Solidification Structure Of Ingots Research Articles

Simulation of Solidification Structure in the Vacuum Arc Remelting Process of Titanium Alloy TC4 Based on 3D CAFE Method

Vacuum arc remelting is the main production method of titanium alloy ingots at present. In order to obtain good quality ingots, it is of great significance to study the formation of the solidification structure of ingots via vacuum arc remelting. In order to select and optimize the nucleation parameters for the solidification microstructure simulation of an ingot, a 3D CAFE model for microstructure evolution during vacuum arc remelting was established, taking into account heat transfer, flow, and solute diffusion. The Gaussian distribution continuous nucleation model and extended KGT model were used to describe the grain nucleation and dendrite tip growth rates, respectively. The multi-point mass source and moving boundary method were used to simulate the ingot growth. The results show that there are three typical crystal regions in the solidification structure of vacuum arc remelting titanium alloy ingots, namely the surface fine crystal region, columnar crystal region, and central equiaxed crystal region. The proportion of the columnar crystal region in the solidification structure of an ingot increases gradually with the increase in the undercooling of the maximum bulk nucleation. With an increase in the maximum bulk nucleation density, the equiaxed grain zone gradually increases, and the grain size gradually decreases. The proportion of the columnar crystal region in the solidification structure of an ingot increases gradually with an increase in the undercooling of the maximum bulk nucleation. The maximum volume nucleation variance has no obvious effect on the change in the solidification structure. When the maximum volume nucleation undercooling is 5.5 K, the maximum volume nucleation standard deviation is 4 K, and the maximum volume nucleation density is 5 × 108. The solidification structure simulation results are in good agreement with the experimental results.

Effect of hollow insulation riser on shrinkage porosity and solidification structure of ingot

Effect of hollow insulation riser on shrinkage porosity and solidification structure of ingot

Fine grain mechanism of ultrasonic vibration depth in large diameter aluminum ingot hot-top casting

With the development of the aerospace industry and the need for industrialized production, the casting processes of large diameter aluminum alloy ingot have come into focus in the industry. Among them, ultrasonic-assisted casting technology is widely used. Ultrasonic-assisted casting technology has the advantages of improving solute segregation of ingot and refining solidification organization. Other advantages have been widely reported. At present, most of the aluminum ingots used in the non-hot top ultrasonic casting process with very shallow liquid cavities, while the casting process does not involve the issue of ultrasonic vibration depth. With the use of a hot-top mold for ultrasound in the casting and casting process of large diameter ingot, the liquid level of aluminum melt is very high. The ultrasonic vibration depth will affect the cavitation range and finally affect the fine grain effect of the ingot. In the present study, a double source ultrasonic vibration system was applied in the process of semi-continuous casting of aluminum alloy with a diameter of 650 mm, and the influence of ultrasonic immersion depth on the macroscopic solidification structure of ingot was studied. Based on the test results of the solidified microstructure of aluminum alloy ingot and the simulation results of the sound field of the finite element software such as ANSYS, the mechanism of the microstructure refinement of the aluminum alloy ingot under different vibration depths was discussed at length. Study results show that, with increasing vibrational depth of the supersonic radiation rod, the whole cross section of the ingot is further refined, and grain shape changs from developed dendrites to equiaxed dendrites. Because of the end faces of the ultrasonic radiation rod, there is a vibrational peak at the fixed position, which leads to different ultrasonic cavities under different ultrasonic vibrational depths in the aluminum melt. This leads to different refinement mechanisms of the solidified structure.

Effects of Mould Rotation on Element Segregation and Compact Density of Electroslag Ingots during Electroslag Remelting Process

AbstractSteel solidification process control, especially in the solidification process of high-alloy steel, and improving the solidification structure have been increasingly gaining interest among metallurgists, particularly the electroslag workers. To further develop the electroslag remelting (ESR) process and to improve the ingot solidification structure, the effects of mould rotation on chemical element distribution and the compact density were investigated in this study. The experimental results showed that chemical element distribution would become more uniform when the mould keeps the reasonable rotation rate. However, the excessive rotation rate would deteriorate the solidification structure of steel. When mould rotation rate was between 0 and 28 r/min, maximum segregation of carbon could decrease from 3.19 to 1.084, and statistical segregation decreased from 0.2636 to 0.0554. Maximum segregation of chromium could decrease from 1.316 to 1.131, and statistical segregation decreased from 0.2753 to 0.0657. The compact density increased from 0.7693 to 0.94. But element segregation would become bigger and compact density would become smaller if rotation rate further increased. The improvement in the solidification structure could be attributed to reasonable mould rotation rate which could initiate movement in the slag pool and further increase the uniformity of the temperature in the slag pool. At the same time, the movement in the slag pool could also affect the metal molten droplet, scattering the liquid drop randomly in the metal pool. But the excessive rotation rate made the slag pool violent motion, so as to drive the molten metal pool to rotate which would carry off enriched steel surrounding the dendrites in the mushy zone and reduce the solute content in the region. As a result, the element segregation would occur.

Numerical Simulation of Titanium Alloy Ingot Solidification Structure during VAR Process Based on Three-Dimensional CAFE Method

Abstract A multiscale three-dimensional (3D) mathematical model has been established for simulating the temperature field, the fluid flow and the solidification structure of Ti-6Al-4V alloy ingot during vacuum arc remelting (VAR) process, which consists of the macroscopic mass, the momentum and energy conservation equations and the macroscale model of the nucleation and growth of grains. On the basis of heat transfer and fluid flow calculation, the 3D solidification structure formation of the ingot during whole VAR process has been obtained. Comparing the simulation result with the experimental observation, a reasonably qualitative agreement is achieved on grain structure and grain growth pattern. In particular, when taking the heat radiation into consideration during the calculation, the columnar grains on the ingot top are predicted well. Furthermore, a sensitivity study of the effect of natural convection on the grain structure has been carried out. The results show that the natural convection has a great influence on columnar-to-equiaxed transition (CET) and grain size, expressing as promoting the CET and refining the grain.

Effect of Steel Strip-Feeding Process on Solidification Structure

It is investigated that effect of steel strip-feeding ratio and superheat degree of molten steel on solidification structure of ingot by the steel strip-feeding experiment in the mold. The results show that: at the same superheat, with the increase of feeding ratio, the area proportion of equiaxed grain zone increases and the average size of equiaxed grain decreases, and at the same feeding ratio, the higher the superheat is, the smaller the proportion of equiaxed grain zone is, and the larger the average grain size is.

Effects of relative motion between consumable electrodes and mould on solidification structure of electroslag ingots during electroslag remelting process

Steel solidification process control, especially in the solidification process of high alloy steel, and improvement of the solidification structure have been increasingly gaining interest among metallurgists, particularly the electroslag workers. To further develop the electroslag remelting (ESR) process and to improve the advantage of the ingot solidification structure, the effects of relative motion between the consumable electrodes and the mould (namely, mould rotation) on chemical element distribution were observed in this study, as well as the compact density changes in electroslag ingots. Experiment results show that applying relative motion between the mould and the consumable electrodes in ESR results in a more uniform chemical element distribution in the electroslag ingots. Compared with the electroslag ingot of conventional ESR, maximum segregation of carbon could decrease from 3·19 to 1·146, and statistical segregation decreased from 0·2636 to 0·0608. Maximum segregation of chromium could decrease from 1·316 to 1·253, and statistical segregation decreased from 0·2753 to 0·1201. The compact density for the stationary mould increased from 0·7693 to a compact density of 0·9501 for the rotating mould. The improvement in the solidification structure of the electroslag ingot can be attributed to mould motion, which led to the generation of a shallow pool and the improvement of the solidification structure. But the excessive rotation rate is harmful to solidification structure instead due to the molten metal pool motion caused by violent slag pool motion.

Inclusions for Ultra-pure Ferritic Stainless Steels Containing 21% Chromium

As stabilizing elements added into ultra-pure ferritic stainless steels, niobium and titanium react with carbon and nitrogen to form carbonitrides and have great effects on the ratio of equiaxed zone and the grain size of solidification structure of ingots, which remarkably affect the quality of cold-rolled sheets. Combined with thermodynamic calculation, style and precipitation progress of inclusions in ultra-pure ferritic stainless steels were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy. The results indicate that the inclusions are mainly Ti-Al-N-O system inclusions in ultra-pure ferritic stainless steels. Al2O3 starts to precipitate firstly and then TiOx and TiN precipitates sequently. The inclusions are mainly single TiN particles and complex inclusions with Al2O3-Ti2O3 as cores and covered with TiN under the condition of 0.31% titanium addition and mainly Al2O3 under the condition of 0.01% titanium addition. A few (Nb, Ti) N particles precipitate because of no enough titanium to react with nitrogen when titanium addition is 0.01%. In addition, fine Nb(C, N) particles with size of less than 500 nm precipitate at relatively low temperature.

Control of the IN100 Superalloy Ingot Solidification Structure with Linear Electromagnetic Stirring

In order to achieve high quality superalloy ingots, an investigation of applying linear electromagnetic stirring to the superalloy vacuum casting solidifying process has been put into effect with electroprobe microanalysis and optical microscope. The results indicate that an one sided, upward linear electromagnetic stirring with 50Hz frequency and 140A current can effectively refine the isometric crystals and shorten the ratio of central shrinkage cavity in superalloy ingots.

A Multiscale Transient Modeling Approach for Predicting the Solidification Structure in VAR-Processed Alloy 718 Ingots

This paper describes the development and validation of a comprehensive multiscale modeling approach capable of predicting at the mesoscopic scale level the ingot solidification structure and solidification-related defects commonly occurring during the vacuum arc remelting (VAR) process. The approach consists of a coupling between a fully transient macroscopic code and a mesoscopic solidification structure code. The predictions from the multiscale model, including grain morphology and size and columnar-to-equiaxed transition, were validated against experimental measurements for a 20-inch (508 mm) diameter VAR alloy 718 ingots. The validated model was then used to investigate the effects of melting rate and ingot diameter on the solidification structure of VAR processed 718 ingots.

Restraining solute segregation of Al–1%Si alloy in diverse physical field

It is well known that in the melt treated by power ultrasonic treatment (UT) or electromagnetic stirring (EMS), the solidification structure is refined, and the solute segregation is improved. However, few studies in the literature involve the comparative study of UT and EMS. This report examines the effect of diverse physical field (UT or EMS) on solidification structure and solute distribution of Al–1%Si alloy. The experimental results show that the solidification structure of ingots can be refined using UT or EMS solely, and by the compound of UT and EMS, the structure is further refined. At the same time, the grain boundary segregation of Si element is restrained in the sole physical field; in compound physical field of UT and EMS, the restraining effect is enhanced.

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.

Effect of ultrasonic stirring on temperature distribution and grain refinement in Al-1.65%Si alloy melt

A series of experiments were conducted for AI-1.65%Si (mass fraction) alloy melt to study the formation of grain refining structure with ultrasonic stirring. The cooling curves of ingots with ultrasonic were measured and compared with those without ultrasonic. At the same time, the effect of the time of ultrasonic stirring on solidification structure of ingots was investigated. The influence of ultrasonic on the grain-refining efficiency of ingots was analyzed. In order to well understand the melts behavior under ultrasonic, by using ammonium chloride solution, the simulation experiment was carried out and the temperature distribution in ingot with or without ultrasonic was compared. The results indicate that the ultrasonic reduces the temperature inhomogeneity of melt, i.e the ultrasonic helps to homogenize the melt temperature. The effect of stirring and heat generation in ingot start to occur with increasing the time of ultrasonic stirring.