Billet Continuous Casting Research Articles

Mathematical Modeling of Cooling of a Continuously Cast Ingot for Reducing Heat Losses

We consider thermal processes running in the course of cooling of a continuously cast ingot in a continuous billet casting machine with regard for the heat of phase transformations. For the solution of the problem of rational utilization of the heat of melts, we propose to improve the technology of continuous casting of steel, which would make it possible to use the heat of the liquid core of an ingot for leveling the temperature field over its cross section and guarantee the minimum losses of the heat at the exit of the continuous billet-casting machine. We develop a mathematical model of cooling of continuously cast ingots in a two-dimensional space representation with regard for the release of the heat of crystallization in the two-phase zone. The numerical realization of the model is performed with the help of the implicit difference scheme of coordinate-wise splitting. The adequacy of the model is checked by analyzing the convergence of the experimental and numerical data according to the Fisher, Student, and Mann–Whitney criteria. In modeling, we simulated the control action in the zone of secondary cooling. It is established that, in the case of application of the control action in this zone, the surface temperature increases by 160°C, while the average mass temperature increases by 100–160°C. We choose criteria for the rational modes of cooling of continuously cast ingots. To preserve the heat content of an ingot, it is proposed to use heat insulation after the zone of water–air cooling. We determine relationships between the parameters affecting the surface temperature of the ingot and represent them in the form of nomograms. It is shown that, before the machine of gas cutting, as a result of heat insulation in the zone of air cooling, the ingot is thermostatted as a result of which the temperature of its most vulnerable zones (corners and surfaces) increases. It is established that, for the rational modes of casting of steels, the ratio of the length of the zone of heat insulation to the total length of the continuous billet casting machine varies within the range 0.3–0.6. To determine the heat losses in the process of subsequent cooling of the ingot in air after leaving the zone of machine gas cutting, according to the existing technology of transportation of slabs to compression, the time of modeling was set equal to 90–105 min. To preserve the heat content of the ingot and level temperatures over its cross section, it is also necessary either to use a thermally insulated transmission roller conveyer or to hold ingots in a thermostat.

Fluid Flow and Solidified Shell Remelting in F-EMS During Billet Continuous Casting

A method involving a two-dimensional (2-D) heat transfer model combined with a three-dimensional (3-D) coupled electromagnetic, fluid flow, heat transfer, and solidification model has been developed to simulate the fluid flow and solidified shell remelting at the final stage of the billet continuous casting process. The electromagnetic force was coupled by loading into the momentum equation as the momentum source. The effects of various stirrer currents on the fluid flow behavior of the strand was discussed. Remelting of the solidified shell was analyzed, considering the force on the molten steel. The results showed that the maximum velocity of the molten steel increased from 0.06 m/s to 0.08 m/s with increase of the stirring current from 340 A to 400 A. Solidified shell remelting was caused by the impact of the molten steel, mainly driven by tangential electromagnetic and centrifugal forces.

Analysis of titanium nitrides precipitated during medium carbon steels solidification

For certain applications, coarse titanium nitride (TiN) precipitates can be deleterious for the final properties of the material. Hence, in order to better understand the mechanisms involved in the generation of these precipitates, a characterization of the particles observed in steels with different titanium and nitrogen content was carried out. Samples from liquid steel (tundish), continuous casting billets and final product were evaluated using an Automatic Particle Analyzer (APA) coupled to a Scanning Electron Microscope (SEM). The location, frequency, size distribution and composition of the different particles observed were assessed. While only few TiN precipitates were observed in liquid steel samples, the density of this type of particles significantly increased in the continuous casting billets samples. Particles ranging from 1 to 10μm were mainly found in the interdendritic zones of the as-cast structure. The density of TiN particles observed in these samples did not change after re-heating and rolling operations. A microsegregation model previously developed was adapted to predict TiN precipitation during solidification. A reasonable agreement was found between model results and measured data. Results of this analysis confirmed that the precipitated fraction of TiN increases as the product of steel Ti and N contents rises.

RESEARCH OF THE BEHAVIOR OF MACROSTRUCTURE DEFECTS OF THE PRE-DEFORMED CONTINUOUS CAST BILLETS DURING ROLLING

The most significant trend in recent decades in the field of continuous casting of steel billets is a partial transfer of the process of deformation of the exposure to the field of complete solidification (rolling mill) in the area of two-phase (solid-liquid)state (technological line of CCM). However, the implementation of such two-stage deformation of the continuous cast ingot leads to the need for changes to the methodology of physical simulation of the behavior of defects (surface and bulk) in the course of the subsequent rolling, first and foremost, in terms of the correct choice of their geometric shape and spatial orientation. The paper presents the results of a study of the influence of spatial orientation of the surface defects and continuity of the macrostructure of the metal axial region deformed in the line of the continuous casting machine using layered physical models. An experimental study performed in the conditions of deformation of reduced billets by two schemes with rolling simulation scale1:5: in smooth rolls, simulating the process of groоvelles rolling as applied to the first two stands of the crimp group of medium-section mill 300; in the first and second pairs of rectangular grooves of breakdown stand of the mill 500/370 of PJSC “Donetsk Metal Rolling Plant”. According to the multiplicity of the problem, the universal design of physical models was developed to simulate the spatial location of both surface and internal defects. Studies have shown that in case of rolling of physical models with extract ratio over 2.0 and an angle of misalignment defects imitators close to 60° their complete “healing” is possible. In turn, decrease in the angle to 30° contributes to greater extraction of the defect-simulator and only a small decrease in their width. In the case of total misalignment of defect-simulators (angle 90°) there is a broadening of the defects and their deposition to the initial length after tilting by 90°. The obtained experimental data allowed understanding of the mechanisms of “healing” defects integrity of metal depending on magnitude of the total extracts, the angle of misalignment of the longitudinal axis of the defect with the rolling direction and the distance of their occurrence from the longitudinal-transverse plane of symmetry.

Effects of Angle of Rotation of Submerged Entry Nozzle on Fluid Flows in a Square Billet Casting Mold

Having knowledge of fluid flows within the mold region of a billet continuous caster is of paramount importance to reduce a product’s internal and external defects. In this regard, a three-dimensional numerical model was developed to simulate the influence of the orientation of a five-port submerged entry nozzle (SEN) on the flow field of liquid steel within the mold region of a curved, square billet, continuous caster. The realizable k– epsilon turbulence model, together with the volume of fluid multiphase model, was used to simulate the effects of turbulence on these fluid flows, and their impact on the liquefied mold powder layer sitting on top of the liquid steel within the mold. The behavior of flows generated in the mold cavity was validated against previous experimental work. The numerical results showed that the modified SEN’s horizontal angle of rotation can significantly change the flow pattern within the billet mold. These changes can stabilize the liquid steel meniscus, which is expected to improve the quality of continuously cast products by decreasing mold powder entrainment.

A new experimental apparatus for emissivity measurements of steel and the application of multi-wavelength thermometry to continuous casting billets.

An experimental apparatus has been designed for measuring the emissivity of a steel surface in both vacuum and oxidation atmosphere. The sample is heated with the method of electromagnetic induction in order to ensure the temperature uniformity. The radiance emitted from a sample is measured using a fiber-optic Fourier transform infrared spectrometer. Using this unique apparatus, we investigated the spectral (2-6 μm) and directional (0°-86°) emissivity of stainless steel 304 with different degrees of surface oxidation at temperatures ranging from 800 to 1100 °C. The experimental results show that the emissivity increases slightly with increasing temperature, which accords with the Hagen-Rubens relation. The emissivity increases rapidly at the initial stage of oxidation, but gradually reaches to a constant value after 20 min. In addition, the directional emissivity has a maximum value at the measuring angle of about 75°. The maximum uncertainty of emissivity is only 3.0% over all the measuring ranges, indicating that this experimental apparatus has a high reliability. In order to measure the surface temperature of casting billets based on multi-wavelength thermometry, the bivariate emissivity function with the two variables, wavelength and temperature, is determined. Temperature measurement results based on our technique are compared with those from common dual-wavelength radiation thermometry. Our approach reduces the measured temperature fluctuation from ±20.7 °C to ±2.8 °C and reflects the temperature variation with the changes of production parameters in real time.

Formation of Transverse Surface Cracks During Peritectic Steel Continuous Casting

Various mechanisms of transverse crack formation within the surface of continuously-cast billets in the pouring temperature range are analyzed. It is shown that low mechanical properties of peritectic steels in the high-temperature region are due to the high temperature for completion of the δ→γ transformation (Tγ). The effect is considered individually of grain size on metal mechanical properties. Conditions are analyzed for the formation of coarse grains during continuous casting of peritectic steels. It is shown that in the low-temperature region key effects are stress concentration conditions at grain boundaries and intergranular bond forces. On the basis of this analysis, a series of recommendations is proposed for reducing the probability of forming surface cracks in billets.

Numerical Simulation of Macrosegregation Impurities in the Solidifying Continuous Casting Steel Billet

<p>In this study, new theoretical conceptions have been developed about an impurity segregation mechanism at the time of alloy solidification considering present microvolumes with different chemical compositions during alloy solidification. It has been concluded that this conception allows to establish and optimize technologic parameters that influence the production of the main types of macro-heterogeneity. The derived model conceptions have confirmed the final condition of real continuous casting billets by using the advanced analyzing methods. </p><p>Highlights </p><p>· The quasi-equilibrium theory used to study the hardening processes of alloys has been expanded and improved.<br />· The development of a numerical model for macrosegregation impurities in solidifying continuous casting billet is suggested.<br />· The adequacy of the developed model is checked under the industrial conditions using comparison theoretical<br />· calculations and practical data.<br />· The results and developments that are obtained are discussed.</p>

Producing Structural-Steel Bar from Continuous-Cast Billet

The expanded use of continuous-cast billet in the production of structural-steel bar is considered. The quality of 135 × 135 mm continuous-cast billet produced on a standard continuous-casting machine and the bar derived from it is evaluated. At more recently built plants, the production of quality bar from continuous- cast billet requires total extension of the order of 6–7. On the basis of the analysis developed in the present work, it is possible to determine the maximum critical bar cross section such that the required properties are ensured.

Theoretical Foundations of the Design of a Lever Mechanism of Oscillations of the Mold of a Sorting Machine for the Continuous Casting of Billets

We consider specific features of the design of the lever mechanism of oscillation for the mold of a radial sorting machine with continuous casting of billets under the conditions of the maximum correspondence of the vibration motion of the mold with the axis of extrusion of ingots from this mold. It is shown that the traditional kinematic scheme of the oscillation mechanism does not guarantee high accuracy of the codirectional motion of the mold relative to the technological axis of the channel of this machine.

Development of a New Horizontal Continuous Casting Machine Construction for Nonferrous and Precious Metal Billets

The work is devoted to development of a new design of horizontal continuous billet casting machine (HCBCM) for non-ferrous and precious metals. The possibility of calculation and design of horizontal casting machine elements by means of computer simulation using the software created is demonstrated. Based on the proposed methods of calculation and design as well as analysis of mathematical modeling results, new designs of HCBCM elements are created that enhance the efficiency of the machine. Appraisal trials of HCBCM structural elements created are performed successfully to measure the effectiveness of this work and introduction into production.

MASTERING THE PRODUCTION OF A CONTINUOUS CASTING BILLET DIAMETER 200 MM FROM CHROME-MOLYBDENUM STEEL GRADES FOR THE PRODUCTION OF SEAMLESS PIPES AT THE OJSC «BSW – MANAGEMENT COMPANY OF HOLDING «BMC»

Growth in demand for drilling and perforated pipes in the Russian Federation and the USA requires an increase in the production of seamless pipes. In turn, the specific operating conditions of the pipes present special requirements to the product for strength and resistance in aggressive media. This article describes the experience of mastering the production of continuous casting billets from chromium-molybdenum steel grades at the OJSC «BSW – Management Company of the Holding «BMC».

СХЕМА НАПРЯЖЕННО-ДЕФОРМИРОВАННОГО СОСТОЯНИЯ НЕПРЕРЫВНО-ЛИТОГО СЛЯБА В ТЕХНОЛОГИЧЕСКОЙ ЛИНИИ МНЛЗ

The aim of the work is to develop a model of the deformation-stressed state of a continuous-cast billet, taking into account its behavior in the continuous casting machine line. A new physical model of the ingot crust bending process in the inter-roller gap has been proposed. The model is based on the regularities of the change in the deformed state of the surface of the crust under the action of ferrostatic pressure. It is established that the crust undergoes a cyclic alternating deformation in the process of moving it across the inter-roller gap. It is shown that the surface of the crust comes into contact with the surface of the roller before approaching the inter-roller gap. This causes the appearance of an anomalous area with a constant curvature of the crust at the final stage of its buckling. The second anomalous deformation zone of the ingot crust is the junction zone of the previous crust and the subsequent inter-roller gap, where the crust instantly changes its curvature. In combination with the flat scheme of the stress-strain state, a physical model is presented, which makes it possible to identify in each of the inter-roller gaps the zone of maximum values of the tensile strain rate. Identifying the zone of maximum values of the tensile strain indicator and comparing it with the maximum allowable one allows determining and correcting the length of the inter-roller gaps of the continuous casting machine.

Effects of electromagnetic stirring on fluid flow and temperature distribution in billet continuous casting mould and solidification structure of 55SiCr

The optimal combination of current intensity and frequency of mould electromagnetic stirring (M-EMS) in continuous casting billet was a crucial compromise for improving inner quality of cast billet such as reduction in center segregation and porosity of medium-high carbon steel. In the present study, a decoupled three-dimensional mathematic model of electromagnetic field, fluid flow and heat transfer in continue casting billet mould with EMS has been developed, and the effects of current intensity and frequency on the system were also discussed. In addition, the industrial trials were carried out to investigate the magnetic field characteristics in the mould with M-EMS and the influence of M-EMS on the solidification structure of 55SiCr. According to the calculations and analysis, the optimal combination range of current intensity and frequency was 300–320 A and 3–4 Hz, respectively. The results showed that inner quality in as-cast billet of 55SiCr has been improved significantly with optimal parameter of 320 A and 3 Hz. For instance, central equiaxed zone increased from 19% to 33%, the center carbon segregation ratio decreased from 1.13 to 1.05 as well as center porosity has nearly disappeared.

Improving Refractory Constructions in the System “Steel-Pouring Ladle – Pouring Basket” of CBCM

The refractory equipment of the system “steel-pouring ladle – pouring basket” of continuous billet casting machines (CBCM) is considered. Designs of elements of the unit intended for protecting streams of metal in the course of pouring steel are developed. Designs of the unit with the use of inserts made of plastic refractories to prevent passage of air into the metal stream as it is being poured and assure rational parameters of the delivery of argon into the annular groove of the refractory tube are considered. Stability of the pouring process and an increase in the quality of the poured metal are achieved as a result.

A pseudo-transient heat transfer simulation of a continuous casting process, employing the element-free Galerkin method

The present work has been conducted in order to develop a novel solution for the heat transfer problem during the continuous casting of steel billets and blooms, by using the element-free Galerkin method under a pseudo-transient moving cross-section slice approach. The transport laws, non-linear aspects and boundary conditions of the initial value problem have been specified. A detailed explanation concerning the characteristics inherent to the application of the element-free Galerkin method to this problem has also been provided. The feasibility and suitability of this novel approach has been verified by comparison with the numerical techniques proposed and the results reported by other researchers as well as an analytical solution of a simple 1-D alloy solidification problem. The results have revealed that this technique could be used successfully in the pseudo transient moving cross-section solution of the heat transfer problem involved in the continuous casting of blooms and square billets.

Numerical study of an application of a divergent reverse TurboSwirl nozzle in the billet continuous casting process

ABSTRACTThe swirling flow has widely been investigated for liquid steel flowing in the continuous casting process. In this paper, a new design of the submerged entry nozzle (SEN) is applied by using a reverse TurboSwirl device with a divergent nozzle. This divergent reverse TurboSwirl nozzle (DRTSN) is shown to gain a more beneficial flow pattern compared to the straight nozzle. A stronger swirling flow can be obtained at the SEN outlet, which leads to a calmer flow field and an appropriately active meniscus flow that could improve the heat and mass transfer near the meniscus. The swirl number in the SEN is independent of the casting speed, while a lower casting speed yields a lower maximum wall shear stress. The DRTSN is connected to the tundish by an elbow and a horizontal runner. A longer horizontal runner supplies a more uniform velocity profile and a more symmetrical flow pattern.

Зміна традиційних позицій українського експорту

Зміна традиційних позицій українського експорту

Magnetohydrodynamic Calculation for Electromagnetic Stirring Coupling Fluid Flow and Solidification in Continuously Cast Billets

A new magnetohydrodynamic (MHD) model considering flow field and solidification is developed to simulate electromagnetic stirring (EMS) during billet continuous casting. Based on the model, the influence of fluid flow on the calculation of magnetic field, induced current, and electromagnetic force is investigated in comparison to the traditional calculation model. Furthermore, the characteristics of fluid flow affected by electromagnetic stirring, including three‐dimensional streamlines, tangential velocity, and meniscus fluctuation, are studied to evaluate the new MHD model. The MHD calculation reveals that the flow field in mold has a certain influence on the magnetic field, while the effect resulting from the interaction between flow field and magnetic field on the electromagnetic force is significant. As a consequence, increased velocity at the meniscus has been obtained compared to the traditional calculation, indicating a more intense meniscus fluctuation.

Numerical investigation of in-mold electromagnetic stirring process for fluid flow and solidification

PurposeThe purpose of present investigation is to analyze the in-mold electromagnetic stirring (M-EMS) process and the effect of stirrer frequency on fluid flow and solidification in a continuous casting billet caster mold.Design/methodology/approachA hybrid approach involving finite element and finite volume method has been used for the study. Finite element model is used to calculate time variable magnetic field, which is further coupled with fluid flow and solidification equations for magneto-hydrodynamic analysis with finite volume model.FindingsResults show that though superheat given to steel before its entry into the mold is quickly removed, solid shell formation is delayed by the use of M-EMS. Final solid shell thickness, however, is slightly reduced. Increase in frequency is found to increase the magnetic flux density and tangential velocity of liquid steel and decrease in diameter of liquid core.Practical implicationsThe work is of great industrial relevance. The model may be used to design industrial setup of in-mold electromagnetic stirrer and process could be analyzed and optimized numerically.Originality/valueThe paper evaluates the influence of M-EMS and its frequency on solidification and flow behavior in the continuous casting mold. The iso-surface temperatures from pouring temperature to liquidus temperature inside the mold have been shown. The findings may be useful for the steelmakers to reduce the defect in continuous casting.