Continuous Casting Process Research Articles

Study on the nanocarbon containing Al2O3 – C continuous casting refractories with reduced fixed carbon content

Alumina-carbon refractories are widely used in the continuous casting process for steelmaking due to their suitable comprehensive properties. Conventionally, these refractories contain 25-30 wt% carbon, with graphite as the major source, especially to improve corrosion and thermal shock resistances. However, the presence of high carbon encompasses several problems like high energy loss, carbon pick-up in steel, oxidation, increased CO2 generation, etc. To avoid these issues, in the present work, alumina-carbon refractories are prepared and evaluated with reduced and fixed carbon content by partially replacing the graphite with nanocarbon. Free carbon addition is maintained at 4 wt% level by varying combination of nanocarbon and graphite content. The alumina carbon refractory compositions are processed through pressing, curing, coking, and evaluated for properties like bulk density and cold crushing strength. Phase analysis and microstructural variations in the compositions are studied along with oxidation resistance at different temperatures. Because of its smaller particle size, nanocarbon can easily fill the gaps between the other refractory particles thereby reduces porosity and improves strength. Also, greater extent of in situ aluminum carbide formation improves the strength in case of nanocarbon containing compositions.

High Quality Steel Casting by Using Advanced Mathematical Methods

The main concept of this paper is to utilize advanced numerical modelling techniques with self-regulation algorithm in order to reach optimal casting conditions for real-time casting control. Fully 3-D macro-solidification model for the continuous casting (CC) process and an original fuzzy logic regulator are combined. The fuzzy logic (FL) regulator reacts on signals from two data inputs, the temperature field and the historical steel quality database. FL adjust the cooling intensity as a function of casting speed and pouring temperature. This approach was originally designed for the special high-quality high-additive steel grades such as higher strength grades, steel for acidic environments, steel for the offshore technology and so forth. However, mentioned approach can be also used for any arbitrary low-carbon steel grades. The usability and results of this approach are demonstrated for steel grade S355, were the real historical data from quality database contains approximately 2000 heats. The presented original solution together with the large steel quality databases can be used as an independent CC prediction control system.

Design and Application of CSC-Roll for Heavy Reduction of the Bloom Continuous Casting Process

Center quality control is a key issue affecting large-section bloom production and product quality. The central convex roll could avoid the bloom side part and yield a high reduction amount, which benefit the implement of heavy reduction (HR) for bloom continuous casting process without upgrading the mechanical and hydraulic system of withdrawal and straightening machine. In this work, a curving surface convex roll (CSC-Roll), which could significantly improve bloom center quality, was designed by finite element simulation for a 360 mm × 450 mm #45 steel continuous casting bloom. The optimal roll surface shape of the CSC-Roll was determined based on an analysis of the distribution of the reduction amount in the bloom center and the strain of the bloom centerline and inner surface. The calculation results showed that the optimal size of the CSC-Roll was 200 mm in convex platform region length, 30 mm in convex platform region height, and 80 mm in gradient curvature region length. The bloom heat transfer and deformation behavior in the CSC-Roll reduction process were then analyzed. The results showed that in the CSC-Roll HR process, 61.71 pct of the reduction amount could be transmitted to the inner side of the porosity zone. Macrographs of the 360 mm × 450 mm #45 steel continuous casting bloom proved that the bloom center quality was significantly improved after CSC-Roll HR was applied.

Study of the Effect of Carbon on the Contraction of Hypo-Peritectic Steels during Initial Solidification by Surface Roughness

In the continuous casting process, the shrinkage of the peritectic phase transition during the initial solidification process has an important influence on the surface quality of peritectic steel. The initial solidification process of 0.10C%, 0.14C%, and 0.16C% peritectic steels was observed in situ by a high temperature laser confocal microscope, and the contraction degree during initial solidification was characterized by surface roughness. The results showed that under the cooling rate of 20 °C/s, the surface roughness value Ra(δ/γ) of 0.10C% peritectic steel was 32 μm, the Ra(δ/γ) value of 0.14C% peritectic steel was 25 μm, and the Ra(δ/γ) value of 0.16C% peritectic steel was 17 μm. With increasing carbon content, the contraction degree of the δ→γ transformation decreased, and the value of the surface roughness Ra(δ/γ) declined. Therefore, surface roughness can characterize the contraction degree of the δ→γ transformation in the initial solidification process of peritectic steel under the condition of a large cooling rate.

Experimental investigation on segregation and remelting behaviors of boron-containing steel with low carbon

Abstract Boron in low carbon steel can improve hardenability and hot ductility remarkably. However, defects including cracks, internal half way cracks, and even breakouts commonly appear during the continuous casting process, due to the segregation and remelting behaviors of boron-containing steel. In the present investigation, morphology characteristics around the crack were observed by optical microscope (OM). The segregation and distribution of boron around grain boundary were observed by secondary ion mass spectroscopy (SIMS), and the remelting phenomenon around the crack was observed by the high temperature confocal laser scanning microscope (CLSM). Results show that BN particles are detected in the crack region, Boron is concentrated at grain boundaries. Due to the boron segregation, liquid phase is observed at 1420–1400 °C and 1340–1330 °C in cooling process with boron content even of 0.0013 wt%. The low and high temperature brittle zones are revealed based on boron segregation and remelting behavior.

Applied Mathematical Modelling of Continuous Casting Processes: A Review

With readily available and ever-increasing computational resources, the modelling of continuous casting processes—mainly for steel, but also for copper and aluminium alloys—has predominantly focused on large-scale numerical simulation. Whilst there is certainly a need for this type of modelling, this paper highlights an alternative approach more grounded in applied mathematics, which lies between overly simplified analytical models and multi-dimensional simulations. In this approach, the governing equations are nondimensionalized and systematically simplified to obtain a formulation which is numerically much cheaper to compute, yet does not sacrifice any of the physics that was present in the original problem; in addition, the results should agree also quantitatively with those of the original model. This approach is well-suited to the modelling of continuous casting processes, which often involve the interaction of complex multiphysics. Recent examples involving mould taper, oscillation-mark formation, solidification shrinkage-induced macrosegregation and electromagnetic stirring are considered, as are the possibilities for the modelling of exudation, columnar-to-equiaxed transition, V-segregation, centreline porosity and mechanical soft reduction.

High power phased EMAT arrays for nondestructive testing of as-cast steel

A new high-power electromagnetic acoustic transducer (EMAT) solid state pulser system has been developed that is capable of driving up to 4 EMAT coils with programmable phase delays, allowing for focusing and steering of the acoustic field. Each channel is capable of supplying an excitation current of up to 1.75 kA for a pulse with a rise time of 1 μs. Finite element and experimental data are presented which demonstrate a signal enhancement by a factor of 3.5 (compared to a single EMAT coil) when using the system to transmit a longitudinal ultrasound pulse through a 22.5 cm thick as-cast steel slab sample. Further signal enhancement is demonstrated through the use of an array of detection EMATs, and a demonstration of artificial internal defect detection is presented on a thick steel sample. The design of this system is such that it has the potential to be employed at elevated temperatures for diagnostic measurements of steel during the continuous casting process.

Thermomechanical Treatment of High-Shear Melt-Conditioned Twin-Roll Cast Strip of Recycled AA5754 Alloy

A continuous high-shear melt conditioning twin-roll casting process has been developed for production of recycled aluminum alloy strip with minimum casting defects. High-shear melt conditioning is applied to increase the impurities tolerance of recycled aluminum. The results of this study showed that solidification during twin-roll casting can be controlled by using intensive melt conditioning prior to casting, which can promote equiaxed growth with minimal defects and result in improved sheet quality. Melt-conditioned twin-roll cast (MC-TRC) AA5754 alloy exhibited fine equiaxed grains and homogenized matrix structure while centerline segregation was eliminated. As-cast melt-conditioned twin-roll cast AA5754 strips showed clear grain recrystallization after thermomechanical treatment at 430°C for 30 min, representing an improvement over conventional twin-roll casting. The MC-TRC strip showed 57.2% higher elongation and 4.1% higher ultimate tensile strength compared with the TRC strip after applying melt conditioning with thermomechanical treatment.

Inclusions in Continuous Steel Casting: Formation, Characterization, Tracking and Influences on the Quality of the Product

The formation mechanisms and characterization (distribution, size and morphology) of the inclusions during continuous casting process of steels were investigated in this study. Samples were took out from several steps of the process and then, fully characterized via metallographic techniques, microscopic investigations and elemental analysis. Results showed that the addition of ferroalloys can intensify the formation of inclusions in some steps of the steelmaking process. Also, it was confirmed that the total oxygen content of the samples can be considered as a criteria of the clarity (purity and inclusion-free) of the steels, if the samples prepared carefully.

Numerical simulation of flow and solidification in continuous casting process with mold electromagnetic stirring

The magnetic, heat transfer and flow phenomenon occurring in the continuous casting process under the mold electromagnetic stirring was further analyzed by solving the 3-D electromagnetic field mathematical model and flow solidification model with finite element method and finite volume method, respectively. The results indicate that the solidified shell thickness located in the effective stirring region fluctuates because of the unsteady scouring under the mold electromagnetic stirring. The maximum rotational velocity is a key parameter to the solidification of the billet when controlling the stirring intensity. When the rotational velocity reaches 0.32 m/s, the mush zone enlarges significantly and the solidification rate is further accelerated. The number of vortexes in the lower recirculation zone is not only two and depends on the stirring parameters. Besides, the secondary flow is closely associated with the solidification. Compared with the results of the model ignoring the influence of solidification on the flow of molten steel, the flow pattern within the lower recirculation region changes dramatically, and thus a coupling analysis of the flow, heat transfer, and solidification is essential when simulating the electromagnetic continuous casting process.

Novel Opposite Stirring Mode in Bloom Continuous Casting Mould by Combining Swirling Flow Nozzle with EMS

The metallurgical performances in a mold cavity were investigated using a conventional bilateral-port nozzle or a swirling flow nozzle (SFN) plus with in-mold electromagnetic stirring (M-EMS) for bloom continuous casting (CC) process. To this end, a coupled model of electromagnetism, flow, and heat transfer was developed. Meanwhile, corresponding plant trials were conducted to evaluate the influence of a melt feeding mode on the internal quality of an as-cast bloom in Shaoguan Steel, China. Under the case of the SFN plus with M-EMS, a novel opposite stirring mode in the bloom CC mold cavity can be observed. A swirling flow in the anti-clockwise direction generated by the SFN, and the other swirling flow in the clockwise direction induced by the M-EMS were formed in regions with distances ranging from 0 m to 0.11 m and 0.218 m to 1.4 m from the meniscus, respectively. As compared to the case of the bilateral-port nozzle plus with M-EMS, the opposite stirring mode in the mold cavity can promote the melt superheat dissipation, improve the casting soundness and the componential homogeneity, inhibit the mold level fluctuation, and also be beneficial to prevent slag erosion for the nozzle external wall at the meniscus. Here, the fluctuation range of carbon segregation along the casting direction is reduced from 0.16 to 0.06, and the magnitude of mold level fluctuation is reduced from 5.6 mm to 2.3 mm under the adoption of SFN plus with M-EMS, respectively.

Nonisothermal Crystallization Kinetics of Glassy Mold Fluxes

Crystallization of the solid glassy mold flux film occurring in the gap between the initial shell and mold wall is important, as it determines the in-mold heat transfer and mold lubrication during the process of continuous casting. In order to study the nonisothermal crystallization behavior of the glassy mold flux film in the continuous casting mold, the continuous heating transformation diagram, crystallization mechanism, and precipitate phases were investigated using the single hot thermocouple technique, kinetic models, a scanning electron microscope, and an energy-dispersive spectrometer (EDS). The results show that the initial crystallization temperature for CaO-SiO2 based flux A ranges from [1086 K to 1147 K (813 °C to 874 °C)], which is lower than the case of CaO-Al2O3 based flux B ranging from [1205 K to 1245 K (932 °C to 972 °C)]. The crystallization kinetics for flux A are constant nucleation rate, two-dimensional growth, and control by diffusion. For flux B, they are constant nucleation rate, three-dimensional growth, and control by interface reaction. Besides, the EDS results indicate that the precipitate crystals in fluxes A and B are CaSiO3 and Ca2AlSiO4, respectively.

The Influence of Centerline Segregation on the Mechanical Performance and Microstructure of X70 Pipeline Steel

Centerline segregation is an inherent phenomenon during solidification. It is controlled by optimizing the continuous casting process, but is not easy to be avoided. According to the severity of centerline segregation of the slab, it affects the mechanical properties and final microstructure of rolled strip. The objective of this paper is to study the influence of centerline segregation degree on the microstructure and mechanical properties of X70 pipeline steels. In this study, the mechanical properties of strips produced from the slabs are examined and the results show that centerline segregation is some adverse effect on Charpy impact toughness and tensile properties of hot‐rolled strips. The strips from slab with higher degree of segregation, exhibits lower Charpy impact toughness, higher tensile strength, higher microhardness. The segregated degree of slab is studied by using the method of Mannesmann, indicating that it could be up to class 3–4. Moreover, the results from Electron Probe Micro Analyzer (EPMA) shows that high level of Mn content is obtained at the centerline of strips processed from the slab with segregation degree of class 3–4. The corresponding microstructure is identified as lath martensite, which should be contributed to the undesirable mechanical properties.

A Metaheuristic Method for the Task Assignment Problem in Continuous-Casting Production

The steelmaking and continuous-casting (SCC) process in integrated iron and steel enterprises can be described as two stages: the upstream stage and downstream stage. Raw materials are transformed into molten steel in the upstream stage, while the downstream stage is responsible for transforming molten steel which is released at regular intervals and has a limited time for being turned into slabs. This article focuses on the task assignment problem in the downstream stage within the given information resulting from the upstream stage. This problem is formulated as a nonlinear mixed-integer programming model aimed at minimizing total tardiness within the resource constraints and time windows constraints for the tasks. An improved solution algorithm based on particle swam optimization is developed to efficiently solve the proposed model. Finally, computational experiments are implemented to evaluate the performance of the solution algorithm in terms of solution quality and computational time.

Experimental modelling of continuous casting of steel in slab moulds using low melting liquid metals

Electromagnetic actuators are widely used in industry for contactless control of the steel flow in the continuous casting process. However, a real control of the flow structure by those actuators is a challenging task due to the lack of flow monitoring devices. Even a satisfying non real-time characterisation of the melt flow from plant measurements is missing. Beside numerical simulations, only a very few spatially and temporally limited measurements in liquid steel are available to investigate the actual action of the magnetic fields on the fluid.Therefore, model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in the mould of a continuous caster. Their advantage is the availability of a variety of measurement techniques for quantitative flow measurements. The application of the Ultrasonic-Doppler-Velocimetry (UDV) and the Contactless-Inductive-Flow-Tomography (CIFT) allows for a detailed characterization of the mould flow with a reasonable spatial and temporal resolution.In recent experiments at HZDR, the systematic study on the influence of an electromagnetic brake on the mould flow in a slab caster was continued. The measurements were carried out using a 1:2 scaled model operated with SnBi and a 1:8 scaled model operated with GaInSn, respectively. The melt surface was partly measured by a laser scanner system. In particular, the immersion depth of the submergence entry nozzle (SEN) was varied during the experiments. It became obvious that changes in the mould flow had a strong influence on the free surface of the melt, where strong perturbations can significantly impair the surface quality of the final steel strands. Moreover, effects from the “artificial” clogging of one SEN-port or the injection of Argon gas at the stopper rod were investigated.

Research on Scheduling of Iron and Steel Scrap Steelmaking and Continuous Casting Process Aiming at Power Saving and Carbon Emissions Reducing

Iron and steel scrap could substitute ironstone as the raw material for steelmaking and continuous casting (CC) production, and effectively reduce emissions of waste gas, water, and residue. The iron and steel scrap steelmaking and continuous casting (ISSSC) process is a compact production process involving scrap steel as a raw material, electric arc furnace, refining (RH/CAS/KIP/LF), and CC. Traditional scheduling of ISSSC has emphasized production performance indexes without considering energy and environmental factors. This study presents a new mathematical programming model for the scheduling of ISSSC that considers energy consumption with time-of-use electricity price and associated carbon emissions in addition to production performance indexes. The complexity of the multiobjective mixed-integer programming problem increases if the interval of the time-of-use electricity price is enlarged, the main and accessorial equipment is considered separately, and the flexible processing time is controllable. Under the linearization augmented Lagrangian relaxation framework, a solution methodology, based on controllable direction and a step surrogate subgradient Lagrangian algorithm, is developed according to the charge-based subproblem splitting policy. This solution could keep a smaller intersection angle between the gradient and the optimal direction, damping the zigzag, reducing the number of iterations, and ensuring the optimization efficiency for the scheduling of ISSSC. Numerical testing results show that the method generates high quality schedules in a timely fashion, while considering the time-of-use electricity price and associated carbon emissions.

Pulse electromagnetic force microstructural control at continuous billet casting 7xxx Al-alloys

In this study, the original equipment and methods for the macro/microstructure managed formation in the crystallizers of continuous casting processes by the applying of the amplitude modulated (AM) pulsing magnetic fields (PMF) it the electromagnetic stirrer (EMS) has been developed and tested.Method has provide the complex electrodynamic, hydrodynamic and acoustic pulse-force processing of unsolidified casting product portion for providing equalizing of solidification front in the billet mushy zone. Resulted non-dendritic type of microstructure has been provide by the means applying: Pulse magnetic field with periodically changing in time amplitude (AM-PMF); Pulse amplitude-modulated rotating melt stirring (AM-PRMF); Pulse amplitude-modulated 3D-helicoidally rotating melt stirring.Study efficiency applying of unidirectional axial pulse magnetic field (AM-PMF) with pulse frequency in range 5~15Hz, carried frequency in range 22∼55Hz, at intensity of MF 0.05∼0.1T, for semi-continuous 7xxx alloys (analogue 7075 alloy) 7 ‘billet casting on micro- and macrostructure billet formation has been show reaching the stabile effect for non-dendrite state microstructure formation in all billet cross-section. As well-achieved uniform and homogeneity microstructure state with average grain size not more 100μm, and for middle and central billet part in range 60∼80μm, in 3∼5 times lowest instead grain sizes 200∼650μm at DC casting without EMS, or instead 150μm grain sizes as for conventional rotating EMS. As well, fully solved problems of axial and structural segregation, hot-crack ability or micro-cracks on grains edges and micro-porosity occurring.

Вплив періодичних коливань і флуктуацій рівня металу в кристалізаторі на процес безперервного розливання

Вплив періодичних коливань і флуктуацій рівня металу в кристалізаторі на процес безперервного розливання

Precipitation behavior, microstructure and properties of aged Cu-1.7 wt% Be alloy

A process of heating-cooling combined mold horizontal continuous casting→cold rolling→solid-solution treatment was used to produce Cu-1.7 wt% Be alloy sheet, and the precipitation behavior, microstructure and properties of the Cu-1.7 wt% Be alloy sheet during aging were investigated. The results showed that the phase transformation sequence of the alloy during aging at 325 °C was GP zone→γ″→γ′→γ equilibrium phase. The reasonable aging parameters were aging temperature of 325 °C and aging time of 3 h, and the hardness, tensile strength and yield strength of the aged alloy reached the peak values of 375 HV, 1042 MPa and 778 MPa, which were 172%, 116%, and 255% higher than those of the solid-solution alloy, respectively, and the electrical conductivity was 22.4% IACS. The formation of a large number of dispersed nano-sized γ′ phase was mainly responsible for the high strength of the alloy. A dynamic model of aging precipitation was established and the yield strength of the peak-aged alloy was calculated by the strengthening model. The deviation of the calculated value (797 MPa) and the measured value (778 MPa) was 2.4%, and the strengthening mechanism of the peak-aged alloy was determined as the Orowan bypass mechanism.

Application of exchangeable carbon-bonded alumina foam filters in an industrial tundish for the continuous casting of steel

Various melt refining techniques were developed in the past and led to ongoing improvement of casting quality. One of these processes is the so-called metal melt filtration, which became state of the art especially in aluminum foundry operations by using ceramic foam filters. Attempts to adapt the technique for the continuous casting of steel showed numerous difficulties due to the severe thermomechanical conditions and the high quantity of processed melt. Premature blockage or failure of ceramic foam filters implemented in the tundish promoted the application of flow control devices and multi-hole filters as alternatives. In the present study, a new approach for ceramic foam filters in the continuous casting of steel was tested. Thereby, the main disadvantage of limited filter service lifetime was circumvented by the application of an exchangeable filter system without disturbing the underlying continuous casting process. Cylindrical carbon-bonded alumina foam filters were prepared and mounted on alumina-carbon shafts using different adhesives and slag protection measures. The filters were immersed by a crane into the steel melt in an industrial tundish with 80 t capacity. During each test, one batch with approximately 380 t of steel was cast at over 1550 °C before removing the filter. The application of high-alumina mortar as adhesive and a compact filter geometry without macro channels proved to be essential for the successful operation. Samples of the corresponding filter were analyzed by digital light microscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and electron backscatter diffraction. The complementary investigations revealed the formation of pronounced clogging layers based on aluminum-rich calcium aluminates, which can be clearly distinguished from the synthetic slag material containing silicon and other trace elements. At the bottom of the filter pronounced clusters of coral-like and plate-like inclusions were observed, which approached the filter surface by buoyancy.