Twin-roll Strip Casting Research Articles

The evolution of Σ3 grain boundaries in the strip-cast Hi-B grain orientated Fe-6.5% Si alloy

A novel high magnetic induction Fe-6.5%Si alloy with B800 that reached up to 1.77 Telsa was prepared by twin-roll strip casting. Electron backscattered diffraction (EBSD) investigations demonstrated that Σ3 grain boundaries formed in the body-centered cubic (BCC) metal solidified microstructure without phase transition where the ratio of grain boundaries was greater than 20%. Transmission electron microscopy (TEM) revealed that the partial Σ3 grain boundaries are BCC structured twinning. A certain amount of Σ3 boundaries were inherited from the process of warm rolling, cold rolling and annealing, which acted to stabilize the matrix grain boundaries, resulting in the formation of a perfect Goss microstructure with excellent magnetic properties.

Microstructure and Precipitate Evolution in Cu-3.2Ni-0.75Si Alloy Processed by Twin-Roll Strip Casting

Given the sub-rapid solidification characteristics of twin-roll strip casting (TRSC), the solidification structure and growth process of precipitates during aging treatment were studied. The results showed that TRSC could refine the solidification structure and inhibit the microsegregation of Cu-3.2Ni-0.75Si alloy. During aging treatment, the precipitates mainly consisted of rod β-Ni3Si and disk δ-Ni2Si. The precipitate size was increased by increasing the aging time, which altered the mechanism of precipitation strengthening. Also, the experimental results indicated that precipitate strengthening arises either from the cutover mechanism or from the Orowan mechanism. Furthermore, the Avrami equation, which describes the kinetics of phase transformation and electrical conductivity during aging were established for the Cu-Ni-Si alloy, and the calculated results are consistent with the data. The Cu-3.2Ni-0.75Si alloy after aging treatment at 450 °C for 4 h exhibited optimum performance, and the tensile strength and electrical conductivity were as high as 711 MPa and 43.2% IACS, respectively.

The Evolution of Σ3 Grain Boundary in Strip-Cast Hi-B Grain Orientated Fe-6.5%Si Alloy

A novel high magnetic Fe-6.5%Si alloy with B 8 1.74T was prepared by the method of twin-roll strip casting. The results showed that a sea of Σ3 grain boundaries from the {112} twin boundary were discovered in the FCC solidified microstructure without phase transition, where the solidified embryo ratio was over 20 %. In addition, strengthening grain boundary with inhibitors, some Σ3 grain boundaries were maintained from the process of warm rolling-cold rolling-annealing and transformed into a complete Goss microstructure with the accurate orientation, leading to achieving a good magnetic property.

Effect of cooling route on microstructure and mechanical properties of twin-roll casting low carbon steels with an application of oxide metallurgy technology

The oxide metallurgy was employed in the fabrication of twin-roll strip casting low carbon steels. The quantitative dependences of the microstructure and mechanical properties on cooling parameters were revealed and emphatically investigated. After twin-roll strip casting, a two-step cooling route closed to the actual process was designed and the cooling rates exhibited great influences on the proportion of polygonal ferrite (PF) and acicular ferrite (AF). With increasing cooling rates in both steps, the AF volume fraction raised from 0.04 to 0.75 because the rapid cooling restrained the formation of PF. The AF laths were induced by fine Al–Si–Ti–Mn composite oxides (0.2–2 μm), leading to a heterogeneous microstructure consisting of PF and AF clusters with high proportion of large-angle (≥15°) grain boundaries. It was found that the AF laths kept K–S relationship with austenite and AF laths with collinear growth direction belong to the same codirectional variants group in one AF cluster. With the increase of AF volume fraction, the yield strength (YS) and the ultimate tensile strength (UTS) were improved, while the strip retained excellent elongation. The improved YS was mainly ascribed to the grain boundary strengthening and dislocation strengthening.

Fe-Rich Intermetallic Formation and Mechanical Properties of Recycled AA6111 Alloy Strips Produced by Melt Conditioning Twin Roll Casting

The impact of high shear melt conditioning on the morphology and distribution of Fe intermetallic compounds was investigated in the processing of recycled AA6111 alloy by the twin roll casting process.The optical and scanning electron microscope (SEM) micrograph studies were carried out on twin roll casting (TRC) and melt conditioning twin roll casting (MC-TRC) samples. The microstructural analysis showed fine and uniformly distributed Fe-rich intermetallic phases for MC-TRC strips compared with the TRC strips. There was a significant improvement in the mechanical properties of MC-TRC strips after applying melt conditioning. The as-cast MC-TRC samples showed 18.7%, 19.2% and 9.8% increases in elongation, yield strength and ultimate tensile strength, respectively, in the longitudinal direction, while in the transverse section, the MC-TRC samples showed 32.3%, 2.2% and 3.8% increases in elongation, yield strength and ultimate tensile strength, respectively.

Texture evolution in twin-roll strip cast non-oriented electrical steel with strong Cube and Goss texture

Increasing magnetically favorable <100>//ND texture components is a key challenge in the preparation of high-efficiency non-oriented electrical steels. In this study, an Fe-1.3 wt% Si steel with strong Cube ({100}<001>) and Goss ({110}<001>) texture was successfully produced by novel twin-roll strip casting, cold rolling and annealing process. The microstructure and texture of the material was characterized by optical microscopy, electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). The origin and formation mechanism of texture are described from the perspective of deformation and recrystallization behavior of specifically oriented grains. It was observed that initial Cube rotated toward {013}<031>-{110}<110> besides rotation toward {001}<130>-{001}<120> during cold rolling. In addition, new Cube deformation bands were developed in the deformed {115}<051>-{115}<161> grains. Cube components were partly retained as large block, small band structure and crystallite after heavy cold rolling. The Cube deformation structures served as nucleation sites of new Cube grains. The shear band within {114}<110>, {112}<110> and {111}<112> matrix also provided some Cube nuclei. Morphology change from near bar-shaped to equiaxed occurred during the growth of Cube and Goss grains. The formation of recrystallization texture is attributed to the oriented nucleation mechanism, and the orientation pinning and size effects that impacted the intensity of texture component. The low thickness of strip and coarse solidification microstructure with strong {100} texture are the decisive factors to obtain strong Cube and Goss texture in strip-cast non-oriented electrical steel.

Microstructure, tensile and fatigue properties of high strength Al 7075 alloy manufactured via twin-roll strip casting

High strength Al 7075 alloy was manufactured via twin-roll strip casting (TRC) process, and its microstructure, tensile and fatigue properties were investigated. Commercial Al 7075 alloy fabricated via direct-chill (DC) casting process was also used for comparison. T6 and T651 heat treatments were implemented for both the materials to precipitate MgZn2(η) phases. The TRC alloy showed globular grain shape with η phases evenly distributed at the grain boundary and matrix interior, while the DC alloy showed elongated grains due to hot forging process and η phases clumped together at grain boundaries. The TRC alloy’s yield strength was 518.5 MPa, tensile strength was 578.2 MPa, and elongation was 6.9%. Comparing both the alloys’ mechanical properties, the TRC alloy’s strength was at least about 40 MPa higher and elongation was about 4% lower than the DC alloy. The TRC alloy showed about 20 MPa higher fatigue (fatigue limit) than the DC alloy. The DC alloy was observed to have coarse cracks on fatigue fractured surface. By contrast, the TRC alloy showed uniform fractured surface without coarse cracks, and the evenly-distributed η phases improved fatigue resistance efficiently. The present study sought to examine the correlation among TRC process-led microstructure, tensile and high-cycle fatigue properties while discussing the strengthening mechanism.

Zr55Cu30Al10Ni5 amorphous alloy sheets with large plasticity fabricated by twin-roll strip casting

Zr55Cu30Al10Ni5 (at.%) amorphous sheets with thickness of ~0.5 mm and width of ~75 mm were successfully fabricated by twin-roll strip casting. The amorphous alloy sheets fabricated using a high rolling force exhibited a high-energy state, a high free-volume content, and structural inhomogeneity, which led to an engineering strain greater than 62% in compression at room temperature. This study provides an effective method for fabricating large amorphous alloy sheets with good plasticity.

Size effects of Y-enriched intermetallic precipitates in Fe-20Cr-5Al-0.25Y alloy on the spallation resistance of thermally grown α-Al2O3 scales

Standard ingot casting and twin-roll strip casting (TRSC) were used to process Fe-20Cr-5Al-0.25Y (wt.%) alloy, in which Y-enriched intermetallic precipitates with different sizes had been formed. Cyclic oxidation tests were carried out at 1200℃ in air, and the size effects of precipitates in alloy on the spallation resistance of thermally grown α-Al2O3 scales were investigated. The results clearly demonstrated that the spallation resistance of α-Al2O3 scales could be improved by refining the Y-enriched precipitates, which was attributed to the fact that the small precipitates can generate high density of interfacial oxides to effectively key the alumina scale to the substrate.

Secondary Recrystallization Behavior in Fe-3%Si Grain-oriented Silicon Steel Produced by Twin-roll Casting and Simplified Secondary Annealing

Grain-oriented silicon steels were produced by the shortest processing route involving twin-roll strip casting, two-stage cold rolling with intermediate annealing, and simulated continuous annealing. The secondary recrystallization behavior of grain-oriented silicon steels under different inhibition conditions was in-situ observed by combining the confocal laser scanning microscopy (CLSM) and electron backscattered diffraction (EBSD) techniques. The results revealed that the optimal temperature of secondary recrystallization showed a proportional relationship with the Zenner pinning force. In the case of weak pinning force, the abnormal grain growth occurred quickly at ~1050 °C. The corresponding growth rates were in the range of 60–1400 μm/min and decreased gradually as the secondary recrystallization proceeded. In the case of strong pinning force, the incubation time and onset temperature of the secondary recrystallization was significantly increased, but the total time of the secondary recrystallization was obviously shortened from 685 s to 479 s, and the final magnetic induction of B8 was increased from 1.7 T to 1.85 T. After the secondary annealing, some island grains and coarse primary grains were retained. The formation of island grain was related to the low migration of grain boundaries. The findings of coarse γ- grains indicated that the primary grain size also played a crucial role during secondary recrystallization, apart from the primary recrystallized texture, which attracted more attention previously.

Revealing the recrystallization behavior of an excellent strip casting 4.5 wt% Si non-oriented electrical steel

An excellent 4.5 wt%Si non-oriented electrical steel was fabricated by warm rolling and isothermal annealing of twin-roll cast strip. The detailed evolution of microstructure and texture was studied using the combination of electron back-scattering diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscope (TEM) for revealing the recrystallization behavior. The favorable {100}〈013〉 nuclei originate in the shear bands within deformed {111}⟨11-2⟩ and {110}⟨1-10⟩ grains. Based on the EBSD analysis, oriented nucleation is the predominant mechanism for the formation of strong {100}⟨013⟩ texture. The rearrangement of dislocations and cell transformation to sub-grains were characterized. The mechanisms of (sub-)grain coalescence, as well as strain induced grain boundary migration, take effect simultaneously, during the nucleation.

Mg-Based Materials with Quasiamorphous Phase Produced by Vertical Twin-Roll Casting Process

Metallic materials with micron grains, submicron grains, or amorphous structures have attracted great interest in recent decades owing to their excellent mechanical properties and corrosion resistance. Compared with traditional forming processes, rapid solidification technology has shown great superiority and potential in the preparation of materials in such structures. In this study, fine-grained quasiamorphous Mg-based alloy strips fabricated by a twin-roll strip casting process were explored using simulation and experimental methods. The concept of critical casting speed was proposed to reflect the optimum casting conditions. The product of critical casting speed and strip thickness was used to evaluate the cooling capacity of the casting system. Based on simulation results, a twin-roll strip-casting experiment was performed on a Mg-rare earth alloy. A novel puddle-like microstructure of the as-cast alloy strip was obtained. Tensile testing results showed that the novel strip exhibited improved ductility.

Heterogeneous microstructure-mediated ductile fracture of twin-roll cast Al–Mn strip

The microstructure and mechanical properties of the twin-roll cast (TRC) and traditional direct-chill cast (DC) Al–Mn strip have been compared using electron backscattered diffraction, scanning electron microscope, transmission electron microscope, and atom-probe tomography. The TRC Al–Mn strip showed a heterogeneous microstructure and texture along the thickness direction of the strip, forming a 'hard shell-soft core' structure. This heterogeneous microstructure resulted in a mutual constraint between the surface region and the center region, enabling the TRC strip to be plastically deformed to a total elongation >30% prior to fracture. In comparison, the DC strip, with a relatively homogeneous microstructure and texture, exhibited a uniform elongation close to zero. The distinct tensile properties presented by the two strips have been rationalized in terms of the differences in their microstructural features, including grain size/orientation, dislocation density, coarse constituent particles and solute atoms. A micromechanics model has been employed to understand the superior ductility of the TRC strip.

Iterative Learning Control With Time-Delay Compensation: An Application to Twin-Roll Strip Casting

In this article, we propose an iterative learning control (ILC) algorithm for a class of periodic processes with a variable time-delay that is greater than one iteration of the process. We propose a definition of the time delay as the sum of an integer and a residual such that the two components can be estimated separately. This structure enables the derivation of a stability law for an ILC algorithm that is a function of the delay-estimation error. Additional remarks are given regarding the steady-state performance of the combined time-delay-estimation and ILC algorithm. The proposed algorithm is then applied to a twin-roll strip casting process. We demonstrate the sensitivity of the ILC algorithm to the time-delay-estimation error through simulation results and define an upper bound for the time-delay-estimation error that can be tolerated before the ILC algorithm begins to amplify the disturbance. We then validate the combined time-delay-estimation and ILC algorithm's performance using experimental process data from an industrial twin-roll strip casting process.

Continuous Strip Casting of Aluminum Alloy AC7A Using Commercial Scale Twin Roll Caster

This paper describes a commercial scale twin roll strip casting process for producing aluminum alloy strip of AC7A. Twin roll casting process is able to produce a strip from molten metal directly. Thus this process has a possibility to reduce total cost of strip making. However, strip casting process has some disadvantage. Casting speed depends on the material properties. It is difficult to decide the casting conditions. Many paper on the strip casting are reported. However, there are few reports on the commercial scale machine. In this study, the effect of roll speed on the strip casting was investigated. Continuous strip could not be produced at the roll speed 5 m/min. Continuous strip could be produced at the roll speed 10 m/min. However, the cracks were observed. Continuous strip was produced at the roll speed 20 m/min. However, cracks were observed too.

Copper Clad Steel Strips Produced by a Modified Twin-Roll Casting Process

Twin-roll strip casting of steel provides a resource and energy efficient way to produce thin hot strips directly from the liquid phase. Clad metals offer less costly alternatives to monolithic alloys for a wide range of applications, but their various production routes are extensive, expensive, or slow. In order to exploit the strengths of twin-roll strip casting to provide a possibly more cost and energy efficient production route for clad thin strips, research into the expansion of twin-roll strip casting process is conducted. The aim of the current research is the combination of steel with copper. For this purpose, a prefabricated cladding strip of commercially pure copper is inserted into the twin-roll strip casting process. Bonding between the copper strip and the cast steel strip (DC01) is realized by exploiting the process heat. The bonding zone of the clad strip is subsequently analyzed under the optical microscope and in the electron micro probe analyzer. The imagery shows an irregular bonding interface with straight and locally altered regions alternating. These irregularities can be classified into four groups based on their morphology and suspected forming mechanism. Bond strength and formability of the clad strips is qualitatively examined in rolling and bending tests. Rolling was possible without delamination and a total height reduction of approx. 40% while defect-free bending of 2 mm and 3 mm thick specimens was possible up to a bending angle of 90° for a bending radius of 5 mm.

Mechanical Properties of Cold-Rolled and Annealed Al–12%Mg Alloy Sheet with High Mg Solid Solubility Fabricated from Vertical-Type High-Speed Twin-Roll Cast Strip

Mechanical Properties of Cold-Rolled and Annealed Al–12%Mg Alloy Sheet with High Mg Solid Solubility Fabricated from Vertical-Type High-Speed Twin-Roll Cast Strip

A modified processing route for high strength Al-Mg-Si aluminum conductors based on twin-roll cast strip

In the present analysis, it was shown that an altered process sequence involving ageing prior to cold rolling of a twin-roll cast strip can provide a viable manufacturing route generating high strength conductor Al-Mg-Si materials. The process sequence twin roll casting, age-hardening, cold rolling and optional back-annealing enables tailoring the conductor’s properties. For maximum strength, age-hardening annealing and heavy cold rolling are applied, resulting in a yield strength of ∼250 MPa at a conductivity exceeding 32 MS/m. For maximum conductivity, an additional back-annealing is introduced yielding about 34 MS/m and a moderate yield strength greater than 180 MPa. Both options provide an improved strength to conductivity ratio compared to material from standard processing.

Microstructural evolution and magnetic properties in strip cast non-oriented silicon steel produced by warm rolling

In this study, a specific warm rolling was implemented to process Fe-2.8%Si steel by novel twin-roll strip casting. The impact of warm deformation on mechanical behavior, microstructural evolution and magnetic properties is presented. The study indicated that dynamic strain aging (DSA) occurred in the temperature range of 150–300 °C. The elevated rolling temperature strengthened DSA effect and promoted the formation of shear bands. The nucleation process of Cube ({100} 〈001〉) grains during annealing was weakened on introducing warm rolling, while that of Goss grains ({110} < 001>) was enhanced. Moreover, the recrystallization texture pattern of (Cube + Goss) gradually transformed into a pattern of only pronounced Goss texture. The corresponding values of magnetic induction B50 at rolling direction and transverse direction were obviously improved. This confirms the feasibility of processing ultra-high-permeability non-oriented silicon steel based on twin-roll strip casting combined with DSA-control rolling. However, the rolling process increased the nucleation site for recrystallization and decreased the size of precipitates in annealed sheet, leading to a reduction in grain size and an increase in core loss.

Influences of cooling rates on solidification and segregation characteristics of Fe-Cr-Ni-Mo-N super austenitic stainless steel

Solidification and segregation characteristics of Fe-Cr-Ni-Mo-N super austenitic stainless steel were quantitatively analyzed at cooling rate from 0.1 to 90 ℃/s by means of differential scanning calorimetry (DSC) and confocal scanning laser microscopy (CSLM). The results show that phase-transition characteristics in DSC curves correspond to the in-situ microstructures evolution in CSLM experiments. As the cooling rate varied from low to high, the value of crystallization temperature, the size of dendrite arm spacing and the volume fraction of eutectics were characterized as functions of cooling rate, in which corresponding expressions were established. All of these variables decreased with the increase of cooling rate. By applying the conclusions draw from CSLM experiments, the solidification and segregation characteristics in ingot casting (IC) and twin-roll strip casting (TRSC) were predicted and compared to the actual experimental microstructures. The results show good matches between predicted and experimental values except a small error in predicting the volume fraction of eutectics in cast strip (CS). The specific reasons were analyzed from casting processes. It is concluded that the available sub-rapid cooling rate and the loaded rolling force in TRSC take effect concurrently for inhibiting the formation of eutectics in CS. In addition, solute partition coefficients of alloying elements in different conditions, i.e. IC, CSLM and TRSC, show that the segregation degree was relieved with increasing cooling rate and thus the formation of eutectics in the interdendritic regions was inhibited.