State of Segregation with Bubble in Continuously Cast Slab of Ultra Low Carbon Steel

Kasai, Norifumi; Mizukami, Hideo; Mutou, Akifumi

doi:10.2355/tetsutohagane1955.89.11_1120

Cited by 11 publications

(10 citation statements)

References 8 publications

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“…Although this is much greater than the original argon gas density of 1.6228 kg/m 3 , it is still far smaller than that of the molten steel, so it has little effect on the bubble motion or bubble residence time in the strand (Eq. [12]). The inclusions attached to each bubble also have a size distribution (Figure 22(b)).…”

Section: Resultsmentioning

confidence: 93%

“…[7,8,10,11,12] Aided by surface tension forces from nonwetting contact, most solid inclusions tend to collect on surfaces such as bubbles ( Figure 1). [13,14] Line defects on the surface of finished strip products are several tens of micrometers to millimeter in width and as long as 0.1 to 1 m. [15] Serious ''sliver'' defects result from clusters of nonmetallic inclusions caught near the surface of the slab (,15 mm from the surface).…”

Section: A Defectsmentioning

confidence: 99%

“…[12] is the drag force per unit particle mass, the second term is the gravitational force, the third term is the ''virtual mass'' force [4] accelerating the fluid surrounding the particle, and the fourth term is the force stemming from the pressure gradient in the fluid. The lift force is ignored in the current study.…”

Section: A Model Formulationmentioning

confidence: 99%

“…[47,48] The trajectories of bubbles are calculated by Eqs. [12] through [15], which include the effect of chaotic turbulent motion using the random walk model. Inclusion trajectories calculated with this approach match reasonably well with those by large eddy simulation.…”

Section: A Model Formulation and Flow Patternmentioning

confidence: 99%

See 3 more Smart Citations

Inclusion removal by bubble flotation in a continuous casting mold

Zhang

Aoki

Thomas

2006

Metall Mater Trans B

172

129

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Fundamentally based computational models are developed and applied to quantify the removal of inclusions by bubbles during the continuous casting of steel. First, the attachment probability of inclusions on a bubble surface is investigated based on fundamental fluid flow simulations, incorporating the turbulent inclusion trajectory and sliding time of each individual inclusion along the bubble surface as a function of particle and bubble size. Then, the turbulent fluid flow in a typical continuous casting mold, trajectories of bubbles, and their path length in the mold are calculated. The change in inclusion distribution due to removal by bubble transport in the mold is calculated based on the computed attachment probability of inclusions on each bubble and the computed path length of the bubbles. In addition to quantifying inclusion removal for many different cases, the results are important to evaluate the significance of different inclusion-removal mechanisms. The modeling approach presented here is a powerful tool for investigating multiscale phenomena in steelmaking and casting operations to learn how to optimize conditions to lower defects.

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Section: Resultsmentioning

confidence: 93%

Section: A Defectsmentioning

confidence: 99%

Section: A Model Formulationmentioning

confidence: 99%

Section: A Model Formulation and Flow Patternmentioning

confidence: 99%

See 2 more Smart Citations

Inclusion removal by bubble flotation in a continuous casting mold

Zhang

Aoki

Thomas

2006

Metall Mater Trans B

172

129

View full text Add to dashboard Cite

show abstract

“…The Pushing Engulfment Transition (PET) model [2][3][4][5][6][7] suggests that the bubble/particle at the interface is engulfed into the solid shell when the growth rate of the shell exceeds the critical rate. The initial growth rate of the shell in the steel continuous casting is much higher than the critical rate, 22) most bubbles which touch the solidifying interface at the initial solidifying shell are engulfed and become the cause of surface defects.…”

Section: Thermal and Solutal Marangoni Force Calculationmentioning

confidence: 99%

Numerical Analysis of Surface Tension Gradient Effect on the Behavior of Gas Bubbles at the Solid/Liquid Interface of Steel

et al. 2012

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The mechanism which governs the behavior of bubbles in the vicinity of the solidification front where both the concentration and temperature gradients exist was investigated and the effect of the solutal and thermal marangoni forces to the entrapment of bubble were compared and discussed.When a bubble approaches the solid/liquid interface, it first encounters the thermal boundary layer, which is much thicker than the concentration boundary layer, and experiences the thermal marangoni force. This force, which occurs due to the temperature gradient in the thermal boundary layer, pushes the bubble away from the solidification front if the sulfur concentration is lower than the critical value which was found to be around 47-60 ppm, but pulls it toward the solidification front if the sulfur concentration is higher than the critical value. Only if the bubble passes through the thermal boundary layer successfully, it then arrives at the concentration boundary layer where a strong solutal marangoni force comes into action on the bubble to pull it to the solid/liquid interface.The above analysis predicts that the bubble-induced surface defect of a cast be strongly affected by the sulfur concentration and there exists a critical sulfur concentration above which the surface defect becomes increasing. The above prediction was validated by the CFD (Computational Fluid Dynamics) simulation and the trial at the commercial casting plant, and they were in good agreement with each other.

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Effect of Temperature and Multichannel Stopper Rod on Bubbles in Water Model of a Steel Continuous Caster

Liu

Zhou

Zhang

et al. 2021

steel research int.

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Argon gas has been widely injected into submerged entry nozzles (SENs) to prevent nozzle clogging during the slab continuous casting (CC) process. Meanwhile, argon bubbles also reduce the negative pressure and air aspiration, [1,2] promoting the mixing and flotation of inclusions from the molten steel in the CC mold. [3][4][5][6] Abnormal larger bubbles float up close to the outer wall of the SEN and escape from the top surface quickly, which causes slag entrainment into the molten steel. [7,8] Smaller bubbles are easily captured by the solidified shell, causing segregation, [9] pencil blister, and sliver defects. [10][11][12] Therefore, it is necessary to better understand and optimize the bubble size and distribution in the CC mold to avoid bubble-related defects.The gas injection method, casting parameters, [13,14] nozzle design, [15] physical properties of the gas and liquid phases, [16] and temperature have a great effect on the bubble size and distribution inside the SEN and the CC mold. Water model measurements have shown that bubble diameters decrease with a higher casting speed and submergence depth of the SEN, as well as with a lower gas flow rate. [14,[17][18][19][20] However, the effect of temperature on the bubble size has been rarely studied in the water model of a continuous steel caster. The gas injection method in the water model experiment included the gas channel of the stopper rod, [21][22][23][24][25] small holes or porous refractory in the upper tundish nozzle (UTN), [16,[26][27][28] and the slide gate of the SEN. [11,29] Bai and Thomas [16] investigated the effects of the liquid velocity, gas-injection flow rate, injection hole diameter, and gas composition on the initial bubble-formation behavior. The gas was injected through a square tube below the tundish tank outlet. Kasai and Iguchi [29] obtained the critical value of the water flow rate to carry the gas injected through the slide gate into the mold. The variation of the bubble size inside the SEN and the mold was also studied. [30] Lee et al. [31] investigated the effect of refractory properties on the initial stages of bubble formation. Air was injected through the porous refractory in the center of the UTN wall. For gas injection from the stopper rod tip, single [21,23,31] and multichannel [32,33] blowing methods have been studied in recent years. Gas injection from a single channel created abnormal large bubbles or gas pockets, and produced slug or annular flows inside the SEN, resulting in unstable flow and violent level fluctuations, whereas gas injection from multiple channels produced a more stable surface level in the mold and retarded the clogging on the stopper rod tip. [24] However, studies on the effect of the hole diameter of the gas channel of the stopper rod on the bubble size distribution are little reported.In this study, the bubble size and distribution in the CC mold were investigated and measured using a 0.5-scale water model. First, the effect of the water temperature on the bubble size and

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State of Segregation with Bubble in Continuously Cast Slab of Ultra Low Carbon Steel

Cited by 11 publications

References 8 publications

Inclusion removal by bubble flotation in a continuous casting mold

Inclusion removal by bubble flotation in a continuous casting mold

Numerical Analysis of Surface Tension Gradient Effect on the Behavior of Gas Bubbles at the Solid/Liquid Interface of Steel

Effect of Temperature and Multichannel Stopper Rod on Bubbles in Water Model of a Steel Continuous Caster

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