Bloom Continuous Casting Research Articles

Homogenization Path Based on 250 mm × 280 mm Bloom under Mixed Light and Heavy Presses: Simulation and Industrial Studies

This study proposed a new method for homogenizing continuous casting blooms based on solidification simulation calculations and industrial tests. The text describes a theoretical analysis of the solidification route of a cast billet of high-carbon alloy steel (B300A) under different process conditions. It summarizes the changing law of different under-pressure process parameters and under-pressure efficiency. The text also presents a solution to the seriousness of center shrinkage defects in the continuous casting of a large square billet of high-carbon alloy steel with the synergistic control technology of mixed light and heavy mixing under pressure. The study indicates that the center carbon segregation index of a high carbon steel continuous casting billet is 1.05, with a carbon extreme difference of not more than 0.08% and a proportion of 98.4%. Additionally, the center shrinkage is not more than a 0.5 level with a proportion of 99.5%. Meanwhile, the internal quality of cast billets has been improved, allowing for the rolling of large-size bars with a low consolidation ratio. The pass rate for internal ultrasonic flaw detection using the GB/T4162A grade is now higher than 99.95%, significantly reducing process costs and improving production efficiency for continuous casting and rolling.

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

Analysis and control of surface cracks in a B-bearing continuous casting blooms

Abstract In this work, normal manufacture of a B-bearing steel was hampered by cracks in steel. In order to control these cracks, the formation mechanism has been examined through a comprehensive analysis of crack morphology, element segregation, high temperature mechanical properties, and precipitates. The high-temperature thermoplastic capabilities of the steel were found to be reduced by boron nitride particles precipitated at grain boundary. This led to the formation of a brittle zone in the straightening zone of the continuous casting process, which in turn caused cracks. Based on the formation mechanism of these cracks, the cracks were successfully controlled by adding an appropriate amount of Ti element to the steel and reducing the charging temperature of the heating furnace.

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.

Semi-macrosegregation and carbide banding in high-carbon chromium bearing steels: Characteristics, evolution, and control

Semi-macrosegregation in continuously cast blooms and its associated carbide banding defects in hot-rolled bars were investigated to explore the characteristics, evolution, and control methods in high-carbon chromium bearing steel. It was found that the semi-macrosegregation exists only in the central equiaxed crystal zone of the blooms, and C, Cr solute elements inside show typical spot-like positive segregation. Carbide banding appears as white bright bands along the rolling direction, composed of high number density M3C carbide particles, with a significant effect on the mechanical properties of the rolled products. The hereditary evolution from semi-macrosegregation to carbide banding was established by means of banded segregation. Morphologically, normal semi-macrosegregation and carbide-typed semi-macrosegregation are formed based on whether Cr-rich primary carbides are generated. These two types of semi-macrosegregation evolved into two kinds of carbide banding respectively, that is, dark bands and bright bands defined according to the ability to reflect light under OM. To alleviate the carbide banding defect in rolling products of high-carbon chromium bearing steel, the morphology and area ratio of equiaxed crystals in continuous cast blooms should be modified. It is observed that the equiaxed crystal ratio in the bloom can be decreased from 62.5 % to 28 % by increasing liquid steel superheat and inhibiting superheat dissipation in the mold through casting practices. Additionally, the morphology of equiaxed crystals is related to the as-cast solidification structure, and when the equiaxed crystal ratio is large, the equiaxed crystals turn out to be coarser ones with only cellular primary dendrite; when the columnar crystals are longer, however, the equiaxed crystals appear as a dendrite structure with fine secondary dendrites. As a result, semi-macrosegregation was improved obviously with the fine dendrite structure splitting the local residual liquid phase, leading to the decrease of the maximum width of carbide banding from 268.41 μm to 73.72 μm, and the increase of mechanical properties in the rolled bar of high-carbon chromium bearing steel.

Effect of electromagnetic stirrer centered outside the mold on steel flow field of bloom continuous casting

Effect of electromagnetic stirrer centered outside the mold on steel flow field of bloom continuous casting

Study on the metallurgical function of mold electromagnetic stirring in continuous casting bloom

The metallurgical function of mold electromagnetic stirring(M-EMS) was investigated by simulation according to the following factors: flow field, temperature field, solidification, removal of inclusions, slag entrainment, and macrosegregation. When the current intensity increased from 0 A to 490 A, the rotational flow induced by M-EMS enhanced gradually, and the impinging effect of jet flow on the solidification front decreased obviously. The average speed on the top surface increased from 0.015 m/s to 0.038 m/s. The temperature of the molten steel was more uniform, and the temperature on the top surface decreased from 1788.5 K to 1785.9 K. The depth of depressions induced by the jet flow decreased from 6.1 mm to 0.7 mm. When the current intensity of M-EMS was 390 A, the removal fraction of inclusions was the highest. When the current intensity of M-EMS was 0 A, no slag entrainment occurred. With the current intensity of M-EMS increasing from 290 A to 490 A, the net slag entrainment rate was 0.003, 0.013, and 0.047 kg/s. When the current intensity of M-EMS increased from 0 A to 490 A, the minimum carbon content of negative segregation in the subsurface of the bloom worsened from 0.176% to 0.167%. For the bloom CC process, the M-EMS scheme should be weak or no M-EMS to decrease the occurrence of slag entrainment and improve the negative segregation in the subsurface of the bloom.

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.

Effect of the current intensity and positions of mold electromagnetic stirring on the macrosegregation in the full-length curved continuous casting bloom

A full-length curved continuous casting bloom mathematical model, coupling flow field, heat transfer, solidification, and electromagnetic stirring, was established to investigate the effect of the current intensity and positions of mold electromagnetic stirring (M-EMS) on the macrosegregation. M-EMS can optimize the negative segregation in the subsurface of the bloom and the positive segregation in the bloom center. With the current intensity of M-EMS increasing from 0 A to 350 A, the minimum carbon content in the subsurface of the bloom was 0.165%, 0.169%, 0.176%, and 0.182%. The carbon content in the bloom center was 0.246%, 0.243%, 0.241%, and 0.238%. The installation position of M-EMS can change the flow field and then affected the macrosegregation. When the positions of M-EMS were 0.77 m, 0.57 m, and 0.37 m beneath the meniscus, the minimum carbon content of negative segregation in the subsurface of the bloom was 0.174%, 0.182%, and 0.175%. The carbon content in the bloom center was 0.245%, 0.238%, and 0.235% respectively.

Numerical simulation and application of argon blowing from tundish cover for bloom continuous casting

During the continuous casting process, the remaining oxygen in the tundish can be significantly decreased by argon blowing from the tundish cover(ABTC). As a result, the effect of protective casting can be obviously improved, which helps decrease the reoxidation of molten steel in tundish. In the present work, numerical models for ABTC of a six-strand continuous casting machine were established and verified by the measured oxygen mass fraction in tundish during ABTC. The results indicate that the best conditions of ABTC are installing the argon pipes on either side of the tundish cover holes, sealing the baking holes, and keeping stopper rod holes open. The argon flow rate should be ?120m3/h during the period of empty tundish and ?60m3/h during the period of normal casting. Industrial trials of ABTC based on the calculation results were carried out. The results indicated that the increased nitrogen in steel(?w[N]) from the end of RH to tundish decreased by 21.5% from 8.78?10-6 to 6.89?10-6, and the amount of inclusions except for MnS in bloom (scanned size: 8mm?8mm) decreased by 21.3% from 13.43 to 10.57, and the average size of inclusions decreased by 19.0% from 9.27?m to 7.51?m.

The Investigation of Phase Transition and Solute Transport for Bloom Continuous Casting with Steel Strip‐Feeding Process and Mold Electromagnetic Stirring: A Comparative Study

Based on the finite volume method, a continuum model that coupled enthalpy‐porosity approach is developed herein to investigate the fluid flow, phase transition, and macrosegregation in the solidification process for bloom continuous casting. The optimal parameters of the process of feeding strip technology (FST) are obtained, and the effects of different processes of regular continuous casting, mold electromagnetic stirring (M‐EMS), and FST on the superheat degree and macrosegregation are compared. The results show that the process of FST can not only greatly reduce the superheat degree of liquid steel and improve the macrosegregation in the bloom center, but also effectively avoid the deterioration of negative segregation defects at the edge of bloom, compared with the processes of regular continuous casting and M‐EMS. The best process parameters for the process of FST are as follows: the strip feeding position is 0.12 m far away from the bloom centerline, and the steel strip feeding velocity is 0.20 m s−1.

Optimization of Heavy Reduction Process on Continuous-Casting Bloom

Heavy reduction (HR) is an effective technique to control V segregation in continuous casting bloom, but the effect of segregation improvement is limited by the parameters such as reduction position and reduction amounts. In order to improve the macrosegregation of bloom, numerical simulation and plant experiments are adopted in this research. A heat transfer model and a reduction model with comprehensive thermo-physical parameters were established. The two models were verified by comparing the measured surface temperature and the theoretical strain at the solidification front. It is determined that the position of the HR of the bearing steel bloom is 20.82 m~24.97 m from the meniscus, and the solid fraction in the center of the bloom is 0.6~1. The total reduction of the HR is set to 30 mm, and the reduction of each roller in the reduction range is set to 4 mm, 5 mm, 9 mm, 7 mm, and 5 mm, respectively, to prevent the formation of internal cracks. Plant trials were conducted to verify the effect of the optimized HR. The results show that the carbon segregation degree on the V channel and non-channel of the bloom decreases from 1.2 to 1.16 and increases from 0.93 to 0.95, respectively, and the central carbon segregation degree decreases from 1.17 to 1.15. Meanwhile, the internal crack was not found in the bloom.

Multi-GPU accelerated cellular automaton model for simulating the solidification structure of continuous casting bloom

Multi-GPU accelerated cellular automaton model for simulating the solidification structure of continuous casting bloom

Formation and Control of Central Cracks in Alloy Steel ZKG223

When the molten steel contains high carbon and alloy elements, the continuous casting bloom is prone to internal defects. Soft reduction is an effectively means of improvement and is widely utilized in the continuous casting process. Herein, the generation mechanism of the central cracks in alloy steel ZKG223 is analyzed in detail; that is, the tensile stress is generated by the accelerated solidification and shrinkage in the core of the bloom at the end of solidification, which acts on the dendrites and causes central cracks. In order to reduce the shrinkage stress during the solidification of the bloom, the reasonable reduction parameters of the bloom are determined by establishing a soft reduction model, and the industrial test is carried out. Through the implementation of well‐designed soft reduction, the central cracks in the bloom are significantly bridged, and the secondary dendrite spacing in the center of the bloom is shortened from 315 to 230 μm. The maximum positive and negative carbon segregation indices in the cross section of the bloom are changed from 1.039 and 0.957 to 1.020 and 0.977, respectively, which greatly improve the uniformity of element distribution and the internal quality of the bloom.

Effect of steel strip feeding on the columnar-equiaxed solidification in a large continuous casting round bloom

The steel strip feeding process can effectively improve the macrosegregation, central porosity, shrinkage, cracking, and other defects of continuous casting (CC) round blooms. Based on the volume-averaged method, a three-phase mix columnar-equiaxed solidification model is established, which considers the nucleation, growth of the columnar and equiaxed crystals, deposition of equiaxed crystals, and transmission of solutes. The effect of the feeding strip on the temperature, velocity, phase distribution, and macrosegregation distribution in a large vertical CC round bloom was studied. The results show that the CC bloom shell is built by columnar crystals, and equiaxed crystals fabricate the central zone. The feeding of the steel strip enhanced the flow inside the liquid core, which changed the flow direction of the center and end of the liquid core. The liquid phase and the temperature field display a similar distribution, and the liquid core and V-shaped high-temperature zone will gradually shorten with the increasing feeding ratio. A highly consistent distribution of the phase and the macrosegregation was found, and the increase in feeding ratio promotes columnar-to-equiaxed transformation (CET) and improves macrosegregation. Compared with no feeding strip, the extreme values of the macrosegregation index of 1.0% feeding ratio decreased by 37.1%, and the CET point at the sectional radius increased by 17.39%.

Optimizing of Submerged Entry Nozzle for Bloom Continuous Casting Based on Physical and Numerical Simulation

Herein, a physical model with a geometric similarity ratio of 1:1 and a 3D numerical model of macrosegregation are established to study the initial metallurgy behavior of the 410 mm × 530 mm section bloom continuous casting (CC). The results show that the average wave height, liquid surface velocity, and washing velocity of the five‐port nozzle are greater than those of the straight nozzle, but the center temperature and the temperature gradient at the solidification front are lower. Meanwhile, the diagonally installed five‐port nozzle can avoid the excessive washing effect under the orthogonally installed five‐port nozzle, which improves the minimum subsurface negative segregation index, which is increased from 0.753 to 0.802. For the Steel 45 bloom CC process, when the straight nozzle is changed to the diagonally installed five‐port nozzle, the length of the equiaxed crystal zone is increased from 97.5 to 198.5 mm, and the asymmetry of the solidification structure is improved.

Numerical simulation for EMS induced solidification and inclusion behavior in bloom caster CC mold with bifurcated SEN

A three-dimensional mathematical model has been developed to investigate solidification and non-metallic inclusions behavior in bloom caster mold with bifurcated submerged entry nozzle (SEN) under the influence of in-mold electromagnetic stirring (EMS). An enthalpy porosity approach is applied for the solidification analysis and the stochastic tracking model is used to track the motion of non-metallic inclusions. A numerical investigation has been carried out to study the influence of the stirrer current intensity on turbulent flow, shell generation and inclusion transport. The complex interplay of the induced flow with the inertial impinging jet from the SEN has been investigated. The effect of inclusion density and size on the removal rate of non-metallic inclusion has also been analyzed. The results show that in-mold EMS plays a significant role in solidification and inclusion behavior. With current intensity of 375 A, the inclusion removal rate is higher than that of 0 A, 300 A and 450 A stirrer current. This research suggests that the optimal current intensity of EMS gives a better internal quality of the continuous casting (CC) bloom mold.

Effect of mold electromagnetic stirring on solidification structure and solute segregation in continuous casting bloom

Effect of mold electromagnetic stirring on solidification structure and solute segregation in continuous casting bloom

Improvement of the secondary cooling mode for continuous casting of round billets at Ural Steel JSC

Formation of hot cracks on continuously cast round billets is the frequent problem in metallurgical production. The article presents the results of a study of the macrostructure, surface quality and technology of continuous casting of round billets with a diameter of 455 mm, produced at the bloom caster of Ural Steel JSC. The main defects of such billets are identified as surface cracks of “combined” type, namely, transverse cracks (the share among the billets with defects is 9.1%), cracks of the mesh form (the share among the billets with defects is 8.3%). The main reasons for the unsatisfactory quality of the ingot are determined: increased overheating of metal in the tundish, which can be partially compensated by reduction of the casting speed, and intensive cooling of billet surface in the first segments of secondary cooling, which increase thermal stresses in metal with consequent heating of surface layers. It was decided that the most effective way to minimize billet defects is to improve the secondary cooling technology in compliance with the regulated casting temperature and speed procedure. Thermal calculations of billet solidification are conducted. It was revealed that overcooling of billet surface occurs in the first segments of secondary cooling under the existing secondary cooling modes and temperature and speed modes of casting, which leads to additional thermal and phase stresses. In the third segment of the secondary cooling zone, heating of the billet surface is observed due to the heat of the central part. Rational flow rates of cooling agent for the secondary cooling segments of the bloom continuous casting machine are proposed. They include expansion of the active section of secondary cooling with a reduction of cooling agent consumption in the first segments will reduce the thermal cycling processes in the hardened crust and minimize the likelihood of cracking. The work was conducted under financial support of the RF Ministry of Science and High Education (project No. FZRU-2020-0011).

Improvement the Round Bloom Continuous Casting Technology at JSC “Ural Steel”

The results of assessment of macrostructure and surface quality of round blooms 455 mm in diameter, cast on 4-strand continuous casting machine (CCM) at JSC “Ural Steel” are presented. The analysis of technological casting parameters of round blooms 455 mm in diameter (from steel grade “2”) at bloom caster of JSC “Ural Steel” are completed. Violations in casting temperature and rate parameters, which deteriorate thermal conditions of solidification and quality of continuous casting blooms, have been revealed. The main causes of unsatisfactory bloom quality have been determined, which are the increased overheating of cast metal and irrational secondary cooling mode. The results of the experiment to evaluate the surface temperature dynamics of a round bloom in the secondary cooling zone are presented, which confirmed the inefficiency of the secondary cooling mode for the defect-free bloom formation. As a result of thermal calculations of round blooms solidification of 455 mm in diameter, rational coolant flow rates by secondary cooling sections for bloom caster of JSC “Ural Steel” have been proposed. Optimized secondary cooling parameters provide a softer secondary cooling of the round bloom, which reduces the probability of the surface and internal defects development.