Frequent delays will be experienced in the start-up of molten steel on the converter equipment during the steelmaking–continuous casting (SCC) production process due to the untimely supply of molten ...iron or scrap, which may cause conflicts between adjacent heat on the same equipment or in the same casting. The casting machine is cut off, resulting in the failure of the static scheduling plan. SCC production ladle re-scheduling is based on the premise that the production process path remains unchanged, the operation of adjacent heat on the converter and refining furnace does not conflict, and the casting of adjacent heat within the same casting is continuous. The ladle re-scheduling of steelmaking and continuous casting production aims at continuously casting many charges with the same cast and avoiding conflicts of adjacent charges on the same machine. This mechanism proposes a method of ladle re-scheduling in the production process of steelmaking–refining–continuous casting, which is divided into two parts: plan re-scheduling and ladle optimisation scheduling. Firstly, a re-scheduling optimisation model of the steelmaking and continuous casting production is built. This model aims at minimising the waiting time of all charges. The re-scheduling strategy of steelmaking and continuous casting production is proposed by interval processing time of charges and scheduling expert experience. This strategy is composed of two parts: re-scheduling charge decision and charge processing machine decision. Then, the first-order rule learning is used to select the optimisation target to establish the ladle optimal scheduling model. The ladle matching rules are extracted on the basis of the rule reasoning of the minimum general generalisation. The ladle optimisation scheduling method that consists of the optimal selection of the ladle and the preparation of the optimal path of the ladle is proposed. Ladle selection is based on the production process and adopts rule-based reasoning to select decarburised ladle after choosing dephosphorised ladle. Ladle path preparation, which is a multi-priority heuristic method, is designed to decide the path of the ladle from the converter to the refining furnace to the continuous casting machine. Finally, this mechanism was actually verified based on the large-scale data of a steel company in Shanghai, China. Results showed that the production efficiency of steelmaking-refining-continuous casting was improved.
Composite sheets fabricated by the Twin roll casting (TRC) process often suffer from quality issues, primarily microporosity resulting from solidification shrinkage. The presence of fabrication ...defects can be controlled by varying the casting parameters such as casting speed, superheat temperature, rolling force, and the height of the liquid metal in the melt pool. The present study developed a three-dimensional model to analyze the solidification and flow behavior of the melt with increasing melt pool height (4 cm, 6 cm, 8 cm) to see the quality of the fabricated Al-Mg2Si composite sheet. The developed model was validated using the optimized inlet temperature and interlamellar spacing. This model studies the effect of melt pool height on the solidification behavior, optimized inlet temperature, temperature gradient and heat flux. Results show that the increasing melt pool height shifts a solidification temperature above the roll exit and requires a higher inlet temperature for continuous sheet fabrication. Increased melt pool height decreases the heat flux from the roller surface and shows a lesser velocity fluctuation at the top and bottom of the melt pool. Experimental investigation demonstrates that a rise in melt pool height lowers the porosity in the casted sheet from 10.9% to 2.7% due to improved temperature gradient and pressure at the roller exit, enhancing sheet quality within the TRC process.
•Calculation of heat transfer coefficient in continuous casting is complex phenomenon.•Present study calculates heat transfer coefficient in a twin roll strip casting mold.•Hybrid method using the experimental and simulation approach.•Novel approach to calculating heat transfer coefficient used a solidification criterion.
•The SCC scheduling problem is modeled as a mixed-integer programming (MIP) problem.•A Lagrangian relaxation (LR) approach based on machine capacity relaxation is presented to address the MIP ...problem.•An improved subgradient level algorithm with global convergence is presented to solve the Lagrangian dual problem.•To deal with the unboundedness of the LR problem in iterations, we propose a boundedness detection method and a time horizon method.
One of the largest bottlenecks in iron and steel production is the steelmaking-continuous casting (SCC) process, which consists of steel-making, refining and continuous casting. The SCC scheduling is a complex hybrid flowshop (HFS) scheduling problem with the following features: job grouping and precedence constraints, no idle time within the same group of jobs and setup time constraints on the casters. This paper first models the scheduling problem as a mixed-integer programming (MIP) problem with the objective of minimizing the total weighted earliness/tardiness penalties and job waiting. Next, a Lagrangian relaxation (LR) approach relaxing the machine capacity constraints is presented to solve the MIP problem, which decomposes the relaxed problem into two tractable subproblems by separating the continuous variables from the integer ones. Additionally, two methods, i.e., the boundedness detection method and time horizon method, are explored to handle the unboundedness of the decomposed subproblems in iterations. Furthermore, an improved subgradient level algorithm with global convergence is developed to solve the Lagrangian dual (LD) problem. The computational results and comparisons demonstrate that the proposed LR approach outperforms the conventional LR approaches in terms of solution quality, with a significantly shorter running time being observed.
Continuous casting in steel production uses specially developed oxyfluoride glasses (mold fluxes) to lubricate a mold and control the solidification of the steel in the mold. The composition of the ...flux impacts properties, including basicity, viscosity, and crystallization rate, all of which affect the stability of the casting process and the quality of the solidified steel. However, mold fluxes interact with steel during the casting process, resulting in flux chemistry changes that must be considered in the flux design. Currently, the chemical composition of mold flux must be determined by extracting flux samples from the mold during casting and then processing these samples offline to estimate the working chemical composition and, therefore, the expected properties of the flux. Raman spectroscopy offers an alternative method for performing flux analysis with the potential to perform measurements online during the casting process. Raman spectroscopy uniquely identifies specific chemical bonds and symmetries in the glassy flux by revealing peaks that are a fingerprint of the vibration modes of molecules in the flux. The intensities of specific peaks in Raman spectra can be correlated with the chemical composition of the melt and associated properties such as basicity and viscosity. This paper reports on the first use of a portable fiber-optic Raman sensor for in situ Raman spectroscopic measurements of molten flux at 1400 °C. The work demonstrates the advantages of fiber-optic Raman spectroscopy to document the structure and chemical composition of flux samples at temperatures typically encountered in the mold during continuous caster operation. Experimental results demonstrate that the composition-dependent Raman signal shifts can be detected at caster operating temperatures, and the use of high-temperature Raman analysis for in-line flux monitoring shows significant promise for the in situ detection of changes in flux composition and physical properties during casting.
•A full 3D numerical model for transient flow field, temperature, solidification, and segregation during slab continuous casting.•An improved capture criterion for inclusion entrapment that including ...the primary dendrite arm spacing, solute concentration, force analysis, and critical capture speed is proposed.•Prediction on the number, size, and spatial distribution of inclusions on the entire cross section of the CC slab.•Four accumulation zones of inclusions along the thickness of the CC slab are predicted.
In the current study, the LES turbulent model, heat transfer, solidification, species transport model, and discrete phase model (DPM) were coupled to investigate the three-dimensional transient flow, temperature, solidification, segregation, and inclusion transport during the slab continuous casting (CC) process. The number, size, and spatial distribution of inclusions on the entire cross section of the CC slab were successfully predicted using the coupled full solidification model, DPM, and capture criteria at the solidification front. The improved capture criteria that considering the primary dendrite arm spacing (PDAS), different forces acting on inclusions, and the critical capture speed, successfully eliminated the banded distribution characteristics of inclusions under the simple capture criterion. The prediction results were in good agreement with the detection results. Four accumulation zones of inclusions along the thickness of the CC slab were predicted, including the 1/4 thickness and 3/4 thickness from the loose side, and the layer beneath the surface of the CC slab. Two accumulation zones near the layer beneath the surface of the CC slab were issued from the double roll flow pattern in the CC strand. The probability of inclusions contacting the solidification front in the upper recirculation zone increased, increasing the entrapment rate. The accumulation zones near the 1/4 thickness and 3/4 thickness from the loose side were corresponded to the peak value of the Marangoni force on inclusions at the 1/4 thickness and 3/4 thickness from the loose side. The Marangoni force increased the probability of inclusions being pushed to the solidification front. In addition, the accumulation near the 1/4 thickness from the loose side became more severe as the diameter of the inclusions increased due to the buoyancy.
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•A multiphase model combining microstructure, segregation and deformation is built.•The asymmetrical bulging profile has a stronger effect on the centerline segregation.•A greater reduction applied ...before solidification end can reduce macrosegregation.•The heavy reduction is an effective method to further reduce macrosegregation.
The various influence factors of macrosegregation are complex and have been researched widely due to their undesirable effect on continuous casting slab. Based on an Eulerian approach, a multiphase solidification model combining turbulent fluid flow, heat transfer, microstructure evolution, solute transport with back diffusion and shell deformation were developed in this work to investigate the fluid flow and macrosegregation in continuous casting slabs under the effects of shell bulging and mechanical reduction. In this model, five phases of the slab were considered: the liquid phase, inter-dendritic melt phase of equiaxed grains, solid phase of equiaxed grains, inter-dendritic melt phase of columnar dendrites, and solid phase of columnar dendrites. The predicted temperature, shell thickness and solute element distribution were verified by the results of thermal infrared imaging, nail-shooting experiments, macrostructure analysis, and carbon-sulphur analysis. In this model, the asymmetrical bulging between two adjacent supporting rollers was considered, and its effect on the fluid flow and macrosegregation of the slab was investigated. The calculation results show that the positive centreline segregation considering the asymmetrical bulging profiles was more serious than that considering the regular sinusoidal shell profiles. Using this model, the slab macrosegregation was investigated with different reduction mechanisms in the mushy zone; a large reduction applied just before the solidification end could significantly reverse the flow of solute-enriched melt and reduce the macrosegregation. These results were also verified by an industrial application.
A Cu-3.0 wt% Ti alloy is fabricated by a novel non-vacuum short-process based on heating-cooling combined mold (HCCM) continuous casting in this study. Similar properties including tensile strength, ...hardness and electrical conductivity are obtained by this newly developed process, compared to its counterpart alloy prepared by conventional vacuum smelting. The tensile strength, total elongation and conductivity of the HCCM prepared Cu-3 wt% Ti alloy were 895 MPa, 13% and 13.00% IACS, respectively, after 95% deformation and aging treatment at 450 °C for 1 h. The cast materials fabricated by HCCM method can be directly cold rolled and aged after solution treatment without hot deformation such as hot forging. Through the HCCM continuous casting method, not only the Cu-Ti alloy can be fabricated under non-vacuum conditions, but also the fabrication process can apparently shortened by shortening the solid solution treatment time. Similar precipitation process is also found in the Cu-3.0 wt% Ti alloy prepared by this method. The precipitation of the ordered, metastable and coherent β'-Cu4Ti phase with body-centered tetragonal (bct) structure are formed in the early stage of aging treatment, which is transformed into stable β-Cu3Ti with an orthogonal structure in the over-aging stage. The precipitation hardening of β'-Cu4Ti phase, i.e., Orowan strengthening effect, is believed to be the leading strengthening mechanism in this alloy.
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•Cu-3 wt% Ti alloy with high properties was prepared without vacuum for the first time.•New process without hot deformation was developed to improve yield and economy.•Solid solution time was significantly shortened by HCCM continuous casting.
In this work, the change in steel grade in a tundish of 20.3 tons with two exits employed from low to medium carbon grade steels is analyzed by numerical simulation, using multiphase flow modeling ...conditions in an isothermal state and non-isothermal, considering heat losses by radiation in the slag opening zone. The Tundish Volume Fraction (TVF) method determines the overlapping steel up to 10, 25, and 50% of the remaining steel. For non-isothermal cases, the temperature gradient over the incoming and old steel was 17 K. The model is validated through plant temperature measurements and steel heat losses at the tundish exits. The results indicate that heat transfer substantially modifies the fluid-dynamic behavior of steel. Likewise, the short circuit phenomenon is visible in the case of a 50% reduction of steel attributed to a non-reported elsewhere flow memory loss phenomenon once the tundish work level was recovered during the simulation under isothermal conditions. On the other hand, the intermixed steel is reduced as the amount of old steel remaining in the tundish is reduced; in addition, for the same case under isothermal conditions, the calculation of this amount is higher by a value close to 3 times that calculated under non-isothermal conditions.
This paper studies the steelmaking-refining-continuous casting (SRCC) scheduling problem with considering variable electricity price (SRCCSPVEP). SRCC is one of the critical production processes for ...steel manufacturing and energy intensive. Combining the technical rules used in iron-steel production practice, time-dependent electricity price is considered to reduce the electricity cost and the associate production cost. A decomposition approach is proposed for the SRCCSPVEP. Without considering the electrical factor, the first phase applies the mathematical programming method to determine the relative schedule plan for each cast. In the second phase, we formulate a scheduling problem of all casts subject to resource constraint and time-dependent electricity price. A heuristic algorithm combined with the constraint propagation is developed to solve this scheduling problem. To investigate and measure the performance of the proposed approach, numerous instances are randomly generated according to the collective data from a well-known iron-steel plant in China. Computational results demonstrate that our algorithm is very efficient and effective in providing high-quality scheduling plans, and the electricity cost can be reduced for the iron-steel plant.
•Effect of homogenization on HCCM continuous casting tube billets is clarified.•HCCM continuous casting improves homogenization effectiveness significantly.•Peculiar interlaced Mg2Si and Al6(Fe,Mn) ...phases are obtained by HCCM continuous casting.
AA 5052 aluminum alloy tube billets were prepared by HCCM vertical continuous casting to study the effect of homogenization temperature and time on the second phases and mechanical properties. The volume fraction of constituent, length of constituent colonies, number density and volume fraction of dispersoids were examined in different homogenization conditions. Optimized homogenization can be obtained at 560 °C for 20 h, and the elongation of the HCCM continuous casting billet increases from 25.5% (as-cast) to 35.5%, while that of the semicontinuous casting billets only increases from 21.5% (as-cast) to 23.5%. In particular, fine and interlaced Mg2Si and Al6(Fe,Mn) phases are obtained after HCCM continuous casting, which is different from the separated distribution phases after traditional semicontinuous casting and improves the effectiveness of homogenization treatment.
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