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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.

0.3 mm‐thick grain‐oriented silicon steel sheets with varying Y contents are produced via twin‐roll strip‐casting and two‐stage cold rolling process. This study primarily investigates the evolution of microstructure, texture, and precipitation along the processing. Specifically, the effect of rare earth Y on second‐phase particle precipitation in ultralow carbon grain‐oriented silicon steel is examined. Results indicate that higher Y content will consume beneficial inhibitor elements such as S and N, leading to the formation of coarse rare earth inclusions (≈10 μm) in the cast strip. This significantly diminishes inhibition ability and magnetic induction (B8 = 1.58 T≈1.71 T). On the contrary, the addition of trace Y can accelerate the precipitation of inhibitors. During the intermediate annealing stage, steel with trace Y exhibits a significant enhancement in precipitate distribution density (from 2.8 μm−2 to 13.6 μm−2), and the final magnetic induction B8 increases from 1.86 T to 1.91 T compared to steel without Y. In addition, the results of first‐principle calculations based on density functional theory reveal that the doped Y atom prefers to segregate at the Al–N interface, and the interface energy reduces from 1.871 J m−2 to 1.024 J m−2, thereby promoting the precipitation of AlN. [ABSTRACT FROM AUTHOR]

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.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Electrical steels can be classified into two groups: grain-oriented (GO) and non-oriented (NGO) electrical steel. NGO electrical steels are mainly considered as core materials for different devices, such as electric motors, generators, and rotating machines. The magnetic properties and texture evolution of NGO electrical steels depend on multiple factors (such as chemical content, heat-treatment, and rolling process) making the development of new products a complex task. In this review, studies on the magnetic properties of NGO electrical steels and the corresponding texture evolution are summarized. The results indicate that further research is required for NGO electrical steels to ensure high permeability and low core loss properties. [ABSTRACT FROM AUTHOR]

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.

A magnesium alloy containing essential, non-toxic, biodegradable elements such as Ca and Zn has been fabricated using a novel twin-roll casting process (TRC). Microstructure, mechanical properties, in vivo corrosion and biocompatibility have been assessed and compared to the properties of the rare earth (RE) element containing WE43 alloy. TRC Mg-0.5 wt% Zn- 0.5 wt% Ca exhibited fine grains with an average grain size ranging from 70 to 150 μm. Mechanical properties of a TRC Mg-0.5Zn-0.5Ca alloy showed an ultimate tensile strength of 220 MPa and ductility of 9.3%. The TRC Mg-0.5Zn-0.5Ca alloy showed a degradation rate of 0.51 ± 0.07 mm/y similar to that of the WE43 alloy (0.47 ± 0.09 mm/y) in the rat model after 1 week of implantation. By week 4 the biodegradation rates of both alloys studied were lowered and stabilized with fewer gas pockets around the implant. The histological analysis shows that both WE43 and TRC Mg-0.5Zn-0.5Ca alloy triggered comparable tissue healing responses at respective times of implantation. The presence of more organized scarring tissue around the TRC Mg-0.5Zn-0.5Ca alloys suggests that the biodegradation of the RE-free alloy may be more conducive to the tissue proliferation and remodelling process.

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.

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.

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.

FeCrAlY alloys are widely used as thin‐gauge catalyst carriers for automotive exhaust gas purification. However, they exhibit low ductility due to coarse Fe–Y phases in the alloys, which decreases the carrier yield. To improve the plasticity of the alloys, a novel method for fabricating FeCrAlY alloys using twin‐roll strip casting (TRSC) is proposed. It is found that the plasticity of the FeCrAlY alloy is significantly improved by TRSC compared to conventional ingot casting. Then, to understand the mechanism of plasticity improvement, the microstructures of the alloys are investigated. The Fe–Y phases and grains are significantly refined by TRSC due to its characteristics of subrapid solidification. In addition, the TRSC samples produce several low‐Σ coincidence site lattice (CSL) boundaries, and some of these CSL grain boundaries are inherited by the cold‐rolled sheets. The impact characteristic of steel liquid in the TRSC is the major reason for the formation of CSL grain boundaries. The finer microstructure and greater number of low‐Σ CSL boundaries in the TRSC samples result in strong resistance to fracture, which improves the plasticity of the FeCrAl alloys. [ABSTRACT FROM AUTHOR]

Electrical steels can be classified into two groups: grain-oriented (GO) and non-oriented (NGO) electrical steel. NGO electrical steels are mainly considered as core materials for different devices, such as electric motors, generators, and rotating machines. The magnetic properties and texture evolution of NGO electrical steels depend on multiple factors (such as chemical content, heat-treatment, and rolling process) making the development of new products a complex task. In this review, studies on the magnetic properties of NGO electrical steels and the corresponding texture evolution are summarized. The results indicate that further research is required for NGO electrical steels to ensure high permeability and low core loss properties.

Two FeCrAlZr alloys are fabricated by twin‐roll strip casting (TRSC) and ingot casting (IC), and different Zr distributions are formed. After cyclic oxidation tests at 1200 °C for 200 h in air, it is found that the scale spallation resistance in the FeCrAlZr alloy is improved by homogenizing the Zr distribution by TRSC. To understand the improvement in oxidation resistance, the composition and microstructure of the thermally grown scales are investigated. During oxidation, Zr diffuses toward the scale and forms ZrO2 particles in the scale and at the surface of the oxide scale. Meanwhile, the outward diffusion of Zr inhibits the formation of interfacial voids and S segregation regardless of Zr distribution. However, the TRSC sample with a more uniform Zr distribution can form the high‐density oxide penetrations, keying the scale to the matrix and improving scale adhesion. The Zr fluxes toward the scales are calculated to explain the difference in the distribution of oxide penetrations in the TRSC and IC samples during oxidation. [ABSTRACT FROM AUTHOR]

Metallic materials have historic and served as critical enablers of human progress, wealth, and wellbeing over millennia. Recently, the global demand for the development of environment-friendly and energy-saving technology has been increasing, with the aim to support the sustainability of metallic materials. Twin-roll strip casting (TRC) is one of the most cutting-edge technologies and a near-net-shape manufacturing method in the steel industry, which conforms to the green fabrication trend of next-generation high-performance metallic materials. By utilizing the dominant characteristics of sub-rapid solidification, and integration of solidification, solid-state transformation, and deformation; TRC has become a meaningful way to deal with the most challenging issues in the processing of metallic materials, and made a significant contribution to materials manufacturing. Hence, we review the TRC process of various metallic materials, including plain carbon steels, stainless steels, Fe-Si electrical steels, high-strength steels, clad steels, aluminum alloys, magnesium alloys, metallic glasses, and so on This paper offers an outlook of future opportunities for various advanced metallic materials development through the TRC process, and inspires more in-depth research. [ABSTRACT FROM AUTHOR]

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.

Abstract During the oscillating twin-roll strip casting process, the quality of final products is directly influenced by the flow field distribution of molten metal in the pool. The variation in the flow field is caused by oscillating roller benefits, for homogeneous distribution of strip impurity, and decreasing the grain size. Thus, the quality of the strip could be improved. A numerical model was developed using the multiphase flow technology, coupled with heat transfer, fluid flow, solidification, and oscillation. Furthermore, a transient algorithm was adopted for simulating the oscillating twin-roll strip casting process of AlSi9Cu3 and 3104 aluminum alloy. This paper focuses on the flow distribution in the pool, in comparison with the traditional vertical twin-roll strip casting process, while the amplitude or frequency is changing with the definite value of casting velocity, roller diameter, nozzle angle, and the strip thickness. Consequently, the conclusions were experimentally validated by oscillating twin-roll 3104 aluminum alloy strip casting. Vibrating casting technology can change the flow field in the pool by vibration, which can improve the quality of the strip core.

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. [ABSTRACT FROM AUTHOR]

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. Image, graphical abstract [ABSTRACT FROM AUTHOR]

A unique bimodal microstructure is proposed to improve the mechanical properties of low‐carbon steels produced by twin‐roll casting. The ultrafine inclusions (0.2–2.0 μm) are produced in the as‐cast matrix. A high proportion of ultrafine acicular ferrite (UFAF) is induced due to these inclusions by controlling the critical processing factor, i.e., the cooling rate during γ → α transformation process. Therefore, heterogeneous microstructure is characterized by UFAF cluster, and network‐like coarse polygonal ferrite (PF) with a bimodal grain size distribution is engineered, significantly increasing the strength while not obviously damaging the plasticity. In addition, a new acicular ferrite (AF) heterogeneous nucleation mechanism is reported. [ABSTRACT FROM AUTHOR]

Twin-roll strip casters for near-net-shape manufacture of steels have received increased attention in the steel industry. Although negative segregation of phosphorus occurred in twin-roll strip casting (TRSC) steels in our prior work, its mechanism is still unclear. In this work, V-shaped molds were designed and used to simulate a meta-rapid solidification process without roll separating force during twin roll casting of carbon steels. Experimental results show that no obvious phosphorus segregation exist in the V-shaped mold casting (VMC) steels. By comparing TRSC and the VMC, it is proposed that the negative phosphorus segregation during TRSC results from phosphorus redistribution driven by recirculating and vortex flow in the molten pool. Meanwhile, solute atoms near the advancing interface are overtaken and incorporated into the solid because of the high solidification speed. The high rolling force could promote the negative segregation of alloying elements in TRSC.

Cube texture and microstructural evolution of as-cast non-oriented silicon steel (1.3% Si) during cold rolling and annealing were studied. The results showed that the as-cast microstructure with grain size in the range of 100–500 μm had a weak texture. The strong orientation was mainly located at {100} and {110} planes. A significant content of shear-deformed grains oriented with {110} were obtained by cold-rolling, and many regions oriented with Cube texture were distributed in the shear bands. During cold-rolling, the orientation of the shear-deformed microstructure tilted towards the {111} orientation, while the matrix orientation retained {110}. On further cold-rolling, the residual part of {110} experienced shear deformation, forming more shear bands, strengthening the Cube orientation. During annealing, Cube orientation grains nucleated in the shear bands leading to strong Cube texture, and corresponding B50 was 1.83T/1.79T.

Abstract A new method for producing high permeability thin-gauge non-oriented electrical steels with 2.3 mm thick Fe-3.2% Si steel as-cast strip was studied. The evolution of microstructure and texture was characterized during the entire processing route. Furthermore, the effects of cold-rolling with large reduction and intermediate annealing process on magnetic properties were studied. The results indicated that the as-cast strip with coarse grains exhibited strong λ-fiber. Coarse equiaxed grains with Cube texture were obtained after first-stage cold-rolling with a reduction of 71.74% and intermediate annealing at 900 °C, which promoted the formation of λ-fiber and α-fiber components in the final cold-rolled sheets. {100}⟨0vw⟩ texture was partially retained from the intermediate annealed grains, and new Cube and Goss components were nucleated within {110}〈110〉 shear bands. The magnetic properties of 0.2 mm final sheets were greatly improved by strengthening λ-fiber component with two-stage rolling process, and best magnetic properties were B 50 = 1.758 T, P 15/50 = 2.065 W/kg, P 10/400 = 15.173 W/kg, P 10/1k = 59.48 W/kg. Highlights • Thin-gauge non-oriented silicon steel with high magnetic properties was produced by twin-roll strip casting. • The effects of cold-rolling with large reduction and intermediate annealing process on magnetic properties were studied. • Role of rolling methods in microstructure and texture evolution along the entire route was explored. • The magnetic properties were improved by strong {100}⟨0vw⟩ texture. [ABSTRACT FROM AUTHOR]

Abstract High borated stainless steel sheets have been widely applied in the nuclear power industry because of good thermal neutron absorption property. However, the large and network-like borides existing around the austenite grains in the conventional ingot casting steel seriously deteriorate the hot workability and the mechanical properties at ambient temperature. In this work, we tried to acquire ultra-fine microstructure by sub-rapid solidification using a novel twin-roll strip casting technology so as to enhance the mechanical properties of 2.1%B austenitic stainless steel. Surprisingly, dispersive and very fine borides mostly smaller than 5 µm were produced in the as-cast microstructure without network-like distribution. The morphologies and crystal structure of borides as well as the stacking faults in borides were investigated in detail. After subsequent hot-rolling and solution treatment, ultra-fine borides were observed with more than 50% of which in a size range of 0.3–1.5 µm, significantly smaller than those of the conventional ingot casted and hot rolled steel. Benefiting from the ultra-fine borides, excellent mechanical properties which had not been reported were obtained. In particular, a total elongation of 14.1% was exhibited, which was twice as high as that of the conventional ingot casted and hot rolled steel. Thus a new structure-function combining high borated stainless steel sheet was achieved. The strengthening and plasticity increasing mechanism was discussed based on Hall-Petch relationship, Orowan mechanism and strain-hardening rate analysis. The fracture behavior in tensile deformation was studied in detail. A characteristic fracture process accompanied with the initiation and coalescence of cavities in austenite matrix was found. This work not only developed a new processing way to produce high borated stainless steel with excellent mechanical properties, but also provided a potential solution for some other hard-worked metallic materials with brittle eutectic phase. [ABSTRACT FROM AUTHOR]

Abstract Isothermal aging treatments in the temperature range from 550 to 1150 °C for the aging time range from 2 to 2880 min were carried out on 20Cr-24Ni-6Mo super-austenitic stainless steel plates, which were processed by conventional casting and twin-roll strip casting (TRSC). Precipitation behaviors were comparatively studied, from which Time-Temperature-Precipitation (TTP) curves were developed. The results show that two TTP curves basically exhibited C-shapes and each TTP curve was the superposition of sigma and Laves precipitation kinetics curves. When the temperature was higher than about 825 °C, TTP curves were mainly sigma precipitation kinetics curves. On the contrary, TTP curves were mainly sigma and Laves precipitation kinetics curves. Aging temperatures of the precipitation sensitive interval were about in the range from 875 to 1025 °C. The nose temperature of conventional specimen was about 925 °C and the corresponding incubation time was about 2 min. However, the nose temperature of cast strip (CS) specimen was about 950 °C and the corresponding incubation time was about 4 min. TTP curve of CS specimens moved to the upper right as compared to that of conventional specimens, indicating that the precipitation in CS specimens was delayed. By analyzing the compositional distribution in the conventional and CS specimens after solution treatment, it was found that after the completion of solution treatment, the distribution of alloying elements in the CS plate was more homogeneous than that in conventional plate. Therefore, the conventional specimen was more susceptible to the formation of precipitates in aging treatments. Highlights • Precipitation kinetics for conventional and cast strip (CS) specimens was established. • TTP curves of conventional and CS specimens basically exhibited C-shapes. • Each TTP curve was the superposition of σ and Laves precipitation kinetics curves. • The sensitive precipitation processes were about 925 °C & 2 min for conventional specimens and 950 °C & 4 min for CS specimens. • σ was detected at 650–1050 °C, while Laves was mainly detected below 825 °C. [ABSTRACT FROM AUTHOR]

The Nb-bearing grain-oriented silicon steel sheets were produced by conventional route and novel twin-roll casting route, respectively. The microstructure, texture and precipitate evolution were comparatively investigated by using electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). The findings revealed that the precipitation behavior and the texture evolution were totally different between the two processing routes. In the conventional route, a great number of nanoscale niobium nitride particles (NbN), which acted as mainly grain growth inhibitors were precipitated during hot rolling, while in the twin-roll casting route, due to the rapid solidification, the precipitation of NbN were suppressed and a new type Nb-bearing precipitate enriched with sulfur element was observed in the as-cast strip. Besides, the primary recrystallized texture of conventional specimens was characterized by strong γ-fiber with a peak at {111} , together with very few Goss components. While in the case of twin-roll casting specimens, the strongest primary recrystallized texture was {111} texture and the area fraction of Goss component was much higher than that of conventional specimens. After final high temperature annealing, complete secondary recrystallization was obtained in twin-roll casting specimens and the magnetic induction of B8 was 0.1 T higher than that of conventional specimens.

The thin strip of novel TRIP‐aided Ni‐free lean duplex stainless steel with good corrosion resistance is fabricated by twin‐roll strip casting. The microstructure, corrosion resistance, and mechanical properties of the present Ni‐free steel (DSS‐2) are investigated in detail in this study. Meanwhile, comparison with duplex stainless steel containing about 2% Ni (DSS‐1) is also conducted to discuss the effect of alloying Ni on corrosion resistance and mechanical properties. The DSS‐2 has the more excellent mechanical properties than the comparison steel DSS‐1 due to the strain induced martensitic transformation during plastic deformation, which the ultimate tensile strength and total elongation are measured to be about 960 MPa and 55%, respectively. The strain induced martensitic transformation in DSS‐2 will be suppressed with the increase of solid solution treatment temperature and strain rate. The austenitic stability is more dependent on element partitioning in austenite phase than on grain size of austenite for the present TRIP‐aided Ni‐free lean duplex stainless steel. The novel Ni‐free steel has the better corrosion resistance and mechanical properties than the austenitic stainless steel SUS304, which may potentially be applied to substitute SUS304 in some fields as anti‐corrosive structural material. [ABSTRACT FROM AUTHOR]

A 3.1 mm thick non-oriented Fe-1.0% Si steel as-cast strip was produced by twin-roll strip casting. Samples with/without strip annealing were cold rolled to 0.5 mm and then annealed. The development of microstructure, precipitate and texture was characterized along the entire processing route. It was found that annealing after strip casting had a minor influence on the average grain size and texture of the as-cast strip. A large number of particles precipitated and coarsened during the strip annealing process. Meanwhile, precipitates hindered dislocation slip and crystal rotation such that more significant in-grain shear bands were formed in cold rolled sheets. During recrystallization annealing process, the newly formed fine precipitates in directly cold-rolled sheets consumed stored strain energy and also hindered grain growth. But the initial precipitates in the annealed strip grew further and the effect of pinning of dislocations and grain boundary was lost. Therefore, annealed sheets with strip annealing process showed homogeneous equiaxed grains and the recrystallization texture was characterized by strong λ-fiber texture, which led to high permeability. [ABSTRACT FROM AUTHOR]

Low-carbon microalloyed steel was produced via twin-roll strip casting in the laboratory. The solidification structure， microstructure at room temperature， precipitate and dislocation of the as-cast strip were analyzed by OM， SEM and TEM. The results showed that the secondary dendrite arm spacing of the solidification structure is in the range of 12~15μm， which is much finer than that of the slab produced by the traditional process. The prior austenite grain of the as-cast strip is quite coarse with a size range of 250~410μm. The microstructure of the as-cast strip consists of Widmanstatten ferrite， pearlite and irregular ferrite. The nano-sized TiC precipitate and rod-like cementite are observed in the as-cast structure. The TiC precipitate in the as-cast strip is not obviously suppressed by the rapid solidification rate and secondary cooling rate (cooling in air) of the twin-roll strip casting. Furthermore， a large amount of dislocations in the as-cast strip are also observed， formed by rolling force among the casting rollers and nonuniform cooling rate of the second cooling process. [ABSTRACT FROM AUTHOR]

Texture optimization has always been a challenge to fabricate non-oriented electrical steels (NOES). In the present study, thin-gauge NOES with high permeability was successfully processed using an innovative and convenient twin-roll strip casting process without hot rolling. The relation between the as-cast microstructure, processing route and texture evolution was studied. The results indicated that as-cast strip with coarse grains exhibited strong {100}〈0vw〉 texture and unique {110}〈110〉 component. Annealed sheets processed by one-stage rolling displayed pronounced {111}〈112〉, {223}〈110〉 components and weak Cube and Goss texture. Micro-texture characteristics revealed that {100}〈0vw〉 texture was partially retained from initial grains, and new Cube and Goss substructures were generated within {110}〈110〉 deformed grains during cold rolling. This was responsible for the development of Cube and Goss recrystallization texture. Furthermore, the application of two-stage rolling not only reinforced these two behavior, but also accelerated the nucleation of η grains because of the increased shear bands in cold-rolled sheets. In this manner, an improved texture consisting of dominant η-fiber, weak γ-fiber and optimized magnetic properties (B 50 = 1.72 T, P 10/400 = 14.91 W/kg) were obtained. [ABSTRACT FROM AUTHOR]

Twin-roll strip casters for near-net-shape manufacture of steels have received increased attention in the steel industry. Although negative segregation of phosphorus occurred in twin-roll strip casting (TRSC) steels in our prior work, its mechanism is still unclear. In this work, V-shaped molds were designed and used to simulate a meta-rapid solidification process without roll separating force during twin roll casting of carbon steels. Experimental results show that no obvious phosphorus segregation exist in the V-shaped mold casting (VMC) steels. By comparing TRSC and the VMC, it is proposed that the negative phosphorus segregation during TRSC results from phosphorus redistribution driven by recirculating and vortex flow in the molten pool. Meanwhile, solute atoms near the advancing interface are overtaken and incorporated into the solid because of the high solidification speed. The high rolling force could promote the negative segregation of alloying elements in TRSC. [ABSTRACT FROM AUTHOR]

Increasing popularity of clad metals leads to a higher demand. To increase productivity and reduce production costs in comparison to established production routes, the production of clad steel strips by means of twin-roll casting is investigated. After first successful trials, the influence of downstream treatment on the bond within clad steel strips consisting of a stainless steel (X5CrNi18-10) cladding strip and a high manganese (Fe-17Mn-0.6C-1.5Al) cast strip produced by twin-roll casting is investigated in the present study. After hot rolling of the strips with a reduction of 20% and annealing for 1 h at 1150 °C, the bonding interface for three different conditions − rolled, annealed, as well as rolled and annealed − is examined and the bonding strength is determined qualitatively and quantitatively. The obtained results are then compared to previously obtained results with as-clad strips. The highest bonding strength is found in the hot rolled strips. It rises from an average of 250 MPa for as-clad strips to over 400 MPa. For the additionally annealed strips bonding strength decreases by approximately 40 MPa, while the lowest bonding strength has been measured for strips that have been annealed and not rolled. [ABSTRACT FROM AUTHOR]

The evolution of {411}<148> texture in a promising twin-roll strip casting of 4.5 wt% Si electrical steel was skillfully investigated. The results show that the selective growth mechanism, caused by orientation pinning, is responsible for the formation of the sharp {411}<148> component which is beyond the preferred nucleus spectrum. [ABSTRACT FROM AUTHOR]

The twin-roll cast Fe-2.8% Si-0.8% Al strips were directly cold rolled and annealed to investigate the effect of cold rolling reduction on deformation and recrystallization texture. The deformation texture is mainly composed of α， γ and λ fibers with peak at 001<110>， 111<110> and 001<110>~<210>， respectively. The main deformation texture components are enhanced when the reduction increases from 40% to 90%， while the shear banding becomes the most notable feature at 60% reduction. The recrystallization texture is characterized by Goss， λ fiber， 113<361>， Cube and 111<112> components. The dominant nucleation sites transform from shear bands to deformation bands and grain boundary regions as the cold rolling reduction increases， resulting in the weakening of Goss and the strengthening of λ fiber， 113<361>， Cube and 111<112> components. [ABSTRACT FROM AUTHOR]

• A large number of Σ3 grain boundaries characterized with twin were found in the solidification structure of strip-cast Fe-6.5 %Si alloy, especially the ratio over 15% in the solidified shell. • Σ3 grain boundaries was inherited into recrystallization structure during warm-rolling and heat treatment process, which could improve the plastic workability of oriented Fe-6.5 wt%Si. • Completely abnormal grain growth with accurate Goss orientation was obtained, resulting in magnetic induction intensity B8 of 1.76 T and iron loss of P 10/50 = 0.59 W/kg. 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, B 800 and P 10/50 were 1.76 T and 0.59 W/kg, respectively. [ABSTRACT FROM AUTHOR]

To adapt to the requirements of temperature variations in the process of twin-roll strip casting, a three-dimensional mathematical model was developed to analyze the heat transfer and temperature drop in the ladle using the finite volume method in the present study. The results showed that the temperature drop rate of the melt was 1·1 K·min−1 in the ladle of traditional casting, which could not satisfy with the demands in the process of twin-roll strip casting, and the temperature drop rate of the melt was 0·31 K·min−1 when more than 40 mm of a shielding agent was added on the slag surface and nanoporous materials were used as an insulation layer with thickness of more than 16 mm, which is considered to be favourable to provide the suitable temperature drop of the melt in the ladle to maintain the twin-roll strip casting process and improve the strip quality. [ABSTRACT FROM AUTHOR]

Non-oriented electrical steel as-cast strip was produced by twin roll strip casting process, and subsequently cold rolled and annealed at heating rates in the range of 3–450 °C/s with the aim to elucidate the effect of heating rate on the evolution of recrystallized microstructure and texture. The average grain size was rapidly increased when the heating rate was increased from 3 to 25 °C/s, and decreased when the heating rate was greater than 25 °C/s. The average grain size did not increase linearly with heating rate, which was related to different degree of nucleation and growth rate. The recrystallization texture exhibited pronounced improvement during rapid annealing. At high heating rate, the Goss and Cube had a higher probability of nucleation of shear bands with high stored energy, while the intensity of the γ-fiber texture was significantly reduced. The highest B 50 value attained was 1.803 T at a heating rate of 300 °C/s. The study indicates that rapid heating has strong effect on the recrystallization behavior in non-oriented electrical steels, which facilitates optimization of microstructure and texture, especially in the coarse-grained structure. [ABSTRACT FROM AUTHOR]

In this work, a high-manganese Fe–29Mn–0.3C TWIP steel was produced by twin-roll strip casting and subjected to additional thermo-mechanical treatment. The evolution of microstructure and texture in each processing condition was investigated and correlated with the corresponding mechanical properties. Due to pronounced microsegregations, chemical gradients and an inhomogeneous microstructure in the as-cast and hot-rolled material, regions of strongly varying stacking fault energy caused undesired austenite–martensite transformation and inhomogeneous mechanical properties. The specimens after additional cold rolling and annealing at temperatures as low as 900 °C revealed a microstructure with a homogeneous grain size distribution and significantly reduced microsegregations. The resulting mechanical properties were comparable to those of industrial advanced high strength steels and TWIP steel produced by conventional processing, where energy-consuming homogenization is necessary. Therefore, twin-roll strip casting offers the possibility for cost-effective processing of TWIP steel with competitive mechanical properties. [ABSTRACT FROM AUTHOR]

Twin-roll strip casting is an effective technology to produce magnesium alloy strips economically. The aim of this work is to propose suitable (optimized) process parameters for manufacturing AZ61 strips using the twin-roll strip casting technology. Experiments on twin-roll strip casting of an AZ61 magnesium alloy were carried out. Temperature fields, fluid flow fields, and stress fields accompanying the process were simulated using thermal-fluid and thermal-mechanical finite element methods. The effects of casting speed and pouring temperature on temperature fields, fluid flow fields, and stress fields during the process were analyzed. It was found that the optimum pouring temperature should be in the range 690∼715 °C and the optimum casting speed in the range 2.3 and 2.5 m/min. [ABSTRACT FROM AUTHOR]

Twin-roll strip casting represents a promising alternative for the production of high manganese steels. The present work demonstrates the opportunities for the production and further processing of a Fe-17Mn-0.6C-1.5Al TWIP steel. The mechanical properties are increased along the process chain and the cold strip exhibits a true stress of σ = 1500 MPa at a logarithmic strain of ɛ = 0.5. Combined EPMA and EBSD measurements allow for analyzing the influence of the inhomogeneous as-cast structure with pronounced microsegregations on twinning behavior. It was shown that twinning starts in the areas with a lower element concentration and thus with a lower local stacking fault energy. In addition, the fine as-cast structure with segregations only on the micron-scale has no negative influence on the resulting mechanical properties in the recrystallized cold strip. [ABSTRACT FROM AUTHOR]