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2023 Vol. 42 No. 2
Published: 2023-04-18
Continuous Casting Technology
Strand Quality
Continuous Casting Equipment
Technology Exchange
Continuous Casting Technology
1
ZHANG Guo-xin, LIU Guang-qiang, LIU Kun, HAN Peng
Numerical simulation of internal flow field characteristics of full-scale high-pressure descaling nozzle
In order to fully consider the influence of filters and flow stabilizers on the internal flow field of high-pressure scale-removal nozzles, numerical modeling of full-size scale-removal nozzles and study of the internal flow field characteristics were carried out using CFD. The influence of nozzle structure and inlet pressure on the internal flow field characteristics of the nozzle was analyzed to reveal the characteristics of the flow field distribution in the central axis and to clarify the mathematical relationship between the exit velocity and inlet pressure. The results show that, compared with the simplified model, the internal pressure of the full-size model is lower, and there is a deviation of (2-4) × 10
5
Pa between the two.For the full-size model, the internal pressure decay of the nozzle mainly occurs at the end of the shrinkage section and the nozzle outlet, where the pressure decay is about 0.6 MPa when the water flows through the filter and stabilizer. For different regions, the same conditions, the speed of the nozzle section. The change is much greater than the filter and shrinkage section. With the increase in the inlet pressure, the internal flow field pressure decay gradually increased, while the entire internal flow field speed also increased accordingly, and the greater the pressure, the more obvious the change in speed, that is, the nozzle inlet pressure and exit speed to meet the positive correlation.
2023 Vol. 42 (2): 1-9 [
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10
LIU Dong-xu, GONG Wei, ZHU Jiang-jiang, CAO Rui-hong, FAN Ding-dong, DENG Ai-jun
Numerical simulation and optimization of flow field in tundish by flow control device
The numerical simulation method is adopted,and the 3D mathematical model is established by ANSYS simulation software to simulate the flow behavior of molten steel in tundish with or without flow control device and different combinations of flow control device.The results show that the diversion wall and dam in tundish have a significant effect on the flow behavior of molten steel.The change of the distance between the diversion wall and dam mainly affects the liquid steel flow between the diversion wall and dam,and the liquid steel flow in the right area of the diversion dam.The height of the diversion wall mainly affects the turbulent liquid steel re-flux flow on the left side of the diversion wall and the velocity of liquid steel flowing to the nozzle.The change of the diversion dam height affects the flow of molten steel on the right side of the dam.Too low diversion dam causes the short circuit flow of molten steel in tundish.A relatively ideal optimization flow control combination is that the height of diversion wall is 550 mm,the height of diversion dam is 350 mm,the distance of diversion wall from the entrance is 800 mm,and the distance between diversion wall and dam is 400 mm.The industrial production verification shows that the optimized combination of the flow control device has an obvious upward removal effect on medium and large inclusions.The total proportion of medium and large inclusions over 20 μm is reduced from 23.7% to 9.1%,and no large inclusions over 200 μm are detected in the slab.It is expected that a series of quality defects such as internal inclusion,surface slag and nodulation of microalloyed slab can be eliminated or alleviated by optimizing the parameters of flow control device.
2023 Vol. 42 (2): 10-18 [
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19
TIAN Bao-sheng, FANG Qing, WANG Jia-hui, WU Xian-min, HUO Li-qiao, ZHANG Hua
Physical modelling on optimization of flow behaviors in a two-strand tundish by gas curtain
The installation position and gas blowing rate of gas curtain are the key parameters to improve cleanliness of molten steel in tundish. Taking a double-flow slab tundish as the research object,the flow field and residence time distribution (RTD) curves in a two-stand slab tundish of a steelmaking plant with and without gas curtain were analyzed by water model experiments, and the effects of installation position and gas blowing rate on flow behaviors in the tundish were comparatively investigated. The results showed that after the tundish was equipped with gas curtain, the average residence time of molten steel appears no significant change, while the dead zone volume fraction decreases from 14.58% to 5.32%, which is beneficial to the mixing of molten steel. The installation position and gas blowing rate of gas curtain has a significant effect on the dead zone volume fraction of the tundish, but have less effect on the average residence time. The optimal installation position for the gas curtain is 500 mm away from the submerged entry nozzle (SEN), by which the dead zone volume faction is 5.32%, compared to the cases of 600 mm, 700 mm and 800 mm away from the SEN, the dead zone volume fraction is reduced by 1.66%, 1.62% and 0.87%, respectively. The optimal gas blowing rate is 0.4 m
3
/h, compared to the cases with gas blowing rate of 0.5 m
3
/h and 0.6 m
3
/h, the dead zone volume fraction is reduced by 2.8% and 1.11%, respectively. The mean value of total oxygen and the proportion of single class inclusions above grade 1.0 decreased by 9.5% and over 20%, respectively.
2023 Vol. 42 (2): 19-27 [
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28
JIAO Ao-teng, YANG Shu-feng, LI Jing-she, SONG Jing-ling, LI Heng-hua, ZHANG Fu-jun
Evolution of inclusions in 26CrMo7S steel produced by EAF-LF-VD-CC process
In order to control the inclusions in 26CrMo7S steel and improve the mechanical properties of the steel, the cleanliness analysis of the whole process was used to explore the evolution of inclusions in the EAF→LF→VD→CC process of a mills. The results show that the LF pitted inclusions are mainly composed of Al
2
O
3
, MgO and CaS combined with uneven composition and irregular morphology.After LF and VD refining, Al
2
O
3
, MgO, CaO, and CaS form non-uniform polygonal or nearly spherical composite inclusions, and the continuous increase of the CaO content. After calcium treatment, the inclusions were further spheroidized, and the main components were uniform composite inclusions of oxides wrapped with CaS. In the EAF-LF-VD-CC process, the number density of inclusions first decreased and then increased, and the number density decreased to a minimum of 16.1 mm
-2
in the VD process,and the average size showed a trend of first increase and then decrease, and the size in the VD process A maximum value of 2.83 μm is reached. The LF refining time is short, the calcium treatment is unreasonable, and the secondary oxidation of continuous casting is the main reason for the excessive inclusions in the molten steel. Increasing LF processing time appropriately, ensuring sufficient weak stirring, finding out appropriate calcium treatment “window”, ensuring the inclusion denature and not excessive introduction of CaO inclusion, using argon sealing, tundish argon blowing protection means in continuous casting process can effectively improve the cleanliness of liquid steel.
2023 Vol. 42 (2): 28-33 [
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34
ZHAO Shuo, WANG Bing-shan, LÜ Jing-cai, LIN Wen, ZHU Shi-bin
Electromagnetic heating finite element simulation of 718 Ni alloy recycled by additive manufacturing
Inconel718 alloy was one of the most widely used materials in additive manufacturing. Due to the low effective utilization rate of powder in the additive manufacturing process, a large amount of powder had to be recovered. However, there was a problem of slow melting speed in the recovery and remelting process. Therefore, the melting process of Inconel718 metal powder was simulated by induction furnace heating, the change of melting rate of recycling powder under different conditions was investigated by changing the diameter, shape, distribution of powder, power, frequency, atmosphere, number of coils and the distance between the coils and crucible center. The simulation results show that in a certain size range, the melting rate of Inconel718 powder is the fastest when the prepared sphere diameter is 0.010 m and the large particle size powder is distributed under the crucible. At the same time, the melting rate increases with the increase of heating power, frequency and number of coils, and decreases with the increase of the distance between the coils and crucible center, the heating atmosphere can be argon or vacuum.
2023 Vol. 42 (2): 34-42 [
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43
ZHOU Guo-tao, CHEN Jin, HUANG Biao-cai, YAN Wei, LI Jing
Numerical simulation of solidification and heat transfer of Q355B slab during continuous casting
In order to solve the problem that the continuous casting parameters of Q355B slab in a steel plant do not match with each other when the casting speed is increased, ProCAST software was employed to establish the solidification heat transfer model of the slab, and the solidification characteristics of the slab under different continuous casting parameters were studied. The results show that the casting speed has the greatest influence on the slab solidification, followed by the specific water flow rate, and the smallest is superheat in the calculated range. With the increase of casting speed or the decrease of specific water rate or the increase of superheat, the slab temperature, the solidification end and the length of two-phase zone increase to different degrees except the shell thickness. In the actual production process,it is found that changing the casting speed billet production without changing the specific water volume and the position under light pressure, the three failed to effectively cooperate with each other, resulting in serious intermediate cracks. Based on simulation results, when the casting speed is increased to 1.0 m/min, the specific water flow rate is increased from 0.38 L/kg to 0.55 L/kg, as a result, the generation ratio of intermediate crack is reduced from 70% to about 11%, and the center segregation of slab above the level of C1.5 increases by 24.5%.
2023 Vol. 42 (2): 43-51 [
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52
LI Da-ming, LIN Jun, HE Jia-jia, DENG Xiang-yang, WU Wei, PANG Zhuo-chun
Development practice of the soft reduction process in mild steel con-casting
By establishing two-dimensional transient heat transfer and solidification model for continuous casting of 160 mm×160 mm square billet QD08, the slab temperature and slab solidification rate at each roll position were calculated, and the effects of reduction and position on the macrostructure quality of billet longitudinal section were studied. The results indicated, compared with the central solid rate, low carbon steel is more suitable for characterizing the soft reduction position and adjusting the reduction process with solidification rate. The billet central quality was best reduced in 0.961-1.000 solidification range. Shrinkage cavity existed in the center of the billet reduced in 0.986-1.000 solidification range.Certer cracks existed when soft reduction was carried out in 0.931-0.961 solidification range. Cracks occuried more eassily at high casting speed under the same reduction proccess. Less reduction quantity significantly decreased the center cracks.
2023 Vol. 42 (2): 52-56 [
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Strand Quality
57
SONG Bao-min, SHI Shu-guang, LIU Kun-long, LÜ Ming
Formation and evolution of nonmetallic inclusions in 27SiMn steel
In order to study the formation and evolution of non-metallic inclusions in 27SiMn steel, the production status of a steel plant was systematically analyzed. The evolution behavior of inclusions in each stage of “LF inlet→before calcium treatment→after soft blowing→tundish→slab” was explored through industrial experiments. According to the current situation of calcium treatment of 27SiMn steel, the Al-Ca equilibrium reaction in the molten steel treated with calcium was calculated by thermodynamics. The results show that the inclusions before calcium treatment are mainly CaO-MgO-Al
2
O
3
ternary inclusions, and the mass fraction of Al
2
O
3
is about 67%. After soft blowing, in the ternary phase diagram of CaO-MgO-Al
2
O
3
system, the mass fraction of Al
2
O
3
was reduced by about 35%, and the inclusions moved to the side with high CaO mass fraction on average. In the ternary phase diagram of CaS-CaO-Al
2
O
3
system, the inclusion composition does not enter the liquid phase region because of the high CaS mass fraction in the inclusion composition, which is about 21%. In the casting process, most of the inclusions were transformed into spherical CaO-MgO-Al
2
O
3
-SiO
2
composite inclusions, and a large number of CaS inclusions were observed. Through thermodynamic analysis, at 1 873 K, when
w
([Al])=0.022% in steel,
w
([Ca]) is controlled between 0.001 3% and 0.003 5%, which is in the region conducive to the formation of 12CaO·7Al
2
O
3
, which can improve the liquid modification effect of inclusions. At the same time, in order to prevent the precipitation of pure CaS inclusions in molten steel,
w
([S]) should be controlled below 0.004 8%.
2023 Vol. 42 (2): 57-62 [
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63
SONG Hong-wei, WANG Dong-xing, REN Yi, WANG Wu-lei, YANG Wei-yong, WANG Chun-mei
Analysis and improvement of prestressed high-strength steel PSB930
In order to study the cause of surface depression, crack and other defects of PSB930 billet. By means of pickling, chemical composition, scanning electron microscope and energy spectrum analysis, it is confirmed that the concave defects of PSB930 billet are mainly caused by the stress concentration formed by improper cooling in the mold, and the surface crack defects are mainly caused by sulfide inclusions formed by high S content, and the intergranular cracks produced by the combined action of thermal stress and sulfide inclusions during cooling. By optimizing the refining deoxidation and desulfurization system, adjusting the water volume of the continuous casting mold to 115-120 m
3
/h, the specific water volume of the secondary cooling to 0.5 L/kg, the water distribution ratio to 31∶26∶20∶13∶10, controlling the superheat of the tundish to 20-30 ℃, optimizing the basicity of the mold powder to 0.95, and the viscosity to 2.5 Pa·s, the concavity and crack defects on the surface of the slab were basically eliminated, and the product quality of the rolled material was guaranteed.
2023 Vol. 42 (2): 63-69 [
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70
HAN Jie, WANG Yi, LIU Cheng-bao, XU Rong-chang, SUN Zong-hui, LUAN Yi-kun
Analysis on modification behavior of rare earth to inclusions in GCr15 bearing steel
In order to analyze the modification behavior rules of rare earth on inclusions in bearing steel, the modification behavior of different rare earth contents to inclusions in GCr15 bearing steel was investigated through industrial test, by means of scanning electron microscope, EDS analysis, non-destructive extraction of inclusions, ASPEX analysis, etc. The modification effect of rare earth on inclusions in steel varies greatly with the addition amount. It was found in production that addition of 0.015% rare earth plays a significant role in refining the larger inclusions. The inclusions are layered when 0.005% rare earth is added. When adding 0.003% rare earth, the proportion of rare earth in the inclusions is very small, and the effect of rare earth encapsulation is weakened. Research analysis shows that the oxide and sulfide inclusions of Al
2
O
3
, CaO, MgO, MnS and CaS in bearing steel can be effectively transformed into rare earth oxygen sulfide RE
2
O
2
S. The size of the inclusions is refined from 10 μm above to less than 5 μm, and the shape is spherical or elliptic.
2023 Vol. 42 (2): 70-77 [
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78
ZHANG Ya-bing, WANG Dong-xing, ZHAO Li, ZUO Xiao-tan, HUANG Yan, YANG Wei-yong
Solute distribution of 35CrMnSi structural alloy steel billet under the effect of PMO
In order to improve the central segregation and radial distribution of solutes of the 35CrMnSi alloy constructional steel continuous casting billet with a section diameter of 300 mm, Pulsed Magneto-Osillation (PMO) technology developed by the Center for Advanced Solidification Technology was applied. With the PMO treatment in the secondary cooling zone, the distribution uniformity of C along the radial direction of the billet was improved, the range of C decreased by more than 40%, and the ranges of Cr, Mn, Si in the center of the billet decreased by 18%, 16% and 33%, respectively. The serious segregation phenomena of C, Cr, Mn and Si in the center of the billet were eliminated. The solutes distribution of 35CrMnSi alloy constructional steel billet was improved without changing the original continuous casting process. It provides a new method to improve the central segregation by improving the center quality of
ø
300 mm round billet.
2023 Vol. 42 (2): 78-83 [
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84
SHI Wei-ning
Effect of mold water flow rate in 40Cr billet continuous casting on surface crack
In order to improve the surface cracks of 40Cr steel billet produced by Xianggang’s No. 2 continuous casting machine, the evolution of surface quality of the billet under different mold water flow rates was studied. The results show that with the increase of the mold water flow rate, the heat flux density increases first and then decreases, and the grain size on the billet surface decreases first and then increases. When the mold water flow rate is less than 2 250 L/min, a large number of abnormally grown austenite grain structures are displayed and the grain sizes are not uniform on the billet surface, the surface cracks of the billet mainly propagate along the grain boundaries. When the mold water flow rate is greater than 2 333.33 L/min, with the increase of the mold water flow rate, the heat flux density decreases, the grain sizes on the billet surface increase again, but surface cracks on the billet disappear. When the mold water flow rate is 2 333.33 L/min, the nucleation rate of molten steel near the mold wall is the largest, the grain size of the billet surface is the smallest and uniform, and the grain structure that is the most conducive to resisting stress cracking is obtained. This analysis method provides a new idea for solving the problem of billet surface cracks.
2023 Vol. 42 (2): 84-89 [
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Continuous Casting Equipment
90
HAN Lun-jie, CAO Xue-qian, XIE Yi-kui, WANG Qian
Analysis of causes for deformation of copper tubein rectangular mold
To control the deformation of rectangular crystallizer copper tube cavity in the casting process, reference is provided for optimizing copper tube design.The maximum deflection of crystallizer copper tube was calculated by the uniform load formula of simply supported beam, the thermal deformation was calculated by combining temperature gradient and thermal expansion coefficient and the changes of inner wall size and taper of copper tube under different water pressures were analyzed. The temperature field and deformation distribution in the mold were simulated by MSC Software. The analysis results show that the cooling water pressure is the main cause of copper tube deformation, the largest deformation position is in the center of the copper tube cavity and maximum deformation value 1.76 mm. The taper of the copper tube of the crystallizer increases in the upper part and decreases in the lower part. The simulation results show that the plane area of the copper tube cavity is prone to thermal stress and deformation. The deformation in the middle area is larger, and the deformation in the quarter is 72% of that in the center. Cooling water pressure and deformation is proportional to the linear relationship, and under the same pressure conditions, the copper tube wall thickness decreased 4 mm, deformation increased by 35%.
2023 Vol. 42 (2): 90-98 [
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99
LI Hao, LI Xin, TAO Cheng-gang, WANG Guo-cai
Design characteristics and production practice of bloom caster for special steel
The core process and key equipment of special steel bloom caster in a plant was discussed, the key equipment, technical points and process practice of controlling slab quality were expounded, emphatically described the important role of light and heavy reduction process in improving the internal quality of bloom, and introduced in detail the metallurgical effect of the caster in producing typical high carbon steel. The production practice shown that the central segregation of bearing steel can be significantly reduced, the central porosity can be improved and the central shrinkage can be eliminated by determining the reasonable soft and hard reduction interval and reduction process parameters under the condition of keeping the production drawing speed constant. The typical steel GCr15 produced by bloom caster was poured at a constant casting speed, the carbon segregation index of billet was between 0.97-1.06, the proportion of central porosity not greater than 1.0 is 100%, and there was no central shrinkage defect.
2023 Vol. 42 (2): 99-105 [
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Technology Exchange
106
WANG Zheng-hao, FANG Yan-hong, WANG Cheng-rui, DUAN Hua-mei
Carbonation reaction conditions and product analysis of calcium oxide
In the context of carbon neutrality, carbon capture and storage using steel slag can achieve both carbon emission reduction and “using waste to treat waste”. Since steel slag contains more free calcium oxide, untreated steel slag has poor stability and is difficult to be used in other fields. After carbonation of steel slag, the free calcium oxide content of steel slag is greatly reduced, which can be used in building materials. It is the most promising method for steel slag treatment. Therefore, it is of direct guiding significance to investigate the carbonation reaction conditions of pure calcium oxide for improving the stability of carbon fixation by steel slag. The thermodynamic calculation of CaO and Ca(OH)
2
carbonation was carried out by FactSage. The results showed that both CaO and Ca(OH)
2
could spontaneously carbonate at 0-900 ℃. The influence of calcination temperature, CaO mass, liquid-solid ratio and CO
2
flow rate on CaO carbonation rate was investigated. The results show that when the calcination temperature is 700 ℃, the mass of CaO is 3 g, the liquid-solid ratio is 1.67, and the CO
2
flow rate is 35 mL/min, the carbonation rate is the highest, which is 60.9%. The results of this study can be a reference for improving the resource utilization of steel slag.
2023 Vol. 42 (2): 106-112 [
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113
ZHOU Ye-lian, JIANG Zhong-kuai, ZHANG Fa-bin
Control process and mechanism analysis for tundish fluxes to form the solidified crusts
The slag crust not only deteriorates the effect of tundish metallurgy, but also hinders the development of smart continuous casting in the steel plant. In order to solve the solidified crusts of tundish fluxes, the effects of steel temperature, composition and melting point of tundish fluxes, and casting heats on the solidified crust at tundish stream zone were investigation in detail. The results show that fluxes thickness and thermal insulating property were the main factors for solidified crust at the tundish stream zone. For the poor fluxes thermal insulating property, the surface of tundish fluxes was melted during the ladle initial pouring stage. With the casting heats increasing, the thermal resistance of the tundish fluxes increasing, resulting in resolidating of the surface fluxes. In order to improving the insulating property of the upper tundish fluxes, the lower specific weight carbonized rice husks were chosen as heat preservation agent instead of carbonized rice ball, preventing the surface of tundish fluxes melt during the ladle initial pouring stage. After implementation, the solidified crust rate of the tundish fluxes in the No.1 continuous casting plant and No.2 continuous casting plant decreased from 47.3% and 35.3% to 15.0% and 10.7%, respectively.
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