Search

This article studies the shrinkage porosity model for steel ingots with reduction deformation during solidification, and examines the effect of reduction deformation on the shrinkage porosity. Initial investigations involve conducting experiments on reduction deformation during steel ingot solidification, entailing laboratory‐based high‐temperature melting and jack reduction process, with a focus on diverse reduction amounts and cooling times before reduction. Post‐experimental procedures include sample sectioning, acid etching, and low‐magnification structural analysis. Following this, numerical simulations are employed to model the solidification and reduction deformation processes of the steel ingot. Ultimately, a shrinkage porosity criterion model is developed, integrating the equivalent plastic strain resulting from reduction deformation during solidification into the micro‐porosity criterion model. This approach facilitates the prediction of micro‐porosity distribution following reduction deformation. Findings reveal that the shrinkage porosity criterion G2L−5/3ε/εa, which includes the equivalent plastic strain coefficient, effectively predicts the distribution of micro‐porosity subsequent to reduction deformation during steel ingot solidification. A higher reduction amount during the solidification process corresponds to a lowered level of internal micro‐porosity. [ABSTRACT FROM AUTHOR]

The article focuses on analyzing the utilization of external influences, such as metal modification, vibration, stirring the metal pool, and hot topping of steel ingots. It demonstrates the positive impact of external influences on the conditions of crystallization and solidification in various ingots. A conclusion was made that an effective approach to influencing the molding of a steel ingot can involve a combination of heating and stirring in the hot top by introducing a device into the core of the ingot, setting the liquid metal in motion. [ABSTRACT FROM AUTHOR]

Steel ingot with a large height-to-diameter ratio is utilized to produce multiple products by one stock in practice. Water cooling is a usual way to enhance production efficiency. However, the combination of the two factors will generate internal defects, such as shrinkage porosity and hot crack. The characteristic of internal shrinkage crack in a 10 t water-cooled steel ingot with a large height-to-diameter ratio was examined by an ultrasonic test. A slice was sectioned from the ingot middle part where billets containing star-like crack were further extracted. The billets were examined by X-ray high energy industrial CT, and the compactness was reconstructed in three dimensions. Microstructure near the crack was observed using scanning electron microscopy, and the solidification process and grain size were studied by high temperature confocal microscopy. Moreover, thermomechanical simulation and post-processing were carried out to analyze the formation of shrinkage porosity and hot crack. A new criterion considering mushy zone mechanical behavior in brittle temperature as well as grain size distribution was proposed to evaluate hot cracking potential in the ingot. The results show that a deep shrinkage porosity band easily forms in the center line of such an ingot with a large height-to-diameter ratio, and watercooling further generates excessive tensile stress tearing the liquid films around the porosities. Then, hot cracks begin to propagate along grain boundaries. The grain size in the upper and center of the ingot is large, which leads to an inverted cone shape defects zone in the ingot center.

In this paper, the temperature field and heat transfer stress mathematical model of the unidirectional solidification ingot of the traditional water-cooled chassis and the improved water-cooled chassis are established, and the numerical simulation calculation of 45 tons unidirectional solidification ingot is carried out by using the finite element simulation analysis method. The results show that adding proper forced cooling conditions to the bottom of ingot is beneficial to the balanced advance of the solidification front of molten steel. The improvement of the bottom forced cooling scheme obviously shortens the solidification time of the ingot. The water cooling at the bottom of the ingot is adapted to the air gap distribution to achieve uniform air gap distribution. The ingot solidifies evenly in the longitudinal direction to avoid bottom warpage.

Shrinkage cavity has significant influence on macrosegregation in steel ingots. An arbitrary Lagrangian-Eulerian (ALE) model based on volume averaging method is developed to predict the coupled formation progress of macrosegregation and shrinkage cavity during solidification of steel ingots. The combined effect of thermal-solutal convection and solidification shrinkage on macrosegregation is considered in the model. A specially designed mesh update algorithm is proposed to consider the formation of shrinkage cavity. The streamline-upwind/Petrov–Galerkin (SUPG) stabilized finite element algorithm is adopted to solve the conservation equations. Two solution methods for the energy conservation equation are proposed, i.e. the temperature-based solver and enthalpy-based solver. A Pb-48wt.%Sn solidification benchmark is used for validation. Then, the ALE model is applied to a Fe-3.6wt.%C industrial steel ingot. The formation progress of macrosegregation coupled with shrinkage cavity is predicted. By comparison with the predictions of the finite element model and finite volume model, the effect of shrinkage cavity formation on macrosegregation is investigated. Results show that the formation of shrinkage cavity can significantly change the segregation region and segregation degree at the hot top. It is demonstrated that the ALE model can predict the coupled formation of macrosegregation and shrinkage cavity in steel ingots.

The paper deals with the inoculant–freigrator effect on some parameters of the structure: grain size and contamination index. The “beads” extracted from steelmaking slags were used as the inoculant. The effect of the fractional composition and the number of introduced “beads” were investigated. The “beads” were preliminarily crushed to the fraction of 100 – 1 500 μm and were introduced into the melt in the amount of 0,5 – 1,5 % by mass. It was established that the introduction of the “beads” of the fraction of 500 – 600 microns in the amount of 1 – 1,5 % as the inoculant contributed to the grinding of grain, reduced the tendency to segregation and dendre formation.

A new type of optimized riser structure was proposed, in which a low-emissivity board was inserted into the hollow interlayer of the material to increase the yield of the steel ingot. The insulation effect of different riser heights on the solidification process of steel ingot is numerical simulated. The results show that when the riser height can be reduced from 350 mm to 300 mm, the ingot yield can be increased by 1,92 %. As the number of low-emissivity boards is increases, the riser insulation performance is also increased.

Steel ingot with a large height-to-diameter ratio is utilized to produce multiple products by one stock in practice. Water cooling is a usual way to enhance production efficiency. However, the combination of the two factors will generate internal defects, such as shrinkage porosity and hot crack. The characteristic of internal shrinkage crack in a 10 t water-cooled steel ingot with a large height-to-diameter ratio was examined by an ultrasonic test. A slice was sectioned from the ingot middle part where billets containing star-like crack were further extracted. The billets were examined by X-ray high energy industrial CT, and the compactness was reconstructed in three dimensions. Microstructure near the crack was observed using scanning electron microscopy, and the solidification process and grain size were studied by high temperature confocal microscopy. Moreover, thermomechanical simulation and post-processing were carried out to analyze the formation of shrinkage porosity and hot crack. A new criterion considering mushy zone mechanical behavior in brittle temperature as well as grain size distribution was proposed to evaluate hot cracking potential in the ingot. The results show that a deep shrinkage porosity band easily forms in the center line of such an ingot with a large height-to-diameter ratio, and water-cooling further generates excessive tensile stress tearing the liquid films around the porosities. Then, hot cracks begin to propagate along grain boundaries. The grain size in the upper and center of the ingot is large, which leads to an inverted cone shape defects zone in the ingot center. [ABSTRACT FROM AUTHOR]

The effect of a hollow riser on the upper heat dissipation of 76 tons and 8 corners ingots is studied by numerical simulation in this paper. Through the simulation of the heat transfer of the traditional riser, the 1 gap riser and the 2 gaps riser ingot, this paper draws a conclusion that the solidification time of the riser part of the riser is the longest in the 2 gaps scheme, and the solidification time of the central molten steel is 31417s, which is far higher than the other two schemes. The heat flux in the riser of the 2 gaps scheme is obviously larger than the other two schemes, which slows down the advance of the solidification front. The 2 gaps scheme is stronger than the other two schemes for reducing the cooling speed of the riser line center and the shoulder joint. It is particularly significant to reduce the cooling rate of the shoulder joints, which is more conducive to expanding the angle of the solidification front and fully filling.

In this paper, the temperature field and heat transfer stress mathematical model of the unidirectional solidification ingot of the traditional water-cooled chassis and the improved water-cooled chassis are established, and the numerical simulation calculation of 45 tons unidirectional solidification ingot is carried out by using the finite element simulation analysis method. The results show that adding proper forced cooling conditions to the bottom of ingot is beneficial to the balanced advance of the solidification front of molten steel. The improvement of the bottom forced cooling scheme obviously shortens the solidification time of the ingot. The water cooling at the bottom of the ingot is adapted to the air gap distribution to achieve uniform air gap distribution. The ingot solidifies evenly in the longitudinal direction to avoid bottom warpage. [ABSTRACT FROM AUTHOR]

Macrosegregation is the major defect in large steel ingots caused by solute partitioning and melt convection during casting. In this study, a three-phase (liquid, columnar dendrites, and equiaxed grains) model is proposed to simulate macrosegregation in a 36-t steel ingot. A supplementary set of conservation equations are employed in the model such that two types of equiaxed grains, either settling or adhering to the solid shell, are well simulated. The predicted concentration agrees quantitatively with the experimental value. A negative segregation cone was located at the bottom owing to the grain settlement and solute-enriched melt leaving from the mushy zone. The interdendritic liquid flow was carefully analyzed, and the formation of A-type segregations in the mid-height of the ingot is discussed. Negative segregation was observed near the riser neck due to the specific relationship between flow direction and temperature gradient. Additionally, the as-cast macrostructure of the ingot is presented, including the grain size distribution and columnar-equiaxed transition. [ABSTRACT FROM AUTHOR]

Central shrinkage crack is a common defect encountered in steel ingot casting. It is necessary to limit the degree of crack in case of further propagation in forging. A 234-t steel ingot was dissected to check the internal quality, and a central shrinkage crack band of 1,400 mm in height and 120 mm in width, was found at a distance of 450 mm under the riser bottom line. Then, thermo-mechanical simulation using an elasto-viscoplastic finite-element model was conducted to analyze the stress-strain evolution during ingot solidification. A new criterion considering mush mechanical property in the brittle temperature range as well as shrinkage porosity was used to identify the shrinkage crack potential, where the degree of shrinkage porosity is regarded as a probability factor using a modified sigmoid function. Different casting processes, such as pouring speed, mould preheating and riser insulation, were optimized with the simulation model. The results show that fast pouring, proper mould preheating and good riser insulation can alleviate shrinkage crack potential in the ingot center.

Copyright of Electrometallurgy Today / Sovremennaya Elektrometallurgiya is the property of International Association Welding (Paton Publishing House) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The paper deals with the inoculant-freigrator effect on some parameters of the structure: grain size and contamination index. The "beads" extracted from steelmaking slags were used as the inoculant. The effect of the fractional composition and the number of introduced "beads" were investigated. The "beads" were preliminarily crushed to the fraction of 100 - 1 500 µm and were introduced into the melt in the amount of 0,5 - 1,5% by mass. It was established that the introduction of the "beads" of the fraction of 500 - 600 microns in the amount of 1 - 1,5% as the inoculant contributed to the grinding of grain, reduced the tendency to segregation and dendre formation. [ABSTRACT FROM AUTHOR]

A new type of optimized riser structure was proposed, in which a low-emissivity board was inserted into the hollow interlayer of the material to increase the yield of the steel ingot. The insulation effect of different riser heights on the solidification process of steel ingot is numerical simulated. The results show that when the riser height can be reduced from 350 mm to 300 mm, the ingot yield can be increased by 1,92%. As the number of low-emissivity boards is increases, the riser insulation performance is also increased. [ABSTRACT FROM AUTHOR]

A model for fluid and heat transfer of early stage of filling of a 19 ton ingot mould was built, and the flow and tempera-ture distribution characteristics during early stage of filling were investigated. Numerical simulations of mould filling with a series of en-trance nozzles with the different top diameters and bottom diameters were carried out, and the effects of entrance nozzle structure on mould powder entrapment during early stage of filling were investigated. The results show that level fluctuation in molten steel is strong and solidified shell grows fast so that mould powder can be entrapped easily. When top-end interior diameter is larger than bottom-end, the velocity of molten steel stream depends on the bottom-end interior diameter, and decreases with the increasing of op-end interior di-ameter. As for 19 ton steel ingot, the risk of mould powder entrapment can be greatly decreased when the bottom-end interior diameter is larger than 90 mm.

The electromagnetic feeding method was used to improve solidification quality of steel ingot, and the feeding principle of electromagnetic riser was introduced. The distribution characteristics of magnetic field in electromagnetic riser were investigated before and after pouring steel by the measures of numerical and physical simulation. The results showed that there’s a good symmetry of magnetic field distribution in electromagnetic feeding riser before pouring steel, but both symmetry and uniformity of magnetic field distribution are broken after pouring steel into riser, and magnetic induction intensity of the surface is higher than that of the inner of feeding riser.

P91 is a new kind of heat-resistant and high-tensile steel. It can be extruded after ingot casting and can be widely used for different pipes in power plants. However, due to its mushy freezing characteristics, a lack of feeding in the ingot center often generates many defects, such as porosity and crack. A six-ton P91 ingot was cast and sliced, and a representative part of the longitudinal section was inspected in more detail. The morphology of crack-like defects was examined by X-ray high energy industrial CT and reconstructed by 3D software. There are five main portions of defects larger than 200 mm3, four of which are interconnected. These initiated from continuous liquid film, and then were torn apart by excessive tensile stress within the brittle temperature range (BTR). The 3D FEM analysis of thermo-mechanical simulation was carried out to analyze the formation of porosity and internal crack defects. The results of shrinkage porosity and Niyama values revealed that the center of the ingot suffers from inadequate feeding. Several criteria based on thermal and mechanical models were used to evaluate the susceptibility of hot crack formation. The Clyne and Davies’ criterion and Katgerman’s criterion successfully predicted the high hot crack susceptibility in the ingot center. Six typical locations in the longitudinal section had been chosen for analysis of the stresses and strains evolution during the BTR. Locations in the defects region showed the highest tensile stresses and relative high strain values, while other locations showed either low tensile stresses or low strain values. In conclusion, hot crack develops only when stress and strain exceed a threshold value at the same time during the BTR.

The generic mathematical model and computational algorithm considering hydrodynamics, heat and mass transfer processes during casting and forming steel ingots and castings are offered. Usage domains for turbulent, convective and non-convective models are determined depending on ingot geometry and thermal overheating of the poured melt. The expert system is developed, enabling to choose a mathematical model depending on the physical statement of a problem.

Based on the mechanisms of macrosegregation evolution in large steel ingots, an approach named as gradual-cooling solidification (GCS) was proposed to alleviate the macrosegregation of large steel ingots. A three-phase mixed columnar dendritic-equiaxed solidification model was employed to investigate the approach. The solidification model considered the dendritic structure of equiaxed grains, nucleation and growth of equiaxed crystals, growth of columnar trunks, thermal-solutal buoyancy, sedimentation of equiaxed crystals, and columnar-to-equiaxed transition (CET). After the verification of model accuracy by a reported experiment results of a 55-ton steel ingot, this model has been used to study the GCS approach. The simulation results showed that the GCS approach has significant potential to alleviate the macrosegregation of the large steel ingot; e.g., for a 55-ton steel ingot, the variation range of segregation value decreased from 0.854 in the conventional casting case to 0.077 in the GCS case. [ABSTRACT FROM AUTHOR]

The present communication presents results of an investigation aimed at developing a ratio between the top mass and the body mass of the forging octagonal dead-melted steel ingot. Technological solutions for the application of various exothermic and thermal insulating materials in the exterior part of the ingot are advanced on the ground of an analysis of the shape and length variation of the pipe zone and shrinkage porosity in conformity with the numerical computer modeling of crystallization. [ABSTRACT FROM AUTHOR]

A new hot cracking potential (HCP) criterion, for the appearance of hot tearing in steel ingot castings, is proposed. The maximum value of the first principal stress, divided by the dynamic yield strength in the brittle temperature range (BTR), was used to identify the HCP. Experiments were carried out on a 6-ton P91 steel ingot in which severe hot tearing was detected in the upper centerline. Another ingot, with a better heat preservation riser, and without hot tearing, was used for comparison. Samples were obtained from the area of the ingot body with hot tearing, and their morphologies were inspected by a X-ray high energy industrial computed tomography. The carbon and sulfur distributions around the hot tearing were characterized by an infrared spectrometry carbon and sulfur analyzer. High temperature mechanical properties were obtained by a Gleeble thermal simulation machine, under different strain rates. Then, thermo-mechanical simulations using an elasto-viscoplastic finite-element model were conducted to analyze the stress and strain evolution during ingot solidification. The results showed that the hot tearing area, which was rich in both carbon and sulfur, was under excessive tensile stress in the BTR, bearing the highest HCP. [ABSTRACT FROM AUTHOR]

A mixed columnar dendritic-equiaxed three-phase solidification model that considers the secondary dendrite arm spacing (SDAS), nucleation and growth of equiaxed crystals, sedimentation of equiaxed crystals, growth of columnar dendritic trunks, and columnar-to-equiaxed transition (CET) was employed to study the formation of macrosegregation in steel ingots of different sizes. A reported experimental case (55,000 kg ingot) was used to verify the rationality of the current three-phase model. The predicted segregation patterns were in good agreement with the experimental results. The formation of macrosegregation in a series of steel ingots with different sizes (50 kg, 400 kg, 3300 kg, 6000 kg, 25,000 kg, 55,000 kg, and 97,000 kg) was studied using this solidification model. The results showed that the severity of macrosegregation increased with the increasing ingot weight. The thermal-solutal buoyancy and sedimentation of the dendritic equiaxed grains played dominated roles in determining the final segregation patterns in the different ingots. Additionally, the maximum negative segregation increased until the ingot weight exceeded 25,000 kg, which was caused by limited packing of the dendritic equiaxed grains. [ABSTRACT FROM AUTHOR]

A model, based on the concept of effective thermal conductivity, was developed to study thermal fields and the resultant solidification behavior of large, round, industrial size ingots. In this, flow and turbulence phenomena during mold filling as well as subsequent solidification were not modeled explicitly but their influence was accounted for by artificially raising the thermal conductivity of solidifying steel. Thus, a conduction like equation embodying a conjugate approach was applied to simultaneously predict the evolution of temperature fields in the mold as well as in the solidifying ingot following teeming. Prior to comparing model predictions against industrial scale measurements, sensitivity of calculations to grid size, time step height, convergence criterion etc. were rigorously assessed. Similarly, modeling of interfacial resistance, chemical reactions and heat effects in the hot top as well as their influence on predicted results were evaluated computationally. Embodying mixed thermal boundary conditions (free convection + radiation) at the mold wall, temperature fields during solidification of two different industrial large ingots were predicted numerically. Parallely, mold wall temperature was monitored as a function of time and surface temperature of ingot was measured at the instant of mold stripping using hand held, radiation pyrometers. Incorporating relevant operating conditions (viz., mold dimensions and size, ingot and hot top dimensions and material, initial mold and liquid temperature etc.) into the calculation scheme, predictions were made via a computational procedure developed in-house and results thus obtained were compared against equivalent industrial scale measurements. Very reasonable agreement between the two was demonstrated. [ABSTRACT FROM AUTHOR]

Numerical simulations of solidification process of steel ingots weighing 19, 8.5, and 3.35 ton are carried out and the calculated results are validated against temperature measurement during solidification of steel ingots. A new concept of 'effective transient thermal resistance' is proposed to help analyze heat transfer resistances of mold, ingot/mold interface, solidified shell, and outer wall of mold. Consequently, the restrictive steps of heat transfer (RSHT) at different stages of solidification of steel ingots are dug out. It is found that the RSHT during solidification of steel ingots weighing 19, 8.5, and 3.35 ton are similar. At early-stage of solidification, the effective transient thermal resistances of the mold and ingot/mold interface increase rapidly. Heat transfers through the mold and ingot/mold interface, are the RSHT. At mid-stage of solidification, the effective transient thermal resistance of the outer wall of the mold is larger than that of other heat transfer sections. Heat transfer section of the outer wall of mold is the RSHT. At late-stage of solidification, the heat transfer section of the solidified shell is the RSHT due to the thickening of the solidified shell. In addition, it was found that variations of pouring temperature and mold's thickness do not change the RSHT during solidification of steel ingots. [ABSTRACT FROM AUTHOR]

The effect of a hollow riser on the upper heat dissipation of 76 tons and 8 corners ingots is studied by numerical simulation in this paper. Through the simulation of the heat transfer of the traditional riser, the 1 gap riser and the 2 gaps riser ingot, this paper draws a conclusion that the solidification time of the riser part of the riser is the longest in the 2 gaps scheme, and the solidification time of the central molten steel is 31417s, which is far higher than the other two schemes. The heat flux in the riser of the 2 gaps scheme is obviously larger than the other two schemes, which slows down the advance of the solidification front. The 2 gaps scheme is stronger than the other two schemes for reducing the cooling speed of the riser line center and the shoulder joint. It is particularly significant to reduce the cooling rate of the shoulder joints, which is more conducive to expanding the angle of the solidification front and fully filling. [ABSTRACT FROM AUTHOR]

The electromagnetic feeding method was used to improve solidification quality of steel ingot, and the feeding principle of electromagnetic riser was introduced. The distribution characteristics of magnetic field in electromagnetic riser were investigated before and after pouring steel by the measures of numerical and physical simulation. The results showed that there's a good symmetry of magnetic field distribution in electromagnetic feeding riser before pouring steel, but both symmetry and uniformity of magnetic field distribution are broken after pouring steel into riser, and magnetic induction intensity of the surface is higher than that of the inner of feeding riser. [ABSTRACT FROM AUTHOR]

In this paper, a complete three-dimensional numerical model of mold filling and solidification of steel ingots is presented. The risk of powder entrapment and defects formation during filling is analyzed in detail, demonstrating the importance of using a comprehensive geometry, with trumpet and runner, compared to conventional simplified models. By using a case study, it was shown that the simplified model significantly underestimates the defects sources, reducing the utility of simulations in supporting mold and process design. An experimental test was also performed on an instrumented mold and the measurements were compared to the calculation results. The good agreement between calculation and trial allowed validating the simulation. [ABSTRACT FROM AUTHOR]

Three-dimensional mathematical model of the solidification of low-carbon steel ingot in a chilled mould has been formulated and invest-igated in the paper. The model is based on theoretical knowledge and it is supplemented with experience data. In the mathematical model the thermo physical data are incorporated which are temperature dependent, what gives nonlinearity to the model. The model is solved by means of the explicit finite difference method - the method of enthalpy. The solidification algorithm has been solved with computer SPERRY 1106 in program language ASCII FORTRAN. The time of solidification, the optimum stripping time, the thickness of the solid skin in any direction, and the potentional prints of possible defects in ingot may be obtained on the basis of the model.

The influence of hot top design on feeder channel segregates (F-CS) and centerline shrinkage porosities (C-SP) were investigated both experimentally and numerically. Two 100-ton 30Cr2Ni4MoV steel ingots with different insulating hot tops were longitudinally sectioned. The experimental results showed few channel segregates but severe shrinkage porosities appeared in the ingot with poorly insulated hot top, while it was the opposite case after the improved hot topping practice. By employing the finite element numerical simulation, the critical condition for the formation of F-CS in 30Cr2Ni4MoV steel was verified to be R2.1G ≤ 1.0 × 10-5 °C mm1.1 s-2.1. Through coupling with the published C-SP criterion (GR-0.5 ≤ 2.5 °C mm-1.5 s0.5), it was found out that the increase of hot-top height and preheating temperature would aggravate F-CS while alleviate C-SP contrarily. Hence, to comprehensively control those two defects, the optimum hot-top height and preheating temperature for 100-ton ingot were suggested to be 700 mm and 600 °C, respectively. Ultimately, the ratio of the solidification time for the whole ingot to the ingot body (tf/tb) was proposed as a novel criterion for hot top design. This practical criterion has been successfully utilized to optimize the hot top of a 5-ton steel ingot. [ABSTRACT FROM AUTHOR]

Large steel ingots with homogeneous internal quality are critical to the key components of the heavy equipments. Multi-pouring (MP) process, i.e. the sequential pouring with different carbon concentration, is widely applied for the production of steel ingots. Multi-pouring process aims to build an initial delaminated carbon concentration distribution for the solidification of steel ingots. However, it still remains unclear on the effect of initial concentration distribution on the macrosegregation. The purpose of current study is to assess this effect by a two phase solidification model. Non-orthgonal grids have been adopted for the geometry boundary fitness. Both teeming and subsequent solidification are included in current simulations for a 231-ton steel with two ladles poured. Besides, a prediction with homogeneous initial concentration distribution is adopted as the reference case. Predictions are compared with measurements along different transverse sections of ingot. It is demonstrated that the initial concentration distribution is an important factor for the macrosegregation formation, and the delaminated concentration distribution after MP process favours to depress the macrosegregation. [ABSTRACT FROM AUTHOR]

Results are reported from studies of the conditions of solidification, cooling, and heating of steel ingots cast in ingot molds. It is shown that optimizing the length of time between the casting of the ingot and its charging into the heating furnace can significantly shorten the heating period and thus increase the unit productivity of the furnace, reduce metal loss from oxidation, and decrease unit fuel consumption. [ABSTRACT FROM AUTHOR]

Part 1 of this two-part investigation presented a multiphase solidification model incorporating the finite diffusion kinetics and ternary phase diagram with the macroscopic transport phenomena (Wu et al., 2013). In Part 2, the importance of proper treatment of the finite diffusion kinetics in the calculation of macrosegregation is addressed. Calculations for a two-dimensional (2D) square casting (50 x 50 mm²) of Fe-0.45 wt.%C-1.06 wt.%Mn considering thermo-solutal convection and crystal sedimentation are performed. The modeling result indicates that the infinite liquid mixing kinetics as assumed by classical models (e.g., the Gulliver-Scheil or lever rule), which cannot properly consider the solute enrichment of the interdendritic or inter-granular melt at the early stage of solidification, might lead to an erroneous estimation of the macrosegregation. To confirm this statement, further theoretical and experimental evaluations are desired. The pattern and intensity of the flow and crystal sedimentation are dependent on the crystal morphologies (columnar or equiaxed); hence, the potential error of the calculated macrosegregation caused by the assumed growth kinetics depends on the crystal morphology. Finally, an illustrative simulation of an engineering 2.45-ton steel ingot is performed, and the results are compared with experimental results. This example demonstrates the model applicability for engineering castings regarding both the calculation efficiency and functionality. [ABSTRACT FROM AUTHOR]

This is the first of three articles devoted to studying the effect of ingot geometry on its solidification features based on cold simulation. In the first part, the experimental procedure, calculation of similarity criteria, and construction of a laboratory unit are described in detail. [ABSTRACT FROM AUTHOR]

Background. In recent years the steel companies tend to increase the amount of metal produced in CCMs while 20 % are still cast in the mold from the top. It is known that the ingots quality depends on the nature of the pouring stream, which is determined by the nozzle configuration and the casting speed. But to date, due to the lack of systematic research the casting speed is hardly ever used as a process parameter to control the structure formation and internal and external faulting of the ingot. Materials and/or methods. The work with the help of computer simulation and mathematical analysis examines the influence of the casting speed on the following processes: the distribution of convective flows, the increase of the solid phase, the changes in the length of crystalline zones and creation of shrinkage defects. The simulation of casting was carried out in three speed ranges corresponding to low (0.7 to 1.3 m/min), average (1.4...2 m/min) and high (2.1 to 2.5 m/min) speed. Results. It has been determined that within each speed group the character of the solid phase increase practically does not change: at regular intervals it increases uniformly, but the most intensive solid phase increase is observed in the low casting speed group. It is shown that the average casting speed range is characterized by the minimum damage of the ingots surface area by the defects due to metal stream spatter. 3D modeling and calculation by the finite difference method show that shrinkage defects are concentrated in the exterior part of the ingot and do not penetrate into the chill, while the volume of centerline weakness decreases by 2 %. It has been defined that the thickness of the rim zone reduces 1.5 times with the increase of casting speed, while its width also decreases with height by 1.5 %. The width of the columnar zone reduces 1.16 times with the increase of the casting speed, at this the height of the precipitation cone increases by about 1.5 %. Conclusion. The article shows that the regulation of the casting speed is an important technological factor which would produce the desired structure of ingots, favorable location of shrinkage defects and improve the properties of the resulting forging. Therefore, the ingots quality control based on correctly chosen casting speed is an important area of ingots technology development, which does not require costly investment in production. [ABSTRACT FROM AUTHOR]

continuum model is adopted to study the macrosegregation phenomena during solidification of large steel ingots. Evolution of temperature, melt velocity, and compositional concentration field during a 22 t steel ingot solidification are illustrated by using the finite volume method. Numerical results of temperature distribution are validated by experiments. The influence of local permeability relates to the friction that the melt experienced in mushy region is investigated. It is shown that the continuum model is able to predict the temperature field, and the variation of permeability obviously affects the melt flowing behavior and the final compositional distribution. [ABSTRACT FROM AUTHOR]

Thermosolutal convection and macrosegregation formation during the solidification of steel ingots are numerically simulated in three dimensions. The simulation is based on a fully coupled model for mass, momentum, energy, and species conservation equations. The interdendritic flow in the mushy zone is governed by Darcy's law, and the permeability term is discretized using an interpolated liquid fraction method. The numerical results for a benchmark test of macrosegregation in a Pb-Sn alloy are compared with experimental data taken from the literature. The present model is applied to simulate the solidification of industrial steel ingots. Preliminary predictions are obtained, including the positive segregation in the hot top, and the conically shaped negative segregation zone at the bottom of the ingot. The predicted variation of the segregation ratio in carbon along the vertical centreline of an ingot is compared with measurements, and generally good agreement is observed. Future attention should be paid to the precision of prediction by considering complex solidification issues, such as the sedimentation of free equiaxed grains and the formation of shrinkage cavity. [ABSTRACT FROM AUTHOR]

We analyze theoretically and experimentally solute redistribution in the dendritic solidification process and positive segregation during solidification of steel ingots. Positive segregation is mainly caused by liquid flow in the mushy zone. Changes in the liquid steel velocity are caused by the temperature gradient and by the increase in the solid fraction during solidification. The effects of buoyancy and of the change in the solid fraction on segregation intensity are analyzed. The relationships between the density change, liquid fraction and the steel composition are considered. Such elements as W, Ni, Mo and Cr decrease the effect of the density variations, i.e. they show smaller tendency to segregate. Based on the modeling and experimental results, coefficients are provided controlling the effects of chemical composition, secondary dendrite arm spacing and the solid fraction. [ABSTRACT FROM AUTHOR]

The article studies the macrosegregation phenomena that occur during solidification of steel ingot castings using a computational multi-fluid dynamics approach. The authors describe four different cases, which include feeding-induced macrosegregations in one-dimensional unidirectional solidification, macrosegregations caused by thermosolutal buoyancy driven flow, macrosegregations caused by grain sedimentation and macrosegregations caused by thermosolutal convection.