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2020 Vol. 39 No. 6
Published: 2020-12-20
Continuous Casting Technology
Strand Quality
Continuous Casting Equipment
Continuous Casting Technology
1
WU Ying-dong, LIU Zhong-qiu, LI Bao-kuan
Effect of conductivity of shell on multiphysics in continuous casting mold under electromagnetic braking
Reynolds-Averaged-Navier-Stokes (RANS) method with standard
k-ε
model has been adopted to study the effect of the conductivity of the solidified shell on the flow field and electromagnetic field in the slab continuous casting mold under electromagnetic braking. Three different cases were simulated, 1—neglecting the conductivity of the solidified shell being, 2—setting the value of conductivity of solidified shell equal to that of the molten steel, 3—the conductivity of the solidified shell varying with temperature. The distributions of induced current density, Lorentz force, Joule heat and flow velocity were compared. The results show that, when the solidified shell is conductive, the upper recirculation is weaker while the lower recirculation is stronger, both vortex regions of upper and lower circulation become larger compared with when the insulating shell situation. The maximum value of induced current density, Joule heat and Lorentz force occur within the nozzle and jet region, having a larger value within the braking region and decreasing steeply with the distance from braking region. The numerical value and distribution range of the shell are obviously increased when the shell is conductive compared with when the shell is insulated. Under electromagnetic braking, the conductivity of solidified shell has a great effect on the flow pattern hence has to be considered in simulation. As the conductivity of solidified shell is so close to molten steel, thus leaving a little difference between case 2 and 3. Still, it can be seen that the differences induced by electrically conducting wall are slightly more distinct in the case 2 than case 3 for the flow field, the induced current density and the Joule heat.
2020 Vol. 39 (6): 1-8 [
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9
LI Kang-kang, ZHANG Cai-jun, XIAO Peng-cheng, ZHANG Yan-chao, HOU Ming-shan, ZHANG Jian-ping
Optimization of electromagnetic brake behavior of thin slab flow in mold
Electromagnetic braking has a significant effect on the flow of molten steel in the mold. In order to clarify the influence of electromagnetic force on the distribution of flow field in thin slab mold with high drawing speed, a three-dimensional mathematical model of molten steel flow in thin slab electromagnetic continuous casting mold was established. The numerical calculation method was used to study the influence of the coupling of magnetic field and flow field on the flow of molten steel. The simulation results show that the stable magnetic field produced by the five stage electromagnetic braking technology can significantly inhibit the turbulent flow of molten steel, reduce the meniscus fluctuation, and stabilize the interface of steel slag. Through the study of the relationship between high pulling speed and braking force, the matching degree between the magnetic induction intensity produced by the coil and different pulling speed is revealed.
2020 Vol. 39 (6): 9-14 [
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15
YE Yu-kui, YAO Cheng, LIU Yu, WANG Min, WANG Xiang-hong, BAO Yan-ping
Numerical simulation of solidification and heat transfer in bloom bearing steel GCr15
Taking a slab section was 280 mm×320 mm bloom bearing steel GCr15 as the research object, two-dimensional generous slab solidification heat transfer model was established by using ProCAST software. The paper studied the casting speed, cooling water and degree of superheat on the solidification process of slab, and through the influence on the central solid rate, determined the position of final electromagnetic stirring and the interval of soft reduction under the optimal matching the casting speed. The results show that the change of casting speed has a great influence on the central solid rate and the position of solidification end point, the influence of cooling water is greater, and the influence of degree of superheat is the least. The solidification end point increases by 1.97 m for every 0.1 m/min of casting speed, and decreases by 0.82 m for every 0.1 L/kg of secondary cooling water, and increases by 0.27 m for every 10 ℃ of degree of superheat. The optimum casting speed is 0.85 m/min. The position of final electromagnetic stirring and the interval of soft reduction match with the reasonable central solid ratio under this casting speed.
2020 Vol. 39 (6): 15-20 [
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21
ZHOU Dong-sheng, FENG Qing-xiao, LI Hua-long
Product characteristics and application progress of thin strip casting and rolling
The thin strip casting and rolling process is a short-process, near-final process that combines rapid solidification and rolling deformation. It has the advantages of short process, less procedures, low energy consumption and less emissions. The microstructure and mechanical properties of the thin strip casting and rolling products were studied, and the results show that the product microstructure is significantly different from the conventional hot continuous rolling process product in terms of grain morphology and grain size under the conditions of rapid solidification, rapid cooling and small reduction rolling of thin strip casting and rolling.Thin strip casting and rolling products have small fluctuations in performance, good isotropy, easy to weld, precise dimensional tolerances, and good surface quality. It is easy to produce high-strength thin-spec products, and has a broad application space under the trend of light weight and “substituting heat for cold”.
2020 Vol. 39 (6): 21-26 [
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27
WANG Jie, HUA Fu-bo, XIE Xiang, YANG Long-fei, WEN An-yi
Tackling on process of increasing scrap ratio of converter in smelting low-Si and Ti-containing hot metal
The scrap ratio is an important economic and technical indicator for converter production, and its value directly affects the iron loss and heat balance of steel smelting in the converter. Increasing the scrap ratio into the furnace is an important technical means to achieve iron saving and steel increase, cost reduction and efficiency increase. However, due to the difficulty of slag formation and dephosphorization of Ti-containing and low-Si molten iron, the scrap ratio into the furnace is not high, which directly affects the production cost of the converter. For this reason, based on the analysis of the characteristics and difficulties of Ti-containing and low-Si molten iron smelting, combined with Shougang Shuicheng Iron and Steel Group Co., Ltd production practice, through the optimization of oxygen lance nozzle and gun position, adding temperature raising agent et al process optimization and technological development,the scrap ratio increased from 7.41% to 13.48% and optimization effect is obvious, which laid a certain foundation for achieve iron saving and steel increase, cost reduction and efficiency increase.
2020 Vol. 39 (6): 27-33 [
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34
CHEN Shou-jie, LI Ji, WANG Jian-wei, ZHU Xian-shi, LI Ju-dong, GAO Jin-xing
Cause analysis and improvement measures to surface slag-scratch of billet 9SiCr steel
During the production of 9SiCr of high-carbon alloy tool steel in Xuanhua Iron and Steel Co., Ltd, serious slag groove defects appear on the slab surface, which will lead to the problem of steel leakage in the slag groove. Based on the field investigation and data analysis, the characteristics of steel, composition of molten steel and performance of mold flux were studied, and it was found that the high quality fraction of hydrogen in steel, the mismatching performance of mold flux and the existing problems of continuous casting process matching were the main reasons leading to the occurrence of slag groove and steel leakage in slag groove. By controlling the hydrogen content of steel within the range of 0.000 17%-0.000 23%, optimizing the performance of mold flux by reducing the basicity of the mold flux from 0.83 to 0.71 and adding 0.8% Li
2
O, and adjusting the technological parameters of continuous casting by controlling the casting temperature at 1 480-1 495 ℃, the nozzle insertion depth at 100-120 mm, and the mold cone angle at 1.2%-1.5%/m, the problems of slag runner defect and breakout problems of 9SiCr billet were solved completely
2020 Vol. 39 (6): 34-37 [
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38
YANG Ke-zhi
Influencing factors analysis and production practice of tundish argon filling replacement in continuous casting
Aiming at the poor results of argon filling replacement in the tundish before the start of pouring in No.4 Steel-making and Rolling General Plant of Ma'anshan Iron and Steel Co., Ltd., the influencing factors of the tundish argon filling replacement were studied under cold measurement experiments by using a portable flue gas analyzer,and the optimization measures were proposed. The results showed that increasing the pressure of argon filling, having a good seal of the bake holes of the tundish, between the tundish lids and the tundish lids between the tundish can effectively improve the effect of argon filling replacement. Under normal production conditions after optimization, when the diameter of the tundish argon filling tube is
ø
30 mm and the argon filling pressure is 1.4-1.6 MPa, the oxygen volume fraction after argon filling can be effectively reduced to less than 1%. When the diameter of the tundish argon filling tube is
ø
15 mm and the argon filling pressure is 0.8-1.0 MPa, the oxygen volume fraction after argon filling can be effectively reduced to less than 2%
2020 Vol. 39 (6): 38-41 [
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42
ZHANG Hong-jie, SHEN Ming-gang, WEN Mao-yuan, CAI Chang-you
Influence of total heat flux on thermal fatigue cracks of casting mold copper
With the increasing number of high speed continuous casting machine in China, the failure of mold copper has become the main form of thermal fatigue crack. The influence of temperature and total heat flux on the thermal fatigue crack of copper plate is studied by ANSYS software. The simulation results show that the temperature distribution of the mold copper is different from that of the thermal fatigue crack in production.The main reason for the thermal crack failure in the meniscus of coppers is that the concentrated area of heat flux moving up and down at certain temperature, namely the "energy flow", tears the copper plate. Therefore, reducing the total heat flux at the meniscus of the mold copper may reduce the generation of thermal fatigue cracks.The design of mold with uniform heat transfer and reducing the cracks of mold copper and continuous casting slab is the direction of future technology development. The calculation results show that groove mold is carved on the surface of copper plate, the total heat flux in the meniscus area can be reduced and the uneven heat transfer of the mold copper can be improved.
2020 Vol. 39 (6): 42-47 [
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Strand Quality
48
WEI Jun-you, ZHAO Wen-bo, CHEN Li, HU Peng, LIU Chong-lin, WAN Xiu-juan
Causes analysis of surface upwarping defects on hot rolled strip
In order to find out the cause of the surface upwarping defects of low carbon steel during hot strip rolling,the morphology and inclusion composition of upwarping defects were analyzed by sampling. The laboratory simulation of forming process of upwarping defect was analyzed by simulating rolling with a
ø
750 mm×550 mm high rigidity double-roll hot strip mill. By establishing different rolling schemes, it is proved that the upwarping defect of hot strip is formed in the finish rolling, and the defect is independent of the billet surface quality and cast edge original microstructure. In the rolling process, the side hollow is formed due to the uneven deformation of the edge. In the rolling process, the rolled material is dented on the side due to the inhomogeneity deformation of the edge, and the depression is compressed and closed by rolling in the subsequent rolling and turns to the surface to become the defect of warping skin. Finally, the industrial production test shows that chamfering slab can improve the temperature and uniformity of rolled edge during rolling, which restrain the uneven deformation of rolled edge, and effectively reduce the incidence of upwarping defects.
2020 Vol. 39 (6): 48-56 [
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57
LI Cheng-bin, LIU Jun, JIANG Peng
Defect analysis of for axle steel EA1N
This paper focuses on the quality of axle steel EA1N, and SEM-EDS was used to observe and perform energy spectrum analysis on defects. The study found that the main types of defects which mainly contain O, Al and other elements, while containing a small number of Ca and Ti, and Mg can be detected occasionally. From the energy spectrum analysis, it is known that the inclusion are the important cause of defects of axle steel EA1N. In the refining process, Al deoxidation forms a large amount of deoxidation products in the molten steel. Under the influence of refining slag and magnesium-containing refractory materials, the content of [Mg] and [Ca] in the molten steel increases, and Al
2
O
3
transformed into composite inclusions containing multiple phases. The inclusion in the steel which can not be removed by floating can easily cause harm in the subsequent rolling and heat treatment process, and lead to defects such as cracks, which directly lead to the degradation of performance. The present study provides a basis for further exploring the correlation between inclusions and defects of axle steel EA1N.
2020 Vol. 39 (6): 57-61 [
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62
YUAN Gang, YANG Zhi-chao, TANG Shu-ping, KONG Yong-jiang, YANG Yun-chao, LIU Gui-fu
Analysis and control of inclusion defects of tinplate steel slab
Aiming at the surface defects of cold-rolled tin plate, the main causes of spot/linear defects of cold-rolled tin plate were obtained by sampling and analyzing with electron microscope. It shows that the main causes of the spot/linear defects of tinplate are the slag entrapment(Al-Ca-Mg-Na-O complex inclusions) and Al
2
O
3
inclusions. By studying the cause of inclusions in the process of converter-RH refining-continuous casting, the inclusions were controlled effectively by controlling the converter tapping oxygen, extending circulation time of deoxidization-alloying and reducing oxygen blowing in RH refining process, optimizing the continuous casting process including nozzle immersion depth, argon flow rate, mold fluxes, and the amendment rate in cold rolling process caused by steelmaking process reduced obviously from 2%-3% to below 0.5%.
2020 Vol. 39 (6): 62-67 [
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68
YUAN Jing, SHI Peng-zhao, SHUAI Yong, LIAO Sang-sang, XU Li-jun, QIU Sheng-tao
Analysis of forming reasons of typical defects in 16MnDR extra-thick steel plate
In order to study and discuss the formation mechanism of typical defects of steel plate and provide theoretical reference for the stability control of steel plate quality, the causes of typical defects such as surface crack, unqualified center flaw detection and unqualified impact performance of extra thick steel plate were studied by means of metallographic microscope and scanning electron microscope. The results show that there are two causes for surface cracks of steel plate, one is the hot embrittlement caused by high harmful elements in steel, the other is the continuous casting billet crack caused by high inclusions and spread during rolling. The reason for the unqualified inspection of steel plate is the large Nb, Ti and V carbonitride precipitated from the steel plate core, accompanied by large MgO and Al
2
O
3
inclusions. The main reasons for the poor impact performance are the banded structure of the rolled plate, the upper martensite/austenitic structure containing carbon in the banded structure, the coarse grain and mixed grain.
2020 Vol. 39 (6): 68-73 [
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Continuous Casting Equipment
74
YANG Zhi-xiong, ZHU Guo-jun, ZHANG Nian-hua, YANG Peng-hui, JIA Jing-wei, SUN Feng-shuo
Analysis on sinuous oscillation parameters of billet continuous casting
According to the characteristics of four-bar linkage vibration and sinusoidal vibration, the vibration frequency, amplitude, negative slip time and other parameters are studied in this paper. The process and surface quality of billet continuous casting machine in a steel plant are introduced. The influencing factors of surface quality of billet are analyzed. The vibration parameters of the mould are analyzed theoretically and optimized. After the optimization of parameters, the surface quality and the leakage rate of the slab have been effectively improved.
2020 Vol. 39 (6): 74-78 [
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79
ZHANG Pei-li, WANG Ji-chao, YUE Zhi-kun, WANG Jian-jun
Common faults and improvement measures of tundish ladle heater optimization
The failure of the mechanical system of the tundish roaster in the continuous casting workshop of a steel plant is the damage of the burner sealing device and the fire shield. Common failures of the media system manifest as damage to the built-in control valve. Common faults in electrical systems are electrical component failure, and blower motor failure. In order to reduce the impact of equipment failure on continuous production, the common causes of roasters are analyzed, and the roasters are adapted to the actual working conditions to improve the service life of the burner sealing device and the fire cover and shorten the service life. The replacement time of the media pipeline valve reduces the failure rate of electrical components and solves the problem of blower motor failure. Through renovation, the daily maintenance cost of the equipment is reduced and the stability of the equipment is improved.
2020 Vol. 39 (6): 79-82 [
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