Formation Of Shrinkage Cavity Research Articles

Influence of hot top geometry on columnar-to-equiaxed transition in a 12 MT steel ingot

In the present work, the impact of hot top geometry and thermal history on the Columnar-to-Equiaxed Transition (CET) point, of a 12 MT steel ingot was determined using finite element modeling. Experimental validation of the model was conducted on an industrial-size ingot, focusing on temperature, macrosegregation, and shrinkage microporosity. The anticipated Columnar-to-Equiaxed Transition point, influenced by the interaction of solid front rate, thermal gradient, and solid fraction was considered in the analysis. The findings revealed a shift in the CET position in new configurations, up to 56 mm, 63 mm, and 60 mm from the ingot wall in the bottom, middle, and top of the ingot, respectively. The changes are attributed to variations in the kinetics of solidification, particularly the solidification time. Thermo-mechanical phenomena, encompassing mold filling, cooling, solutal convection, and flow driven by shrinkage, were incorporated into the model to predict macrosegregation and the risk of porosity and shrinkage cavity formation for different hot top geometries. A criterion is proposed that allows mitigating macrosegregation and minimizing the risk of porosity and shrinkage cavity.

Suppression of Shrinkage Cavity Formation in Silicon Steel by Partial Non-Magnetization

Suppression of Shrinkage Cavity Formation in Silicon Steel by Partial Non-Magnetization

Development of a bilayer NiCrAlY/YSZ coating on IN713 LC superalloy by laser cladding

In this study, bilayer laser cladding of Inconel 713LC superalloy was performed by a Nd:YAG laser. Amdry 997 powder was used as the first layer and Metco 204NS ceramic powder as the second layer. The experiments were carried out with different laser parameters to investigate the influence of heat input and laser power density on the microstructure and the hardness of coating. The study revealed that the susceptibility to crack formation in the clad zone increases with the increase in the heat input due to the high cooling rate and intense thermal stress. The formation of shrinkage cavities in the lower half of the clad zone raises with the increase in the heat input owing to reduction in the solidification rate. Microstructural investigations show that a cellular structure is formed at the interface region. The middle area of coating features columnar dendrites, while the upper area of the coating displays very small equiaxed dendrites. The coating mainly comprises γ-Ni, β-NiAl and γ′-Ni3Al phases and the elements of Ni, Co, Cr, Al, Ta, Zr, and Y are homogeneously distributed in the clad zone. As the heat input increases, the microhardness of the samples decreases due to an increase in the dilution ratio. This leads to a decrease of Co, Cr, and Ta elements in the γ′ and the β intermetallic compounds, as well as a reduction of Zr and Y elements in the clad zone.

Preparation of densified glass-ceramics with less shrinkage cavities from molten copper slag by Petrurgic method

Petrurgic method is used to prepare glass-ceramics by directly controlling crystallization during the cooling process of the melts, which can realize the integrated utilization of both molten copper slag and its sensible heat. In this study, molten copper slag with no added agents was used to fabricate glass-ceramics using Petrurgic method. The temperature difference between the center and edges of molten copper slag with dimensions of 40 mm × 40 mm × 20 mm during the cooling process was measured, and its effects on crystallization and shrinkage cavities were studied. The results showed that the main phases of the glass-ceramics were magnetite and olivine, both of which crystallized significantly during the high-temperature cooling process. There were compact parts, transition parts and large cavity parts in the whole glass-ceramics and the cavities were caused by asynchronous crystallization of olivine owing to the temperature gradient distribution of the molten copper slag in the mold. Increasing the holding temperature during the heat treatment process reduced the temperature difference between the center and the edges and even inhibited the degree of crystallization, which further decreased the formation of shrinkage cavities. When the holding temperature was increased from 900 to 1150 °C, there were no longer large cavity parts in the non-compact parts but only transition parts. A higher holding temperature is thus beneficial for reducing the diameter of shrinkage cavities.

Modelling of continuous casting processes parameters on the shrinkage cavity formation in bearing steel blooms

ABSTRACT Based on the thermal-mechanical coupling model, the distance from the critical position of the shrinkage cavity formation of the two bearing steel blooms to the meniscus is 22 and 19.78 m, respectively, and the critical center solid fraction is 0.7145 and 0.7033, respectively. Furthermore, the effects of superheat and casting speed on the critical value of shrinkage cavity formation are discussed. The results show that the two factors have a great influence on the critical position of shrinkage cavity formation in the former, but basically do not affect the critical solid fraction of shrinkage cavity formation. Finally, the industrial heavy reduction tests in different reduction intervals were carried out, and the results show that when the initial reduction position of the heavy reduction process is set before the critical solid fraction, it can not only eliminate the central shrinkage cavity of the bloom, but also improve the central segregation.

Influence of Mold Design on Shrinkage Porosity of Ti-6Al-4V Alloy Ingots

Mold design is one of the important ways to control shrinkage porosity. In this study, four mold forms with different tapers were first designed, the corresponding three-dimensional finite element models were built using the ProCAST software, and the influence of mold design on the filling and solidification processes of Ti-6Al-4V alloy was investigated. The results showed that the titanium alloy ingots exhibit typical characteristics of layer-by-layer solidification, and that the removal of the riser results in: (a) shortening the time it takes for molten metal to reach the bottom of the mold and the time needed to complete mold filling; (b) decreasing the maximum flow velocity and improving the filling stability; and (c) moving the shrinkage cavities up along the central axis of the ingot and decreasing the cavity volume. Meanwhile, it was also found that the shrinkage cavity volume decreases significantly with increasing mold taper, meaning a significant increase in ingot utilization rate. The shrinkage cavity formation mechanism was revealed through macrostructure analysis. During solidification, a grain frame is formed as a large number of equiaxed crystals intersect, thus creating an isolated liquid phase zone. When the liquid in this zone solidifies, the last zone to do so, its volume shrinkage cannot be compensated, thus leading to the formation of a shrinkage cavity.

Effect of Al Content on the Microstructure and Tensile Properties of Zr-Co-Al Alloy Prepared by Rapid Solidification

The Zr50−x/2Co50−x/2Alx (x = 0, 4, 5, 6, 7, 8) alloy sheets were prepared by copper mold suction casting, and the effect of Al content on the mechanical properties and the strengthening mechanism was thoroughly investigated. With Al addition, a Zr5Co7Al3 intermetallic compound formed and precipitated at the grain boundaries or inside the grains, which produced strong synergistic effects of secondary phase strengthening, fine grain strengthening and solid solution strengthening. However, the precipitation of intermetallic compounds can lead to the formation of shrinkage cavities at grain boundaries, and the negative effect of adding too much Al is greater than the strengthening effect, resulting in a gradual decrease in strength. Therefore, the best synergistic strengthening effect is achieved when the Al content is 5 at.%, the grain size of the alloy is reduced from 60 μm to 4 μm, and the room temperature tensile strength is increased from 240 MPa to 464 MPa.

Numerical Simulation of the Solidification Process with the Convective Movement of the Liquid Phase and the Formation of Shrinkage Cavity

Numerical Simulation of the Solidification Process with the Convective Movement of the Liquid Phase and the Formation of Shrinkage Cavity

Numerical Modeling of Shrinkage Cavity Formation Process in Cast Steel Support

Numerical Modeling of Shrinkage Cavity Formation Process in Cast Steel Support

A Review Study on the Main Sources of Porosity in Al‐Si Cast Alloys

The present study was performed on A356 and B319 alloys in mechanically stirred or degassed condition. Melts were Sr‐modified and grain‐refined. Hydrogen content was varied from less than 0.1 ml/100 g Al to ∼0.4 ml/100 g Al; Fe was increased to 0.8% in B319 alloy. Lanthanum and cerium were added as 99.5% pure metals. Two main techniques were used to investigate porosity formation: fracture surface of tensile or fatigue test bars, or reduced pressure test (RPT) method. Porosity type and shape were examined. The results show that pore size is more influential than small scattered ones from a mechanical point of view. Tensile testing is affected by porosity located at the center of the testing bar, whereas edge porosity is responsible for crack initiation in case of fatigue testing. Intermetallics precipitate in the form of intercepted platelets which restricts the flow of the molten metal, leading to formation of shrinkage cavities. Precipitation of clusters of compounds from the liquid state such as Al2Si2Sr, Mg2Sn, Al3Ti, or added Al2O3particles would as well act as nucleation sites for porosity formation. Most oxides were observed in the form of long branched strings. In some cases, bifilms were also reported in addition to SrO and MgO.

Effect of Pulse Frequency on the Transport Phenomena and Crystal Growth Behavior in Quasi-Continuous-Wave Laser Powder Deposition of Single-Crystal Superalloy

The effect of pulse frequency on the transport phenomena and crystal growth behavior in the quasi-continuous-wave laser powder deposition process of single-crystal superalloy were studied through an improved three-dimensional mathematical model and experiments. Laser powder deposition experiments with single-crystal superalloy were conducted to verify the computational results and analyze the crystal growth behavior. Results showed that the laser mode has a predominant effect on the transport phenomena and the associated crystal growth behavior. The increase of pulse frequency weakens the fluctuation motion of the molten pool and shallows the solidification interface. Under the given processing parameters, the molten pool size decreases quickly with the increase of pulse frequency from 0 to 15 Hz, and then gradually tends to a steady state in the range of 15 to 35 Hz. When the pulse frequency exceeds 35 Hz, the molten pool does not disappear completely during the laser-off period of a pulse cycle. With the increase of pulse frequency from 0 to 35 Hz, the peak temperature of molten pool decreases from 2567.5 K to 2324.7 K, while the peak normal thermal gradient at the solidification interface increases from 2.24 × 106 K/m to 1.01 × 107 K/m. The fast solidification speed driven by the contraction speed of molten pool during the laser-off period of quasi-continuous-wave laser powder deposition process refines the trunk size of columnar dendrites and facilitates the formation of shrinkage cavities and chainlike carbides. Due to the significant increase of thermal gradient and solidification speed, the quasi-continuous-wave laser powder deposition process of single-crystal superalloy features the columnar dendrites with a better epitaxial growth ability, and acts as an effective method to expand the repair-processing window of single-crystal components.

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.

Numerical model of solidification process of Fe-C alloy taking into account the phenomenon of shrinkage cavity formation

Mathematical and numerical models of Fe-C alloy solidification process based on the finite element method (FEM) are presented in the paper. The phenomenon of the defect called "shrinkage cavity" is introduced to the model. It is very important aspect of presented work which makes possible the prediction of the location and shape of mentioned defect depending on the geometry of the casting and cooling condition of the process. An original computer program using Visual C++ environment has been written in order to simulate described process. The results of computer calculations of the three-dimensional solidification problem of the casting with riser are presented and discussed in details.

Solidification Simulation of Pure Metal Castings by Considering the Effects of Shrinkage Cavity Formation Process on Heat Transfer Behavior

Solidification Simulation of Pure Metal Castings by Considering the Effects of Shrinkage Cavity Formation Process on Heat Transfer Behavior

Effectiveness of Blind Feeders in Steel Casting

Existing methods of decreasing feeder size are briefly reviewed, with an account of their advantages and disadvantages. The applicability of methods of optimizing the feeder shape so as to increase the useful volume of the casting is identified. The actual position of shrinkage defects in feeders of different structure is considered. The position and shape of shrinkage cavities are considered as a function of the shape of the feeder’s upper section. Four groups of feeders are distinguished, and their effectiveness is compared. Mathematical modeling is proposed to better understand the formation of shrinkage cavities in feeders with different designs of their upper section and to assess their effectiveness. Mathematical modeling permits analysis of the external factors affecting the thermal processes in the mold, which is difficult in casting practice. SolidCast software is used. The initial and boundary conditions in modeling are identical for feeders of all types. The predictions regarding the shrinkage defects are expressed as isosurfaces, whose dimensions may be used to assess feeder effectiveness. The modeling results are used to develop an approach to assessing the thermal efficiency of feeders of different types. The estimates are based on the position of the shrinkage defect within the feeder. As an example, the effectiveness of feeders of the same size but with different configurations of the upper section is calculated. The proposed efficiency index is in good agreement with the geometric modulus (the ratio of the feeder’s volume to its surface area). Increase in the feeder’s modulus increases its thermal efficiency. The introduction of a notch increases the feeder’s efficiency. Analysis of isothermal lines in the longitudinal section of the feeder permits description of the thermal operation of the notch and its influence on the position of the shrinkage cavity. Recommendations are made for increasing the casting yield by redesigning the feeder’s upper section. The casting yield may be increased by 4%, with accompanying decrease in the rejection rate of the castings, thanks to optimization of the feeder’s upper section.

Using four-phase Eulerian volume averaging approach to model macrosegregation and shrinkage cavity

This work is to extend a previous 3-phase mixed columnar-equiaxed solidification model to treat the formation of shrinkage cavity by including an additional phase. In the previous model the mixed columnar and equiaxed solidification with consideration of multiphase transport phenomena (mass, momentum, species and enthalpy) is proposed to calculate the as- cast structure including columnar-to-equiaxed transition (CET) and formation of macrosegregation. In order to incorporate the formation of shrinkage cavity, an additional phase, i.e. gas phase or covering liquid slag phase, must be considered in addition to the previously introduced 3 phases (parent melt, solidifying columnar dendrite trunks and equiaxed grains). No mass and species transfer between the new and other 3 phases is necessary, but the treatment of the momentum and energy exchanges between them is crucially important for the formation of free surface and shrinkage cavity, which in turn influences the flow field and formation of segregation. A steel ingot is preliminarily calculated to exam the functionalities of the model.

Mathematical model of solidification of the axisymmetric casting while taking into account its shrinkage

In this paper, the mathematical and numerical model of the solidification of a cylindrical shaped casting, while taking into account the process of the mould cavity fill- ing with molten metal, has been proposed. The feeding of the casting by a riser head during solidification and the formation of shrinkage cavity has also been taken into consideration. The shape and depth of the shrinkage cavity distribution was estimated. One aim of the paper is to obtain a casting without shrinkage defects. Velocity fields were obtained by solving the Navier-Stokes equations and the continuity equation, while the thermal fields were obtained by solving the conduction equation containing the convection term. The changes in the thermophysical parameters, with respect to temperature, were taken into account. The problem was solved by the finite element method.

Numerical Analysis of Influence of the Mold Material on the Distribution of Shrinkage Cavities

Abstract Production of castings, like any other field of technology is aimed at providing high-quality product, free from defects. One of the main causes of defects in castings is the phenomenon of shrinkage of the casting. This phenomenon causes the formation of shrinkage cavities and porosity in the casting. The major preventive measure is supplementing a shortage of liquid metal. For supplement to be effective, it is necessary to use risers in proper shapes. Usually, the risers are selected on the basis of determination the place of formation of hot-spots in the castings. Although in these places the shrinkage defects are most likely to occur, shape and size of these defects are also affected by other factors. The article describes the original program setting out the shape and location of possible cavities in the casting. In the program is also taken into account the effect of temperature on the change in volume of liquid metal and the resultant differences in the shape and size of formed shrinkage cavities. The aim of the article is to describe the influence that have material properties of the mold on the simulation results.

Modelling of shrinkage cavity defects during the wheel and belt casting process

Properzi continuous casting is a wheel and belt casting process used for producing aluminium wire rod which is essential to the making of electrical cables and over head lines. One of the main concerns of Properzi process users is to ensure good quality of the final product and to avoid cast defects especially the presence of shrinkage cavity. Numerical models developed with the Alsim software, which allows an automatic calculation of gap dependent heat transfer coefficients at the metal-mould interface due to thermal deformation, are used in order to get a better understanding on the shrinkage cavity formation. Models show the effect of process parameters on the cavity defect development and provide initial guidance for users in order to avoid this kind of casting defect.

Three‐dimensional Simulation of Thermosolutal Convection and Macrosegregation in Steel Ingots

AbstractThermosolutal 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.