Cast Billets Research Articles

Evaluation of Approaches of Numerical Modelling of Solidification of Continuously Cast Steel Billets

Evaluation of Approaches of Numerical Modelling of Solidification of Continuously Cast Steel Billets

Modelling on Inclusion Motion and Entrapment during the Full Solidification in Curved Billet Caster

Inclusions entrapped by the solidifying front during continuous casting would deteriorate the properties of the final steel products. In order to investigate the inclusion motion and the entrapment during the full solidification in curved billet caster, the present work has developed a three-dimensional numerical model coupling the flow, solidification, and inclusion motion. The predicted result indicates that the inclusion distribution inside the liquid pool of the mold is not perfectly symmetrical. Furthermore, the motion and the entrapment of micro inclusions in the mold are mainly affected by the molten steel flow pattern, however, those of macro inclusions depend both on the molten steel flow pattern and the buoyancy force of the inclusions. In the curved part of the strand, macro inclusions shift to the solidifying front of the inner radius as time goes on, while the solidifying front of the outer radius cannot entrap inclusions. The distributions of inclusions smaller than 5 μm in the solidified strand are even. However, for inclusions that are larger than 5 μm, their distributions become uneven. To validate the model, measurement of the strand surface temperature and the detection of inclusions in samples obtained from a plant have been performed. Good agreement is found between the predicted and experimental results.

Behavior of Structural Defects of Already-Deformed Continuous-Cast Bar on Rolling

In the continuous casting of steel ingots, the most significant trend over the last few decades has been the partial transfer of deformation processes from the region of complete solidification (the rolling mill) to the region characterized by a two-phase solid–liquid state (the continuous-casting line). However, such two-stage deformation of the continuous-cast ingot entails changes in the physical modeling of the behavior of surface and interior defects in subsequent rolling. In particular, modifications are required in selecting the geometry and spatial orientation of the defects. In the present work, the influence of the surface-defect orientation and central macrostructure (pore content) of bar billet deformed in the continuous-casting line is investigated by means of laminar physical models. The deformation conditions of reduced-scale (1: 5) continuous- cast billet are studied experimentally in two rolling configurations: (1) the use of smooth rollers to simulate groove-free rolling in the first two stands of the cogging group in the 350 continuous medium-bar mill; (2) rolling in the first and second pairs of straight grooves in the cogging stand of the 500/370 mill at PAO Donetskii Metallurgicheskii Zavod. Since this is a multivariant problem, a universal design has been developed for the physical model, so as to simulate the spatial configuration of both surface and internal defects. The research shows that, in rolling the physical models with an extension coefficient greater than 2.0 and practically 60° inclination of the simulated defects to the rolling axis, their complete elimination is possible. In turn, decreasing the inclination to 30° facilitates greater extension of the simulated defects and only slightly reduces their width. When the inclination of the simulated defects to the rolling axis is 90° (complete lack of coaxiality), broadening of the defects and their compression to the initial length is only observed after 90° rotation. The experimental data provide insights regarding the elimination of internal defects (pores) in the metal as a function of the total extension, the inclination of the defects’ longitudinal axis to the rolling direction, and their distance from the longitudinal–transverse symmetry plane.

A new experimental apparatus for emissivity measurements of steel and the application of multi-wavelength thermometry to continuous casting billets.

An experimental apparatus has been designed for measuring the emissivity of a steel surface in both vacuum and oxidation atmosphere. The sample is heated with the method of electromagnetic induction in order to ensure the temperature uniformity. The radiance emitted from a sample is measured using a fiber-optic Fourier transform infrared spectrometer. Using this unique apparatus, we investigated the spectral (2-6 μm) and directional (0°-86°) emissivity of stainless steel 304 with different degrees of surface oxidation at temperatures ranging from 800 to 1100 °C. The experimental results show that the emissivity increases slightly with increasing temperature, which accords with the Hagen-Rubens relation. The emissivity increases rapidly at the initial stage of oxidation, but gradually reaches to a constant value after 20 min. In addition, the directional emissivity has a maximum value at the measuring angle of about 75°. The maximum uncertainty of emissivity is only 3.0% over all the measuring ranges, indicating that this experimental apparatus has a high reliability. In order to measure the surface temperature of casting billets based on multi-wavelength thermometry, the bivariate emissivity function with the two variables, wavelength and temperature, is determined. Temperature measurement results based on our technique are compared with those from common dual-wavelength radiation thermometry. Our approach reduces the measured temperature fluctuation from ±20.7 °C to ±2.8 °C and reflects the temperature variation with the changes of production parameters in real time.

Study of strength properties of semi-finished products from economically alloyed high-strength aluminium-scandium alloys for application in automobile transport and shipbuilding

Abstract The results of a study on the strength of rolled products from aluminium alloys doped with scandium under various processing conditions of hot and cold rolling are presented. The regularities of metal flow and the level of strength of deformed semi-finished products from aluminum-scandium alloys are established, depending on the total degree of deformation and the various modes of single reduction during rolling. It is shown that when using one heating of a cast billet to obtain high-quality semi-finished products, the temperature during the rolling process should not be lower than 350-370°, and the total degree of deformation does not exceed 50-60%. It was found that the semi-finished products from alloys with a content of scandium in the range 0.11-0.12% in the deformed state had elevated values of ultimate tensile strength and yield strength of the metal, which allows them to be recommended for industrial production of sheet metal products.

Numerical Simulation of Macrosegregation Impurities in the Solidifying Continuous Casting Steel Billet

<p>In this study, new theoretical conceptions have been developed about an impurity segregation mechanism at the time of alloy solidification considering present microvolumes with different chemical compositions during alloy solidification. It has been concluded that this conception allows to establish and optimize technologic parameters that influence the production of the main types of macro-heterogeneity. The derived model conceptions have confirmed the final condition of real continuous casting billets by using the advanced analyzing methods. </p><p>Highlights </p><p>· The quasi-equilibrium theory used to study the hardening processes of alloys has been expanded and improved.<br />· The development of a numerical model for macrosegregation impurities in solidifying continuous casting billet is suggested.<br />· The adequacy of the developed model is checked under the industrial conditions using comparison theoretical<br />· calculations and practical data.<br />· The results and developments that are obtained are discussed.</p>

Analysis of Chip Generation During Bar Rolling

Bar rolling is a semi-continuous rolling process involving a series of rollers, where a cast billet is shaped into the final TMT bar. In these mills, low-thickness bar rolling (< 20 mm) is prone to cobbles, due to several operational reasons, which affects productivity. One major contributor is blockage of slitters and no-twist mill grooves due to excessive chip formation from the rolled bars. In the present work, a detailed investigation was carried out to identify the causes of chip formation through visual and metallographic analysis of the bar samples collected at different stages of rolling. It was found that the chipping was predominantly on a specific side of the bars and was related to quarter distance segregation in the cast billets due to higher sulfides and the use of powders for mold lubrication. The ‘square–round–oval-dog bone’ pass design exposed the lowest quality part of the billet at the slitter, leading to chip formation near the slit surface. Control of sulfur in steel and the use of oil lubrication at the caster reduced the segregation in the billets and subsequently chip off defects at the rolling mill.

Producing Structural-Steel Bar from Continuous-Cast Billet

The expanded use of continuous-cast billet in the production of structural-steel bar is considered. The quality of 135 × 135 mm continuous-cast billet produced on a standard continuous-casting machine and the bar derived from it is evaluated. At more recently built plants, the production of quality bar from continuous- cast billet requires total extension of the order of 6–7. On the basis of the analysis developed in the present work, it is possible to determine the maximum critical bar cross section such that the required properties are ensured.

Control over the Formation of Continuously Cast Billets with the Use of Vibrating Molds in Machines for Continuous Casting

For AD31 aluminum alloy, we study the influences of the shape of the heat-removing surface of the mold and its vibration on the formation of cast billets. It is shown that both factors significantly decrease the area of columnar crystals, lead to grinding of the macro- and microstructures of billets, and improve the properties of the metal. It is shown that the vibration treatment of a billet almost removes the anisotropy of properties over its zones.

Theoretical Foundations of the Design of a Lever Mechanism of Oscillations of the Mold of a Sorting Machine for the Continuous Casting of Billets

We consider specific features of the design of the lever mechanism of oscillation for the mold of a radial sorting machine with continuous casting of billets under the conditions of the maximum correspondence of the vibration motion of the mold with the axis of extrusion of ingots from this mold. It is shown that the traditional kinematic scheme of the oscillation mechanism does not guarantee high accuracy of the codirectional motion of the mold relative to the technological axis of the channel of this machine.

Physical Modeling Technological Regimes of Production Deformed Semi-Finished Products from Experimental Aluminium Alloys Alloyed by Scandium

The combination of weldability, corrosion resistance and sufficient strength make it possible to use deformed semi-finished products from the Al-Mg system alloys for sheathing ships' hulls, in car, aircraft and rocket construction, as well as in other areas of industry. To increase the strength characteristics, it is promising to alloy them with small additives of metals such as titanium, zirconium, scandium, and others. In this paper, studies were carried out to obtain deformed semi-finished products (strips, rods and wires) from aluminum alloys in which the scandium content varied from 0.1 to 0.25%. For this purpose, various metal treatment conditions simulated in the laboratory of School of Non-Ferrous Metals and Material Science in Siberian federal university. For the preparation of sheet semi-finished products regimes of hot and cold rolling of a cast billet simulated from a thickness of 40 mm to a thickness of 3 mm. For the preparation of sheet semi-finished products, the modes of hot and cold rolling of the cast billet from a thickness of 40 mm to a thickness of 1-3 mm have been modeled. To produce a welding wire with a size of 2×2 mm, a combined casting and rolling-extruding (CCRE) process was simulated to produce a 9 mm billet and its further rolling in square gauges. Rods with a diameter of 9 mm were produced on a combined processing unit, and wire on a rolling mill with a roll diameter of 130 mm. In accordance with the research program, the mechanical properties of hot-deformed, cold-deformed and annealed sheet semi-finished products were measured. Then the semi-finished products were welded together with the obtained wire and the quality and properties of the welded joint and their corrosion resistance were evaluated. Research results are currently used to develop industrial technologies for the production of sheets and plates from experimental alloys of the Al-Mg system doped with scandium.

Development of a New Horizontal Continuous Casting Machine Construction for Nonferrous and Precious Metal Billets

The work is devoted to development of a new design of horizontal continuous billet casting machine (HCBCM) for non-ferrous and precious metals. The possibility of calculation and design of horizontal casting machine elements by means of computer simulation using the software created is demonstrated. Based on the proposed methods of calculation and design as well as analysis of mathematical modeling results, new designs of HCBCM elements are created that enhance the efficiency of the machine. Appraisal trials of HCBCM structural elements created are performed successfully to measure the effectiveness of this work and introduction into production.

Thermal and Fluid‐Dynamic Optimization of a Five Strand Asymmetric Delta Shaped Billet Caster Tundish

In this work, the multiphase mathematical simulation (steel‐slag‐air) is performed in order to optimize the fluid dynamics and the homogenization temperature in an asymmetric delta‐type billet caster tundish. The performance of the tundish emulates, when a change of ladle occurs, for which are considered the losses of heat through its frontiers as well as the temperature drop of the steel at the input by means of a user defined function (UDF). Also, a comparison is made for the removal of non‐metallic inclusions using standard entrapment conditions at the steel‐slag interface, as well as a user‐defined function (UDF). This UDF takes into account the multiphase interaction with the critical velocity of the particles that approach this interface. For this analysis, it is necessary to determine the opening area of the slag layer. The results of the model for the temperature drop are validated by means of experimental measurements in plant, which show a good correspondence in the obtained data. Finally, the proposed design of flow modifiers favorably influences the fluid dynamics pattern, allowing a better thermal homogenization, and a substantial cleaning of the steel at its output from the tundish.

Influence of Extrusion Temperature on the Aging Behavior and Mechanical Properties of an AA6060 Aluminum Alloy

Processing of AA6060 aluminum alloys for semi-products usually includes hot extrusion with subsequent artificial aging for several hours. Processing below the recrystallization temperature allows for an increased strength at a significantly reduced annealing time by combining strain hardening and precipitation hardening. In this study, we investigate the potential of cold and warm extrusion as alternative processing routes for high strength aluminum semi-products. Cast billets of the age hardening aluminum alloy AA6060 were solution annealed and then extruded at room temperature, 120 or 170 °C, followed by an aging treatment. Electron microscopy and mechanical testing were performed on the as-extruded as well as the annealed materials to characterize the resulting microstructural features and mechanical properties. All of the extruded profiles exhibit similar, strongly graded microstructures. The strain gradients and the varying extrusion temperatures lead to different stages of dynamic precipitation in the as-extruded materials, which significantly alter the subsequent aging behavior and mechanical properties. The experimental results demonstrate that extrusion below recrystallization temperature allows for high strength at a massively reduced aging time due to dynamic precipitation and/or accelerated precipitation kinetics. The highest strength and ductility were achieved by extrusion at 120 °C and subsequent short-time aging.

MASTERING THE PRODUCTION OF A CONTINUOUS CASTING BILLET DIAMETER 200 MM FROM CHROME-MOLYBDENUM STEEL GRADES FOR THE PRODUCTION OF SEAMLESS PIPES AT THE OJSC «BSW – MANAGEMENT COMPANY OF HOLDING «BMC»

Growth in demand for drilling and perforated pipes in the Russian Federation and the USA requires an increase in the production of seamless pipes. In turn, the specific operating conditions of the pipes present special requirements to the product for strength and resistance in aggressive media. This article describes the experience of mastering the production of continuous casting billets from chromium-molybdenum steel grades at the OJSC «BSW – Management Company of the Holding «BMC».

Improvement in billets quality from billet caster by roller suspension of secondary cooling zone stiffening

Presently, continuous casting machines are widely used in metallurgical industry for production of high quality billets. And the maximum economic and resource-saving effect is achieved by the use of continuously casting small-section billets. Proceeding to the continuous casting has tightened the requirements for product quality and the main objective has become to determine the factors influencing the billet quality. It is necessary to design competently a zone of secondary cooling, for improvement of quality of production. Having changed her design and as a result the loadings operating on a zone of secondary cooling will decrease and the rigidity of a design will increase.

ВЛИЯНИЕ ХАРАКТЕРА И СТЕПЕНИ ЛЕГИРОВАНИЯ НА СКЛОННОСТЬ К ПРОЯВЛЕНИЮ ЛИКВАЦИИ ЛИТЫХ ЗАГОТОВОК ДЕФОРМИРУЕМЫХ АЛЮМИНИЕВЫХ СПЛАВОВ

Production of high-quality semi-finished product from aluminum wrought alloys for subsequent deformation (rolling, stamping or pressing) is provides by obtaining the initial defect-free cast billet. The level of mechanical properties of alloys in the cast and heat-treated state is determined mainly by the internal structure of the grains, therefore one of the main parameters affecting the quality of the cast billet for subsequent plastic deformation is the manifestation of chemical heterogeneity of grains in the content of alloying elements or segregation. In this work, the alloys Al–Mn, Al–Mg and duralumin are investigated according to the method previously proposed by the same authors. These alloys can be conventionally chosen as model ones, to study the influence of the alloying character on the tendency of wrought aluminum alloys to manifest segregation effects in the cast state. Comparing the local content of alloying elements on the axes of dendrites with the brand composition of the alloys, a significant discrepancy was noted. This discrepancy is a measure of the inhomogeneity of the alloy. Taking the degree of deviation of the local composition from the brand as the value characterizing the degree of inhomogeneity of cast alloys Al–Mn, Al–Mg and duralumin, the values of the average homogeneity coefficient of these alloys are calculated. The homogeneity criterion, determined for the aluminum base of alloys, shows the dependence of the degree of homogeneity on the change in the nature of alloying and the content of alloying elements. Significant differences between the local content of alloying elements in the axes of the dendrites and the grade composition of the alloys were revealed.

НАПРАВЛЕНИЯ РАЗВИТИЯ ПРОИЗВОДСТВА МЕЛКОСОРТНЫХ ЗАГОТОВОК ДЛЯ ПОЛУЧЕНИЯ ДЛИННОМЕРНОГО ПРОКАТА

The aim of the work is to study the technological features of the transfer of metallurgical enterprises to the production of small-size and wire metal products from continuously cast billets. The main parameters of the rolling technology are considered: the size of the billet, the choice of the location of the continuous casting machine, the transfer scheme of continuously cast billets to small- size and wire mills. It is shown that when using a continuously cast square billet with a size of 130x130 mm and 150x150 mm, direct combination of a continuous casting machine with a rolling mill is almost impossible due to the difference in the speed of continuous casting and the roughing group of the mill. The performed calculations show that the scheme of cutting the billets and combining with the intermediate furnace is technologically feasible, however, further heating of the billets leads to significant energy losses. It has been established that an effective option for combining the continuous casting machine with a rolling mill is to use a complex of equipment with a furnace-thermostat for a billets 120 m long. This flowchart reduces the energy consumption for heating the billets by at least 53%. The proposed technology of combining the continuous casting machine with a rolling mill will provide metal savings by reducing the thickness of the scale to 0.4-0.73 mm (an average of 1.1% of the mass of the billet), improve its quality by reducing the depth of the decarburized layer from 1.1 mm to 0.3 mm. The technology provides for the transportation of liquid steel in the ladle from the steel-smelting shop, casting on the continuous casting machine, identification of defects in the billets in a hot condition, supply of the billets with a temperature of 8500С to high-temperature furnaces for heating and subsequent rolling.

Study of feature extraction method of multi-information source for continuous casting process parameters

The control of the roll gap of the segment is one of the key links to ensure the quality of cast billet. In this paper, the big data in traditional continuous casting production operations is studied through in-depth experimental comparative analysis of linear and nonlinear dimension reduction method. The method is suitable for continuous casting to obtain the data of the dimension reduction. The method of principal component analysis is improved by using standardized data increment method. A faster and more efficient method of dimension reduction is obtained when the unrelated data, training time and reconstruction error are removed. Actual data simulation results show that this method is more efficient and suitable for continuous casting than any other dimension reduction method.

Importance of the experimental investigation of a concasting technology

The solidification and cooling of a continuously cast billet, slab or cylinder, generally of a concasting and the simultaneous heating of the mold is a very complicated problem of three-dimensional (3D) transient heat and mass transfer. The solving of such a problem is impossible without numerical models of the temperature field of the concasting itself which it is being processed through the concasting machine (caster). The application of the numerical model requires systematic experimentation and measurement of operational parameters on a real caster as well as in the laboratory. The measurement results, especially temperatures, serve not only for the verification of the exactness of the model, but mainly for optímization of the process procedure: real process → input data → numerical analyses → optimization → correction of real process. The most important part of the investigation is the measurement of the temperatures in the walls of the mold and the surface of the slab in the zones of secondary and tertiary cooling.