation location of F-EMS is from 6.81-8.19 m change to 6.66-8.04 m.When mold water quantity is 120m3/h,casting speed is 1.8m/min,spray water intensity of secondary cooling zone is 1.1L/Kg,the liquid core is 9.02 m,the distance from meniscus to installation location of F-EMS is 6.00-7.29 m.(3)When current intensity is constant,with increasing of the frequency,the electromagnetic force firstly increases and then decreases,it reaches its maximum in4.5Hz.When the frequency is constant,with increasing of the current intensity,the electromagnetic force increases.Under different current intensity and different stirring frequency,the electromagnetic force increased firstly and then decreased,the electromagnetic force reaches the maximum at 4.5Hz,Therefore,the optimal stirring frequency is 4.5Hz.