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2021 Vol. 40 No. 6
Published: 2021-12-18
Continuous Casting Technology
Strand Quality
Continuous Casting Equipment
1
WANG Xing-juan, ZHOU Le-jun
Preface
2021 Vol. 40 (6): 1-1 [
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Continuous Casting Technology
2
ZHU Li-guang, ZHANG Li-min, WANG Xing-juan, ZHANG Cai-jun, HAN Yi-hua, SUN Li-gen
Physical experiment and numerical simulation of flow field on funnel mold surface
When the casting speed of FTSC thin slab is increased to 4-6 m/min, the amount of steel passing through the submerged nozzle increases, the disturbance of flow field in mold intensifies, and the rate of slag entrapent increases, which will have a great influence on the running of production and the quality of slab. Therefore, in order to understand the flow field distribution on the mold surface, this paper made a 1∶1 mold water physical model according to the actual production, and carried out numerical simulation of the flow field on the mold surface through Fluent software, and studied the influence of the submerged entry nozzle depth and casting speed on the flow field on the liquid surface. The results show that the mold surface velocity increases with the increase of the casting speed in the range of 4-6 m/min, and its maximum value ranges from 0.401 m/s to 0.693 m/s when the nozzle immersion depth is constant 130 mm. At a constant casting speed of 6 m/min, the nozzle immersion depth is in the range of 130-190 mm, and the surface velocity of the mold decreases with the increase of the nozzle immersion depth, with the maximum range of 0.503-0.690 m/s. In the numerical simulation, when the nozzle immersion depth is constant at 130 mm and the casting speed is in the range of 4-6 m/min, the surface velocity of mold increases with the increase of the casting speed, and its maximum value ranges from 0.50 to 0.75 m/s. At a constant casting speed of 6 m/min, the nozzle immersion depth is in the range of 130-190 mm, and the surface velocity of the mold decreased with the increase of the nozzle immersion depth, with the maximum range of 0.65-0.75 m/s. The velocity of the mold surface increases first and then decreases with the increase of the distance from the center of the nozzle.
2021 Vol. 40 (6): 2-8 [
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9
LI Si-jun, PENG Yong-xiang, LI Ping, NING Wei, DU Jin-ke, FU Chang-wei
Optimization of asymmetric flow field and temperature field of ultra-thin and large section beam blank mould
A 0.7∶1 hydraulic test model was established to optimize the nozzle structure to improve the flow field of ultra-thin large section blank, and the three-dimensional flow field and temperature field of molten steel in the mold and its secondary cooling section were numerically simulated under actual production conditions. It was showed that the flow field distribution in the existing through nozzle mould was extremely asymmetric and the response time of each position of the mould was quite different, resulting in the uneven distribution of temperature and composition in the mold. The optimized three-side hole and one bottom-hole nozzle effectively solves the problem of long and inconsistent response time at different positions of the mould and improves the serious asymmetric flow field during single-point straight-through nozzle pouring. The temperature difference between the pouring side and the non pouring side is significantly reduced, and the temperature change along the drawing direction is also more reasonable, which is conducive to the formation of a good solidified shell. This process provides guidance for actual production.
2021 Vol. 40 (6): 9-16 [
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17
ZHANG Lu-ping, XIAO Peng-cheng, LIU Zeng-xun, ZHANG Zhao-yang, ZHU Li-guang, ZHANG Shi-jun
Heat transfer behavior of inner shell of ultra-high speed continuous casting mould
The growth rate of slab shell in the mould of ultra-high speed continuous casting funnel has a significant effect on the surface quality of slab. Based on the node temperature inheritance algorithm (NTI), the three-dimensional transient thermal conductivity model of molten steel solidification in mold was established by using ANSYS finite element software, and the influence of casting temperature and casting speed on the heat transfer behavior of thin slab was analyzed. The results show that with the increase of casting speed from 4.0 to 6.0 m/min, the maximum thickness of slab shell at the exit of mold decreases from 26 to 12.8 mm, and the maximum surface temperature of slab shell at the exit of mold increases from 1 209 ℃ to 1 305 ℃. However, the increase of casting temperature from 1 550 ℃ to 1 560 ℃ has little effect on the surface temperature and thickness of slab shell.
2021 Vol. 40 (6): 17-23 [
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24
SHI Hong-yan, WU Chun-lei, LIU Li, TIAN Sheng-lin, LIU Xiao-ming, WANG Qiang
Liquid level fluctuation in mold controlled by electromagnetic nozzle swirling flow in continuous casting of round bloom
In the continuous casting production of round bloom, vigorous mold electromagnetic stirring (M-EMS) could cause violent liquid level fluctuation in the mold, which affects the surface and internal quality in the bloom. An electromagnetic swirling flow in the nozzle (EMSFN) was applied together with the mold electromagnetic stirrer during the continuous casting. The secondary flow induced by M-EMS was weakened by adjusting the stirring direction and the current intensity of the EMSFN device, so that the liquid level fluctuation in the mold could be controlled within a small range. The results show that when the stirring direction of EMSFN device is opposite and the current intensity is 400 A, the fluctuation proportion more than ±2 mm is decreased from 0.62% to 0.13%, and the fluctuation proportion within ±1 mm to ±2 mm is decreased from 5.90% to 3.56%, compared with the results by using only M-EMS in the same strand. When the stirring direction of EMSFN device is the same, the control effect on the liquid level fluctuation more than ±2 mm is not good. Therefore, the liquid level fluctuation can be controlled by the opposite nozzle swirling flow at certain stirring magnitude.
2021 Vol. 40 (6): 24-28 [
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29
LIU Bin, WANG Ming-lin, ZHANG Hui, WU Xuan, YU Yue, WANG Xue-bing
Effect of casting speed on molten steel flow in slab chamfered mould
In order to study the casting speed on the condition of solidified slab shell has effects on the flow and heat transfer in the slab chamfered mould, a three-dimensional mathematical model of flow, heat transfer and solidification of slab chamfered mould and a physical model of slab chamfered mould with section size of 1 490 mm×230 mm and similarity ratio of 1∶1 were established by combining numerical simulation and physical simulation. The comparison between numerical simulation and physical simulation of flow field morphology and flow velocity at the same position of liquid surface shows that the trend of numerical simulation and water simulation is consistent. Casting speed has obvious effect on the numerical value of the flow field and temperature field in the chamfered mould, but has little effect on the overall shape. when the casting speed is increased to 1.7 m/min, the liquid surface velocity is too fast and fluctuates sharply, and slag entrapment is easy to occur.With the increase of casting speed, the impact of molten steel stream on the narrow surface solidified billet shell will be strengthened, resulting in remelting and thinning of the billet shell.Within the scope of this experiment, a better comprehensive effect can be achieved by producing at a casting speed of 1.5 m/min.
2021 Vol. 40 (6): 29-37 [
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38
PEI Ying-hao, ZHU Tao, WANG Ru-yu, XIAO Chao, WANG Hai-jun
Influence of nozzle immersion depth on liquid steel flow in CSP mould
In order to solve the problem of CSP slab surface quality under high-speed production conditions, the liquid steel flow and level fluctuation of the CSP mould has been studied by numerical calculation method with FLUENT for the CSP continuous caster of a factory. The research results show that the flow field in the mould is basically the same when different nozzle immersion depths. Increasing the nozzle immersion depth has no obvious effect on the mould flow field. The immersion depth of the nozzle directly determines the position where the stream flowing from the nozzle hits the narrow surface of the mould. Furthermore, when the immersion depth of the nozzle increases from 300, 340 to 380 mm, the maximum flow velocity at the liquid level is 0.180, 0.160 and 0.127 m/s respectively. When the nozzle is immersed in depth, the disturbance of the mold backflow on the mould level fluctuation will be weakened, and the corresponding number of slag coiling will be reduced.
2021 Vol. 40 (6): 38-43 [
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44
FENG Yong-ping, ZHENG Na, TANG Lei, XIE Jian
Simulation of solidification and heat transfer for steel in mold of thin slab continuous casting
To investigate the growth process of solidified shell in the mold at high casting speed for thin slab continuous casting. A two-dimensional solidification and heat transfer finite element model was developed based on ANSYS software. The rationality of model was verified by tested shell thickness. The process of shell formation is simulated for Q235B steel 1 500 mm×60 mm shin slab, and the effect of different casting speed and mold cooling water was studied. The results show that: the thickness of billet shell increases with the decrease of drawing speed, As the cooling water flow of the mold increases, the thickness of the blank shell increases, the trend of simulation and measurement was consistent, which provide the theoretical reference for optimizing process parameters.
2021 Vol. 40 (6): 44-47 [
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Strand Quality
48
WANG Wan-lin, YAN Xiong, ZHOU Le-jun, LUO Hao, HE Hang, SONG Guang-xin
Properties of mold fluxes for casting high carbon steel
In order to study the compatibility of mold fluxes for casting high carbon steel in the process of continuous casting, the melting, wettability, viscosity, phase distribution and heat transfer ability of typical mold fluxes for casting high carbon steel have been investigated. The results show that the ranges of the initial melting temperature, wetting angle, viscosity, breaking temperature and liquid layer ratio of the four mold fluxes are 1 110-1 129 ℃, 30.1°-37.8°, 0.210-0.312 Pa·s, 1 046-1 130 ℃ and 14.7%~18.9%, respectively. Among these mold fluxes, mold flux 1 can melt very fast to form liquid slag, and infiltrate the gap between mold wall and shell to form even slag film, since its melting temperature (1 110-1 345 ℃) and viscosity (0.264 Pa·s) are relatively low, liquid layer ratio (18.9%) is relatively high, and break temperature (1 059 ℃), as well as heat transfer ability are appropriate. These advantages can reduce the stick breakout and cracks, meanwhile smooth the high carbon steel continuous casting process.
2021 Vol. 40 (6): 48-53 [
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54
ZHOU Le-jun, YANG Yang, WANG Wan-lin, PAN Zi-hang
Effect of boron oxide on dissolution kinetics of TiO
2
in mold flux
In the continuous casting process of titanium containing steel, some TiO
2
inclusions enter the mold flux, which leads to the deterioration of slag properties and affects the slab quality. The relationship between the dissolution rate of TiO
2
in mold flux and the factors such as rotation speed, temperature and B
2
O
3
content was studied by rotation method. The results show that the dissolution rate of TiO
2
in mold flux is directly proportional to the square root of the angular velocity of rod rotation. The dissolution rate of TiO
2
in mold flux increased significantly with the increase of temperature. When
w
(B
2
O
3
) = 0-9%, with the increase of B
2
O
3
content, the dissolution rate of TiO
2
increases, and dissolution activation energy decreases from 162.99 to 123.95 J/mol, but the effect of B
2
O
3
content on the dissolution rate is significantly less than that of temperature. The above research results better clarify the dissolution mechanism of TiO
2
in mold flux, which can provide a certain reference for the continuous casting process of titanium containing steel.
2021 Vol. 40 (6): 54-58 [
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JIN He-bin, JI Jun-de, WANG Shi-song, ZHANG Xu-bin, WANG Qiang-qiang, HE Sheng-ping
Effect of steel-slag reaction on physicochemical properties of mold fluxes of high-Titanium steel
Aiming at the problem of steel-slag reaction in the continuous casting of high-Titanium steel and the variation of slag properties before and after reaction, in the current study the mold slag for casting high-Titanium steel was focused on. The reactivity of the high-titanium steel and mold slags was studied through experiments, and the changes of composition and properties of two continuous casting slags with different TiO
2
contents before and after reaction were compared. Experimental results show that, with the Titanium content in steel of 0.68% and the increase of the TiO
2
content in slag from 10% to 15%, the steel-slag reaction occurred between Titanium in steel and oxide components in slag, but the reaction was obviously inhibited. After the steel-slag reaction, the melting point, viscosity and breaking temperature of mold slags increased slightly. Crystalline phases of these slags were mainly LiTiO
2
and BaTiO
3
, and changed less before and after the steel-slag reaction.
2021 Vol. 40 (6): 59-64 [
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CHEN Bo-tao, WANG Feng-kang, ZENG Jie, WANG Wan-lin, JU Yin-jun
Analysis of surface and internal defects for continuous casting billet of 82A tire cord steel
The surface crack defects and central segregation of cord steel are the key factors affecting the billet quality. The macro defect analysis on the surface of billet, micro morphology characterization of crack, Gleeble high temperature mechanical properties and central segregation measurements are applied, and the surface and internal quality defects of continuous casting 150 mm×150 mm billet of 82A cord steel under steady and unsteady state are analyzed. The results show that the distance between the vibration marks of the billet is 13 mm and the vibration marks at the corners are disordered. Obvious transverse cracks are observed at the vibration mark trough and pit on the surface of unsteady billet, but no transverse cracks are appeared in the steady-state samples. Moreover, an obvious central crack with a length of 55 mm along the central shrinkage cavity in the billet is found and the average central carbon segregation index of the billet is 1.09. Based on the analysis of high temperature mechanical and cracks morphology, the appearance of surface cracks is mainly related to the straightening in the low-temperature brittle zone due to uneven cooling under the unsteady condition, The local temperature is in the third brittle temperature zone during bending and straightening. An obvious liquid film appeared on the surface of the inner central crack, which was formed at the solidification stage of the first brittle zone.
2021 Vol. 40 (6): 65-70 [
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YANG Zhi-gang, XU Zi-qian, HUANG Wei-li, DONG Gen-lai, HUO Li-qiao
Research and control of longitudinal corner cracks in continuous casting slab
Aiming at the problem that the incidence of cracks at the corners of the cast slab increases after the double-strand slab caster is raised to 1.4-1.5 m/min, through chemical composition analysis of the longitudinal crack specimen and metallographic microscopic observation, scanning electron microscopy of the longitudinal crack and energy spectrum analysis, water simulation experiment to study the formation mechanism of corner cracks. The results show that there are a large number of oxidation dots on both sides of the crack, and the longitudinal crack occurs in the mold. By optimizing the amount of cooling water in the mold, controlling the reasonable inverted taper of the mold and the amount of steel through the mold, the occurrence of longitudinal cracks at the corners of the continuous casting slab is reduced.
2021 Vol. 40 (6): 71-75 [
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Continuous Casting Equipment
76
LIU Zhi-yuan, YANG Quan-hai, WANG Chong-jun, BAI Xiao-wei, DING Ning
Non-sinusoidal vibration parameters optimization of slab crystallizer
High casting speed production of continuous casting machine is one of the most effective measures to greatly improve the production efficiency of continuous casting. In order to solve the problems of surface quality caused by high casting speed, the non-sinusoidal vibration system of radium is optimized. After optimization, the positive slip time is extend and the consumption of covering slag increased to 0.4 to 0.6 kg/t,and the negative slip time and the amplitude is increased which improve the effect of casting mold release and the surface quality.
2021 Vol. 40 (6): 76-78 [
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79
FENG Jun, BI Yu-yu, WANG Ju-yan, XIONG Jin-lei, WEI Zhi-qian, YE Peng-liang
Study on heat transfer model of grid continuous casting mold
Heat transfer process of continuous casting grids mold determines the acceptable quality of continuous casting grids. The heat transfer in continuous casting grids mold on the basis of the first law of thermodynamics and the Fourier law (the law of heat conduction) was analyzed and studied. According to simplified model of continuous casting grids mold established the steady-state compound heat transfer model of the cooling oil end cover air,the high temperature lead liquid and the outer cylinder of the moving mold and the cooling oil and the heat release calculation model of the cooling oil.Then the heat transfer dynamic balance equation of continuous casting mold was established. In order to guide the production practice, the operation function of operation process is established. Through the theoretical analysis of the heat transfer process of the grid continuous casting mold, this study has certain guiding significance for improving the continuous and stable production of the grid continuous casting mold and realizing the automatic temperature control of the grid continuous casting mold.
2021 Vol. 40 (6): 79-84 [
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YUAN Ji-bai, MA Zhi-min, YIN Pan, ZHANG Hua
Design of flow control device on 4-strand H-type double channels tundish with induction heating
Two flow control devices which are inverted eight type and V type weir were put forward in order to improve the characteristics of flow field in the new 4-strand H-type double channels tundish with induction heating in a special steel plant. The flow field, RTD curve and temperature field in tundish with different flow control devices were simulated by numerical method. The results show that the average residence time of the inverted eight type is 1 469.6 s, the dead zone volume fraction is 5.83%, and the maximum temperature difference between the edge nozzle and the middle nozzle is 3 K. Compared with the V-type flow control device, the average residence time is prolonged by 41.9 s, the dead zone volume fraction is correspondingly reduced by 4.09%, and the maximum temperature difference between the edge nozzle and the middle nozzle is reduced by 2 ℃. The design of turbulence suppressor + inverted eight flow control device has better flow control effect on the new 4-strand H-type double channels tundish with induction heating.
2021 Vol. 40 (6): 85-90 [
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LIU Tao, CHEN Yong-feng, JIAO Kui-ming, ZHANG Hong-biao, ZUO Xiao-tan, ZHAO Li
Research on secondary cooling spray structure of billet continuous casting machine based on uniform cooling
The billet produced by the 180 mm billet continuous caster in a certain factory has serious corner subcutaneous cracks. Through modeling and numerical simulation of the casting machine, the surface center and corner temperature of the casting slab solidification process are obtained. Based on the principle of uniform cooling of the secondary cooling, the simulation evaluation and optimization of the secondary cooling spray structure of the cast slab, including the cooling uniformity analysis of the cast slab in the longitudinal and circumferential directions. According to the optimized structure plan, the 10th stream and second cold spray structure of the casting machine was actually modified and the production test was carried out. Comparing the low-magnification morphology of cast slabs produced without modification (other streams) and after modification (10 streams), it is found that the subcutaneous cracks at the corners of the slab produced by 10 streams have been significantly improved.
2021 Vol. 40 (6): 91-97 [
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