Height Of Ingot Research Articles

Effect of dynamic formation of multiphase slag skin on heat transfer and magneto-hydrodynamic flow in electroslag remelting process

During the electroslag remelting (ESR) process, the effect of dynamic formation of slag skin on magneto-hydrodynamic multiphase flow and temperature field is studied using a 2-D axisymmetric model. The electromagnetic field is described by user-defined functions. The dynamic formation and distribution of multiphase slag skin, as well as the interface between slag and metal, are investigated by using the volume of fluid (VOF) model and the dynamic meshing method. Especially, the effect of slag skin/air gap on heat transfer characteristics is considered and developed by user-defined functions. The results show that the thickness of slag skin at the interface between slag and metal increases as the axial distance from free surface of slag rises, reaching a maximum of about 25 mm. With the height of ingot increasing, the thickness of slag skin drops to 17 mm. When the current changes from 2.0 kA to 3.0 KA in the ESR process, the current density, Joule heat, velocity and temperature increases. In the meanwhile, the slag skin becomes thinner and the melt pool becomes deeper. The vibration of electrode has a weak effect on the formation behavior of slag skin, and only has effects on formation of metal droplet and velocity field.

A New Approach to Calculate the Velocity of Interdendritic Fluid Flow during Solidification Using Etched Surface Height of Actual Metal Ingot

Macrosegregation remains one of main defects affecting metal materials properties, which is mainly caused by interdendritic fluid flow during solidifying. However, as for controlling actual specific segregation, it is still difficult to effectively measure or simulate this kind flow instead of pure fluid flow, especially in complex casting processes of high-grade materials. Herein, a new method for obtaining velocity magnitude and direction of interdendritic fluid flow during metal solidifying is proposed from boundary layer and standard deviation obtained by measuring etched surface heights of the actual ingot and using statistical principles. Taking continuous casting bloom of GCr15 bearing steel as an example, it is indicated that the calculated velocity magnitudes under different sides and superheats can be explained by process features and, hence, solidification mechanism. The velocity magnitude and fluctuation are higher on the inner curve side and under low superheat. Meanwhile, it is found that the fluctuation extent of secondary arm spacing is more relevant with interdendritic fluid flow, although its magnitude is mainly determined by the cooling rate. Moreover, on the basis of the calculated velocity directions and magnitudes, there is a positive correlation between segregation area ratio and the effective ratio between interdendritic flow velocity and growth velocity especially in the equiaxed grain zone, which corresponds with classic macrosegregation formation theory. The above findings and comparison with other results demonstrate the validity of the new approach, which can obtain the magnitude and the direction of interdendritic fluid velocity for two or three-dimensional multiscale velocity distribution by tailoring measuring length and numbers.

Evaluating Plasticity of Alloy AD31 on Ingot Height

The authors present the results of evaluating the distribution of plastic properties on the height of a log ingot with the diameter of 145 mm, obtained by means of semi-continuous casting, from the aluminum alloy AD31. The authors study semi-continuous alloys of three manufacturers. One part of ingots was obtained with the use of only primary aluminum, secondary raw materials and secondary raw materials with the addition of primary aluminum. With the purpose of stabilizing the process of presswork the authors define the values of yield stress in the ingot lower and upper parts and study its microstructure. The research was conducted for the ingots without thermal treatment after accelerated homogenization. It is shown that the ingots, produced with the use of primary aluminum only, have less scattered plastic properties in terms of the height. That is why, for the case of press-working the items with thin components, it is reasonable to use the ingots from primary aluminum.

Хімічна і фізична неоднорідності та гази у великому сталевому зливку

For creation of the high-tech equipment that is used in energy, heavy engineering, chemistry and transport, the unique large-sized steel products are required. In the manufacture of such products, large forging ingots in the mass to 600 tons are used. However, an increase in the mass of the ingots leads to the formation of chemical and physical heterogeneity, enlargement and unfavorable distribution of non-metallic inclusions, of the development of segregation defects in them, which reduce the strength and exploitation characteristics of the metal. In this connection, the quality forgings and finished parts are not always meet the producing demands and the loss of metal, in the form of technological waste and rejects are reaching significant values. It is known that eccentric zonal segregation, especially it’s the most dangerous variety - cords, significantly reduce the quality and properties of products from large steel ingots. In connection with the continuous expansion of the production of large ingots, the problem of creating optimal technologies for their formation, which reduce or exclude the possibility of the formation of chemical heterogeneity and cords in steel during crystallization, it is currently important and relevant. In this paper it are presented the results of studies of the structure, gas distribution, physical and chemical heterogeneities in the cross section and height of an ingot in the mass of 140 tons, which was casted in vacuum from steel 25KHN3MFA. It is shown that depending on the temperature and time conditions of ingot hardening, among which the crystallization interval (due to the chemical composition of steels), cooling intensity in different volumes in height and cross section of ingot, temperature gradient before the crystallization front, solubility of alloying elements and gas content in the melt, etc. Based on this, when developing technology for large ingots to ensure their quality, optimal structure and properties should take into account not only their dimensions, but also the combination of these thermokinetic parameters on the crystallization process, dendritic structure formation, manifestations of liquation in different ingot volumes. Keywords: ingot, segregation strip and inclusions, dendrites, structure, oxygen, oxides, sulfides.

The Design of Slag and Electroslag Remelting Production Technology of Steel Containing Zirconium

Slag–metal reaction experiments in MoSi2 resistance furnace combined with electroslag remelting (ESR) experiments in ESR furnace are used to study the effect of slag on zirconium distribution in ESR ingot by establishing a new mass transfer model of slag–metal reaction. The mass transfer model consists of Al + Al2O3, Si + SiO2, Zr + ZrO2, and Fe + FeO systems based on the penetration and film theories. Both experimental and simulated results show that the returned slag (CaF2:CaO:Al2O3:MgO:ZrO2 = 57:20:16:3:3) combined with extra 4% Al2O3 added into molten slag in the first slag-temperature-rising period can control the zirconium in ESR ingot ranging from 0.35 to 0.40% and improve the homogeneous distribution of zirconium in ESR ingot. The returned slag of Exp.A containing low silica being used in Exp.C can not only contribute to the recycling of returned slag, but also improve the homogeneous distribution of Zr along the height of ESR ingot.

Distribution of nonmetallic inclusions in molten steel under hot-top pulsed magneto-oscillation treatment

To control the distribution of nonmetallic inclusions in molten steel is of highly commercial importance. A newly developed method, hot-top pulsed magneto-oscillation (HPMO), was employed to control nonmetallic inclusions in a medium-carbon steel ingot. The experimental results present that the position of nonmetallic inclusions of spinel (Al–Mg–O) and Mn–S inclusions is significantly influenced by HPMO. The number of nonmetallic inclusions gradually increased from the lateral wall to the center of ingot along the radial direction under the impact of HPMO treatment, whereas this distribution trend cannot be observed in the reference sample without HPMO treatment. In addition, the number of inclusions along vertical direction is proportional to the height of ingot, especially for the inclusions with the size of larger than 10 μm. It indicates that the application of HPMO can push away inclusions from lateral to center, and then the expelled inclusions aggregate and rise up to the top of ingot.

Aluminum, titanium and oxygen control during electroslag remelting of stainless steel based on thermodynamic analysis

Experimental investigation and thermodynamic calculation were carried out to study the effect of slag on alloying elements during electroslag remelting with developing a thermodynamic model to control titanium and aluminum in ingot. The thermodynamic model based on ion and molecule coexistence theory and conservation law of element atoms was established to analyze the change in aluminum and titanium along the height of ingot. The results show that low CaO slag is suitable for electroslag remelting of metal containing high titanium-to-aluminum ratio. As electroslag remelting process consists of slag temperature-rising and temperature-stable periods, TiO2 should be added into water-cooled copper mold during temperature-rising period in order to keep the thermodynamic equilibrium between titanium and aluminum, and the amount of TiO2 is the difference value calculated by the reaction between titanium and alumina at 1477 and 1677 °C.

Determination of heat transfer coefficient between AK7ch (A356) aluminum alloy casting and no-bake mold

Determined the iHTC (interface Heat Transfer Coefficient) between AK7ch (A356) aluminum alloy casting and no-bake mold. The heat transfer coefficient is determined by minimizing the error function values, representing the difference between the experimental and calculated temperature in the mold values during pouring, solidification and cooling. Determined the values of the heat transfer coefficient above the liquidus temperature of the alloy hL = 900 W/(m2·K) and below the solidus temperature hS = 600 W/(m2·K). Changing of the heat transfer coefficient within hL = 900÷1200 W/(m2·K) and hS = 500÷900 W/(m2·K) has no sufficient effect on the error value, and it remains within ~22 °C. It was shown the usability of the simplified approach using constant heat transfer coefficient h = 500 W/(m2·K), whereas error value is 23,8 °C. Changing of iHTC as function of height of the cylindrical ingot was experimentally confirmed. This owes to the different values of metallostatic pressure applied to the solid skin of the solidifying casting, leads to closer contact of the metal and mold in the bottom of the casting.

Effect of calcium-oxide on the removal of calcium during industrial directional solidification of upgraded metallurgical-grade silicon

Directional solidification is often used to remove metallic impurity in the photovoltaic industry for the low equilibrium distribution coefficient between solid and melt. However, in our present experiments, compared with other impurities, the removal of calcium is variable at the low height of ingot, which is caused by the existence of insoluble CaO particle. CaO exists as insoluble particle in the feedstock. During directional solidification stage, CaO motions with the melt convection, and it is likely to envelop in solid. Consequently, the content of calcium is relatively high if many CaO particles are just contained, which is verified by the analysis of SEM-EDS. In a word, the removal efficiency depends upon the chemical state of calcium. The reason why CaO exists is studied, and the envelopment of the particle is mainly discussed by means of thermodynamics, especially on gravitational force, repulsive force, and drag force.

Mechanical Properties Improvement of AlCrFeNi2Ti0.5 High Entropy Alloy through Annealing Design and its Relationship with its Particle-reinforced Microstructures

High entropy alloy has attracted increasing attentions. However, to enhance the alloy strength often leads to impairment of the ductility, or vice versa. Here we reported a heat treatment approach on AlCrFeNi2Ti0.5 high entropy alloy, which can elevate the strength and ductility simultaneously. An ingot of AlCrFeNi2Ti0.5 weighing 2.5 kg was firstly fabricated by medium frequency induction melting. Then samples from the same height of the bulk ingot were annealed for 6 h at 600, 700, 800 and 1000 °C, respectively. After 1000 °C annealing, an optimal microstructure was obtained by using our approach which can make some precipitation particles distribute homogeneously in the dendrite interior while keep the interdendrite structure as a single solid solution phase. The mechanical test on this AlCrFeNi2Ti0.5 alloy sample showed that, the compressive fracture strength σbc was increased by about 600 MPa and the plastic strain ep was doubled, compared with those of the as-cast sample. Our approach can be readily adapted to large-scale industrial production of high entropy alloys with high strength and ductility by proper annealing treatment.

Iron Management in Multicrystalline Silicon through Predictive Simulation: Point Defects, Precipitates, and Structural Defect Interactions

In multicrystalline silicon for photovoltaic applications, high concentrations of iron are usually found, which deteriorate material performance. Due to the limited solubility of iron in silicon, only a small fraction of the total iron concentration is present as interstitial solute atoms while the vast majority is present as iron silicide precipates. The concentration of iron interstitials can be effectively reduced during phosphorus diffusion gettering (PDG), but this strongly depends on the size and density of iron precipitates, which partly dissolve during high-temperature processing. The distribution of precipitated iron varies along the height of a mc-Si ingot and is not significantly reduced during standard PDG steps. However, the removal of both iron interstitials and precipitates can be enhanced by controlling their kinetics through carefully engineered time-temperature profiles, guided by simulations.

Estimation of solidification interface shapes in a boron–phosphorus compensated multicrystalline silicon ingot via photoluminescence imaging

This paper introduces a method for estimating the shape of the solidification front along the height of a directionally-solidified multicrystalline silicon ingot. The technique uses net dopant density images, obtained on wafers via photoluminescence imaging under surface limited conditions, after the impact of grain boundaries is eliminated through an image processing procedure. By modeling the dopant distribution according to Scheil's law, solidification interface images are derived sequentially along the ingot height. The technique is demonstrated on a compensated boron–phosphorus doped multicrystalline ingot. The reconstructed three dimensional interface images, together with their evolution along the ingot height, allows for subsequent optimization of the ingot growth process.

Growth of dislocation clusters during directional solidification of multicrystalline silicon ingots

Highly detrimental dislocation clusters are frequently observed in lab-scale as well as industrially produced multicrystalline silicon ingots for solar cell applications. This paper presents an investigation of dislocation clusters and how they develop over the whole height of a pilot-scale ingot. A 12-kg ingot, cast in a pilot-scale directional solidification furnace using a standard slip cast silica crucible and standard coating containing silicon nitride powder, was studied with respect to dislocation clusters. Dislocation clusters originating from grain boundaries were identified and followed from an early stage to the top of the ingot. One possible model for growth and multiplication of the dislocations in the clusters during solidification where slip on the {11¯0}〈110〉 system must be allowed is described in detail. Another possible mechanism is also discussed.

Resistivity Distribution of Multicrystalline Silicon Ingot Grown by Directional Solidification

The effects of impurities on the resistivity distribution and polarity of multicrystalline silicon ingot prepared by directional solidification were investigated in this article. The shape of the equivalence line of the resistivity in the vertical and cross sections was determined by the solid-liquid interface. Along the solidification height of silicon ingot, the conductive type changed from p-type in the lower part of the silicon ingot to n-type in the upper part of the silicon ingot. The resistivity in the vertical section of the silicon ingot initially increased along the height of the solidified part, and reached its maximum at the polarity transition position, then decreased rapidly along the height of solidified part and approached zero on the top of the ingot because of the accumulation of impurities. The variation of resistivity in the vertical section of the ingot has been proven to be deeply relevant to the distribution of Al, B, and P in the growth direction of solidification.

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 operating time.

Solidification processing of Al-Al2O3 composite using turbine stirrer

Solidification processing of Al-Al2O3 composites involves mixing of nonwetting alumina particles in molten aluminum alloy resulting in a slurry where the particles are often attached to bubbles sucked at the center of vortex below the stirrer. The internal surface of bubbles is eventually oxidized by oxygen from air entrapped in it. These bubble-particle combines may float or settle during casting depending on the overall density influencing the particle and porosity distribution in a cast composite ingot where the performance of a stirrer may be evaluated under a given condition of processing. Particle incorporation is more for turbine stirrers instead of flat blade stirrers, but the porosity also increases. Flotation of bubble-particle combines during casting of ingot results in higher particle content at the top. Microstructure shows clusters of particles along circular boundaries of thin oxides at the top of the ingot and sometimes at the bottom. This may be a consequence of filling of bubbles to different extents by surrounding liquid puncturing the oxide layer, if necessary, during solidification. When the manner of stirring is changed to 2 minutes of stirring of particles into molten alloy with an intermediate 2-minute period of no stirring before stirring the slurry again for 2 minutes, relatively uniform particle incorporation results along the height of cast ingot compared to that obtained by continuous stirring. This difference in particle distribution may be attributed to flotation of bubble-particle combines to release the particles on the top of the slurry when stirring ceases and its remixing into the slurry when it is stirred again. However, an increase in the intermediate period of no stirring and a higher processing temperature result in enhanced porosity and a more inhomogeneous particle distribution along the height of the ingot.

低炭素リムド鋼塊底部の大型介在物の生成に関する2, 3の現象について

In the rimming steel ingots, large inclusions exist characteristically in the bottom part of ingots. The formation of large inclusions is related to the formation of “mushy zone” which grows up from bottom of molten steel in mold during the period of rimming action.“Mushy zone” can be observed macro-scopically at the cross-section of solidified ingot.The result of investigation of tested ingots under the various conditions indicates that amount of large inclusions in “mushy zone” increases with increase of height of “mushy zone”. Rimming time and height of ingot have an important influence on the growth of“mushy zone” or amount of large inclusions. It is observed that when rimming time becomes longer or ingot becomes higher, both height of “mushy zone” and amount of large inclusions increase.