Round Billet Research Articles

Microstructure, billet surface quality and tensile property of (Al 2O 3 + Al 3Zr) p/Al composites in situ synthesized with electromagnetic field

The aluminum matrix composites reinforced by Al 2O 3 and Al 3Zr particulates were fabricated via in situ chemical reaction between Al–15 wt.% Zr(CO 3) 2 systems. In the process of in situ reaction, a low frequency electromagnetic field (EMF) is employed to improve the conditions of reaction between reactants powder and melt. The optimized electromagnetic density of low frequency EMF is 0.025 T. During the direct chill casting process of composites melt, the custom-designed electromagnetic fields are introduced to control the microstructures and improve the billet surface quality. XRD analysis shows that Al 2O 3 and Al 3Zr reinforcement phases have been obtained. The Lorenz force improves the kinetic condition and accelerates the nucleation of endogenetic particulates. Microstructure analysis by SEM indicates that the average size of particulates and grain size of matrix are refined to 0.5–1 μm and 20–40 μm, respectively. The surface quality of round billet is greatly improved by the high frequency EMF. The results of tensile properties test show that the tensile strength of composites in situ fabricated with EMF is 254.6 MPa, which is increased by about 104 MPa and 69.4% compared with those of composites in situ fabricated without EMF.

Continuous casting novel mould for round steel billet optimised by solidification shrinkage simulation

A thermal–mechanical coupled model has been employed to simulate the temperature and strain–stress fields of continuous casting steel billets with ANSYSTM software. In the model, a gap dependent heat transfer condition was introduced to modify the function of heat flux between mould wall and billet surface. The thermal and mechanical properties of materials as well as yield function were used considering the effect of temperature. The shrinkage behaviours of four round billets which solidified within four different petal‐like moulds were studied by indirect coupled method. The simulation results showed that the six‐petal mould is the best one in the four optional moulds. According to the evolution of shrinkage and the principle of compensating, a petal‐like inner cavity and excessive taper were designed for continuous casting of round steel billets. The designed mould was tested in steel factory, which was equivalent or even better than the existing advanced moulds in terms of the surface and inner qualities of billets.

Simulation Study on Horizontal Continuous Casting of Round Copper Billet with Electromagnetic Stirring

In this paper, a comprehensive three dimensional mathematical model is built to investigate the effect of electromagnetic stirring (EMS) on continuous casting process of copper round billet. The electromagnetic field is simulated by ANSYS software and the thermal-flow field is simulated by FLUENT software. The coupling between electromagnetic field and thermal-flow field is implemented by user-defined subroutines. The simulation results have good agreement with the experiment ones. The results show that electromagnetic frequency and current intensity have significant influence on the fluid velocity, temperature gradient and sump depth. The optimum current intensity and frequency are found to be 40A and 10Hz respectively.

Thermomechanical analysis of direct chill casting using finite element method

The transient nature of the start-up phase is the most critical phase in the direct chill (DC) casting during which the quality of the ingot is questioned. The hot crack and cold crack are the two major problems in the DC casting which originate during and after the solidification. In this work, the thermal, metallurgical, and the mechanical fields of DC casting are modeled. The attention is focused on the mushy state of alloy where the chances are high for the hot tearing. The heat conduction and metallurgical phase-change phenomenon are modeled together in a strongly coupled manner. An isothermal staggered approach is followed to couple the thermal and mechanical parts within a time step. Finite element method is used to discretize the thermal and mechanical field equations. A temperature-based fixed grid method is followed to incorporate the latent heat. The mushy state of alloy is characterized through the Norton-Hoff viscoplastic law and the solid phase is modeled through the Garafalo law. An axisymmetric round billet is simulated. The casting material is considered as AA1201 aluminum alloy. It is found that all the components of stress and viscoplastic strain are maximum at the billet center. Further, the start-up phase stresses and strains are always higher than the steady state phase. Therefore, the chances of hot crack formation are higher during the start-up phase and specifically at the billet center. It is proved that through the ramping procedure, the vulnerability of start-up phase can be lowered.

Modeling Solidification Microstructures of Steel Round Billets Obtained by Continuous Casting

The knowledge of the position of the columnar to equaxial transition (CET) is of paramount importance to evaluate the internal quality of continuous casting (CC) products. One way to control the operational CC conditions with the objective of assuring a given quality level is to develop a numerical program able to calculate the local solidification rate (R), the local thermal gradient (G) and the local time of solidification (tf) and to relate these parameters to the CET by means of a predictive model. In the present investigation, the dendritic morphology and the CET transition of three round billets made of a low carbon steel (0.14%C) and produced by CC are characterized, and a computer model is developed to evaluate the R, G and tf-parameters. Referencing the well-known CET transition model developed by Hunt, a simple prediction equation is thus obtained for the steel under study and it is used to propose guidelines for the optimization of the CC operational parameters.

Development of Anti-entrapment Mould Flux which Crystallizes into Melilite as a Main Phase

Two characteristics, high basicity and high viscosity, are required for the anti-entrapment mould flux. However, it had been difficult to apply the high basicity and high viscosity mould flux for a round billet casting because of heat flux fluctuations in the mould.We supposed that the heat flux fluctuations were caused by unstable crystallization of the flux film between the mould and the solidified shell. Assuming that the contaminating constituents which do not compose the main crystal phase bring the unstable crystallization of the flux film, we have researched an adequate main crystal for the high basicity and high viscosity mould flux which has proper composition and melting point. As a result, there was no proper single crystal, but we have found an adequate combination of two crystals, gehlenite and akermanite. These two crystals have similar constructions each other to make a solid solution, melilite. Melilite behaves as a single phase crystal as well as it can take any compositions between gehlenite and akermanite. These properties of melilite diminish restraints on mould flux design.Consequently, we have successfully developed the anti-entrapment mould flux for the round billet casting, achieving a result to reduce mould flux defects effectively.

The tempering behavior of granular structure in a Mn-series low carbon steel

The granular structure in a Mn-series low carbon steel composed of ferrite matrix and martensite–austenite islands does not exhibit temper brittleness which is quite different from common microstructures in steels. This characteristic facilitates the performance optimization through adjusting tempering temperature. A good combination of tensile strength (750–1000MPa) and impact toughness (Aku, 138–154J) can be obtained after quenching and tempering at 400°C for a round billet with 250mm in diameter.

Study on Wall Thickness Eccentricity of Seamless Steel Tube

Wall thickness is measured by a micrometer on shells after piercing, hollows after rolling and tubes after stretch reducing in an Assel production line for seamless steel tubes. The characteristics of wall thickness eccentricity are exhibited, and the heredity and origin of wall thickness eccentricity are analyzed. Finally, the factors influencing wall thickness eccentricity are discussed. The results show that: (1) Wall thickness eccentricity originates from temperature eccentricity in cross section of round billets, comes into being on shells in piercing process, and is passed down to hollows and finally to tubes; (2) Bigger feed angle of piercing, smaller plug diameter and less stability of plug bar will increase wall thickness eccentricity, while complying to the influence of temperature eccentricity on round billets.

Research on the Tendency of Inner Crack during 3-Roll Skew Rolling Process of Round Billets

Concerning the 3-roll skew rolling process of round billets, a 3-D thermo-mechanical coupled simulation is performed with the aid of commercial FE code MSC.SuperForm. The influence of the feed angle and inlet cone angle of the roll on the strain and damage filed are investigated. It is found that the distribution pattern of the equivalent plastic strain in the longitudinal section of the billet presents U-shape, and that the feed angle and inlet cone angle of the roll make difference in the gradient of deformation intensity in radial direction of round billet. The ring-shaped distribution of the damage field in transverse cross section of the billet indicates a high tendency for the ring-shaped inner crack to occur, instead of the center crack appearing in 2-roll skew rolling of round billet. The results show that the critical parameters to control the ring-shaped crack during the 3-roll skew rolling process are the feed angle and inlet surface cone angle of the roll. It should be avoided to use too large feed angles so as to reduce the tendency of annular inner crack in the actual rolling of high-alloy steels with poor hot workability.

Mathematical Modeling of Hot Tearing in the Solidification of Continuously Cast Round Billets

Billets produced by continuous casting sometimes show the presence of subsurface cracks that can compromise the quality of the final product. The presence of these cracks is revealed by Baumann prints of billet cross sections in which the chill zone is visible and the short radial cracks are located only where the chill zone thickness is thinner. This experimental finding induces the hypothesis that cracks are formed as a result of the presence of unevenness in the mold heat extraction around the billet perimeter. Cracks start to open in the dendritic front in regions where the shell growth in the mold is slower. The study presented in this article focused on steels with a sulfur content of about 300 ppm. The Baumann prints taken from billet samples of numerous different heats allowed detecting the presence of subsurface cracks and their location nearby visible chill zone thinning areas. To understand the mechanisms of crack formation and to define the possible corrections, a modeling activity has been carried out using the finite element technique on 148-mm diameter billets continuously cast at TenarisDalmine (Dalmine, Italy). The model performs a two-dimensional thermomechanical analysis of the solidification in the mold and within about 4 cm below the mold exit, along which the shell surface is cooled only by radiation to the environment, before the sprays of the first ring impact on the strand. The model includes the contact of the shell with the mold inner surface, which moves according to taper and distortion (this last part is calculated by means of a separate mold model); the steel creep behavior; the calculation of the heat transfer through the gap depending on the local mutual distance between the two surfaces; the effect of the liquid steel fluid dynamics on the solidification growth as a result of the temperature distribution; and the calculation of a hot tearing indicator represented by the porosity fraction caused by mechanical strains applied at the dendrite roots. From the simulation results, it is concluded that subsurface cracks are generated in the space between the mold exit and the first cooling ring; the involved mechanisms of formation also are withdrawn. Nucleation of MnS precipitates of large dimensions is an additional cause of defectiveness in controlled sulfur steels. As a final conclusion of this work, the most important actions to eliminate subsurface cracks are derived.

Electromagnetic Continuous Casting Process for Near Net Shape Aluminum Alloy Billet

A new method and apparatus for the fabrication of high-quality, near net shaped aluminum alloy billets is developed by the combination of continuous casting and electromagnetic casting/stirring technique. Traditional machine for continuous casting process involves round, square and rectangular billets; therefore it requires additional multistep forging process to fabricate final products of complicated shape. A new process for the fabrication of near net shaped aluminum billets offers some advantages: the process of extrusion and forging is simplified and the cost of plastic working can be greatly reduced. In order to reduce the peculiar problems such as surface crack and internal defect due to inhomogeneous heat transfer of solidified billets, electromagnetic casting and stirring technique were adopted. The effect of electromagnetic field was compared by observing the microstructure of billets. Grain refinement of aluminum billet was clearly observed by applying electromagnetic field to continuous casting process.

English

The extrusion of section from round billet poses a great challenge for theoretical modeling of the process using upper bound method. The greatest difficulty in three-dimensional upper bound method is to determine kinematically admissible velocity field. The SERR (Spatial Elementary Rigid Region) technique is fairly applicable for analyzing extrusion of sections having re-entrant corners. A modified version of SERR technique has been used for extrusion of hexagon sections from round billet through a linearly converging die. The circular cross section of the round billet is approximated by a regular polygon of equal area. The extrusion pressure has been computed for different boundary condition at the die billet interface. The optimum die geometry has been determined. An extrusion test rig is designed and all extrusion is carried out using round billets for extrusion of hexagonal sections using converging dies. The experimental results are validated with SERR analysis.

Three-Dimensional Magnetohydrodynamic Calculation for Coupling Multiphase Flow in Round Billet Continuous Casting Mold With Electromagnetic Stirring

A 3-D combined finite element-finite volume for magnetohydrodynamic (MHD) calculation method considering the coupling flow field, heat transfer, and inclusion trajectory was developed, and the flow characteristics of molten steel and inclusion trajectory in round billet mold using electromagnetic stirring (EMS) were numerically investigated. The calculation results of magnetic field and temperature in the mold are in a good agreement with the measured data. The influence of EMS on the turbulent flow and temperature in the mold is estimated by the model, which shows that EMS has an obvious effect on the flow and temperature distribution of molten steel, and the macrostructure of the billet.

Development of Swirling-flow Submerged Entry Nozzles for Slab Casting

We began development of swirling-flow submerged entry nozzles in 1997 as a fundamental and effective measure for controlling the flow pattern in continuous casting molds. As a first step, we developed a swirling-flow submerged entry nozzle for round billet casting at the Wakayama works. We then began developing swirling-flow submerged entry nozzles for slab casting. The main purpose of the present work was to demonstrate that the formation of swirling flow in submerged entry nozzle improves productivity and the quality of products in continuous casting. We examined swirling-flow submerged entry nozzles with a swirl blade in these main bodies because such an arrangement is the easiest way to apply swirling flow to submerged entry nozzles in continuous casters without investment by facilities. We had only to change the submerged entry nozzle in the experiment. Swirling-flow submerged entry nozzles for slab casting were developed and their operation examined at the Wakayama and Kashima works. It was found that the proposed submerged entry nozzles increased the casting speed and improved the surface quality of slabs and steel sheets.

Three Dimensional Upper Bound Modelling for Extrusion of Round-to-Octagon Section Using Linearly Converging Die

The extrusion of section from round billet poses a great challenge for theoretical modeling of the process using upper bound method. The greatest difficulty in three-dimensional upper bound method is to determine kinematically admissible velocity field. The SERR (Spatial Elementary Rigid Region) technique is fairly applicable for analyzing extrusion of sections having re-entrant corners. A modified version of SERR technique has been used for extrusion of octagon sections from round billet through a linearly converging die. The circular cross section of the round billet is approximated by a regular polygon of equal area. The extrusion pressure has been computed for different boundary condition at the die billet interface. The optimum die geometry has been determined.

Investigation of Process Parameters for the Backward Extrusion of Arbitrary-Shaped Tubes from Round Billets Using Finite Element Analysis

Process simulation for the backward extrusion of internally arbitrary-shaped tubes from circular billets is presented in this article. ABAQUS/Explicit finite element method has been used to analyze the problem. This kind of analysis has been done before using analytical methods such as the upper bound theorem. However, the FEM solution presented here is the first of its kind. Values of stress, strain, and spatial velocity at different points in the deformation field were obtained. To observe the flow of the material during the process, grid deformations were also produced for the backward extrusion using the FEM package. Circular shape for the initial billet and arbitrary shapes for the final tube’s cross sections were considered and FEM solutions were given for each. The shapes considered were elliptical, rectangular, and circular-shaped tubes and circular billets. The variation of extrusion load for the backward extrusion process was obtained for different values of reduction of area, aspect ratio, and friction factor. Also, the effect of these parameters on velocity field and free surface configuration were investigated in this simulation. The results produced from this work were compared with the theoretical and experimental results of other workers and good agreements were observed and some improvements in some of the results were also seen.

Effect of electromagnetic stirring in mold on the macroscopic quality of high carbon steel billet

An industrial plant trial for optimizing the process parameters in a round billet continuous casting mold with electromagnetic stirring (M-EMS) was performed, in which the influences of stirring parameters with M-EMS on the solidification macrostructure of high carbon steel were investigated. The results show that the billet quality is not well controlled under the condition of working current and frequency with EMS, in which the subsurface crack of grade 1.0–2.0 ups to 38.09%, the central pipe of grade 1.0–1.5 reaches to 14.28%, and the central porosity of grade 1.5 is 14.29%. The parameters of current 260 A and frequency 8 Hz as the final optimum scheme has a remarkable effect for improving the macroscopic quality of billet, in which the subsurface crack, central pipe and skin blowhole are all disappeared, and the central porosity and carbon segregation are also well improved.

Three-dimensional analysis of round-to-angle section extrusion through straight converging die

The increasing interest in the modeling of metal-forming processes in recent years has brought the development of different analytical and/or numerical technique. However, due to the complexity nature of the problem, most of the attempts are made with plain strain assumptions. Among the different techniques used, the upper bound method is a convenient tool for evaluating the rate of work in processes involving predominantly plastic deformation of rigid/perfectly plastic material. The present study is an endeavor to remodel and apply the spatial elementary rigid region technique for analyzing extrusion of angle-section bars from round billets through the linearly converging die. Optimized values of the nondimensional average extrusion pressure at various area reductions have been computed and compared with experimental results. It is observed that the proposed technique can be used effectively with adequate accuracy to predict the optimal die geometry which requires a minimal forming stress at different reduction of areas and friction conditions.

An approximate load estimation method for three dimensional metal forming problems

Slip line field solutions have been presented only for plane strain and axisymmetric problems in the literature. In fact due to the very nature of the differential equations for the slip line field theory, it has never been possible to apply the theory to three dimensional problems. In this paper a three dimensional solution is presented for metal forming processes using an approximate load estimation method based on the slip line field theory. This has been done by extending the axisymmetric solution and modifying it in order to apply it to the three dimensional case. Using the idea of stream lines and stream surfaces, the deforming region has been defined. A generic stream surface was developed which was a ruled surface with a three dimensional shape. The slip line field theory could only be applied to flat surfaces in the case of axisymmetric problem. Here using some assumptions an approximate load estimation method was developed so that it was applied to the three dimensional stream surfaces and hence to the deforming region under considerations. This method was applied to the forward extrusion of elliptical sections from round billets. Experiments were also carried out by authors to verify the theory. The results obtained from the new formulations were compared to the results obtained from other analytical, numerical and experimental methods. It was shown that there exist good agreements between these results.

Rational argon stirring for a 150-t ladle furnace

Based on the principle of similarity, water modeling experiments were carried out for a 150-t ladle furnace. The rational parameters of argon stirring were determined as the optimized positions of nozzles, top area of the porous brick, and gas flow rate. The following results are obtained: 1) the optimized positions of two nozzles are at 0.333 R ( R refers to the radius of the ladle at bottom) with an angle of 135°; 2) the top diameter of the porous brick should be 130 mm; 3) the flow rate of gas should be 25.0-30.6 m 3/h. The plant trial shows that the improved process is effective in enhancing the cleanliness of round billets. The total oxygen content, microinclusions, and macroinclusions in round billets are reduced by 12.5%, 8.2%, and 20%, respectively.