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Acta Metall Sin  2019, Vol. 55 Issue (7): 875-884    DOI: 10.11900/0412.1961.2018.00487
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Influence of Electromagnetic Swirling Flow in Nozzle on Solidification Structure and Macrosegregation of Continuous Casting Square Billet
Chunlei WU,Dewei LI,Xiaowei ZHU,Qiang WANG()
1. Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shenyang 110819, China
2. School of Metallurgy, Northeastern University, Shenyang 110819, China
3. School of Resources and Materials, Northeastern University at Qinhuangdao, Qinhuangdao 066004, China
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Abstract  

During continuous casting production of square billet, the quality of steel billet is determined by equiaxed grain rate and defect grade of centerline segregation. The application of mold electromagnetic stirrer (M-EMS) can improve the quality, but it also brings some negative effects. Some researchers have attempted to make a swirling flow generated in submerged entry nozzle keep rotating in the mold to replace M-EMS. In this work, the influence of electromagnetic swirling flow in nozzle (EMSFN) on morphology of solidification structure and macrosegregation characteristics of carbon and sulfur was studied under different industrial test conditions, and the results were compared with those obtained by M-EMS. The results show that when the current frequency of EMSFN device is 50 Hz, with the current intensity increasing from 200 A to 600 A, the quantity of equiaxed grains increases gradually, while the severity of centerline segregation decreases first and then increases. The optimum value of centerline segregation was obtained when solidification structure was dominated by fine columnar crystals. Therefore, the swirling flow intensity of molten steel in submerged entry nozzle can be changed by adjusting the current parameters of EMSFN device, and thus the billets with different morphology of solidification structure and severity of macrosegregation can be obtained. Under the experimental condition, when the current parameters of EMSFN device reach certain values, EMSFN can achieve the same or even better effect as M-EMS in improving the quality of billet.

Key words:  continuous casting      solidification structure      macrosegregation      electromagnetic swirling flow      submerged entry nozzle     
Received:  30 October 2018     
ZTFLH:  TF777.1  
Fund: National Key Research and Development Program of China(No.2017YFB0304400);National Natural Science Foundation of China—Joint Research Fund for Iron and Steel of Baosteel Group Co., Ltd.(No.U1560207);Program for Liaoning Innovative Research Team in University(No.LT2017011)
Corresponding Authors:  Qiang WANG     E-mail:  wangq@epm.neu.edu.cn

Cite this article: 

Chunlei WU,Dewei LI,Xiaowei ZHU,Qiang WANG. Influence of Electromagnetic Swirling Flow in Nozzle on Solidification Structure and Macrosegregation of Continuous Casting Square Billet. Acta Metall Sin, 2019, 55(7): 875-884.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2018.00487     OR     https://www.ams.org.cn/EN/Y2019/V55/I7/875

Fig.1  Dimension and structure schematic of EMSFN device, M-EMS, SEN and mold applied in industrial test (EMSFN—electromagnetic swirling flow in nozzle, M-EMS—mold electromagnetic stirrer, SEN—submerged entry nozzle)
ItemValueUnit
Steel grade70#
Cross section140×140mm2
Pouring rate0.74m·s-1
Pouring temperature1773K
Casting rate2.56m·min-1
M-EMSON/OFF
M-EMS current intensity500A
M-EMS current frequency4Hz
F-EMSON
F-EMS current intensity500A
F-EMS current frequency12Hz
EMSFNON/OFF
Current frequency50Hz
Current intensity200, 400, 600A
Table 1  Process parameters of continuous casting

Sample No.

EMSFN

M-EMS[border:border-top:solid;border-left:solid;border-right:solid;]

F-EMS

Current frequency / HzCurrent intensity / A
150200OFFON
250400OFFON
350600OFFON
4OFFONON
Table 2  Sample number with different experimental conditions
Fig.2  Schematic of sample position (a) and solidification structures after macro etching under the conditions of EMSFN 200 A (b), EMSFN 400 A, (c) EMSFN 600 A (d) and M-EMS (e)
Fig.3  Equiaxed grain rates under different current intensities of EMSFN
Fig.4  The results of secondary dendrite arm spacing (SDAS) under different conditions
Fig.5  Segregation indexes of carbon (a) and sulfur (b) under different conditions
Fig.6  Sulfur segregation spots distributings after sulfur print under different conditions(a) EMSFN, 200A (b) EMSFN, 400 A (c) EMSFN, 600 A (d) M-EMS
Fig.7  Dimensions and distributions of sulfur segregation spots(a) EMSFN, 200 A (b) EMSFN, 400 A (c) EMSFN, 600A (d) M-EMS
Fig.8  Schematic of partition method (a) and distributing proportion results under different conditions (b) of sulfur segregation spots
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