Cast Billets Research Articles

A Strain Integrated Gas Infusion Process (SIGI) for Magnesium Alloy Castings

This study presents a Strain Integrated Gas Infusion Process (SIGI) to manufacture high-performance cast AZ91 magnesium alloys without the addition of secondary alloying elements/reinforcements or secondary processing. The current SIGI process involves a combination of agitation and localized rapid heat extraction via strain integration and high-energy gas infiltration. The SIGI casting process has been compared systematically with conventional techniques. The critical process parameters, including hole diameter, bubble diameter, and flow rate, have been optimized through numerical calculations, simulations, extensive experiments, and comprehensive analysis. The study also focused on investigating the effect of gas bubbles on the molten metal and established the mechanisms involved in improved solidification. Gas infusion combined with strain integration impacts the solidification process, ensuring uniform alloying element distribution and reducing segregation and microporosity. This manufacturing strategy eliminates casting defects such as segregation and microporosity, resulting in a non-dendritic homogeneous microstructure. The significant refinement in morphologies of both primary (α-Mg dendrites) and secondary (β-Mg17Al12 phase) phases highlights the success of the current SIGI process. Compared to the conventional casting processes, a remarkable improvement in strength-ductility synergy is achieved in the current SIGI process. The scientific know-how and efficiency of the current SIGI process are established and discussed in detail, providing a promising solution to address the existing challenges encountered in magnesium alloy billet castings. The SIGI process improves the mechanical properties and corrosion resistance of billet-cast magnesium alloys. The SIGI process is suitable for the billet casting, offering significantly improved properties but faces limitations in complex mold casting applications. The billets casted by SIGI process can be used as a high-quality precursors for downstream processes to create industrial components.

Influence of Gas Oven Temperature on the Microstructure and Extrudability of Al-Mg-Si Aluminium Alloys

The microstructure of Al-Mg-Si aluminium alloys is well characterised when it comes to the initial state of the cast billet or the artificially aged profile. Typically, a gas oven coupled with an induction oven is used to preheat the billets before extrusion. Preheating reduces the flow stress of the aluminium and dissolves the phases that have precipitated during cooling after homogenisation. In this paper, the influence of the gas oven temperature on the partial or complete dissolution of the precipitated phases will be shown. In addition, the negative effect of a wrong choice of parameters on the volume content of the MgSi phases will be shown.

Inducing columnar-to-equiaxed transition by gradient impediment-flow optimization mechanism: The inheritance chain of solidification

Optimization of the metal solidification microstructure is a long-standing topic. It is the initial and critical guarantee of fabricating high performance metal materials, especially in the context of external field control, for example, for electromagnetic fields. However, tailoring the final solidification microstructure is extremely difficult because its mechanism is a long process inheritance chain which can be hardly observed by experiments. In this study, systematically simulations of the continuous casting using an electromagnetic swirling flow nozzle (EMSFN) was made to clarify this inheritance chain. It was newly found that a relatively uniform flow field inherited from a magnetic field generates a gradient impediment-flow optimization mechanism (GIFO), which is beneficial for both columnar-to-equiaxed transition (CET) and grain refinement. Specifically, 600 A increases the superheat dissipation, and the temperatures of the solidification front at 200 mm and 400 mm below the meniscus are increased by 15.47 K and 12.27 K, respectively, and the temperature gradient is decreased by 17.3 % and 22.8 %. The concentration gradient at the solidification front decreased by 89.9 %, 31.1 %, and 51.3 % at 200 mm, 400 mm, and 650 mm below the meniscus, respectively. Coupled changes in the temperature and concentration gradients impede dendritic growth and promote equiaxed grain nucleation. In addition, more equiaxed grain nuclei are transported to the forefront of the growing dendrite when the molten steel rotates and is transported from the inner to the outer regions. According to the simulation, the experimental validation proved that electromagnetic swirling flow nozzle was a convenient method for promoting this mechanism. It can optimize the solidification structure of Grade 70 carbon spring steel continuous casting billets with an increase of 21.26 % in the equiaxed grain ratio extremely low carbon segregation, and improved mechanical properties. This newly found mechanism can be considered as a generic theory for optimizing the solidification microstructure of alloys, which can guide the process design of various external field control technology.

STUDY OF THE SEAMLESS PIPES PROPERTIES OBTAINED FROM A HOLLOW BILLET

The article researched the influence on the pipes mechanical properties initial billet obtained by the traditional method and the proposed method, in which the piercing process is excluded. The proposed method involves casting the initial billet for the production of seamless pipes with a cavity obtained on a continuous casting machine. The production of hotrolled seamless pipes from a hollow billet is an urgent issue today, since central porosity and axial segregation after casting are excluded, affecting the quality of the pipes obtained in the subsequent stages of production: rolling on a mandrel mill and reducing. The possibility of producing seamless hot-rolled pipes from a hollow billet is substantiated, providing the necessary set of mechanical properties that are regulated by the standards GOST 632-80, GOST 633-80 and API 5CT. The result is a minimal deviation of the mechanical properties of steel samples obtained by double deformation of a hollow continuously cast billet from samples obtained according to the traditional scheme, including the piercing process. Keywords: hollow billet, steel, 09Mn2Si, seamless pipe, piercing process.

Selection of internal design of crystallizer sleeves for continuous casting of 200 mm billets

The crystallizer is the most critical and most important functional unit of a continuous casting machine (hereinafter referred to as CCM). It is the main technological unit of the CCM, an assembly for removing heat during the solidification of the solidifying metal and the formation of the ingot. The main requirement for the crystallizer is to provide maximum heat removal from the solidifying steel to the cooling water, and to obtain a strong ingot shell with a good surface at the outlet of the crystallizer, which would not be destroyed by the heat of the liquid phase and the ferrostatic pressure. During the reconstruction of the CCM by the contractor company, drawings of crystallizers and crystallizer sleeves with a double‑cone internal geometry for casting 200 mm continuous cast billets were developed. The 200 mm continuous cast billet is a billet for the production of hot‑rolled seamless steel pipes. During the operation of the crystallizer sleeves with a double‑cone internal geometry, an accelerated wear of the protective coating in the lower part of the sleeve was noted, as well as an increased rejection of hot‑rolled pipes due to defects on the outer surface of the pipes. In order to identify the cause of the defect formation, complex metallographic studies of the outer surface of the pipes were carried out. As a result of the metallographic study, surface defects classified as steel mill scale on the outer surface of the pipes were identified. To minimize the “steel mill scale” defect and reduce the wear of the protective coating of the crystallizer sleeves, work was carried out to select the optimal conditions for the crystallization of the continuous cast billet: the use of crystallizer sleeves with a three‑cone internal geometry compared to a double‑cone was investigated; maintaining the temperature difference of the water at the inlet and outlet of the crystallizer within specified limits (ΔT) was tested. It was found that the use of a crystallizer sleeve with a three‑cone internal geometry for casting 200 mm billets and the stable behavior of the ΔT parameter made it possible to ensure the required quality of the surface of seamless pipes, reduce the wear of the protective coating of the crystallizer sleeves and increase the productivity of the CCM.

Deoxidation of steel with calcium carbide. Influence of calcium carbide addition on steel contamination by non‑metallic inclusions

One of the main factors determining the final properties of metal products is the quantity, morphology and distribution of non‑metallic inclusions in steel. The article deals with the issues related to the use of calcium carbide in steelmaking production, instead of secondary aluminum and other deoxidizing materials, in order to improve the quality of the products. During the experimental work on the use of calcium carbide in steelmaking production, instead of secondary aluminum and other deoxidizing materials, second grade calcium carbide according to GOST 1460–81 was used. To determine the contamination of steel with non‑metallic inclusions, sampling was carried out from hot‑rolled products obtained from continuously cast billets. According to the results, it was found that the improvement of melt deoxidation in melts using calcium carbide can be achieved by increasing its consumption. In turn, the use of calcium carbide for deoxidation of the melt upon its release from the electric arc furnace into the ladle, instead of secondary aluminum ingots of grade AB87 according to GOST 295–98, helps to reduce the contamination of steel with non‑metallic inclusions.

Enhancing tensile and fatigue properties of high-speed-extruded Mg–5Bi–3Al alloy using non-homogenized extrusion billet

This study aims to improve the tensile and high-cycle fatigue properties of a high-speed-extruded BA53 (Mg–5Bi–3Al, wt.%) alloy using a non-homogenized extrusion billet. Homogenization treatment of the BA53 billet leads to a significant reduction in the area fraction of Mg3Bi2 particles from 12.9% to 2.5% and an increase in the average grain size from 142 to 189 μm. The BA53 material produced via the high-speed extrusion of the cast billet (Cast-E) and that produced via the high-speed extrusion of the homogenized billet (Homo-E) both exhibit a fully recrystallized microstructure. However, Cast-E has a finer grain size and many more Mg3Bi2 particles than Homo-E. In addition, the tensile yield strength and elongation of Cast-E are 211 MPa and 9.4%, respectively, higher than those of Homo-E (198 MPa and 7.9%). This higher strength is attributed to the strengthening effects of the higher number of Mg3Bi2 particles, the finer grain size, and the higher internal strain energy. The fatigue limit for Cast-E is 100 MPa, which is 25% higher than that of Homo-E (80 MPa). This occurs because the numerous fine Mg3Bi2 particles in Cast-E inhibit the formation of persistent slip bands on the specimen surface and impede crack propagation. This study proposes a new manufacturing process that does not require billet homogenization, thus simultaneously improving the productivity of the extrusion process and the tensile and fatigue properties of the resulting BA53 alloy.

Internal Quality Inspection and Characterization of Casting Billets Based on Ultrasonic Microscopy

Abstract For evaluating the internal quality of casting billets, the low-power experimental and metallographic methods have the disadvantages of the complex process, the small detection range and the destructive evaluation. In addition, the internal defects of the casting billet are analyzed by the one-dimensional waveform and two-dimensional image for the traditional ultrasonic testing, which can not describe directly the three-dimensional spatial information. Hence, a new method is proposed based on ultrasonic microscopy to detect and characterize the internal defection of the casting billet. In this paper, 42CrMo casting billet is regarded as objective, five sets of samples are fabricated by adjusting temperature gradient field and the number of presses. The ultrasonic sequence images of the present samples are achieved by using ultrasonic microscopy, and the spatial distributions, number, and sizes are obtained for the defects of the casting billet by reconstructing the three-dimensional appearance of microdefects to characterize the internal mass of the casting billet. Finally, the effective and accuracy of the proposed method are validated by using metallographic method.

Experimental Study on the Characteristics and High‐Temperature Heat Transfer of Secondary Cooling Nozzle for High‐Efficiency Slab Continuous Casting Process

In the continuous casting process, the heat transfer effect of secondary cooling plays an important role in the quality of the slab. The cooling intensity and cooling uniformity of the secondary cooling nozzle need more efficient spray cooling to achieve. Herein, the cold characteristics of different types of nozzles were compared. It is found that the second type of air mist nozzles have more uniform water density and striking force. On this basis, high‐temperature heat transfer experiments for casting billets were carried out to study the heat transfer coefficients of different air mist nozzles in the secondary cooling zone of continuous casting. It is found that the heat transfer coefficient increases as the distance of the temperature measurement point from the nozzle directly below increases. The heat transfer coefficients of the casting billet in both the jet and non‐jet zones are decreasing to varying degrees. When the temperature drops to 600 °C, the second type of air mist nozzle shows a faster temperature drop at the point of measurement, a smaller difference in time taken for temperature drop between jet and non‐jet zones, and faster and more uniform spraying, leading to a more significant trend of increasing heat transfer coefficient.

Analysis of carbon shell of billets with high casting speed

Abstract The increasing casting speed of billets is beneficial for improving single-machine production efficiency, reducing refractory material consumption, and achieving energy conservation and consumption reduction. However, as the casting speed increases, the probability of steel leakage also increases. An analysis of the thickness of the billet shell under high casting speed allows us to analyze the reasons for steel leakage and propose targeted solutions. This article analyzes the steel leakage billet shell of grade 40 steel and concludes that the thickness of the billet shell is between 8-20 mm at the upper of the mold, and only 5-10 mm at the lower of the mold. At the beginning of its formation, the shell of the cast billet is not uniform, with a maximum difference of up to 8 mm. As the casting progresses, the shell of the billet actually becomes thinner. At a distance of 100-200 mm from the mold, the maximum air gap between the billet shell and the copper tube reaches about 5.5 mm. The air gap reduces the uniformity of heat transfer, resulting in an uneven billet shell. After the liquid steel is injected into the shell, it will cause remelting of the solidification shell, resulting in thinning of the casting shell and causing steel leakage at the outlet of the mold.

Initial Solidification Behavior of Spring Steel Billet Near the Mold Corner During Continuous Casting Process

Strand surface defects originate from the initial solidification of molten steel in continuous casting mold. This article investigates the initial solidification behavior during the continuous casting of 55SiCr spring steel billet using a novel mold simulator. First, the high‐frequency responding temperatures and high‐frequency heat fluxes across the mold corner and hot face are calculated by the 2D‐inverse heat conduction program mathematical model and the fast Fourier transformation, and the results indicate that the temperature variations and heat flux fluctuations around mold corner are stronger than those at mold hot face. Then, the characteristic heat fluxes around the meniscus at mold corner and hot face are analyzed, and their four corresponding signals are discussed with the help of power spectral density analysis. The average solidification factor K for shell corner is greater than shell face, which indicates that the cooling intensity of shell at corner is stronger due to the two‐dimensional heat transfer near mold corner, as demonstrated by heat transfer and dendrite structure analysis. Finally, the interrelations between the shell profile, mold oscillation, heat flux change rate, high‐frequency heat flux, temperature change rate, and high‐frequency temperature for the two cases are discussed.

Modeling and investigation of combined processes of casting, rolling, and extrusion to produce electrical wire from alloys Al–Zr system

The results of modeling and research of casting, rolling, and extrusion processes for producing wire from Al–Zr system alloys and determining its physical and mechanical properties have been presented. When implementing combined processes for processing aluminum alloys, the number of operations is significantly reduced, productivity and yield are increased.As a result of the conducted research, the influence of alloy preparation modes and their chemical composition on the physical, mechanical and electrical properties of longish semifinished products from Al–Zr system alloys obtained by combined rolling-extrusion (CRE) and ingotless rolling-extrusion (IRE) methods were investigated.The simulation of the CRE process for one of these alloys of the system was carried out in the DEFORM 3D software package using data on its rheological properties obtained by the hot torsion method. Based on the modeling results, the optimal modes for conducting experimental studies were selected.The features of metal forming were experimentally studied, the temperature-velocity and technological parameters of combined processing were found, as well as the properties of cast billets, including those obtained using an electromagnetic mold (EMM). The results of experimental studies of the CRE and IRE processes suggest that it is possible to obtain longish deformed semifinished products from alloys Al–Zr system with a level of physical, mechanical and electrical properties that meet international standards.At all technological stages, including drawing, the structure of the metal was studied, and data on the physical and mechanical properties of hot-extruded rods and wire in cold-deformed and annealed states was obtained.The heat resistance of wire made from the investigated alloys was studied and it was found that after testing at a temperature of 280 °C and a holding time of 1 h, it satisfies the requirements of the AT3 type standard with a maximum permissible long-term operating temperature of 210 °C.Recommendations are given for industrial implementation; alloys containing 0.15–0.20% zirconium and 0.10–0.15% iron are recommended for the manufacture of AT1 type wire without heat treatment, as well as 0.25–0.30% Zr and 0.2–0.25% Fe for AT3 wire type with heat treatment.

Effects of Ce addition on inclusion modification in martensitic stainless steel

The control of inclusion features, i.e., chemical composition, distribution, quantity, and size, is in high demand for stainless steels to achieve good surface quality, pitting corrosion resistance, and mechanical properties. In this paper, the effects of rare earth (RE) modification on the inclusions of martensitic stainless steel were explored. Martensitic stainless steels with various contents of Ce were prepared, and the inclusions in the cast billets were characterized by field emission scanning electron microscopy (FE-SEM) and an automatic analysis system for nonmetallic inclusions in steels (OTS). The effect of Ce on the modification of nonmetallic inclusions during solidification was explored with thermodynamic calculations. The results showed that the addition of Ce modified the oxygen and sulfur inclusions by transforming them from irregular elongated inclusions to nearly spherical RE composite inclusions. Compared with those in basic martensitic stainless steel, nine types of RE inclusions were found in the presence of Ce. As the Ce content increased from 0.048 wt% to 0.092 wt%, the CeAlO3 content decreased, whereas the Ce2O2S content increased. Moreover, there were 80% fewer inclusions than in the basic martensitic stainless steel.

Обоснование технологии получения заготовки для ножа исполнительного органа геохода

Introduction. In the construction of the geohod, a blade executive body is used as a working body, which is an element of screw blades rigidly connected to each other in the center of the geohod. The shape of the body is proposed to be made in a helicoid shape, taking into account the specifics of the operation of the underground unit. Therefore, at present, the development and justification of technological solutions for the manufacture of knives of various shapes of the executive body is an urgent task. Materials and methods. The paper considers the main methods for obtaining a body blank of the executive body of the geohod, based on the structural, functional and technological features of the geohod design. To determine the rational variant of the casting method, the main technological capabilities of the casting methods are analyzed. To assess the effectiveness of casting methods, such indicators as: the material utilization factor and the technological cost of the work piece are considered. It is noted that one of the traditional approaches for obtaining a billet is the method of metalworking by pressure. To obtain a blank of the body, the possibility of using rolling and bending technology is considered. The choice of pressure treatment technology is justified. Research results and their discussions. The results of calculations of the technological cost of the casting billet show that it is advisable to use shell casting to obtain a body billet in the conditions of mass production of underground aggregates. Also, the results of determining the technological cost of the work piece by pressure treatment show that it is advisable to use the bending method to obtain a body blank in conditions of small-scale production and medium-scale production of equipment. Conclusion. To choose a method for obtaining a blank body of the executive body, it is necessary to take into account a number of features of the application of methods for obtaining a blank. First of all, it is necessary to take into account the type of production, the degree of ensuring accuracy and quality, especially in terms of strength characteristics, the possibility of using high-performance equipment to increase the productivity of the enterprise. Resume. The article presents the results of research to determine the choice of a method for obtaining a body blank of the executive body of the geohod. It is established that when choosing a method for obtaining a work piece, it is necessary to take into account the type of production, the degree of accuracy and quality, especially in terms of strength characteristics, and the possibility of using high-performance equipment to increase production productivity. Suggestions for practical application and direction of future research can be made in the implementation of the body manufacturing technology of the executive body of the geohod, taking into account the optimal geometry of the cutting edge of the body and the type of production of tunneling units.

Study on the synergistic effect of electromagnetic stirring and mechanical reduction on the improvement of the internal homogeneity of high-carbon steel billet

The synergistic effect of electromagnetic stirring (EMS) and mechanical reduction on the improvement of the internal homogeneity has been studied during the continuous casting of high-carbon steel billet. Plant trials were conducted with different parameters both for mold electromagnetic stirring (M-EMS) and final electromagnetic stirring (F-EMS), at the same casting condition and with a unified mechanical reduction process. As the stirring intensity of EMS increases, both the initiation and termination of columnar to equiaxed transition occur at an earlier timing. The results also indicate that, EMS could result in a decline trend for the compactness of the casting billet to a certain extent, especially in the pure equiaxed crystal zone at the core part of the billet. Under the proper intensity setting of M-EMS and F-EMS, the crack susceptibility of the high-carbon steel billet was markedly decreased by enlarging the mixed crystal zone, which is not arrayed with distinct directionality while featured with a relatively high compactness. The effect of EMS on the solidification behavior, and therefore on the crack susceptibility of the high-carbon steel billet was further explained with the numerical simulation. Consequently, a superior inner quality of high-carbon steel billet was successfully achieved with the effective synergy of EMS and mechanical reduction.

Growth and transition of dendrites in steel strands under different electromagnetic stirring methods

In the industrial continuous casting process, some central defects such as shrinkage cavity, porosity, segregation and crack are generated especially at the final solidification zone of steel strands because of the poor fluidity and feeding ability of molten steel in the center of strand, especially for the special steel strand. In this paper, a new type of vertical linear electromagnetic stirring (V-LEMS) was proposed to apply in the casting of Incoloy 825 alloy ingot and investigate the growth and transition of dendrites, distribution of Ti in the special steel, and compare its effect with the generally conventional industrial rotary electromagnetic stirring (R-EMS). The results shown that the growth direction of primary dendrite under R-EMS is perpendicular to the mold wall, but the primary dendrite growth under V-LEMS have present an upstream dendrite growth state. It proves that the V-LEMS can generate a longitudinal circulation convection in the height direction of ingot, which can strengthen the temperature and composition mixing of the upper and lower melts of the ingot and promote the homogenization of the overall melt temperature and composition. The radial macrosegregation of Ti under V-LEMS is slightly higher than that of R-EMS, but R-EMS tends to increase the longitudinal macrosegregation of Ti element. The longitudinal macrosegregation degree of Ti element under V-LEMS is less than that without EMS and with R-EMS. V-LEMS makes the longitudinal distribution of Ti element in Incoloy 825 alloy ingot more uniform. The research results give some beneficial suggestions for improving the central quality of special steel continuous casting billet.

Quality prediction and process parameter importance analysis of cord steel during continuous casting

Continuous casting process control is crucial for enhancing the quality of steel. Center segregation, a key indicator of quality, plays a significant role in ensuring the quality of cord steel. However, the complexities of the continuous casting process, such as data silos, delayed inspections, uneven sampling and non-linearity, pose challenges to making timely improvements in quality. This study introduces an ensemble learning algorithm called LOF-KPCA-XGBoost, which combines Local Outlier Factor (LOF) sample weight, Kernel Principal Component Analysis (KPCA) and eXtreme Gradient Boosting (XGBoost) for online prediction of the center segregation coefficient of continuous casting billets. The algorithm achieves an accuracy of 90% and 98% within ±3% and ±5% relative error, respectively, with an average relative error of 1.6%. A sensitivity analysis method that leverages multivariable feature fluctuations is proposed to identify the process parameters that affect billet quality. The proposed method assists steel enterprises in improving the quality of cord steel billets.

Causes of low casting ability for continuously cast billets from 08Kh18N10T steel and development of measures directed on increase of casting sequence

Causes of low casting ability for continuously cast billets from 08Kh18N10T steel and development of measures directed on increase of casting sequence

Homogenization Path Based on 250 mm × 280 mm Bloom under Mixed Light and Heavy Presses: Simulation and Industrial Studies

This study proposed a new method for homogenizing continuous casting blooms based on solidification simulation calculations and industrial tests. The text describes a theoretical analysis of the solidification route of a cast billet of high-carbon alloy steel (B300A) under different process conditions. It summarizes the changing law of different under-pressure process parameters and under-pressure efficiency. The text also presents a solution to the seriousness of center shrinkage defects in the continuous casting of a large square billet of high-carbon alloy steel with the synergistic control technology of mixed light and heavy mixing under pressure. The study indicates that the center carbon segregation index of a high carbon steel continuous casting billet is 1.05, with a carbon extreme difference of not more than 0.08% and a proportion of 98.4%. Additionally, the center shrinkage is not more than a 0.5 level with a proportion of 99.5%. Meanwhile, the internal quality of cast billets has been improved, allowing for the rolling of large-size bars with a low consolidation ratio. The pass rate for internal ultrasonic flaw detection using the GB/T4162A grade is now higher than 99.95%, significantly reducing process costs and improving production efficiency for continuous casting and rolling.

A new hybrid local radial basis function collocation method for 2.5D thermo-mechanical modelling of continuous casting of steel

This study presents a new strong-form meshless method to solve the thermo-mechanical problem of the solidification process in the continuous casting of steel. A two-dimensional slice that travels in the casting direction is modelled in the Lagrangian system. The newly developed mechanical model is one-way coupled to the thermal model, where the heat flux due to the mould, sprays, rolls and radiation are imposed to solve heat transfer in the strand. The resulting temperature and metallostatic pressure govern the Norton-Hoff visco-plastic model used for computing shrinkage of the solid shell and induced residual stresses. The results are used to estimate critical areas susceptible to hot-tearing formation. The mechanical model uses a generalised plane strain assumption that includes linear strains perpendicular to the slice and enables the computation of the straightening of the strand. The thermo-mechanical model is spatially discretised with a local radial basis function collocation method (LRBFCM). The mechanical part includes a new hybrid method that combines LRBFCM with finite differences for increased stability. The presented work shows how the developed model is used to assess the impact of casting velocity on the solid shell shrinkage and the probability of hot-tearing occurrence in the continuous casting of square billets.