Thin Strip Casting Research Articles

Precipitation/recovery kinetics and mechanical properties in rapidly solidified AA6005 AlMgSi sheets via thin strip casting: Effects of casting cooling rate and thermomechanical processing route

Rapidly solidified AA6005 Al-Mg-Si sheets produced via a novel Thin Strip (TS) casting route were characterized and compared with conventional Direct Chill (DC) counterparts for the evolution of microstructure (i.e., precipitation/recovery kinetics) and mechanical properties at various thermo-mechanical tempers. To get to 1 mm final gauge, the DC ingot was homogenized, hot and cold rolled, whereas the TS casting was only cold rolled. After solutionizing (the T4 temper), the final-gauge DC and TS sheets exhibited a similar aging response upon the T6 temper. However, upon artificial aging without solutionizing, termed TSH temper, the as-rolled TS sheets showed a better age hardening kinetics, as manifested in a larger volume fraction of precipitates (primarily β' in this case) and a higher yield strength than the DC sheets (285.1 ± 5.1 MPa vs. 195.2 ± 2.2 MPa, respectively). This was attributed to the higher cooling rates the as-rolled TS sheets experienced during casting; thereby a higher Mg/Si supersaturation in the matrix due to rapid solidification. The TS sheet with the TSH temper exhibited a comparable yield strength to that of the T6 temper, though at a reduced ductility (5.5 ± 0.6% vs. 11.8 ± 0.3% elongation, respectively). Despite with a reduced volume fraction of the hardening precipitates (as compared with the T6 temper), the yield strength of the TS sheet at the TSH temper was compensated for by a considerable amount of remaining cold work from the prior cold rolling stage. Finally, a yield strengths model for the TS-TSH material was developed.

Effect of Annealing Time on Texture Evolution of Fe–3.4 wt% Si Nonoriented Electrical Steel

Herein, the effect of annealing time on the texture evolution in Fe–3.4 wt% Si non‐oriented electrical steel is investigated. Strip samples are cast using a vacuum sampling method, which simulate the solidification conditions of an industrial twin roll thin strip casting (TRSC) process. As‐cast samples with different carbon and sulfur (C&S) levels are hot rolled (HR) with varying levels of hot deformation, cold rolled (CR) to 0.35 mm thickness, and then annealed at 1050 °C for different holding times (1, 6, 24 h). To Fe–3.4 wt% Si nonoriented electrical steel, the observed texture evolution can be divided into different stages as annealing time is increased from 1 to 24 h. With increasing annealing time, the fraction of Goss texture decreases initially and then increases again through the consumption of grains with other textures. With additional time, a decrease of pinning force due to precipitate coarsening results in normal grain growth, resulting in an increase of grain size. In this step, Cube grains can form from rotated Goss grains. A model for core loss is presented and used to explain the core loss results.

Yield strength modelling via precipitation/recovery kinetics in rapidly solidified thin-strip cast AA6005 AlMgSi sheets subjected to cold rolling and direct aging

A comprehensive and experimentally verified yield strength model of AA6005 Al–Mg–Si sheets rapidly solidified via a novel Thin Strip (TS) casting route is developed and presented. The cast sheets were cold-rolled and directly aged via a heat-treatment process (termed TSH) that effectively utilizes the increased solute supersaturation of matrix due to the high casting cooling rates experienced. The TSH conditions were optimized based on the hardness and tensile data, with the peak aging conditions found to be 160°C-4 hrs, 180°C-1 hr and 200°C-15 min. The TEM analysis revealed that, due to the presence of prior cold work, β′ precipitates formed during TSH, i.e., as opposed to the β" precipitates that form upon a typical T6 aging treatment. Also, while the total precipitate volume fraction was comparable among the three peak aging conditions, the sample aged at 200 °C exhibited a lower peak aging strength (300 MPa vs. ∼315 MPa in the other two conditions), i.e., due to a higher dislocation recovery rate and therefore a lower strengthening contribution from the remaining cold work. Interestingly, at each temperature, aging beyond the peak aging time still resulted in an increase in the precipitate volume fraction. The concurrent drop in the yield strength could be explained by the offsetting effect of the recovery of the remaining cold work. Therefore, thanks to the sufficiently high solute supersaturation of the matrix during TSH, together with the remaining cold work (as well as the formation of β′), peak aging at 180 °C is achieved after only 30 min to 1 h, i.e., as opposed to generally 4–6 h of aging needed for a traditional T6 aging. This gives the low-cost, less energy-intensive TS-cast sheets also a significantly faster response to the paint-baking process (typically performed at near 180 °C for around 30 min), thus allowing for a higher strength achieved via a typical automotive body fabrication route. Finally, a robust model of precipitation/recovery kinetics, incorporating precipitate aspect ratio evolution, was developed to simulate the yield strength during TSH. The model predicts a peak-aging time of ∼100 min, aligning well with the observed 60–120 min interval measured from the tensile test results.

Processing and microstructure–property relations of Al-Mg-Si-Fe crossover alloys

This study introduces new alloys, which combine the age-hardening capability of Al-Mg-Si alloys with the microstructure-controlling effect on processing of primary Fe-rich intermetallic phases used in foil stock. In detail, the processing and microstructure–property relations in new crossover aluminum alloys derived from 6xxx and 8xxx foil stock alloys, is shown. A highly Fe-rich intermetallic phase content was deployed to conceptually mimic high scrap content. Fast and slow solidification rates were applied to represent thin strip and direct chill casting, respectively. The effects of adding Fe and Mn to alloy 6016 were examined, while the Si consumed in primary phases was partly adjusted to maintain age-hardening potential. It was shown that upon thermomechanical processing, primary intermetallic phases in the new alloys are finely fragmented and well dispersed, resulting in strong grain refinement and a uniform texture. Attractive combinations of strength and ductility were revealed, also in material processed under direct chill casting conditions. The new alloys’ high elongation values of up to 30%, and their age-hardening response, were similar to those seen in commercial alloy 6016, while their strain hardening capacity was significantly greater. This can be attributed mainly to the formation of geometrically necessary dislocations near primary Fe-rich intermetallic phases. The study discusses microstructure refinement on the basis of particle stimulated nucleation. It uses a simple model to describe the individual contributions to yield strength, including the effect of primary phases. It also models the effect of these particles on increased strain hardening and ductility.

Direct Strip Casting of Magnesium

AbstractA new interest in magnesium alloys has arisen since lightweight constructions have become more and more attractive. Products that are currently available are mostly cast, forged, and extruded. A cost-effective production of sheet metals will render new perspectives in the design of lightweight constructions [1, 2].The development of new casting technologies like thin slab casting or strip casting with an in-line rolling process is expected to result in a shorter processing time featuring a high potential of saving energy, time, and cost [3, 4, 5, 6, 7, 8, 9]. Particular attention is paid to the casting process parameters such as casting speed and solidification speed. This article deals with some aspects of a magnesium-adapted singlebelt caster. Results of casting experiments and material examination are shown as well as some advices given concerning safety and handling of liquid magnesium [10].

Applying crystallographic orientation analysis for exploring deformation mechanism of 6.5 wt.% Si electrical strip during twin-roll thin strip casting process

The study described here is aimed at illuminating deformation mechanism involved in Twin-roll Thin Strip Casting Process (TRSC) with respect to high-permeability 6.5 wt.% Si electrical strip (6.5 wt.% Si strip) in terms of crystal plasticity (CP) theory, and a Visco-plastic Self-consistent model (VPSC) was utilized to explore the deformation mechanism by applying crystallographic orientation (OR) analysis. Results underscore that the activation of overall potential single slip system with regard to studied 6.5 wt.% Si strip including { 110 } < 111 > , { 112 } < 111 > as well as { 123 } < 111 > can contribute to the OR conversion from Cube texture to Rotated-Cube texture, α-fiber texture as well as γ-fiber texture, while with different evolution rate during deformation. The potential multi-slip system of { 112 } < 111 > + { 123 } < 111 > with average number of activated slip system per grain ~9.1–9.4, and multi-slip system of { 110 } < 111 > + { 112 } < 111 > + { 123 } < 111 > with average number of activated slip system per grain ~10.4–10.8 are identified to be the predominant slip systems during deformation by comparing to the actual OR features obtained from TRSC-processed 6.5 wt.% Si strip. The CP-based method proposed in present study is deemed as a reference to investigate deformation behavior involved in the other semi-solid forming process.

Comparison of cracking sensitivity between high-permeability 1.5 wt% Si steel and 6.5 wt% Si steel in mushy zone

Twin-roll thin strip casting process (SC) has been utilized in laboratory to fabricate typical high-permeability electrical steel (HPES) such as 1.5 wt% Si and 6.5 wt% Si steel with ideal crystallographic orientation and excellent permeability after a series of heat treatments. Whereas, there exists a problem associated to the cracking sensitivity in high temperature mushy zone, which further restricts the industrial application of SC to produce HPES. Mechanical behavior of 1.5 wt% Si and 6.5 wt% Si steels in high temperature mushy zone were comparatively studied by Gleeble-3800 physical simulation system under strain rate 3 s−1, systematically. The high temperature brittle region composed of zero strength temperature (ZST) and zero ductility temperature (ZDT) in the mushy zone were quantitatively determined, and the critical strain threshold associated to hot crack initiation in the brittle region were further evaluated following empirical model proposed by Y Won. Results show that the tensile strength and fracture ductility in the mushy zone are both closely associated with the varying volume fraction of network-shaped structure during solidification, and are decreased with decreasing solid fraction concerning studied 1.5 wt% Si and 6.5 wt% Si steels. The high temperature brittle region corresponding to the studied 1.5 wt% Si and 6.5 wt% Si steels in mushy zone are separately confirmed to be 1459 ~ 1465℃ and 1390 ~ 1427℃, and the thresholds of critical strain for hot cracks initiation in high temperature brittle region are calculated to be ~ 1.18% and ~ 0.24%, respectively. Considering from perspective of width of high temperature brittle region and critical strain threshold for hot crack initiation, the cracking sensitivity of 6.5 wt% Si steel in the mushy zone is more serious compared to 1.5 wt% Si steel.

New Technology to Produce 1 GPa Low Carbon Microalloyed Steels from Cast Strip

Global economy requires steel with further increasing mechanical properties and simultaneously decreasing price. In mass manufacturing three major methods can be used to increase strength: (i) increase microalloying element additions (increases cost), (ii) decrease deformation temperature and (iii) increase cooling rate after high temperature processing (both can be challenging for equipment). Thin strip casting is an effective way to reduce cost as it brings a reduction in number of deformation passes and shortens the production line. However, the mechanical properties can be missed due to insufficient microstructure development. In this article, we investigate a recently proposed technology based on Austenite Conditioning followed by Accelerated Cooling and Warm Deformation (AC2WD). Two low carbon steels microalloyed with either 0.012Ti or 0.1Mo-0.064Nb-0.021Ti (wt.%) were subjected to three processing modifications of the AC2WD-technology with two, one or no deformation of cast microstructure in the austenite temperature field. The Ti- and MoNbTi-steels exhibited 685–765 MPa and 880–950 MPa of the yield stress, 780–840 MPa and 1035–1120 MPa of tensile strength, and 20–30% and 22–24% of elongation to failure, respectively. The nature of strengthening mechanisms associated with the AC2WD-technology is discussed on the basis of detailed microstructure characterisation.

Recrystallization behavior in a low-density high-Mn high-Al austenitic steel undergone thin strip casting process

The recrystallization behavior of a high-Mn high-Al lightweight steel (Fe-28.4Mn-8.3Al-1.27 C (wt%)) with 50% cold rolling deformation is investigated at the annealing temperature of 800 °C, 900 °C and 1000 °C. The detailed microstructure evolution is characterized by optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), electron probe micro-analyzer (EPMA) and transmission electron microscopy (TEM). The partial recrystallized bimodal austenite grains and κ-phase (Fe, Mn)3AlC form at 800 °C, while fully recrystallized austenite grains without κ-phase appear at 900 °C and 1000 °C. With the increase in annealing temperature, the increased frequency of annealing twin boundaries reduces the average austenitic grain size and the dispersion of the austenite grain size effectively. The effect of austenite grain size on the tensile properties is discussed. The strain hardening behavior is also investigated by Hollomon analysis and C-J analysis, and the later one is better to explain the strain hardening behavior in different four stages. The recrystallization behavior significantly improves the tensile toughness from 59 MJ/m3 to 436 MJ/m3 at the expense of tensile strength decrease from 1460 MPa to 890 MPa, due to the homogenous fine austenite grains and high frequency of high misorientation angle. The steel with fully recrystallized austenite grains of 10.0 µm annealed at 900 °C exhibits the optimum mechanical properties with excellent tensile strength of 965 MPa, ductility of 48.3%, and good toughness of 400 MJ/m3.

Evolution and Interaction of the Microstructure and Texture at the Different Processing Steps for Ferritic Nonoriented Electrical Steels

The fabrication process of nonoriented electrical steels comprises casting, hot rolling, cold rolling, and final annealing. The development of new technologies for the fabrication of hot band offers new possibilities. In this paper, we will shortly describe the similarities and differences with respect to the evolution of microstructure (grain structure) and texture along the conventional processing route and thin strip casting. We will point out the most relevant features at the different processing steps, which are important for the optimum texture and microstructure of the finally processed material. Thereby, we will regard ferritic FeSi steels, where no homogenization of the microstructure appears due to the austenite–ferrite phase transformation.

Numerical analysis of the twin-roll casting of thin aluminium-steel clad strips

The production of thin aluminium-steel clad strips by means of twin-roll casting is one of the prospective trends in the development of sheet production. The main advantages of twin-roll casting are low specific energy and resource consumption. Besides this, the resulting compound has a high bonding strength owing to the presence of a continuous thin layer of intermetallic phases having an approximate thickness of 3 µm at the interface of the two metals. At the same time, the quality of the clad strip depends on the microstructure and properties of the aluminium layer formed directly from a melt. A deformation immediately following the solidification of the metal between the two rotated, internally water-cooled rolls has a substantial influence on this aluminium layer. Due to the complexity of observing the processes occurring in the melt pool, a numerical simulation became one of the main methods for their investigation. Simulation is widely used to describe the process of twin-roll casting of monomaterial strips, but so far it has not been used for to comprehensively analyse the process of twin-roll casting of clad strips. In the present paper, a two-dimentional finite-element simulation of the system “clad strip—water-cooled rolls” using the ANSYS software is proposed. A joint analysis is carried out of the heat transfer, viscous flow of aluminium melt, its solidification and deformation resulting in the temperature distribution in the cast metal as well as in the tool. The dependences of the deformation strain and outlet temperature of the clad strip on the main technological process parameters; obtained by numerical simulation, are shown.

Advances in the Twin-Roll Strip Casting of Strip with Profiled Cross Section

Direct thin strip casting is an economically end energetically smart process for the production of steel strip. In a single process step, liquid steel can be cast and directly rolled to hot strip in thicknesses ranging from one to four millimeters. With the use of specifically profiled casting rolls it is possible to produce strip with optimized cross-sections, allowing this process to compete with tailor welded and tailor rolled blanks for the production of a class of products already widely applied in industry. Numerical and experimental studies proved the feasibility of this concept and additional simulations were used to optimize the profile to be used for the experiments. A thickness variation of one millimeter from the edge to the center could be successfully achieved. However, the dimensional precision and the roughness distribution along the cross section of the produced strip were not satisfactory. Additional profiles were applied for the experimental analysis leading to better roughness distribution and geometrical accuracy. In order to further improve the uniformity of properties along the profiled section it is necessary to increase the homogeneity of the microstructure. The coating and surface preparation of the casting rolls play a very important role in the strip casting process as they strongly affect the solidification behavior. This observation lead to the idea of selectively coating the casting rolls, applying a less conductive layer on the areas where the casted profile is thinner. Thus, a more homogeneous solidification front can be obtained. The effect of a locally modified casting roll coating on the solidification is numerically investigated and the results applied for the selection of the coating parameters to be used for the experiments.

Microstructure and Texture Evolution of Fe-Si Steels after Hot Dipping and Diffusion Annealing

A homogenous intensity distribution along the cube texture fibre is important to achieve an easy magnetization in non-oriented electrical steels. Several alternatives have been discussed in literature to achieve this goal namely, tertiary recrystallization (surface energy controlled), decarburization annealing, two step cold rolling (strain induced boundary migration), twin-roll thin strip casting (directional solidification), phase transformation (surface energy anisotropy) and columnar grains formation (selective grain growth). In the present study, a hypoeutectic Al-Si alloy was deposited on the surface of cold rolled Fe-Si steels with a hot dipping simulator and subsequently annealed at 1000°C for different times. This procedure was developed previously in order to enrich the substrate with Al and/or Si and consequently improve their resistivity. Of specific interest was the formation of columnar grains in the low Fe-Si steel after annealing. These columnar grains were found to grow from the surface towards the centre of the substrate. The microstructure and texture in the columnar grains were significantly different than those in the middle of the material. Therefore, the evolution of these features during processing was studied in detail in this work.

Studies of Advanced Technologies Used in the Manufacture of Products from Aluminium Alloys

Studies of Advanced Technologies Used in the Manufacture of Products from Aluminium Alloys The test stands already put in operation and still under development, installed in the Light Metals Division Skawina of the Institute of Non-Ferrous Metals in Gliwice are described. The presentation includes 5MN horizontal direct-indirect extrusion press, 2,5MN vertical forging press, "MeltechConfex MC-260" device for continuous rotary extrusion process, "Melt-Spinning" plant for casting of thin strips, melting-casting plant for Mg alloy billets, heat treatment line, and new testing equipment, including Instron 5582 100 kN and Instron 600DX 600 kN testing machines with attachments for tests carried out at low and high temperatures, automatic hardness tester for HB, HV and HRC hardness measurements, portable X-ray diffractometer for measurement of internal stresses, optical emission spectrometer with channels for the analysis of aluminium and magnesium alloys, STEM 200kV transmission electron microscope, and apparatus for hydrogen content measurement in the solid state. Based on the experimental potential and apparatus available, present research opportunities were discussed and modern trends in the advanced technology of Al and Mg alloys fabrication were outlined.

Finite Element Modeling of Casting Roll during Twin-Roll Strip Casting

In twin-roll thin strip casting, the temperature distribution of casting roll affects the roll thermal stress, and influences the thermal deformation, the generation of roll surface cracks, the strip shape, and the service life of casting roll. In this paper, the temperature distributions of casting roll have been analysed, the effects of the roll sleeve thickness on the temperature field and thermal stress of casting roll have been simulated and discussed. The developed temperature model of casting roll is helpful in optimising the processing parameters and the design of casting roll during twin-roll thin strip casting.

Simple macro/microcoupling mathematical model and its predicting on effects of processing factors on solidification structure for 1Cr18Ni9Ti stainless steel twin-roll thin strip

Based on the simple macro/microcoupling mathematical model developed in this paper and its predicted results, the effects of processing factors such as pouring temperature, casting velocity and molten pool height on the solidification structure for 1Cr18Ni9Ti stainless steel thin strip with ideal solidification type are investigated. In the developed model, the latent heat is treated by enthalpy method; the grid and nodes are divided by the assumed streamlines. Moreover, the heterogeneous nucleation and columnar-to-equiaxed transition (CET) models are also introduced, together with the revising of dendrite growth dynamic model of Kurz–Giovanola–Trivedi (KGT). With the help of solid fraction, the coupling of macro/micromodels is realised using different grid sizes and time steps, macro and micro, together with the columnar dendrite front tracing. The predicted results of mathematical models indicate that the effects of pouring temperature, casting velocity and melt pool height on the solidification structure of 1Cr18Ni9Ti stainless steel twin-roll thin strips are very different, in that the effects of molten pool height is greatest, then are casting velocity and pouring temperature respectively. Accordingly, for the actual twin-roll thin strip casting, the molten pool height and casting velocity should be controlled strictly in order to obtain ideal solidification structure.

Study on Casting Roll during Twin-Roll Casting of Thin Strip

In twin-roll thin strip casting, the temperature of casting roll affects the roll thermal stress, and influences the thermal deformation, the generation of roll surface cracks, the strip shape and the service life of casting roll. In this paper, the features of the casting roll materials have been analysed, the effects of the clad materials and thickness on temperature field of the casting roll have been simulated and discussed. The developed temperature model of casting roll is helpful in optimising processing parameters and the design of casting roll during twin-roll thin strip casting.

Microstructure evolution in irons and steels: a tribute to David V. Edmonds

AbstractThe contributions of David Vernon Edmonds to the study of microstructural evolution over the past four decades are reviewed, in a tribute to mark his recent retirement from the Chair of Metallurgy and Materials at the University of Leeds. The scientific discoveries in the Edmonds group are highlighted in the context of microalloyed, ferritic, pearlitic, bainitic and martensitic steels, as well as cementite and cast iron, and in a variety of non-ferrous fields including high-density tungsten and uranium alloys, titanium alloys and twin-roll thin-strip casting.

Computationally efficient numerical technique for primary cooling zone of thin slab continuous casting

Thin slab continuous casting process can be controlled by the water flow rate through the copper mould to obtain the proper shell thickness for a given casting speed. To achieve this, 2D model for the liquid metal flow in the strand and water flow through the mould is developed using stream function and vorticity formulation. The main advantage is faster computation, which is very important for process optimisation, and real-time modelling for process control. The funnel type shape of the mould is efficiently taken into consideration by using body fitted coordinate system. The detailed CFD-based model can be used for analysing the process parameters and variables like heat transfer through the mould flux, casting speed and superheat. The model can be easily adapted for wide range of casting process like slab and billet casting and thin strip casting.

Fundamental investigation of interfaces in particle reinforced steel sheets processed by thin strip casting

AbstractAlong the steel industry history, the production of flat‐steel products has technologically evolved towards reducing slab thickness at the output of the continuous casting machine. This development has been related to the incessant requirement of providing a certain steel quality at lower costs. As a result of this procedure, the thin strip casting technology emerged in a commercial scale at the end of the nineties, with all the advantages of a near‐net‐shape manufacturing process. In particularly, the higher energy efficiency and reduced environmental impact turned it as a very promising and attractive technology for the steel industry.With the purpose of obtaining new types of steel sheets, characterized by improved mechanical and tribological properties, reinforced steel strips have been produced by introducing slight modifications to a twin‐roll caster. In this regard, a considerable enhancement of the mechanical properties has been achieved.