Round Bloom Research Articles

Effect of Swirling Flow Submerged Entry Nozzle on Solidification and Macrosegregation Behavior of a Round Bloom with Mold and Final Electromagnetic Stirring

Effect of Swirling Flow Submerged Entry Nozzle on Solidification and Macrosegregation Behavior of a Round Bloom with Mold and Final Electromagnetic Stirring

Effect of heat preservation cover on solidification quality in large round bloom

Installing heat preservation covers in the air-cooling zone during continuous casting will affect the solidification quality of large blooms. In this study, a multi-stage anti-radiation heat preservation cover model was developed for heat transfer, and stress coupling calculations based on a vertical continuous casting process of a large round 600 mm diameter bloom. The accuracy of the model was verified by comparing the calculated surface temperature of the bloom against industry-standard surface temperature measurements. Results demonstrate that after applying heat preservation covers with the strongest insulation effect, the surface temperature of the bloom at 14 m from the meniscus increases by 19.42%, and the central porosity area decreases by 23.79%. Furthermore, the maximum stress at the point 43 mm from the centre of the bloom within the ZDT-LIT range decreased by 2.032 MPa. This study elucidates the mechanism underlying the effect of heat preservation covers on the formation of shrinkage and central cracks in the blooms, thereby providing theoretical support for the rational application of heat preservation covers in the vertical continuous casting process of large round blooms.

Effect of Electromagnetic Stirring on Solidification Structure and Central Porosity of Large‐Sized Round Bloom in Continuous Casting

The effect of strand (S‐) and final (F‐) electromagnetic stirring (EMS) on solidification structure characteristic of a φ690 mm continuously cast round bloom has been investigated industrially and theoretically. The newly designed S1‐EMS equipped just below the foot zone takes great effect on both equiaxed ratio and distribution alignment, as well as central porosity. Larger current S1‐EMS leads to higher equiaxed ratio, more symmetrical equiaxed zone, and smaller diameter of central porosity, and the effect is much more obvious than conventional S2‐EMS and F‐EMS. It is also noticed that there should be a saturation effect of S1‐EMS on the promotion of equiaxed dendrite nucleation. The S2‐EMS is beneficial for the expanding of equiaxed zone and improving of central porosity. When S1‐EMS is weak, strong S2‐EMS results in more asymmetrical equiaxed zone. However, when S‐EMS is strong, strong S2‐EMS results in more symmetrical distribution of equiaxed zone. The F‐EMS takes a little impact on the expanding of equiaxed zone in the large‐sized round bloom, and almost no effect on the alignment. The central porosity, however, is improved by F‐EMS with the help of decrease in temperature gradient and compensation of solidification contraction.

Removal and distribution behaviors of inclusion particles in the steel melt under different rotation modes during continuous casting

This work investigated the removal and distribution behaviors of non-metallic inclusion particles caused by the flow of molten steel under two rotational modes, i.e. from edge to center (E-C) and from center to edge (C-E). Three-dimensional mathematical models discovering the relation between fluid flow, temperature distribution, solidified shell growth of large round bloom, and the movement of inclusions were established to investigate the mechanism of the differences. The obtained results show that under the C-E rotational mode, the removal rate of inclusions is 7 times and the highest local agglomeration number density of inclusions is reduced by 38.4 % compared to the E-C rotational mode. The current work proposes that the C-E rotating flow of molten steel can effectively raise the removal and uniform distribution of inclusions, thereby providing a new strategy for effective control of inclusion during the continuous casting process utilizing the novel electromagnetic metallurgy.

Reduction Behavior in Large-Sized Round Bloom During Continuous Casting by Numerical Simulation

Reduction Behavior in Large-Sized Round Bloom During Continuous Casting by Numerical Simulation

Numerical investigation on effect of electromagnetic stirring on macrosegregation in continuously cast round bloom via three-phase solidification model

Based on our previously proposed three-phase solidification model, a comprehensive analysis on the impact of the only electromagnetic stirring (EMS) and combined EMS on the microscopic structure evolution and solute segregation behavior in a 500 mm diameter 42CrMo steel of continuously cast round bloom. The results indicate that M-EMS has a notable impact on expediting the dissipation of superheat, enhancing the initiation of grain formation, and enlarging the equiaxed region. The percentage of equiaxed grains increased from 59.26 to 63.37% with the increment in current intensities of M-EMS from 250 to 350 A. However, higher M-EMS current intensities were found to enhance local positive segregation in the transition zone between columnar and equiaxed grains. The impact of M-EMS on improving center positive segregation was minimal, as the ratio of center positive segregation remained consistently around 1.17. Furthermore, the implementation of F-EMS demonstrated its effectiveness in reducing center positive segregation. The ratio of center positive segregation decreased from 1.14 to 1.10, when the current intensity increases from 150 to 250 A. However, it should be noted that F-EMS alone did not contribute to the expansion of the equiaxed zone. On the other hand, when M-EMS was combined with F-EMS (referred to as combined EMS), it showed potential in mitigating center segregation during continuous casting round blooms. The benefits observed with M-EMS in terms of promoting grain nucleation and expanding the equiaxed grain zone were also evident in this combined EMS process. Furthermore, a notable enhancement in the equiaxed grain ratio up to 60.13% was observed combined EMS models were simultaneously employed during continuous casting of round blooms. And, there was a reduction in center segregation ratio for round blooms to as low as 1.09.

A Study on Solidification Behavior of a Large Round Bloom Affected by Swirling Flow Submerged Entry Nozzle Combined with Mold Electromagnetic Stirring

A Study on Solidification Behavior of a Large Round Bloom Affected by Swirling Flow Submerged Entry Nozzle Combined with Mold Electromagnetic Stirring

Structural optimisation of three-strand asymmetric tundish for super large round bloom continuous casting

Structural optimisation of three-strand asymmetric tundish for super large round bloom continuous casting

Influence of External Physical Fields on Grain Distribution in Continuous Cast Round Blooms

Influence of External Physical Fields on Grain Distribution in Continuous Cast Round Blooms

Optimization of Process Parameters for 40Cr Steel Continuous Casting Round Bloom with Pulsed Magneto‐Oscillation Treatment

To reduce the solidification structure defects and the macrosegregation of the Φ300 mm continuous casting round bloom, the pulsed magneto‐oscillation (PMO) treatment is added at the secondary cooling zone. A numerical model for calculating the pulsed electromagnetic field, flow field, and temperature field in continuous casting is established, and the coupling simulations of multiphysical fields under different casting parameters and PMO parameters are performed. Their influence on solidification process and the appropriate parameters are discussed. The industrial experiments conducted under the recommended parameters yield good results. Industrial experiments show that when the peak current is increased from 1350 to 1550 KIA and the casting speed is increased from 0.75 to 0.90 m min−1, PMO can increase the equiaxed grain zone and reduce the carbon macrosegregation of the bloom. Moreover, at high casting speed, PMO treatment can significantly promote columnar‐to‐equiaxed transition and increase the width of mixed grain zone.

An Improved Model Based on YOLO v5s for Intelligent Detection of Center Porosity in Round Bloom

An Improved Model Based on YOLO v5s for Intelligent Detection of Center Porosity in Round Bloom

In Situ Observation of P91 High‐Alloy Steel Solidification Characteristics at Different Cooling Rates

To clarify the effect of different radial cooling intensities on the formation of central cracks in large round bloom continuous casting, it is necessary to study the solidification characteristics and dynamics of P91 high‐alloy steel at different cooling rates (CRs) to improve the central defects. In this article, the solidification characteristics of P91 high‐alloy steel at different CRs are studied by using the Thermo‐Calc software, high‐temperature laser confocal microscopy, scanning electron microscopy, and optical microscopy. Meanwhile, the growth kinetics of δ‐Fe and γ‐Fe phases under different CRs are determined. In the results, it is shown that the solidification path of P91 high‐alloy steel is L(L + δ‐Fe) → (L + γ‐Fe + δ‐Fe) → (δ‐Fe + γ‐Fe). The δ‐Fe and γ‐Fe phase precipitation process is divided into two stages. Stage I is the nucleation and rapid growth phase, in which a high undercooling is required. Stage II is the slow growth stage, where the undercooling decreases and remains constant. The initial growth linear velocities of the δ‐Fe phase are 0.51, 2.72, and 2.09 μm s−1 at CRs of 10, 50, and 100 °C min−1, respectively, while those of the γ‐Fe phase are 0.10, 1.42, and 1.41 μm s−1.

Multiphase Solidification Modeling of Solidification Structure Evolution and Macrosegregation of Round Bloom Continuous Casting Process with Mold Electromagnetic Stirring and Final Electromagnetic Stirring

Based on Eulerian–Eulerian method, a 3D/2D multiphase solidification model, which takes into consideration the heat transfer and fluid flow with grains nucleation and crystal growth, is developed to predict the macrostructure evolution and macrosegregation in continuously cast round bloom. The results show that the mold electromagnetic stirring (M‐EMS) can accelerate superheat dissipation and promote grain nucleation, but the horizontal swirl induced by M‐EMS has a strong washing effect on the solidification front and leads to subsurface negative segregation. When the M‐EMS current intensity increases from 200 to 300 A, the subsurface negative segregation ratio decreases from 0.935 to 0.875. The final electromagnetic stirring (F‐EMS) not only improves the center segregation, but also leads to the formation of negative segregation zone near the round bloom center due to the enhancement of solute washing induced by F‐EMS. As the F‐EMS current intensity increases from 150 to 300 A, the center segregation ratio decreases from 1.148 to 1.075, and the negative segregation ratio near the strand center decreases from 0.985 to 0.977. Another phenomenon is found that the nucleation of equiaxed grain ahead of columnar tips restrains the solute diffusion and leads to a local macrosegregation in columnar‐to‐equiaxed transition zone.

Study on Stirring Effect of Spiral Magnetic Field in Continuous Casting of Round Blooms

Herein, for the continuous casting of round blooms with strand electromagnetic stirring, the effects of rotating magnetic field (RMF) and spiral magnetic field (SMF) on the electromagnetic, fluid flow, heat transfer, solidification, and macrostructure are investigated by numerical simulation and industrial experiments, respectively. The results show that the molten steel flows in a spiral shape along the casting direction with the RMF and SMF. Due to the influence of secondary flow caused by electromagnetic stirring (EMS), and the zone of high velocity of molten steel accounts for 13.7% of the whole stirring range with the RMF. The SMF has a strong stirring effect in the whole range of secondary flow, the zone of high velocity of molten steel accounts for 49.1% of the whole stirring range, and the liquid fraction of the SMF at the liquid core is also lower. The results of the industrial experiments prove that the SMF has a wider stirring depth than the RMF, and the center crack range is significantly reduced.

Effect of Feeding Strip Temperature on Macrosegregation in a Large Continuous Casting Round Bloom

Feeding a cold steel strip into continuous casting (CC) mold is an effective method to improve the quality of large round bloom. However, it is difficult to assess the correlation between the bloom quality and the initial temperature of the strip. Therefore, a three‐phase mixed columnar–equiaxed solidification model is developed to evaluate the effect of feeding strip temperature on macrosegregation and solidification structure in a large vertical CC round bloom. The results show that feeding the steel strip induces “crystal rain” in the liquid core of the bloom and increases the volume fraction of the equiaxed phase. After feeding a strip, the flow direction of molten steel is changed, and the flow velocity is increased in the liquid core of the bloom. Furthermore, with initial temperature of the strip decreases, the production efficiency is improved. Compared to the four conditions investigated, the carbon distribution in the bloom is the most uniform, the negative segregation at the centerline of the bloom is the weakest with the value of −35.50%, and the extreme value difference of the macrosegregation index at 20 m below the meniscus is the smallest with the value of 38.35% under the condition of Tinitial = 500 K.

Flow field, heat transfer and inclusion behavior in a round bloom mold under effect of a swirling flow submerged entry nozzle

Flow field, heat transfer and inclusion behavior in a round bloom mold under effect of a swirling flow submerged entry nozzle

Numerical simulation on solidification behavior and structure of 38CrMoAl large round bloom using CAFE model

Numerical simulation on solidification behavior and structure of 38CrMoAl large round bloom using CAFE model

Study on the positive segregation in columnar-to-equiaxed transition zone

Laboratory experiments of steel ingots under three cooling modes and industrial trials of continuous casting (CC) blooms and billets were conducted, respectively. Corresponding results of the macrosegregation and the solidification structure were investigated. The mechanism of the positive segregation in the columnar-to-equiaxed transition (CET) zone was proposed. For laboratory experiments of ingots under three cooling modes, including water cooling, water cooling for 15 s followed by air cooling, and air cooling, obvious positive segregation was generated in the CET zone, and the degree of segregation was 1.024, 1.025, and 1.015, respectively. For industrial trials of three kinds of steel, CC bloom, round bloom, and billet, positive segregation was formed in the CET zone, and the degree of segregation was 1.06, 1.04, and 1.06, respectively. With the growth of columnar dendrites, solute elements were rejected on the liquid–solid interface. The downward flow near the columnar tip region and the upward flow in the center melt can carry the solute-rich melt to the molten pool. When the CET occurred, equiaxed grains accumulated around the columnar dendrite tips, and the solid network became less permeable. The liquid flow in the network was significantly suppressed, and thereby the solute-enriched liquid was ‘arrested’ locally. Solute-enrich liquid would be further sucked into the interdendritic region owing to the solidification shrinkage. As the sample was fully solidified, the obvious positive segregation was found at the CET zone.

Behavior of Mold Electromagnetic Stirring for Round Bloom Castings and Its Eccentric Stirring Problem.

In this paper, a mold electromagnetic stirring (M-EMS) model was established to investigate the behavior of M-EMS for round bloom castings under different conditions, and an electromagnetic-flow-heat transfer-solidification coupling model was established to explore the problem of eccentric stirring for various formats of round blooms. The results show that the magnetic flux density decreased with the increase in the current frequency, but the electromagnetic torque increases first and then decreases with it, and the same structure of M-EMS for round blooms has the same optimal current frequency at any current intensity. The electromagnetic torque and electromagnetic force both increase as a quadratic function of the current intensity, and the electromagnetic torque, which drives the steel flow, can directly characterize the real M-EMS performance. The mold copper tube has a significant magnetic shielding effect on M-EMS, the stirring intensity decreases rapidly as the tube thickness increases, and the optimal stirring frequency decreases as well. In fact, the deviation between the stirrer center and the geometric center of the strand can result in the eccentric stirring phenomenon. When blooms with a section size of Φ350 mm are produced by Φ650 mm SMS-Concast casting machine, the upper region of the inner arc side and the lower region of the outer arc side are subject to a stronger washing effect, which makes the temperature of the inner and outer arcs show alternating differences. The jet flow from the five-port nozzle can suppress the difference in initial solidification symmetry between the inner and outer arcs of round blooms caused by eccentric stirring. This paper reveals the magnetic shielding effect of the mold copper tube and the magnetic field loss of the air between the stirrer and the inner and outer arcs of the copper, which lead to the stirring intensity and the eccentric stirring phenomenon.

Effect of Swirling Flow Nozzle on Fluid Flow and Solidification in a Round Bloom Continuous Casting Mold

The nozzle structure has an important effect on the fluid flow in the mold, which can significantly improve the solidified shell and product quality of alloy steel round bloom. The transient fluid flow, heat transfer, and solidification behavior under different nozzle structures and mold electromagnetic stirring (M-EMS) are investigated using a 3D transient mathematical model. The results show that a third small recirculation zone appears near the meniscus after the application of the swirling flow nozzle (SFN). The impact depth of SFN is shallower than that of the original submerged entry nozzle (SEN) impact, and the lower circulation zone is shifted upward. The horizontal swirling flow generated by SFN can significantly weaken the washing of the initial shell by high-temperature steel and improve the uneven growth phenomenon of the inner and outer curved solidified shell caused by mold curvature. The swirling flow produced by M-EMS in the mold can also improve the washing of the initial shell by the high-temperature jet and the uneven growth of the inner and outer curved shell. M-EMS can expand the high-temperature zone in the upper part of the mold, promote the superheat dissipation of the molten steel, and promote the growth of the solidified shell. In addition, after the application of M-EMS, the tangential velocity of -15° SFN in the meniscus is smaller, and the resulting liquid level fluctuation is lower at 5.07 mm, which is less likely to produce slag entrapment and is conducive to improving the quality of round bloom.