Twin-roll Strip Research Articles

Hot Deformation Behavior of Free-Al 2.43 wt.% Si Electrical Steel Strip Produced by Twin-Roll Strip Casting and Its Effect on Microstructure and Texture.

Twin-roll strip casting (TRSC) technology has unique advantages in the production of non-oriented electrical steel. However, the hot deformation behavior of high-grade electrical steel produced by TRSC has hardly been reported. This work systematically studied the hot deformation behavior of free-Al 2.43 wt.% Si electrical steel strip produced by twin-roll strip casting. During the simulated hot rolling test, deformation reduction was set as 30%, and the ranges of deformation temperature and strain rate were 750~950 °C and 0.01~5 s-1, respectively. The obtained true stress-strain curves show that the peak true stress decreased with an increase in the deformation temperature and with a decrease in the strain rate. Then, the effect of hot deformation parameters on microstructure and texture was analyzed using optical microstructure observation, X-ray diffraction, and electron backscattered diffraction examination. In addition, based on the obtained true stress-strain curves of the strip cast during hot deformation, the constitutive equation for the studied silicon steel strip was established, from which it can be found that the deformation activation energy of the studied steel strip is 83.367 kJ/mol. Finally, the kinetics model of dynamic recrystallization for predicting the recrystallization volume percent was established and was verified by a hot rolling experiment conducted on a rolling mill.

The comprehensive study on texture evolution and recrystallization behavior of twin-roll strip casting Fe-50 %Co alloy

The iron-cobalt soft magnetic alloy exhibits excellent properties such as high saturation magnetic induction, high magnetic permeability, and high Curie temperature, making it widely used in areas like aviation generators and electric motors. However, traditional iron-cobalt alloy strip materials often suffer from a high magnetic anisotropy constant, which hinders their performance in practical applications. In this study, twin-roll strip casting was employed to produce Fe-50Co soft magnetic alloy cold-rolled strip materials. The research findings reveal that the initial microstructure of the Fe-50Co alloy strip prepared through twin-roll strip casting is primarily composed of coarse columnar grains and equiaxed grains, with a strong {001} orientation for the columnar grains. Notably, a significant number of Σ3 grain boundaries are present within the cast strip. These grain boundaries effectively reduce dislocation accumulation during the cold rolling process and subsequently minimize the nucleation sites for γ-texture during subsequent annealing. Furthermore, a strong {001}<uv0> texture is formed in the finished strip material after cold rolling and annealing, resulting in superior magnetic properties. The alloy exhibited excellent magnetic properties after annealing at 900 ℃ for 5 h followed by furnace cooling to 750 ℃ with the cooling rate of 50 ℃/h and then to 300 ℃ with the cooling rate of 180 ℃/h, the B5000 was ∼ 2.417 T, P1.5/400 was ∼22.651 W/kg and P2/1000 was 183.51 W/kg. These findings provide valuable insights for the development of Fe-50Co alloys with excellent magnetic properties.

Tuning heterogeneous microstructure and improving mechanical properties of twin-roll strip cast low carbon steels by on-line heat treatments

Coarse austenite grains are unavoidable in the low carbon steels processed by twin-roll strip casting. Unfortunately, the polygonal ferrite (PF) grains cannot be refined by conventional on-line cooling process, resulting in low strength. In this work, an on-line heat treatment including reaustenitizing and subsequent controlled cooling was performed in laboratory to form heterogeneous microstructures composed of PF and acicular ferrite (AF). It has been founded that increased prior austenite grain size and the cooling rate led to more AF laths, which inhibited the growth of PF grains. When the prior austenite grain size is less than 60 μm, the formation of AF is suppressed. The tensile tests indicate that the heterostructured steels exhibited higher yield strength than the samples without AF. The improvement of yield strength can be attributed to the grain boundary strengthening, dislocation strengthening and back stress strengthening. The higher AF volume fraction leads to higher dislocation density in PF grains, and more AF/PF interfaces may increase the amount of accumulated geometrically necessary dislocations. Therefore, the contributions of dislocation and back stress strengthening increase with the increase of AF volume fractions. High dislocation density and the generation of back stress contribute a high strain hardening rate to delay the necking and sustain good plasticity. Moreover, the heterostructured steels exhibit the two-stage work hardening behavior during tensile test, which indicates that plastic deformation starts in PF grains while the AF laths remain in elastic state, and then plastic deformation occurs in both strain hardened PF grains and AF laths.

Effect of Low-temperature Annealing on Mechanical Properties of Warm-rolled High Silicon Steel Produced by Twin-roll Strip Casting

Effect of Low-temperature Annealing on Mechanical Properties of Warm-rolled High Silicon Steel Produced by Twin-roll Strip Casting

Solidification behavior and continuous preparation process of high-quality Zr-based metallic glass plates based on twin-roll strip casting

Metallic glasses exhibit excellent comprehensive properties in a variety of disciplines including mechanics, magnetism, electricity, and chemistry, making them highly promising for various applications. However, the current lack of continuous and efficient preparation technology for metallic glasses not only hinders the research and application of various metallic glass products but also contributes to the high cost associated with their production. In this study, we incorporate the twin-roll strip casting technology into the continuous fabrication process of metallic glass plates. By conducting numerical simulations and practical experiments, we elucidated the solidification process of metallic glasses in the twin-roll strip casting process. A process control strategy was developed focusing on "small molten pool height and low exit temperature", which enabled successful preparation of high-quality Zr55Cu30Al10Ni5 metallic glass plates ranging from 0.13 to 0.56 mm in thickness. A reduced pool height can enhance the cooling rate of metallic glasses and suppress the formation of vortices and crystals within the molten pool. By employing a lower exit temperature, it is possible to achieve a metallic glass plate characterized by high-energy microstructure, exceptional mechanical properties, as well as superior shape and surface quality. This research provides valuable guidance for continuous production of superior-grade metallic glass plates using twin-roll strip casting technique.

A hybrid approach towards evaluation of average heat transfer coefficient in twin-roll strip casting mold

Continuous casting stands out as one of the most efficient and productive methods for producing billets, slabs, or thin sheets while conserving energy. Understanding the solidification dynamics and achieving defect-free sheets in continuous casting necessitates the accurate prediction of heat transfer coefficient (HTC) at the mold metal interface. Accurate prediction of HTC helps in selecting process parameters such as superheat temperature and casting velocity, which directly affect the production rate and quality of the cast component. Determining the HTC is a complex process, as it is influenced by various process parameters such as casting size, casting speed, superheat temperature, surface roughness, type of water used as a coolant, nozzle design and wettability. Therefore, the present study proposed a hybrid approach for finding HTC in a twin roll strip casting mold through a solidified shell shape, which is influenced by the factors affecting the heat transfer at the mold-metal interface. This approach integrates the experimental and simulation investigations. The numerical investigation used a three-dimensional coupled fluid flow and heat transfer equations with an assumed range of HTC (100–2000 W/(m2K)). The solidified shell shape for different HTCs was compared with the experimental solidified shape form at the outer wall of the mold using the solidification criteria. Results indicate that the initial HTC range of 100–1000 W/(m2K) does not lead to blockage of the graphite mold outlet. However, as HTC values approach 1000 W/(m2K) to 1400 W/(m2K), the melt obstructs the mold exit based on solidification criteria. The HTC values (1350 ± 150 W/(m2K)) obtained from the proposed methodology for mold, align well with the HTC values (1183 ± 593 W/(m2K)) calculated using lamellar spacing of the Al-Mg2Si composite microstructure. This hybrid approach presents a novel and straightforward method for determining HTC, offering accurate predictions that can enhance the precision of continuous casting models and provide a more nuanced understanding of solidification behavior.

Short-process preparation of grain-oriented electrical steel

The conventional production line of grain-oriented electrical steel (GOES) is long and the columnar grains in the cast slabs have adverse effects on GOES. In this paper, the short preparation process for GOES using top side-pouring twin-roll strip casting (TSTRC) was investigated. The results show that TSTRC can prepare cast strips with equiaxed grains. Conventional slab reheating, hot rolling, and normalization can be eliminated. The origin of Goss grains and the preparation of inhibitors were studied.

Measurement of Molten Steel Level Using a Single Camera in Top Side-Pouring Twin-Roll Casting

The molten steel level in twin-roll strip casting (TRC) has a significant impact on the heat transfer process between the molten steel and the rolls, as well as the subsequent solidification process of the steel. Therefore, ensuring a specific and stable molten steel level is crucial for the quality of as-casting strips. To achieve this, a precise and real-time molten steel level detection system is required. This paper utilizes machine vision technology to measure the molten steel level. A general mathematical model for the molten steel level in the TRC process is established. An image processing method for measuring the molten steel level using a single camera is proposed, including image segmentation, edge detection, and multiple coordinate transformations of the molten pool contour. The adverse effect of the inlet or nozzle is taken into account. Experimental measurements were conducted, and the results indicate that a single camera can accurately measure the molten steel level. Potential sources of error or limitations that may impact the accuracy of the proposed method is discussed.

Effects of Quenching Temperature on the Microstructure and Mechanical Properties of a Strip-Cast Medium-Mn Steel Processed by Quenching and Partitioning

Twin-roll strip casting (TRSC), which is a low-energy and short process to produce strip steel, is a potential approach to produce advanced high-strength steels. Herein, a medium-Mn steel containing 4 wt% Mn was processed using a novel route involving TRSC, hot rolling and quenching and partitioning (QP) to explore the possibility of medium-Mn steel produced by TRSC plus QP process. The effects of quenching temperature on the microstructure and mechanical properties were studied. It was found that primary martensite and retained austenite (RA) were obtained at the quenching temperature of 140–180 °C, while primary martensite, RA and secondary martensite were obtained when the quenching temperature was 220–300 °C. With an increase in quenching temperature from 140 to 260 and to 300 °C, the RA fraction first increased from 15.4% to 31.8% and then decreased to 16.6%. The sample at a quenching temperature of 220 °C yielded mechanical properties with a yield strength of 992 MPa, tensile strength of 1159 MPa and total elongation of 20.4%. The superior mechanical properties were achieved by an optimum combination of high RA fraction (26.5%), appropriate mechanical stability of RA and a small number of the islands of secondary martensite and RA. Hence, the present study provides a viable processing route for medium-Mn steel.

Microstructure Characteristics, Mechanical Properties and Strain Hardening Behavior of B2 Intermetallic Compound-Strengthening Fe-16Mn-9Al-0.8C-3Ni Steel Fabricated by Twin-Roll Strip Casting, Cold Rolling and Annealing.

In this study, the Fe-16Mn-9Al-0.8C-3Ni (wt.%) lightweight steel was fabricated by novel twin-roll strip casting technology. The microstructure, tensile properties and strain-hardening behavior of the present steel have been investigated and compared to those of conventionally processed steels with similar chemical compositions. After annealing, a unique gradient microstructure of intermetallic compound (B2)-austenite was obtained along the thickness direction, consisting of granular B2 (average: 430 nm) and fine austenite (average: 1.82 μm) at the surface layer, blocky B2 (average: 1.03 μm) and medium austenite (average: 3.98 μm) at the quarter layer and polygonal B2 (average: 1.94 μm) and coarse austenite (average: 6.13 μm) at the center layer. The cooperative action of B2 pinning dislocation, plane slip and back stress led to stronger strain hardening, among which the strong back stress effect originated from the multistage discontinuous austenite deformation and the mechanical incompatibility between austenite and B2 is believed to be the most important reason, thereby achieving an excellent balance of strength (ultimate tensile strength: 1147 MPa) and ductility (total elongation: 43.2%). This work not only developed a new processing way to fabricate Ni-containing Fe-Mn-Al-C lightweight steel with outstanding mechanical properties, but also provided a potential solution for manufacturing some other metallic materials accompanied by brittle B2 intermetallic.

Detecting Height of Liquid Level with Computer Vision for Twin-roll Strip Casting

Detecting Height of Liquid Level with Computer Vision for Twin-roll Strip Casting

Microstructure evolution and precipitation behaviour of the Cu-Ni-Si-Cr alloy based on twin-roll strip casting

ABSTRACT The twin-roll strip casting (TRSC) process was introduced because of its sub-rapid solidification characteristics, and the element segregation and ageing precipitation of the Cu-6Ni-1.4Si-0.1Cr alloy were studied. The results are as follows: TRSC can effectively refine grain size and inhibit the segregation of the Cu-6Ni-1.4Si-0.1Cr alloy. Two types of precipitates are formed mainly during the ageing process: disk-shaped δ-Ni2Si and rod-shaped β-Ni3Si. The comprehensive properties of the alloy are improved, and the precipitation strengthening mechanism is either from the dislocation shearing mechanism or the Orowan mechanism in different stages of ageing. The Cu-6Ni-1.4Si-0.1Cr alloy achieves optimum performance after ageing at 350°C for 4 h, where the tensile strength and conductivity are 1112 MPa and 27.35% IACS, respectively. The Avrami equations were established for the alloy to describe the kinetics of phase transformation and electrical conductivity during ageing, and the calculated results are consistent with the experimental data.

Solidification microstructure of Ti-43Al alloy by twin-roll strip casting

Solidification microstructure of Ti-43Al alloy by twin-roll strip casting

Effect of annealing temperature on magnetic and mechanical properties of twin-roll strip casting Cu-bearing non-oriented electrical steel

Effect of annealing temperature on magnetic and mechanical properties of twin-roll strip casting Cu-bearing non-oriented electrical steel

Numerical simulation and experimental research on cracking mechanism of twin-roll strip casting

Abstract Based on the three-dimensional field of molten pool and twin-roll strip casting experiments, this work verified the cracking mechanism of the strip by establishing mathematical model and rolling experiments. The results showed that due to the instability of the thermophysical field of the molten pool and the inconsistency of kiss curve height, the newly solidified strip will undergo incompatible deformation through the rolling. The stress concentration will appear around the large reduction area and then form slip bands. When plastic strain exceeds the limit of the metal, the oblique cracks will appear in the slip bands periodically or completely penetrate the strip. In addition, tensile cracks could also be produced by incompatible deformation. Therefore, keeping the uniformity and stability of the thermal physical field in molten pool is the key factor to restrain cracks.

Modeling effect of cooling conditions on solidification process during thermal cycle of rollers in twin-roll strip casting

Modeling effect of cooling conditions on solidification process during thermal cycle of rollers in twin-roll strip casting

Deformation twinning caused by warm rolling and secondary recrystallization in twin-roll strip casting Fe81Ga19 alloy

In the present work, the body-centered-cubic (BCC) Fe81Ga19 alloy was produced by twin-roll strip casting technology. The following warm rolling and slow heating heat treatment (from 800 ℃ to 1200 ℃, 20 ℃/h) was successfully applied to realize the secondary recrystallization of Goss grains. The magnetostrictive coefficient of the complete secondary recrystallization sheet was ~197 ppm. Deformation twins can be observed by electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) in warm-rolled sheets. An in-situ compression experiment showed that deformation twinning was related to grain orientation. The twins first formed in the grains with a higher Schmid factor and then appeared in the lower Schmid factor grains with the increase of deformation. Besides, deformation twinning can adjust the grain orientation and further activate dislocation slip. The unique Slip-Twinning-Shearing plastic deformation mechanism of BCC Fe-Ga alloy provides the possibility to overcome the intrinsic brittleness and produce sheets by rolling technology.

Effect of Σ3 grain boundaries on microstructure and properties of oriented Fe-6.5 wt%Si in twin-roll strip casting

Oriented Fe-6.5 wt%Si alloy with excellent magnetic properties was prepared by twin-roll strip casting (TRSC). We studied the abnormal Σ3 grain boundaries in the as-cast strip. The experimental results demonstrated that the Σ3 grain boundary (GB) in oriented Fe-6.5 wt%Si steel had a good thermal stability, which could refine the microstructure by inhibiting growth of structure in as-cast strip. Moreover, the Σ3 GB in Fe-6.5 wt%Si as-cast strip could improve the toughness of matrix and restrain the propagation of cracks, which was beneficial to its plastic working. The Σ3 GB was relatively stable during warm rolling and could be inherited partly after annealing. At the same time, the low migration rate of Σ3 GB in primary recrystallization structure could stabilize the matrix and help to obtain the abnormal growth of Goss grains. The finished Fe-6.5 wt%Si steel had excellent magnetic properties, B800 and P10/50 were 1.76 T and 0.59 W/kg, respectively.

Microstructure and properties of ultra-thick Fe-based metallic glass by twin-roll strip casting versus a traditional process

In this study, an ingenious twin-roll strip casting approach is described to process large-size Fe71Ni9P12B4.9Si2.5Cu0.6 amorphous ribbons. The 150 μm thick RT ribbon (novel process) characterized by a completely amorphous structure is 5 to 7 times thicker than the conventional Fe-based RS (conventional process) ribbon. The minimum cooling rates of the RS and RT ribbon were 1.78 × 106 and 5.58 × 105 K/s. The RT ribbon's excellent thermodynamic properties led to fine grain size and a high magnetic induction of 1.63 T. However, high internal stress led to a large magnetocrystalline anisotropy. The hardness of the two ribbons was similar at ∼1160 Hv. Moreover, the significant size effect led to a slight decrease in the fracture toughness of the RT ribbon. The impressive specifications, high impurity tolerance, and good properties of the RT ribbon render twin-roll strip casting promising for industrial applications.

Numerical and experimental research on solidification of T2 copper alloy during the twin-roll casting

Abstract Based on CAFE theory and KGT model, the twin-roll strip casting mathematical model was established to solve the dendrite growth and solidification of T2 copper alloy in the molten pool. The influence mechanism of casting temperature, heat transfer, and other technological conditions on the microstructure of strip was analyzed. The results showed that the liquid metal formed 35 µm chilling layer after touching the rollers, and the layer was consisted of a high number of small and equiaxed crystals. Then some grains would appear close to the newly chilling layer, and grow toward the core of molten pool competitively. The dominant grains mainly grew along the 〈001〉 orientation into columnar crystals, and the rest grains that grew out of alignment were eliminated gradually. The number of grains declined, and the radius of columnar grains became coarsening. The Kiss point is a key factor for solidification structure, and the lower location of the Kiss point could limit the growth spaces of columnar crystals, which refined the grains.