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A medium-Mn steel (Fe–0.3C–4Mn–1.82Al–0.6Si wt-%) was produced by a novel processing route involving twin-roll strip casting, hot rolling and intercritical annealing (IA). Macrosegregation was abse...

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 B50 = 1.758 T, P15/50 = 2.065 W/kg, P10/400 = 15.173 W/kg, P10/1k = 59.48 W/kg.

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 &deg, C. The corresponding growth rates were in the range of 60&ndash, 1400 &mu, m/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 &gamma, 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.

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 (B50 = 1.72 T, P10/400 = 14.91 W/kg) were obtained. Keywords: Thin-gauge non-oriented electrical steel, Twin-roll strip casting, Microstructure, Texture, Magnetic properties

High silicon steel was fabricated by twin-roll strip casting. The cracks on the surfaces of the processed strips were obtained and analyzed by digital camera after series of surface treatment. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to observe and characterize the microstructure nearby crack and fracture surface along the normal direction, respectively, and the crack formation mechanism was further analyzed in conjunction with processing parameters utilized during twin-roll strip casting process. The results indicated that morelongitudinal cracks along the rolling direction were observed in comparison with transverse cracks along the transverse direction on the strip surfaces. Trans granular and intergranular fracture modes both worked during the formations of longitudinal and transverse cracks on the processed strips. The dominant factor causing the formation of crack on the surface of the processed strips was the inhomogeneous transfer of heat during casting and rolling. The inhomogeneous transfer of heat induced by gas gap during casting resulted in variations of dendrite length and secondary dendrite spacing (SDAS). Meanwhile, the casting velocity influenced the formation of gas gap, which further influenced the thermal contraction. So the control of velocity of casting above a certain level proved beneficial to enhancing the performance of strip casting and to improving the quality of strip products.

Grain-oriented 6.5%Si steel was produced by strip-casting, followed hot rolling, cold rolling, primary annealing and secondary annealing. Microstructural and textural evolution was studied with particular focus on the effect of solidified microstructure on the ultimate microstructure and texture. The study indicated that solidified microstructure of the as-cast strip was determined by melt superheat. The relatively low melt superheat resulted in fine equiaxed grains with random texture, whereas large melt superheat led to coarse grains with moderate λ-fiber texture. After cold rolling, the fine-grained steel showed narrow pancake grain structure in comparison to the coarse-grained steel, which was similar to the microstructure of the initial as-cast strip. After primary annealing, fine equiaxed microstructure with favorable {111}⟨112⟩ texture was obtained in the fine-grained steel. While inhomogeneous microstructure with strong α-fiber and moderate γ-fiber texture was obtained in the coarse-grained steel. The desirable microstructure and texture in the fine-grained steel led to abnormal grain growth with B8 = 1.65 T after secondary annealing. By comparison, normal grain growth occurred in the coarse-grained sample with B8 = 1.37 T. Another observation was high frequency core losses of grain-oriented 6.5%Si steel sheet with adequate secondary grains was significantly lower than non-oriented 6.5%Si steel and grain-oriented 3.0%Si steel. The study suggests that the strip-casting is a suitable route to fabricate grain-oriented 6.5%Si steel, and the initial fine grain size with random texture is preferred to obtain adequate abnormal grain growth.

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.

An unconventional cold rolling scheme (inclined rolling at 0°, 30°, 45°, 90° during second-stage cold rolling process) was adopted to process grain-oriented silicon steel based on strip casting process. The influences of inclination angles on microstructure, texture, inhibitor and magnetic properties were studied by a combination of EBSD, XRD and TEM. It was found that the α-fiber texture was weakened and γ-fiber was strengthened in cold rolled sheet with increase in inclination angle. The primary recrystallization sheet exhibited more homogeneous microstructure with relatively strong γ-fiber, medium α-fiber texture, weak λ-fiber texture and Goss component at high inclination angles. Fine and homogeneous inhibitors were obtained after primary annealing with increase in inclination angle from 0° to 90° because of more uniform deformation after inclined rolling. The grain-oriented silicon steel experienced completely secondary recrystallization at various inclination angles after final annealing process, with superior magnetic properties at 0° and 90°. Furthermore, Goss nuclei capable of final secondary recrystallization in strip casting process newly formed both in-grain shear bands and grain boundaries region during second-stage cold rolling and subsequent annealing process, which is different from the well-accepted results that Goss texture originated from the subsurface layer of the hot rolled sheet or during intermediate annealing process. In addition, the Goss texture that nucleated in-grain shear bands was weaker but more accurate as compared to that in grain boundaries region.

A Fe-3.0%Si non-oriented silicon steel was produced by a novel strip casting process. Cold-rolled sheets were annealed at temperatures varying from 900 to 1200 ° C with the aim to investigate the influence of recrystallization annealing process on the microstructure, texture and magnetic properties. The increase in annealing temperature significantly increased the recrystallized grain size and reduced the core loss. However, the oversized microstructure (~360 μm) in 1200 ° C annealed sheets resulted in an augment in core loss. In addition, with increasing annealing temperature, the magnetic induction diminished along the rolling direction while gradually increased along the transverse direction, even though the average value changed slightly. This interesting result could be attributed to the weakening in η -fiber and strengthening in λ -fiber and γ -fiber texture. The best combination of core loss (3.23 W/kg), magnetic induction (1.71 T) and anisotropy was obtained at recrystallization annealing of 1100 ° C. The specified and unspecified errors in this paper have been carefully corrected, and

Thin gauge grain-oriented (GO) silicon steel with high permeability was successfully processed by a simple way based on strip casting process, without hot rolling and decarburization annealing. The primary annealed sheet exhibited unique characteristics of homogeneous precipitation because of near-rapid solidification, and fine-grained recrystallized microstructure with relatively strong Goss texture and pronounced {111} 〈112〉 texture, which was responsible for the subsequent Goss abnormal growth. MnS, (Nb,V)N and AlN precipitates provided strong pinning effect on grain boundaries at different stages during the final annealing process, which is referred as “sequential inhibition behavior”. The thin gauge GO silicon steel experienced complete secondary recrystallization induced by inhibitor, and exhibited sharp Goss texture together with significantly superior magnetic properties (magnetic induction B8 = 1.98 T; iron loss P1.7/50 = 0.7 W/kg). Keywords: Thin gauge grain oriented silicon steel, Strip casting, Magnetic properties, Microstructure, Precipitation, Secondary recrystallization

An ultra-low carbon grain-oriented silicon steel as-cast strip is produced by twin-roll strip casting process, and subsequently subjected to one-pass hot rolling, one-stage cold rolling, primary annealing, and secondary annealing. The effect of hot rolling process on microstructure, texture, and inhibitor evolution is studied. It is shown that the precipitation behavior of AlN particles is significantly affected by the hot rolling temperature and the optimal precipitation temperature is ≈1100 °C. On the other hand, the intensity of Goss texture in hot-rolled sheets is determined by hot rolling reduction, which is limited in the strip casting process and the hot-rolled Goss texture is relatively weak compared to the conventional process. The primary annealed Goss texture can originate from the cold rolling process and this texture is homogeneous through the thickness, besides the inherited hot-rolled Goss texture mainly presented in the subsurface layer. Thus, relatively strong Goss texture in primary annealed sheets is obtained. The results indicate that the hot rolling process is an efficient way to optimize the texture and precipitation in strip-cast silicon steel, and relatively good magnetic properties can be obtained by the strip casting process.

A 0.23 mm grain-oriented 4.5 wt% Si steel sheet was prepared by strip casting, hot rolling, one-stage warm rolling, primary annealing and secondary annealing. A detailed study of microstructure, texture and precipitate was carried out by methods of OM, EBSD, XRD and TEM. It was found that the as-cast strip exhibited equaxied microstructure with random orientation, enabling the fine and homogeneous primary microstructure to be obtained after one-stage warm rolling. After hot rolling, weak Goss texture was observed, which could not act as Goss seed. In contrast, the Goss seed was found to originate within the shear bands in {111}〈112〉 grains during warm rolling. Another finding was that the precipitates was suppressed during strip casting due to the rapid solidification and subsequent cooling rate, and mainly precipitated during hot rolling. After secondary annealing, abnormal Goss grains evolved sufficiently, and showed prominent properties. The B 8 was 1.73 T, which was similar to 1.85 T for grain-oriented 3.0 wt% Si steel, and the core losses were low than the grain-oriented 3.0 wt% Si steel and non-oriented high silicon steel.

A Fe-1.3% Si non-oriented silicon steel strip was produced by twin-roll strip casting process, and subsequently treated with cold rolling and annealing. The effect of heating rates on the recrystallization and precipitation behavior of second phase particles (AlN and MnS) was investigated by MMS-200 thermal mechanical simulator. It was found that the recrystallization area fraction decreased obviously with the increase of heating rate. At the heating rate of 5 °C/s, the recrystallization rate gradually decreased with the extension of holding time, but it increased at the rapid heating rates. The particle’s sizes mainly concentrated in 50~200 nm at the heating rate of 5 °C/s during annealing. The number of particles under 50nm increased gradually and the number of precipitates between 50~400 nm reduced significantly when the heating rate was increased to 50~300 °C/s. The results indicated that the rapid heating rate could refine the size of precipitates and decrease the number of particles above 50nm.

Grain-oriented 6.5% Si steel was produced by strip casting and the effect of warm rolling and cold rolling at the latter stage of rolling was investigated. The result showed the rolling method had a minor influence on the rolling microstructure but significant on the rolling texture. Compared to the cold-rolled sheet, the warm-rolled steel showed strong α -fiber and γ -fiber texture at the surface but weak α -fiber and γ -fiber texture in the center layer. After primary annealing, the warm-rolled sheet showed inhomogeneous microstructure and strong { 2 2 3 } 〈 1 1 0 〉 texture together with weak γ -fiber texture. By comparison, the cold-rolled sheet showed fine equiaxed grain with favorable { 1 1 1 } 〈 1 1 2 〉 texture component. During secondary annealing, the warm-rolled sample displayed significantly normal grain growth at the initial stage and abnormal grain growth at ~1150 °C. The final microstructure was characterized by coarse matrix grains and abnormal Goss grain. In contrast, the cold-rolled sheet showed complete abnormal grain growth. The different secondary annealing behavior was attributed to different grain structure and texture.

An ultra-low carbon Fe–3%Si grain oriented electrical steel strip was produced by a twin roll strip casting process. Next, the strip with or without annealing was cold rolled and subsequently annealed. The effect of annealing after strip casting on the texture development was studied using macro-/micro texture analysis. Due to the rapid solidification, the precipitation behavior of second phase particles was suppressed and very few particles were observed in the as-cast strip. The direct cold rolled texture was characterized by strong α ( //RD) and weak γ ({111}//ND) fibers. While, in the annealed strip, a large number of particles were precipitated during the annealing of the cast strip and these particles hindered the crystal rotation during cold rolling such that part of the initial solidification texture remained in the cold rolled sheet. In the case of the direct cold rolling process, the precipitation occurred before recrystallization during primary annealing. These fine particles had a significant pinning effect on dislocations and further retarded the recrystallization behavior, leading to relatively strong α-fiber in the primary annealed sheet. On the other hand, compared with the fine and dispersed particles precipitated during the strip annealing process, the distribution of particles precipitated during primary annealing were inhomogeneous. Therefore, there was no secondary recrystallization during secondary annealing, which was distinct from the strip annealing process where abnormal growth of Goss grains were observed and the magnetic properties were significantly improved.

Grain oriented silicon steel was produced by strip casting and two-stage cold rolling processes. The development of microstructure and texture was investigated by using optical microscopy, X-ray diffraction and electron backscattered diffraction. It is shown that the microstructure and texture evolutions of strip casting grain oriented silicon steel are significantly distinct from those in the conventional processing route. The as-cast strip is composed of coarse solidification grains and characterized by pronounced 〈001〉//ND texture together with very weak Goss texture. The initial coarse microstructure enhances {111} shear bands formation during the first cold rolling and then leads to the homogeneously distributed Goss grains through the thickness of intermediate annealed sheet. After the secondary cold rolling and primary annealing, strong γ fiber texture with a peak at {111}〈112〉 dominates the primary recrystallization texture, which is beneficial to the abnormal growth of Goss grain during the subsequent high temperature annealing. Therefore, the secondary recrystallization of Goss orientation evolves completely after the high temperature annealing and the grain oriented silicon steel with a good magnetic properties ( B 8 =1.94 T, P 1.7/50 =1.3 W/kg) can be prepared.

Texture evolution in Fe-1.3%Si steels with ultra-high magnetic induction produced by strip casting, cold rolling and annealing was investigated using macro-/micro-texture analysis. A new and strong {1 1 0} fiber has been founded in thin as-cast sheets. The in-grain shear bands with the Cube orientation can be observed in deformed {1 1 0}〈1 1 0〉 grains after cold rolling. The new Cube grains are mainly nucleated and grow within those shear bands at the beginning of recrystallization and consequently determine the overall annealing texture.

A Fe-3wt%Si strip was produced using a vertical type twin-roll strip casting process, and two typical initial structures were observed. One was the solidification structure consisting of coarse columnar grains and the other was the deformed structure which was composed of outer inclined columnar grains and inner fine equxied grains. The solidification structure was characterized by {111}//ND fiber while the deformed structure shows a strong Goss texture. In addition, the size distributions of MnS precipitates, which were used as grain growth inhibiters, were investigated in the as-cast strip. The size of these particles in the deformed grains was smaller than that in the solidified grains, which could be attributed to the strain-induced precipitation mechanism. The differences of the initial structures, texture and precipitation behaviors resulted from the different superheating along the transverse direction of the as-cast strip, which originated from the inhomogeneous flowing of liquid steel.

In this work, the evolution of microstructure, texture and magnetic properties of non-oriented 1.3% silicon steel processed using the twin-roll strip casting was investigated, especially under different solidification structures. A number of microstructures about the as-cast strips show that the initial solidification structure of casting a strip can be controlled by the melt superheats. The microstructures with the average grain size of ∼100–400 μm can be obtained in strips when the melt superheats are from 20 to 60 °C. A nearly random, diffuse, homogeneous texture under a low melt superheat, but comparatively developed {100} oriented grains are formed under a high melt superheat through the cast strip thickness. The relatively low core loss and high magnetic induction can be obtained in the cold rolled and annealed sheets when increasing the initial grain size of cast-strip. The textures in annealed sheets with coarse initial grain size are characterized by the relatively strong Goss component and {001} fiber but weak γ-fiber component, which lead to the high permeability.

The simulation studies were carried out on the oriented silicon steel produced by thin slab casting and rolling (TSCR) and twin-roll strip casting in the laboratory. The precipitation of inhibiter, formation of microstructure and texture were investigated before cold rolling. The inhomogeneous microstructure and texture gradient were observed in the 7-pass hot-rolled strip（2mm）for TSCR process, and texture gradient was not changed after normalizing, and the twin-roll strip casting directly supplied a strip with approx 2mm of thickness being same as that of hot-rolled strip by TSCR. The microstructure of twin-rolling casting strip was almost composed of all equiaxed grains which similar to the normalizing microstructure in TSCR process, but the random texture was obtained by twin-rolling strip casting. The dispersed and clustered precipitates were presented in hot-rolled strip when the ingots were soaked at 1200°C and 1150°C respectively for the TSCR process. And disperse and acicular precipitates were observed by TEM for air-cooling cast strips for process twin-rolling casting.

Grain-oriented 4.5%Si steel is processed by strip casting and two-stage rolling with second rolling reduction varied from 53.3 to 82.7%. The microstructure and texture evolution are studied with emphasis on the effect of second rolling reduction on secondary recrystallization. After secondary annealing, significant abnormal grain growth occurs for all reductions in the range of 53.3–82.7%. The underlying reason is the strong inhibiting force induced by additional Nb, and the grain diameter of the secondary grains increase with increased rolling reduction. Additionally, the sharpness of secondary grains to ideal Goss orientation increase with increase in second rolling reduction. This is attributed to decreased inhibiting force drop rate between abnormal grain growth of precise Goss and deviated Goss grains with increased rolling reduction. Another interesting aspect is enhancement of magnetic induction B8 and significant reduction in high frequency (400–1000 Hz) core losses with increase in second rolling reduction. Optimal magnetic properties are obtained in the steel subjected to 82.7% rolling reduction. The present study suggests that strip casting is an effective approach to fabricate grain-oriented high silicon steel, especially thin-gauged steels with superior magnetic properties.