Large Ingots Research Articles

MAIN STAGES OF DESIGNING RESOURCE-SAVING TECHNOLOGIES FOR INGOT DEFORMATION ON HYDRAULIC PRESSES

Objective. To study the technological process of forging large ingots on hydraulic presses in order to identify and reduce resource consumption. Research methods. A finite element method that makes it possible to assess the stress-strain state of a workpiece, the possibility of levelling it, and homogenising it by controlling the factors that form the optimal forging method for a given workpiece. Results. A resource-saving technological process based on the optimal forging method has been developed, which allows to bring the quality of the designed products to a new level and leads to an increase in technical and economic indicators of production. By controlling the stress-strain state of the metal, high quality forged products can be achieved and resource-saving technologies for forging forgings of high-alloy steel grades and alloys can be created. Scientific novelty. The factors that form the rational resource-saving technological process of plastic deformation and the method of forging large forgings from alloyed, stainless steels and alloys on hydraulic presses, as well as the directions of their optimisation, have been formed. The finite element method allows us to predict the distribution fields of the workpiece’s stress-strain parameters, metal microstructure, and grain size. Practical value. Practically grounded recommendations for optimal modes of forging ingots from tool steel grades were developed. This will reduce energy consumption, save time in the production of forged products and generally intensify the process of plastic deformation. The proposed recommendations can be applied not only in the processes of forging tool steel grades but also in other types of hot plastic deformation of metals of a wide range.

The effect of complex extra-furnace treatment of metal melts on the formation of non-metallic inclusions in large-sized ingots

Abstract The article presents the results of studying non-metallic inclusions (NI) after extra-furnace treatment of the 13Cr9Mo2Co1NiVNbNB steel melt to produce large-sized ingots. The objects of the study were laboratory samples melted in a semi-industrial induction furnace with the capacity of 20 tons (the first batch), and samples obtained after melting in an electric arc furnace with the capacity of 120 tons, followed by modification and double vacuuming (the second batch).
Previously, using the Fact Sage software, modeling of the NI formation processes was carried out. The data were obtained on the possible NI composition and amount in this steel.
Studying NIs (the composition, the contamination index, inclusion parameters) was carried out on an ASPEX Explorer electron microscope using the method of automatic X-ray spectral analysis of particles (Automatic Features Analysis, AFA). It was established that in the samples of the first batch, the main part of the NIs consisted of chromium- and manganese-containing oxides: chromium-manganese spinels (Cr-Mn-O and Mn-Cr-Si-O groups), which occupy more than 94% of the total area of the NIs. In the samples of the second batch, the main part of the Nis was represented by Cr-Mn-O; Al-Cr-O; Cr-Al-Mn-O systems.
It was shown that the average size of non-ferrous substances in the samples of the laboratory batch and in industrial samples after extra-furnace treatment differs slightly (5-12%), however, the contamination index in industrial samples after vacuum treatment and especially after modification and repeated vacuum treatment was reduced by more than 10 times. The results obtained allow recommending vacuum treatment and complex modification with calcium and boron as measures to prevent the formation of non-ferrous metals and to improve metallurgical quality when smelting large ingots using complex alloy steels.

Modeling analysis framework for metallic currency system

Small coins, large coins, and ingots circulated in parallel in the metallic currency system, and they were sorted by different mechanisms based on the transaction value of each form. This is the first attempt to model their boundaries. We construct a model of the market mechanism of the mint which derives two models to achieve our goal. The first model derived is a supply-demand model of small coins that determines the demarcation between small coins and large coins, and the second is a game model whose equilibrium solution determines the dividing line between large coins and ingots.

A dynamic thermal radiation insulation method for directional solidification of polysilicon

To simplify the structure and reduce the high energy consumption of thermal insulation structures for polysilicon directional solidification equipment, an innovative cavity structure with a mirror and diffuse reflector was designed for thermal insulation. This method uses an internal thermal radiation cavity instead of a traditional insulation layer. Compared with the traditional insulation material, its volume was only 16.6 % of the crucible volume, and the energy consumption was reduced by 8.6 %. A mathematical model of the thermal radiation exchange in the cavity was established and solved analytically. Because of the design of mirror and reflector, the self-adjustment of the thermal radiation intensity and angle in the cavity was theoretically verified. It could automatically “trail” the temperature change on the sidewalls of the melt (crucible), and the dynamic thermal compensation was equivalent to an adiabatic construction. Three comparison experiments with a large ingot (0.9 m × 0.9 m × 0.35 m) were performed. When the cavity height to width ratio was greater than 3.33, the thermal compensation was poor and the quality of the ingot is lower than that of the others. The experiments showed that refractory brick and polished brass are a good combination for creating a cavity.

Homogenization Treatment and Plastic Deformation Improve the Carbide Homogeneity of M42 High‐Speed Steel

The mechanical properties of high‐speed steel (HSS) are significantly influenced by the distribution of carbides formed during solidification. Despite extensive research, the nonuniform cooling in large ingots remains an area requiring further investigation. In this study, the microstructure inhomogeneity in M42 HSS with a diameter of 330 mm is examined. Models are developed to predict the dissolution of carbide networks during homogenization, achieving a 39% reduction in hardness variation (Δr) between the center and surface. Further improvements are attained through hot forging and rolling, leading to the fragmentation of the carbide network into a banded structure. Additionally, a detailed carbide tip dissolution model is established, providing a reliable basis for optimizing annealing processes. As a result, the carbide distribution converges significantly, with hardness variations reduced by 88% to only 0.3 hardness Rockwell C scale, showcasing substantial enhancement in material homogeneity.

Single-crystallinity of large-sized tungsten ingots obtained by plasma-induction additive technology

Obtaining large ingots of refractory metals with a single-crystal structure is still a difficult technical task. Large-sized tungsten ingots up to 15 cm cross-section can be obtained at rates of 17…70 mm/min using the technology of additive plasma-induction layer-by-layer growth. The most single-crystalline repeated structure of the tungsten ingot was obtained at 26 mm/min. Some deterioration in the structure of the ingot is associated with a technological change in the rate of surfacing and technical pauses. Volumetric single-crystallinity in the layers of the tungsten ingot is confirmed by research with such analytical criteria as the misorientation angle of the subgrain structure is less than 2°, the deviations in growth directions specified by the primary single-crystal base (seed) not exceeding 0,053° according to reflection Laue, and the volumetric repeatability of physical and mechanical properties.

Evaluation of the Possibilities for Improving Durability of Large Ingot Molds Made of Pig Iron Using Vibration Treatment of the Melt

Evaluation of the Possibilities for Improving Durability of Large Ingot Molds Made of Pig Iron Using Vibration Treatment of the Melt

Thermomechanical Pathways for Accurate Microstructural Control of Ti–7Ag Alloy: Towards a New Generation of Antibacterial Materials for Medical Applications

This study delved into exploring microstructural states in a Ti–7Ag alloy to achieve targeted functional and structural properties. Specifically, the focus was on attaining a homogeneously precipitated state and a solid solution, known for their potential to combine functional traits like corrosion resistance and antibacterial activity with structural properties such as mechanical strength. However, obtaining these optimized microstructures presents challenges due to kinetic considerations. A key finding of this study was the crucial role of a pre-deformation stage, prior to heat treatment, to create an even distribution of fine Ti2Ag precipitates. Moreover, we demonstrated that starting from this precipitated state, a controlled dissolution step could yield a single-phase solid solution with similar grain size. Therefore, a tailored set of thermomechanical treatments was developed to achieve both microstructures, and these metallurgical states were fully characterized combining SEM (BSE imaging and EDS analysis), TEM, and XRD. Associated mechanical properties were also assessed by tensile testing. In addition, the process was proven to be robust enough to overcome potential industrial problems, such as slow cooling rates when water-quenching large ingots. Considering the limited existing documentation on microstructural features in Ti–Ag alloys, this work on this model alloy significantly advanced our current understanding of the broader Ti–Ag alloy system by providing new data and showcasing a tailored approach involving thermomechanical treatments.

Development of a technique for simplified simulation of the thermomechanical processing of large ingots

Development of a technique for simplified simulation of the thermomechanical processing of large ingots

A hot tearing propagation model for steel

Hot tearing is a significant challenge in material preparation process, including high-performance alloy casting, large ingot production and additive manufacturing, etc. However, the propagation process of hot tears, especially in steel, is still unclear at present. This study proposed a new model for hot tearing propagation that considers the energy balance, the relationship between the propagating mode and the growth rate of hot tears when they undergo irreversible and rapid propagation. To evaluate this model, a new testing device was developed and the hot tearing behaviors of low and high carbon steels were observed. The tests demonstrated a notable correlation with the model. Furthermore, a new criterion for propagation of hot tearing was put forward. This work provides a more comprehensive physical model and criteria for simulating and predicting the formation of hot tears.

DETERMINATION OF THE STRESSED METAL STATE DURING HOT ROLLING BY THE FINITE ELEMENT METHOD

Purpose. Determination of the stress-strain state of the metal during the rolling of large ingots to prevent the occurrence of internal defects, and determining the effect of forced cooling of the ingot surface during hot rolling on the stress-strain state.
 Research methods. Finite element method, upper estimate method.
 Results. Based on the finite element method, a comparative simulation of the stress-strain state of the ingot with different cooling times was performed. As a result of the study, it was established that the forced cooling of the ingot surface during hot rolling helps to reduce the probability of the internal continuity defect forming. The given results of comparison of the distribution of strain intensity along the rolling cross-section in the basic version and with additional annealing indicate a decrease in the probability of formation of discontinuities in the axial zone of the ingot. This, in turn, proves the effectiveness of forced annealing of the surface layers of the ingot (workpiece).
 Scientific novelty. A mathematical model of the distribution of the main stress state components was developed. It took into account the redistribution of temperatures and, as a result, the mechanical properties of the metal according to the height of the deformation focus during the hot rolling of relatively large blanks.
 Practical value. The use of forced cooling leads to a significant increase in hydrostatic and normal stresses in the axial zone, reducing the probability of the formation and subsequent growth of internal continuity defects. Thus, the quality of finished products increases, in particular, valuable rolled products made of special grades of steel.

Numerical simulation of macrosegregation phenomenon in Cu-6wt%Ag alloy ingots fabricated by electromagnetic stirring

The development and research of high strength and conductivity materials are essential for the advancement of high-field magnets, including pulsed magnets. This study investigates the effect of electromagnetic fields on the solidification casting of binary Cu-6wt%Ag alloy ingots with diameters of 40 and 160 mm. A 3D numerical simulation is performed utilizing the continuum model with conservation of total momentum, mass, energy, and species. The results indicate that applying electromagnetic stirring (EMS) to small cross-section ingots can cause many randomly distributed small regions with higher segregation degrees inside the ingot, which is not conducive to improving the macrosegregation inside the ingot. For large cross-section ingots without EMS, compared to small cross-section ingots, there is more severe macrosegregation inside the ingot, especially the extreme center segregation with a maximum segregation degree of about 414%. EMS can effectively control macrosegregation within a specific range and eliminate center segregation. When the linear EMS's magnetic induction intensity is set to 0.06 T, the maximum segregation degree near the ingot center can be reduced to less than 260%. Simultaneously, the EMS induced forced convection is also instability, leading to numerous haphazard solute accumulations and depletions, which explains many small segregation regions in the ingot. In terms of improving macrosegregation in large cross-section ingots, Linear EMS has a definite advantage over rotary EMS. It is possible to keep the entire segregation degree in the ingot below 100% when the linear EMS's magnetic induction intensity is set to 0.036 T and the stirring frequency is 4 Hz. The ideal stirring parameters range for linear EMS is to maintain the magnetic induction intensity at around 0.036 T and the stirring frequency in the range of 4–8 Hz.

Design and numerical analysis of a novel argon gas tube to reduce impurities in large size casting crystalline silicon furnace

A novel design of argon gas tube within the silicon casting system was developed employing pipe flow and side jet analysis, which facilitates horizontal ejection of argon gas along the silicon melt surface. The aim was to enhance control over gas flow velocity for removing impurities during large size silicon ingot (1400 kg) growth, with special attention on the edge region of ingot. It was found that the diameter of side-facing outlet holes, when oriented along the corner direction, is about 2 times of that along the side center direction, to achieve an extended jet distance reaching corner region. The gas flow and transport of SiO above the silicon melt surface were studied for the proposed gas tube configuration based on 3D numerical simulations. The simulation results reveal the correlation between argon flow rate and resultant gas velocity at the edge of melt surface, which is consistent with the theoretical analysis, particularly for moderate to high argon flow rates. The numerical simulations demonstrated that the proposed gas tube, equipped with eight optimized outlet holes, outperformed the conventional tube in extracting SiO from both central and corner regions above the silicon melt surface.

Experimental and simulation studies of layer casting on industrial-scale Al-4.5 wt Pct Cu ingot: Effect, defect, and optimization

Macrosegregation is an inevitable defect in large ingots, which intensifies with the increase in ingot size and directly affects the performance of the final product. Though the previously proposed layer casting (LC) process has been successfully conducted to alleviate the macrosegregation in the additively casted laboratory-size ingots, due to macrosegregation showing strong sensitivities to the ingot size, it is still doubtful whether this new approach could still work as expected in actual industrial-scale ingots. In this research, we have studied the effects of LC on macrosegregation and the utilization rate in Φ240 mm× 690 mm Al-4.5 wt pct Cu ingots. The experiment results show that the macrosegregation index is significantly reduced and the utilization rate is greatly improved in the industrial-scale ingot using LC approach. Different from the laboratory-size LC ingots, incomplete fusion defects are found at the interlayer in the current LC ingots, which are caused by insufficient remelting at the edge of the ingot and the oxide film formed on the surface of the previous layer. Periodic negative segregation is formed at the bottom of the multi-layers, which is attributed to the extra nucleation induced by the multi-pouring process. Subsequently, an optimised design is proposed to reduce incomplete fusion defects, and the efficiency is confirmed by the simulated results. This study provides a possible technique approach for promoting the homogenization level of large ingots.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ СКОРОСТИ И СПОСОБА РАЗЛИВКИ РАСПЛАВА НА РАЗВИТИЕ ОСЕВОЙ ЗОНЫ В МОДЕЛЬНЫХ СЛИТКАХ

The paper presents the results of laboratory studies of the effect of the method and speed of casting the melt on the solidification process and the features of the formation of the axial zone of a large ingot. The research was carried out by the method of physical (cold) modeling on a model of an ingot weighing 19.6 tons. Sodium sulfuric acid (crystalline hyposulfite) was used as a modeling solution. The casting of the melt into the mold-mold was carried out from above. It is shown that the change in the melt casting rate has a significant effect on the length of the axial zone. It is established that a decrease in the melt casting rate leads to an increase in the direction of crystallization and an improvement in the structure of the axial zone of the ingot. It has been found that model ingots that were cast with refilling of the profitable part by melt after a certain time interval after pouring the ingot body, solidify 1.4 times faster than the ingot cast according to classical technology.

Selection of a rational heating mode for large cold ingots for metal forming using computer simulation

Selection of a rational heating mode for large cold ingots for metal forming using computer simulation

Formation Mechanism of Secondary Inclusions in Fe-36mass%Ni Alloy Using a Novel Combination Analysis Technique

Controlling the size, number, and composition of secondary inclusions is vital in the production of high-quality steels. In this study, experimental and computational investigation of the relationship between secondary inclusion formation in Fe-36mass%Ni alloy and cooling rate was carried out. Assuming the case of large ingots, solidification experiments using various cooling rates (0.17 to 128 K/min) were employed and the size, number, composition, and distribution of inclusions were analyzed by SEM-EDS automatic inclusion analysis. Like previous studies, inclusion number density increased with increasing cooling rate, while inclusion size decreased with increase of cooling rate. On the contrary, oxide inclusion area fraction was found to have little relationship with the cooling rate and was instead found related with oxygen content of the sample. As a new attempt to investigate the relationship between microsegregation and secondary inclusion formation, a combination of SEM-EDS analysis and EPMA mapping analysis was carried out. By superimposing information of microsegregation and inclusions, it was found that high-Al2O3 inclusions formed during the early stage of solidification, whereas low-Al2O3 inclusions formed during the later stage of solidification. These findings suggest that Al2O3 inclusions formed in the early stage of solidification reacted with the remaining Si-enriched liquid steel and changed into low-Al2O3 inclusions. Experimental results were also confirmed by thermodynamic calculations. Present work made it possible to understand deeper the relationship between microsegregation and secondary inclusion formation.

3D Numerical Modeling of Molten Steel Flow and Inclusion Transports During the Solidification Process of a Large Steel Ingot

3D Numerical Modeling of Molten Steel Flow and Inclusion Transports During the Solidification Process of a Large Steel Ingot

Improving microstructure and segregation of steel ingot by inorganic heat absorption method

A novel method by adding inorganic heat absorption material (IHAM) into the molten steel was proposed to improve the quality of large steel ingots. The IHAM was found to melt and float up after absorbing the heat of molten steel, stirring the melt and thus accelerating the cooling process. The molten steel was also purified as the inclusions were adsorbed during the floating of IHAM. The addition of IHAM rod was conducive to increase the equiaxed grain ratio (EGR) and alleviate the central carbon segregation, while the IHAM cored wire played a more important role in reducing the inclusion index. This method holds broad appeal to solidification of large steel ingot, as it can improve the microstructure of solidified ingot.

Production of detector grade CdZnTe crystal with VGF furnace by analyzing segregation of Zn and In

Production of CdZnTe crystals for radiation detector applications through Bridgman and Vertical Gradient Freeze (VGF) techniques is challenging in many aspects. Due to the structural characteristics of CdZnTe, it is not possible to obtain a large single crystalline ingots from the melt growth technique. In addition, the segregation of dopants and Zn decrease the yield significantly. In order to achieve detector-grade CdZnTe crystals, zinc segregation behavior should be fully understood, and optimum dopant concentration (In) should be determined. In this work, indium-doped Cd0.9Zn0.1Te single crystals grown via the Vertical Gradient Freeze (VGF) technique were compared in terms of dopant segregation, defect concentration, electron mobility, and electrical resistivity. It is observed that Zn segregates towards the tip of the ingot while In segregates towards the heel. Zn segregation coefficient is calculated as 1.35 while In segregation coefficient is found to be 0.4 for the VGF method. The variation of Zn throughout the ingot and excessive In dopant concentration degraded the detector performance. CdZnTe crystals having In doping concentrations of more than 5 ppm were unresponsive to gamma radiation. (µτ)e of VGF-grown crystals in METU Crystal Growth Laboratory is calculated as 4–5 × 10−4 cm2/V.