Microstructure evolution of 3003/4004 clad ingots under diverse physical fields

In order to improve the quality of clad ingots, diverse physical fields including electromagnetic stirring, power ultrasonic and compound field of ultrasonic and electromagnetic stirring were attempted to prepare clad ingots of 3003/4004 alloys. The solidification structures near the interface in clad ingots were investigated. The experiment results indicate that the solidification structure of 4004 alloy changes from dendritic crystals to petal-like grains when the clad ingot is treated by electromagnetic stirring. With the effect of power ultrasonic, the solidified microstructure of 4004 alloy exhibits the refinement of both primary a（A1） and eutectic silicon. Under the compound field, the primary a（A1） is refined, the morphology of eutectic silicon has a transition from a coarse plate-like form without treatment or thin acicular-like form with power ultrasonic to fine coral-like form.

Improvement of tundish shape and optimization of flow control devices for sequence casting heavy steel ingots

The metallurgical effect of a round tundish used to cast heavy steel ingots in machine works at present was evaluated through water modeling experiments. The flow control devices of the improved oval tundish, which was used instead of the round tundish, had been optimized. The results show that the residence time of the round tundish is short, its inclusion removal efficiency is too low, and it has more dead zones and an unreasonable flow field. Compared with the round tundish, the improved oval tundish with the optimized weir and dam has a better effect： its minimum residence time is prolonged by 38.1 s, the average residence time is prolonged by 233.4 s, its dead volume fraction decreases from 26% to 15%, and the ratio of plug volume fraction to dead volume fraction increases from 0.54 to 1.27. The inclusion removal efficiency also increases by 17.5%.

Numerical simulation of macrosegregation in steel ingots using a two-phase model

A two-phase model for the prediction of macrosegregation formed during solidification is presented. This model incorporates the descriptions of heat transfer, melt convection, solute transport, and solid movement on the system scale with microscopic relations for grain nucleation and growth. Then the model is used to simulate the solidification of a benchmark industrial 3.3-t steel ingot. Simulations are per- formed to investigate the effects of grain motion and pipe shrinkage formation on the final macrosegregation pattern. The model predictions are compared with experimental data and numerical results from literatures. It is demonstrated that the model is able to express the overall macrosegregation patterns in the ingot. Furthermore, the results show that it is essential to consider the motion of equiaxed grains and the formation of pipe shrinkage in modelling. Several issues for future model improvements are identified.

Teeming stream protection using an argon shroud during casting of steel ingots

Two kinds of argon shroud protection devices with two different basic structures were designed and investigated. Industrial experiments and numerical simulations were used to examine the protection effect, and the mechanism of air entrapment during the casting of steel ingots was analyzed. The influence of the structure of the argon shroud protection device on the protection effect was investigated. An argon shroud protection device mounted to the nozzle holder on the bottom of the ladle does not provide a good protection effect because air can easily flow into the teeming system and cause reoxidation of molten steel during teeming. By contrast, an argon shroud protection device seated on the top of the central trumpet provides an excellent protection effect, where air has little chance of flowing into the teeming system during casting. The feasibilities of the argon shroud protection devices are discussed.

Effect of Electromagnetic Stirring on the Quality of K417 Superalloy Ingots

The effect of electromagnetic stirring on the inner quality of K417 superalloy ingots is studied with EPMA and optical microscope.The results show that while an electromagnetic stirring with 50Hz frequency and 80A current is imposed,the equiax crystals of K417 superalloy ingots can be effectively refined and increased,and the central shrinkage porosity and the dendritic segregation of K417 superalloy ingots are greatly reduced,so the inner quality of K417 superalloy ingots is obviously improved.

Numerical simulation of temperature distribution and heat transfer during solidification of titanium alloy ingots in vacuum arc remelting process

In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium alloy ingots during VAR process.The results show that the temperature fields obtained by the simulation are well validated through the experiment results.The temperature distribution is different during the whole VAR process and the steady-state molten pool forms at 329 s for d100 mm × 180 mm ingots.At the initial stage of remelting,the heat dissipation of crucible bottom plays an important role in the whole heat dissipation system.At the middle of remelting,the crucible wall becomes a major heat dissipation way.The effect of cooling velocity on the solidification structure of ingots was investigated based on the temperature fields and the results can well explain the macrostructure of titanium alloy ingots.

NUMERICAL SIMULATION OF TEMPERATURE FIELDS IN ELECTROSLAG REMELTING SLAB INGOTS

The method based on transient heat transfer model is adopted to simulate electro-slag remelting process. The calculated results of the model show that the process is in the quasi-steady state, and the shape of pool remains unchanged when the height of ingot is approximately 2.5-3 times the thickness of slab ingot. The change in the shape of pool is found to be strongly dependent on the pattern of melting rate, and hence, the power input; the depth of the molten pool increases with the increase in melting speed. It is concluded that a transient heat transfer model has to be used to obtain reliable input information for the entire, operatina time.

Chemical composition analysis on industrial scale ingots and castings of TiAl alloys

The chemical composition variation of the TiAl-4722 alloys was examined in a batch of the industrial scale master ingots,and in the corresponding castings prepared by conventional vacuum arc remelting(VAR)combined with induction skull melting(ISM)and investment casting processes.The content changes of major elements and interstitial elements were evaluated based on the chemical analysis at the top and bottom of the ingots and castings.Results show that the contents of C,N,H,Fe and Si have almost no change in the ingots and castings,suggesting that the chemical analysis on these elements can be based on the batch analysis.The O content keeps almost the same in different ingots,but exhibits relatively large differences in castings,which was probably influenced by the reaction between the shell mold and the molten alloy,and the spalling of face coat of the shell mold during casting.For the major elements of Al,Nb and Cr,the composition difference between the top and the bottom of the ingots is less than that of the castings.But for the O element,the trend is different,especially for the castings,suggesting that the investment casting is a homogenization process for Cr and Nb,but a differentiation process for O.The contents of major elements in castings fluctuate mainly in the same range as that in the ingots,indicating that the contents of the major elements are controllable during investment casting.

Production and Characterization of Zr Based Bulk Metallic Glass Matrix Composites (BMGMC) in the Form of Wedge Shape Ingots

Bulk metallic glass matrix composites (BMGMC) are unique materials of future having excellent mechanical properties (such as high hardness, strength and profound elastic strain limit). However, they exhibit poor ductility and suffer from catastrophic failure on the application of force. The reasons behind this are still not very well understood. In this study, an effort has been made to overcome this pitfall by solidification processing. Zr based BMGMCs are produced in the form of “as cast” wedges using vacuum arc melting and suction casting button furnace. The idea is to study the effect of cooling rate and inoculation on formability during solidification. Adjustment, manipulation and proper control of processing parameters are observed to reflect upon the quality of ingots such as improved castability, proper mold filling and defect free casting as characterized by NDT. Further, thermal analysis, optical microscopy and hardness measurement confirmed the formation and evolution of in-situcomposite structure. This is first footprint of pathway towards sustainable manufacturing of these alloys in future.

Finite element modeling of macrosegregation coupled with shrinkage cavity in steel ingots using arbitrary Lagrangian-Eulerian model

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.

Experience in the Production of Horizontal Ingots of Platinum Metals and Alloys

The quality of semi-products of platinum metals and alloys, produced by way of plastic working, essentially depends on or, in many cases, is completely determined by the quality of ingots. Plastic working does not make it possible to eliminate or localize metallurgical defects. In many cases it promotes the occurence thereof. Low-rate casting with directional crystallization can ensure the production of dense ingots free of non-metallic inclusions, shrinkage and gas weakness, with observance of certain temperature/rate modes. After comparative tests of vertical and horizontal molds, preference has been given to horizontal water-cooled molds, allowing to cast all alloys in the conditions of directional crystallization.

Numerical Simulation of Thermal Characteristics in the Process of Electroslag Remelting for Production of Large Slab Ingots

The slag pool is a complex system which gathers electromagnetic field,thermal field and flow field in the process of electroslag remelting(ESR)for production of large slab ingots.In this manuscript,mathematic foundation and boundary conditions of the numerical simulation for thermal field in the ESR process of large slab ingots were analyzed, and mathematic model of heat generation in the slag pool and the solidification in the metal molten pool were founded by using the finite element software ANSYS.According to the simulation results,it can be found that the temperature distribution in the process of ESR for production of large slab ingots with double electrode series is different from that in the electroslag furnace with a single electrode.The region of the biggest current density and the highest temperature in the electroslag furnace with a single electrode is below the electrode,while the same region in the process of ESR with the double electrode series for production of large slab ingots locates between the two electrodes.The depth of the metal pool and the temperature of the slag bath simulated by mathematical model were close to the measured value in the experimental process,which verifies the reliability of the simulation method and the model,and it will provide a theoretical basis for the quality control of large slab ingots in the process of ESR.

Volume-averaged modeling of multiphase solidification with equiaxed crystal sedimentation in a steel ingot

Macrosegregation is a critical factor that limits the mechanical properties of materials.The impact of equiaxed crystal sedimentation on macrosegregation has been extensively studied,as it plays a significant role in determining the distribution of alloying elements and impurities within a material.To improve macrosegregation in steel connecting shafts,a multiphase solidification model that couples melt flow,heat transfer,microstructure evolution,and solute transport was established based on the volume-averaged Eulerian-Eulerian approach.In this model,the effects of liquid phase,equiaxed crystals,columnar dendrites,and columnar-to-equiaxed transition(CET)during solidification and evolution of microstructure can be considered simultaneously.The sedimentation of equiaxed crystals contributes to negative macrosegregation,where regions between columnar dendrites and equiaxed crystals undergo significant A-type positive macrosegregation due to the CET.Additionally,noticeable positive macrosegregation occurs in the area of final solidification in the ingot.The improvement in macrosegregation is beneficial for enhancing the mechanical properties of connecting shafts.To mitigate the thermal convection of molten steel resulting from excessive superheating,reducing the superheating during casting without employing external fields or altering the design of the ingot mold is indeed an effective approach to control macrosegregation.

Inclusion Distribution in Ingots Investigated by Dissection

Inclusion distribution in ingots was studied by dissection of a 16.8 t P12 ingot and a 5.0 t H13 ingot, with the analysis of T[O], original position statistic distribution analysis （OPA）, metallographic microscope static analysis and small sample electrolysis. The results showed that the inclusions in ingots were uneven; a positive segregation area was found in the center and lower part of the ingot, while a negative segregation area was present in the central part of ingot top; inclusion segregation in a large size ingot was severer than that in a small one. A new con cept, named inclusion segregation index, was put forward to quantify the segregation degree of inclusion. It was found that the segregation indexes drawn from T[O] analysis and OPA fit well, but they were different from those obtained by metallograpbic microscope static analysis and small sample electrolysis in the investigation of Pl 2 ingot, which contained a higher sulfur content; while the segregation index drawn from T[O] analysis was close to that from metallographic microscope static analysis in the H13 ingot with a lower sulfur content.

A review on prediction of casting defects in steel ingots:from macrosegregation to multi-defect model

Due to the nature of the solute redistribution,the reduction in the solidification rate with time in a square root relationship,and the multiphase melt flow during the solidification,casting defects such as macrosegregation,shrinkage cavity,and porosity will inevitably occur in the steel ingot and intensify with the increase in ingot size.These defects directly affect the performance of the final product and severely restrict the choice of subsequent thermal processing methods and process windows.Therefore,the solidification defects including macrosegregation,shrinkage/porosity,and inclusions encountered in the preparation of large steel ingots and their formation mechanisms were reviewed.The development progress and the latest development of the macrosegregation model for steel ingots were introduced in detail,especially the latest progress in the coupling prediction of macrosegregation and shrinkage as well as macrosegregation and inclusions.Some methods to reduce macrosegregation of ingots were discussed as well.Finally,a new casting method called layered casting was introduced in detail.This method can effectively improve the uniformity of the macrostructure and reduce the macrosegregation of the large ingots and therefore is a promising method for preparing large ingots with high homogeneity.

Effects of Thermal Gradients and Rotational Flows on Grain Growth in 22 t Steel Ingots

Heavy ingots are widely used in many industrial fields. The coarse grains formed during the process of in- got solidification influence the properties and fracture behaviors of the final products. The coarse grain growth was simulated under different thermal gradients. A 30Cr2Ni4MoV steel ingot was melted in a cubic crucible with dimen-sions of 15 cm×10 cm×23 cm, and the cooling conditions on each side of the crucible were controlled by different thermal curves. The influences of thermal gradients and rotational flows on grain growth in heavy steel ingots were then investigated both numerically and experimentally. The results showed that when the amplitude of the rotation angle was 60°, the metal was solidified under a reciprocating horizontal rotational condition when the angular velocity was 10 （°）/s or 20 （°）/s. As the thermal gradient increased, the lengths of the primary columnar grains in- creased, and the diameters of equiaxed grains decreased. When the direction of flow rotation was perpendicular to the direction of grain growth, the columnar grain zone was nearly eliminated, and the average diameter of equiaxed grains was 0.5 mm.

Comprehensive impact of as-cast microstructure and ordered structures on formability of large-scale Fe-6.5 wt.%Si alloy ingots

Large-scale Fe-6.5 wt.%Si ingot with excellent formability is required for a pilot line producing sheets through hot/cold rolling.The variation of the as-cast microstructure,ordered structures and the formability of the Fe-6.5 wt.%Si alloy ingots with the cooling rate during casting was investigated.Under air-cooling condition,inhomogeneous microstructures with a low proportion of equiaxed grains were formed,but the formation of ordered structures was partially inhibited,especially DO3.Homogeneous microstructures with a high proportion of equiaxed grains were observed under the condition of furnace cooling,but the ordered structures were fully generated,and the degree of order is high.It is generally believed that high degree of order is the main factor of brittleness,but the homogeneous microstructure(including grain morphology and size)of the furnace-cooled sample helps to improve the formability.The influence of these two aspects on formability is contradictory.Therefore,the formability is tested through the flow stress during the compression and the microstructure after the compression.The results show that the furnace-cooled sample has better formability.For large-scale ingots,the control of as-cast microstructure becomes more significant than the control of degree of order.Slow cooling during casting is important for the large-scale ingots to have good formability meeting the requirements of direct hot rolling.

Numerical Modeling of Magnetohydrodynamics and Solidification Phenomena in PAM Processed Ti-6Al-4V Ingots

This paper presents a methodology for modeling and analysis of the interaction between two electromagnetic(EM)fields in a solidifying Ti-6A1-4V(Ti-6-4)ingot processed by the plasma arc cold hearth melting(PAM)process. The two EM fields are generated by the induction coils(stirrer)around the ingot mold and by the plasma torch.This methodology is based on the numerical solution of Maxwell's equations,fluid flow,and heat transfer equations,and modeling of the grain structure.Numerical simulations at the macro-level were conducted using a CFD software.A stochastic model was developed and applied to simulate the grain structure at the mesoscopic level.Simulation results for 5-in and 8-in diameter Ti-6-4 ingots show that the plasma torch and the EM stirrer can have strong effects on both the fluid flow and the solidification structure.A comparison with an experimental grain structure of a 5-in diameter Ti-6-4 ingot is also provided.

Melting and floating processes of inorganic materials in molten steel:Visualization physical simulation and mathematical modelling

It has been demonstrated that heat absorption method by using the inorganic material rod to cool the molten steel can significantly reduce the macrosegregation level of the large steel ingot.However,owing to the opacity of the molten steel,the physical mechanism of the heat absorption method is not clear.In this work,a transparent hydraulic physical model with water and paraffin wax was built to simulate the melting and floating processes of inorganic materials in the molten steel.A mathematical simulation was also carried out to analyze the connection between the actual ingot and the physical model.Results show that it is feasible to simulate the molten steel and inorganic materials with water and paraffin wax.With the help of the physical model,the process of the melting of paraffin wax and its floating to the surface of water were clearly observed,during which the temperature of water at some characteristic positions in the mold was recorded.The visualization findings demonstrate that the melting and floating processes of paraffin wax can help to bring the heat from the center of the mold to the top surface more quickly,which reduces the superheat and significantly accelerates the cooling rate of water.The experimental results show that for the water with a certain superheat,the use of a larger mass of paraffin wax can accelerate the cooling of the water,but there is a risk of incomplete melting of the paraffin wax.A higher superheat of water will lead to a quicker melting rate for a given mass of paraffin wax,while a lower superheat leads to the incomplete melting of paraffin wax as well.

Direct-chill semi-continuous casting process of three-layer composite ingot of 4045/3004/4045 aluminum alloys

Three-layer composite ingot of 4045/3004/4045 aluminum alloys was prepared by direct-chill semi-continuous casting process,the temperature field distribution near the composite interface,macro-morphology,microstructure and composition distribution of the composite interface were investigated.The results show that semi-solid layer with a certain thickness forms near the interface due to the effect of cooling plate,which ensures successful implementation of casting the composite ingot.Two different aluminum alloys are well bonded metallurgically.The mechanical properties of composite interface were measured,the tensile and shearing strengths of composite interface are 105 and 88 MPa,respectively,which proves that the composite interface is a kind of metallurgical bonding.