Casting Direction Research Articles

Reduction of Elongation Anisotropy of Roll-Cast Strips by Cold Rolling and Annealing

Roll-cast strips are usually cold-rolled and annealed before forming. The elongation of these strips is known to be different between the casting and lateral directions after thinning by cold rolling. Whether cold rolling is the main factor determining the anisotropy of the elongation is not clear. Likewise, it is not clear whether the elongation anisotropy can be reduced by conventional cold rolling. Roll-cast strips have centerline segregation, forming a so-called band area. The relationship between the anisotropy of the elongation and these defects is not clear. A strip cast using an unequal-diameter twin-roll caster also has a band area but a strip cast using a single-roll caster equipped with a scraper has no centerline segregation or band area. Strips made this way were cold-rolled in the casting and lateral directions, and tensile testing was conducted on the cold-rolled and annealed strips. In this study, the ability of conventional cold rolling and one-time annealing to reduce the elongation anisotropy of a cast strip was clarified. Moreover, the influence of the band area and Fe impurities on the elongation anisotropy was determined.

Multi-gradient structures by cold extrusion of strongly textured continuously cast commercially pure aluminum

During extrusion, the material is subjected to a heterogeneous deformation that results in the formation of gradients of microstructure and thus mechanical properties. In this study, using continuously cast commercially pure aluminum as a reference material, we show how a cast structure with coarse columnar grains affects the formation of these gradients during extrusion at room temperature. Characterization of the initial material as well as the extruded round bars by optical and electron microscopy, X-ray diffraction as well as by means of mechanical testing documents the formation of four characteristic annular sections. For extrusion along the casting direction there is a <100>/<111> double-fiber textured center with lowest hardness, followed by a <111> single-fiber textured ring with a hardness plateau, a double-fiber textured region with grains arranged alternatingly in an iris-like shape, and an (ultra-)fine grained surface layer with highest hardness. For extrusion opposite to the casting direction we find similar characteristics of the center section. With increasing distance from the center follow another double-fiber textured section with increasing hardness, a <111> single-fiber textured ring with nearly homogeneous hardness and a surface layer with a slightly rotated <111> fiber and highest hardness. The key finding is that the macroscopic anisotropy of the cast material, resulting from the grain size, crystal orientation and growth direction of the columnar grains, determines the local material flow during extrusion and thus leads to the formation of these different complex multi-gradient macrostructures that may provide unique properties for complex applications such as light-weight safety-relevant components.

Thermoelectric enhancement in perovskite type textured Me0.85TiO3 ceramics by synergistic high-entropy and microstructure manipulations

Enhancing the figure-of-merit (ZT) for thermoelectric ceramics essentially needs strategies that aim to concurrently optimize electron and phonon transport properties to decouple their coupling relationship. This work developed 〈001〉 -textured Me0.85TiO3(Me = La, Sr, Ba, Ca) ceramics (LSBC-T) with a texture fraction of 92 % fabricated by a tape casting process combined with template grain-growth method, in which 10 wt% (001) oriented plate-like SrTiO3 serves as template seed and A-site deficient high-entropy (La0.25Sr0.25Ba0.25Ca0.25)0.85TiO3 composite was used as matrix material. A peak ZT of 0.27 was attained at 1073 K in the sample parallel to the tape casting direction which was twice the ZT = 0.13 of the non-textured sample. Quantitative analysis of atomic displacement disorder of A-site elements would provide an atomistic-scale understanding of grain orientation evolution with high texture degree and the low thermal conductivity of 1.79 W/(m‧K) at 1073 K. The complex multi-scale defects consist of cation and oxygen vacancies, edge dislocations, parallel grain boundaries, phase interfaces, nanoscale metal/inorganic coexisting clusters, and metal Bi sandwich layer, which act as additional phonon scattering centers while affecting carrier transport, covering all frequency phonons (100 GHz-15 THz). In addition, multi-scale parallel interfaces, including atomic-scale crystal (00l) plane of SrTiO3 seed, nano-scale “core-shell” interface parallel to the (00l) plane, metal Bi particle forming a sandwich layer in SrTiO3 seed, and “brick-wall” textured grain boundaries, make the electrical and thermal conductivity exhibiting obvious anisotropy in this LSBC-T high-entropy textured ceramics. By utilizing texture engineering in high-entropy systems, this work provides a theoretical foundation and technical support for the advancement of microstructure manipulations to reduce the inherent lattice thermal conductivity, achieve electrical and thermal conductivity anisotropy to decouple the electron–phonon coupling relationship, and thereby enhance thermoelectric properties.

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.

Investigation of Solidification Heat Transfer in Slab Continuous Casting Process Based on Different Roll Contact Calculation Methods.

The heat transfer of a slab is significantly influenced by roll contact during the continuous casting process. The influence of roll contact calculation methods on the predicted heat transfer results has not been previously investigated. In this work, the non-uniform solidification of the wide-thick slab was studied with a 2D heat transfer model using real roll contact method (R. method) and equivalent roll contact method (E. method). The predicted slab surface temperature and shell thickness were verified with the measured results of the infrared camera and nail shooting experiments, respectively. Then, the predicted heat transfer results (including the slab surface temperature, mushy region length, and solidification end position) for the wide-thick slab with different thicknesses and different casting speeds were calculated using the E. method and R. method, and the influence of these two roll contact methods on the predicted heat transfer results was discussed for the first time. The results show that both these two roll contact methods could be applied to accurately predict the slab surface temperature without considering the transient temperature dips in the roll-slab contact regions. However, the deviation of the predicted mushy region length and solidification end position using the E. method are obvious. Compared with the R. method, the predicted mushy region length obtained using the E. method is larger and the solidification end obviously subsequently moves along the casting direction.

Interfacial bond behavior between normal OPC concrete and self-compacting geopolymer concrete enhanced by nano-SiO2

This study investigated the interfacial bond performances between ordinary Portland cement concrete (OPCC) and self-compacting geopolymer concrete (SCGC). The studied factors include nano-SiO2, repair material type, curing time, casting direction, and interface pretreatment method. The interfacial bond performances were assessed by Bi-surface shear and drying shrinkage tests. The evolutions in elemental compositions, hydration products, and microstructure in the matrix and interface were verified by BSE/EDS, XRD, and FTIR tests, respectively. ANOVA analysis was conducted to quantitatively analyze the influences of each factor from a statistical approach. The results demonstrated that the bond strength of SCGC increased by 24.5% to 31.7% compared to conventional OPCC. Meanwhile, geopolymers exhibited more compact microstructures but higher drying shrinkage (εsh,u=891 µε). While nanofillers significantly amplified the cracking potential of geopolymers, which was attributed to the higher early-stage autogenous shrinkage instead of drying shrinkage. The SCGC showed a high enrichment degree of calcium at the interface, indicating that more calcium-rich products were formed. In contrast, the use of nano-SiO2 in SCGC caused the enrichment of Na, Al, and Si at the interfacial regions, which provided extra nucleation sites for the polymerization of (C, N)-A-S-H gels. The nano-SiO2 enhanced the intensity of the hydroxide ion and Si-O-T band and promoted the formation of (C, N)-A-S-H gels. The ANOVA analysis proved that the repair material, nano-SiO2, and interface treatment were significant factors to affect the interfacial bond strength. In addition, geopolymer-based repair materials were less sensitive to the casting direction, which differed from the conventional self-compacting OPCC.

Self-Consolidated Concrete-to-Conductive Concrete Interface: Assessment of Bond Strength and Mechanical Properties

In this paper, the mechanical properties and bond strength of composite samples that consist of a conductive concrete (CC) layer and a self-consolidated concrete (SCC) layer are investigated. The bond strength study includes two parameters: (1) surface preparation and (2) casting and testing directions. The surface preparation study shows that, compared to the other methods in this study, the shear key method is the most suitable surface preparation method to fully utilize the CC in a composite. Moreover, the casting direction study reveals that the strength is heavily dependent on the type of test used along with CC’s layer positioning. The flexural strength study confirms that positioning the CC mix in the tensile region is beneficial since it can increase the flexural strength of a structure because of the hybrid steel fibers included in the mixture. Finally, different codes/specifications and published theoretical results are used to predict the CC’s mechanical properties, and the predictions are not as accurate as the SCC predictions, which can be attributed to the presence of conductive fillers in the CC mix.

Study on Stirring Effect of Spiral Magnetic Field in Continuous Casting of Round Blooms

Herein, for the continuous casting of round blooms with strand electromagnetic stirring, the effects of rotating magnetic field (RMF) and spiral magnetic field (SMF) on the electromagnetic, fluid flow, heat transfer, solidification, and macrostructure are investigated by numerical simulation and industrial experiments, respectively. The results show that the molten steel flows in a spiral shape along the casting direction with the RMF and SMF. Due to the influence of secondary flow caused by electromagnetic stirring (EMS), and the zone of high velocity of molten steel accounts for 13.7% of the whole stirring range with the RMF. The SMF has a strong stirring effect in the whole range of secondary flow, the zone of high velocity of molten steel accounts for 49.1% of the whole stirring range, and the liquid fraction of the SMF at the liquid core is also lower. The results of the industrial experiments prove that the SMF has a wider stirring depth than the RMF, and the center crack range is significantly reduced.

Alkali-silica reaction expansion model for confined concrete with stress-dependency and casting direction anisotropy

Alkali-silica reaction (ASR) is a deleterious chemical reaction between alkali hydroxyl ions and types of silica found in some aggregates of concrete. Owners and regulators of nuclear power plants aim to ensure the safety of the concrete structures with optimal maintenance strategies. A new model was developed for predicting the expansion of concrete structures affected by alkali-silica reaction. The model includes a novel combination of existing models as an alkali-silica reaction advancement model, a casting direction anisotropic expansion model, a stress-dependent anisotropic expansion model, and a material property evolution model dependent on the degree of ASR expansion. The model parameters were calibrated based on existing literature data and data generated by previous efforts of this study. The calibrated model was then validated with the experiments carried out in previous efforts of this study. The model was shown to accurately predict the ASR-expansion of large-scale reinforced concrete specimens with confinement.

Numerical Modeling and Experimental Study of Solidification Behavior of Al-Mg2Si Composite Sheet Fabricated Using Continuous Casting Route

Abstract Owing to manufacturing challenges, the fabrication of thin sheets of metal matrix composites has been an area of concern for sheet manufacturers. Converting a billet of composite into a sheet using rolling and extrusion is quite energy-intensive and prone to cracking using the conventional casting route. To address this issue, this study explores the development of particle-reinforced near eutectic Al-Mg2Si composite sheets using a vertical twin-roll continuous casting process. The numerical simulation involves fluid flow, solidification, and heat transfer analysis of the twin-roll continuous casting process for producing thin strips. Processing parameters such as the velocity of rolls and superheat temperature of the melt are optimized to successfully convert the melt into a sheet of composite material. A combined numerical and experimental study show that the continuous casting process is more sensitive to the casting speed. A small change in roller speed (2 rpm) significantly affects the solidified fraction at the roller exit. Optimizing the casting speed to 0.072 m/s and inlet temperature to 886 K, an in situ Al-Mg2Si composite sheet of 3 mm thickness is successfully cast. The particle distribution along the casting direction of the sheet is uniform, ensuring the homogeneous mechanical properties reported in terms of hardness. The entire process does not require external stirring to get uniform distribution of the reinforced particles.

Numerical investigation of solidification behavior and inclusion transport with M-EMS in continuous casting mold

The present study deals with the development of a multiphase numerical model of the continuous casting process of steel bloom. Two SEN configurations that differ in port angles are considered for the study of flow pattern, temperature distribution, solidification thickness, interface fluctuation and inclusion behavior during the process. The influence of mold electromagnetic stirring (M-EMS) on the various output parameters is examined. The results show that the upper circulation loop formed in the 15° port angle case is responsible for higher inclusion removal, high interface level, and low solidification thickness in the meniscus region compared to that of the 30° case. The presence of M-EMS completely changes the flow pattern below SEN. Strong rotational flow coupled with oppositely directed swirl flow provides high tangential velocity near the solidification front and high axial velocity in the core region. It results in fluctuation in shell thickness along the casting direction and decreasing the superheated steam penetration. However, flow patterns remain unaffected above the SEN as upwards swirl flow is not able to reach this region. On applying the M-EMS, inclusion entrapment in solidifying shell increases for both 15° and 30° cases. In contrast, inclusion removal at the interface decreases for 15° case and increases for 30° case.

Modeling study of EMBr effects on molten steel flow, heat transfer and solidification in a continuous casting mold

During continuous casting process, the internal molten steel flow pattern of the mold is one of the important factors affecting the quality of slab products. The application of electromagnetic braking (EMBr) technology in the slab caster provides an effective solution to improve the molten steel flow pattern in the mold. In the current research, one of the commonly used EMBr technology is studied, namely the Ruler-EMBr technology. In detail, the effect of magnetic flux density on the behavior of the molten steel jet flow, heat transfer, and solidification in a 1450 mm × 230 mm slab mold is numerically simulated through a Reynolds-averaged Navier-Stokes (RANS) turbulence model together with an enthalpy-porosity approach. The simulation results indicate that the electromagnetic force generated by the Ruler-EMBr can significantly suppress the diffusion of the impinging jet to the narrow face of the mold with the increase of magnetic flux density. By that, the impact of the upward backflow on the meniscus region in the mold is suppressed. Correspondingly, the uniformity of the temperature distribution in the mold is effectively improved. The parametric studies suggest that the optimized magnetic flux density is 0.3 T to ensure the improvement of steel quality with a casting speed of 1.6 m/min. By applying the magnetic flux density of 0.3 T, the Ruler-EMBr has a better capability to reduce the maximum amplitude of the surface velocity by 24.5% and increase the average surface temperature of the molten steel by 0.25% when compared to the case of No-EMBr. With this electromagnetic parameter, the Ruler-EMBr technology can well prevent the mold flux entrapment and promote solidified shell uniform growth along the casting direction.

New Insights into the Mechanical Behavior of Thin-Film Composite Polymeric Membranes.

Limited predictions of thin-film composite (TFC) membranes' behavior and functional life exist due to the lack of accurate data on their mechanical behavior under different operational conditions. A comprehensive investigation of the mechanical behavior of TFC membranes addressing deformation and failure, temperature and strain rate sensitivity, and anisotropy is presented. Tensile tests were conducted on commercial membranes as well as on individual membrane layers prepared in our laboratories. The results reveal the overall mechanical strength of the membrane is provided by the polyester layer (bottom layer), while the rupture stress for the middle and top layers is at least 10 times smaller than that of the polyester layer. High anisotropic behavior was observed and is attributed to the nonwoven structure of the polyester layer. Rupture stress in the transverse (90°) direction was one-third of the rupture stress in the casting direction. Limited temperature and strain rate dependence was observed in the temperature range that exists during operation. Scanning electron microscopy images of the fractured surfaces were also analyzed and correlated with the mechanical behavior. The presented results provide new insights into the mechanical behavior of thin-film composite membranes and can be used to inform novel membrane designs and fabrication techniques.

Numerical investigation of the influence of casting techniques on fiber orientation distribution in ECC

Engineered cementitious composites (ECC), also known as bendable concrete, were developed based on engineering the interactions between fibers and cementitious matrix. The orientation of fibers, in this regard, is one of the major factors influencing the ductile behavior of this material. In this study, fiber orientation distributions in ECC beams influenced by different casting techniques are evaluated via numerical modeling of the casting process. Two casting directions and two casting positions of the funnel outlet with beam specimens are modeled using a particle-based smoothed particle hydrodynamics (SPH) method. In this SPH approach, fresh mortar and fiber are discretized by separated mortar and fiber particles, which smoothly interact in the computational domain of SPH. The movement of fiber particles is monitored during the casting simulation. Then, the fiber orientations at different sections of specimens are determined after the fresh ECC stops flowing in the formwork. The simulation results show a significant impact of the casting direction on fiber orientation distributions along the longitudinal wall of beams, which eventually influence the flexural strength of beams. In addition, casting positions show negligible influences on the orientation distribution of fibers in the short ECC beam, except under the pouring position.

Strip Casting of Al-4.7%Mg with Impurity Fe Using a Single Roll Caster with a Scraper

Fe was added to Al-4.7%Mg to make model alloys of recycled Al-Mg alloy. The effect of Fe addition on the mechanical properties of the Al-4.7%Mg strip cast using a single-roll caster equipped with a scraper was investigated. The added Fe content was 0.2, 0.4, 0.6, and 0.8%. The as-cast strip cast at 30 m/min was cold rolled down to a thickness of 1 mm thick annealed to conduct a tensile test and a cup test. The as-cast strip could be cold rolled without cracking. The tensile stress and the 0.2% proof stress were only slightly affected by the addition of Fe. The elongation gradually decreased as the Fe content increased. When the Fe content was 0.8%, the elongation in the casting direction was 27.7%. The limiting drawing ratio did not deteriorate until the Fe content was 0.4%. When the Fe content was 0.4% and 0.8%, the limiting drawing ratios were 2.0 and 1.7, respectively.

Effect of casting geometry on distributions of segmented steel fibers in ultra-high performance fiber-reinforced concrete

• 3D statistic of steel fiber dispersion of UHPFRC has been investigated. • Fibers tend to move along the major upward flow the composite. • Different flow patterns and orientations observed due to the wall effect. • Fiber content is the dominant factor affecting the 3D dispersion of fibers. In this study, influence of flow distance and casting direction to properties of steel fibers in ultra-high-performance fiber-reinforced concrete (UHPFRC) was investigated using 3D data on the fibers that accurately obtained through multiple microcomputed tomography (micro-CT) scans and image processing. 3D images of bundled fibers were separated to individual strands by means of a 3D watershed algorithm. The variation in fiber properties according to distance from the casting point and the casting direction was quantitatively analyzed. The results indicated that many fibers were distributed at the casting position for the horizontally casted specimen. The fibers tended to move along the major upward flow of the UHPFRC mixture, which in turn, gradually inclined upward and oriented horizontally in concentric circles. However, different major flow patterns and fiber orientations appeared depending on the casting direction due to the wall effects induced by formwork boundaries. It was also found that fiber content is the dominant factor affecting the 3D dispersion of fibers.

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All My Sons

Study on Microstructure Distribution of Al-Cu-Mg Alloy in Squeeze Casting Process

The squeeze casting process is an advanced technology, which is suitable for a wide range of alloys including Al-Cu-Mg alloys. The high pressure in squeeze casting process both refines the microstructure and enhances the mechanical property of the alloys. The heat transfer and solidification process are complex with the chilling mould and pressure of machine punch. This results in the inhomogeneous microstructure and property in casting alloy. This study focuses on the distribution of microstructure, chemical composition, and hardness of Al-Cu-Mg alloy along the radial direction of casting. The composition and area fraction of eutectic phases are characterized. Moreover, the relationship between the microstructure and mechanical property was also analysed to show the characteristic of microstructure in squeeze casting process.

Direction-dependent behaviour and size effect of steel fibre reinforced concrete based on the double punch test

The post-cracking behaviour of steel fibre reinforced concrete (SFRC) is typically determined following an inverse analysis of flexural prism tests. Although these tests have significant practical merit, it has been argued that the anisotropy of the material due to the dispersion and orientation of the fibres cannot be accounted for in these tests. Multidirectional double punch tests on cubes have been proposed to overcome these issues. These tests are also well-suited to study size effects. However, no generally accepted inverse analysis method for these tests presently exists. This paper presents a simple and mechanically consistent inverse analysis procedure to estimate the residual post-cracking strength of SFRC from the results of double punch tests conducted on cubes. To explore the potential and limitations of this methodology, an experimental investigation was conducted on 30 double punch tests on cubes of varying sizes, varying fibre dosage and loading direction with respect to the concrete casting direction. The results demonstrate that the approach provides useful comparative information on the anisotropy of the material, however further investigation on the input parameters is required to prove its reliability in quantifying the residual tensile stress offered by the fibres.

Grain orientation evolution and multi-scale interfaces enhanced thermoelectric properties of textured Sr0.9La0.1TiO3 based ceramics

Sr0.9La0.1TiO3 based textured ceramics (SLTT-S3T) with a texture fraction of 0.81 are successfully fabricated by the reactive template grain growth method, in which Sr0.9La0.1TiO3/20 wt%Ti was used as matrix and 10 wt% plate-like Sr3Ti2O7 template seeds were used as templates. The phase transition, microstructure evolution, and the anisotropic thermoelectric properties of SLTT-S3T ceramics were investigated. The results show that the ceramics are mainly composed of Sr0.9La0.1TiO3 and rutile TiO2 phases. Grains grow with a preferred orientation along (h00). A maximum ZT of 0.26 at 1073 K was achieved in the direction perpendicular to the tape casting direction. The low lattice thermal conductivity of 1.9 W/(m K) at 1073 K was obtained decreased by 34%, 40%, and 38% compared with non-textured, SrTiO3 and Sr0.9La0.1TiO3 ceramics prepared by the same process, can be attributed to the enhanced phonon scattering by the complex multi-scale boundaries and interfaces. This work provides a strategy of microstructural design for thermoelectric oxides to decrease intrinsic lattice thermal conductivity and further regulate thermoelectric properties via texture engineering.