Goss Grains Research Articles

Role of subsurface Goss-oriented grains in abnormal grain growth in Fe-3% Si steel

In this study, the differences in the crystallographic orientation, grain size, and grain boundary characteristic distribution along the sheet thickness in Si steel sheets were investigated in order to evaluate preferential sites for the abnormal grain growth of Goss-oriented grains. The grains having exact Goss orientation in the subsurface region of the primary recrystallized Si steel sheets had larger grain size, higher fraction, and higher frequencies of HEGBs and Σ9 GBs, which are claimed to be beneficial to the occurrence of the abnormal grain growth than the grains in the central region. On the other hand, the grains having deviated Goss orientation in the central region had larger grain size and higher Σ9 GBs than the grains having same orientation in the subsurface region. Therefore, it is considered that the high Goss selectivity is peculiar to the position of the nuclei and the beneficial conditions for the abnormal grain growth of exact Goss-orientated grains in the subsurface region.

Fatigue crack propagation within Al-Cu-Mg single crystals based on crystal plasticity and XFEM combined with cohesive zone model

A method combining crystal plasticity (CP), the eXtended Finite Element Method (XFEM), and cohesive zone model (CZM) with traction separation law is developed for an Al-Cu-Mg alloy to predict the effect of grain orientation on fatigue crack propagation (FCP) during stage ΙΙ within a single crystal. The simulation results show that of all the orientations, Goss grain possesses the largest fatigue crack deflection, then followed by Cube orientation. Comparatively, Brass, Copper, S and Random grains have relatively small crack deflection angles. Besides, it is found that Goss grain with the largest fatigue crack deflection possesses the lowest FCP rate as compared with other orientations. The results of simulations are consistent with previous experimental observations. This indicates that this coupled CP XFEM CZM simulation method is capable of well predicting the effect of grain orientation on FCP during fatigue stage ΙΙ of Al-Cu-Mg single crystal.

Role of Nb-bearing inhibitors in grain-oriented silicon steel manufactured by low-temperature slab reheating process

ABSTRACT A comparative study of precipitates, microstructure, texture and magnetic properties between conventional and Nb-bearing grain oriented silicon steel was carried out. The results show that fine and dispersed Nb-bearing particles are formed in Nb-bearing steel and show stronger pinning force during the whole heat treatment process, which makes a significant effect on the microstructure and texture evolution during the preparation process. Compared to conventional grain oriented silicon steel, Nb-bearing steel exhibits finer microstructure and possesses more Goss grains in hot-rolled band and normalized band. In primary recrystallized band, fine and uniform microstructure is presented in Nb-bearing steel, meanwhile, it is also characterized by strong γ-fiber and {114}<481> texture. After final annealing, Nb-bearing steel shows better magnetic properties, B 800=1.87 T and P 1.7/50=1.25 W kg-1. In summary, niobium can be used as an effective inhibitor formation element to produce high quality Nb-bearing grain oriented silicon steel manufactured by low-temperature slab reheating process.

Microstructure and magnetic properties of ultra-thin grain-oriented silicon steel: Conventional process versus strip casting

Ultra-thin grain-oriented silicon steels were processed via the conventional process and strip casting process, and the mechanisms of texture inheritance and inhibitor induced secondary recrystallization were comparatively studied in detail. In the conventional route with commercial grain-oriented silicon steel as the starting material, exact {111} 〈112〉 dominated the deformation texture after cold rolling with ~ 63% reduction, and strong Goss texture was formed in 0.08–0.10 mm thin-gauge primary recrystallized sheet. Meanwhile, weak {210} 〈001〉 and {h11} < 1/h12 > textures were also observed because of the inhomogeneous deformation with initial deviated Goss texture. After high temperature annealing, the sheet experienced incomplete secondary recrystallization with abnormal growth of Goss grains accompanied by normal growth of {210} 〈001〉 and {411} 〈148〉 grains, considering the absence of pinning force on grain boundary migration. In the strip casting process, the intensity of γ-fiber texture was increased, while grain size decreased from ~ 13.3 to ~11.4 μm and the area fraction of Goss grains decreased from 2.8% to 0.6% in the primary recrystallized sheet with decrease of thickness from 0.15 to 0.08 mm. During high temperature annealing process, MnS, (Nb,V)N and AlN provided continuous and sufficient inhibition force for normal grain growth, which guaranteed the formation of complete secondary recrystallization of exact Goss grains. Superior magnetic induction B8 was up to 1.97 T in the strip casting process, which was 0.09 T higher than the conventional route. Meanwhile, the iron losses P1.7/50 and P1.0/1000 were as low as 0.85 and 20.7 W/kg, respectively, which were comparable to the reported ultra-thin grain-oriented silicon steels. The present study provided a novel method to produce high efficiency ultra-thin grain-oriented silicon steel, which may significantly contribute to energy saving in high-frequency electrical devices.

Grain-orientation induced stress formation in AA2024 monocrystal and bicrystal using Crystal Plasticity Finite Element Method

Stress formation of monocrystals and bicrystals is investigated in specific oriented grains and grain boundaries of AA2024 alloy by using Crystal Plasticity Finite Element Method (CPFEM). The simulations show that the maximum Schmid factor (SF) value and the number of equivalent initial slip system (EISS) play a principal role in controlling the magnitude of internal stress within monocrystals. For bicrystal model, Goss and Cube grains are not the best ones for relieving stress concentration caused by their orientations, but they are the best ones for relieving grain boundary (GB) stress concentration. To this end, the dependence relations are discussed between GB stress and an advanced comprehensive factor combining SF, and geometry compatibility factor for 5 independent slip systems. It is found that this proposed comprehensive factor considering the contribution from 5 to independent slip systems effectively improves its dependence on GB stress.

Improvement of texture and magnetic properties of strip-cast grain-oriented electrical steel by trace Bi addition

The improvement of recrystallization texture and magnetic properties in grain-oriented electrical steel with trace Bi addition processed by strip casting process was studied in this study. Low casting temperature and sufficient liquid steel flow during strip casting process enabled relatively homogeneous distribution of Bi in the as-cast strip, which accelerated the precipitation during solidification and cooling process. As a result, relatively high density of duplex MnS + AlN, MnS and AlN was formed at grain boundaries and inside grain. Due to the synergistic effect of continuous precipitation and fragmentation of coarse precipitates during cold rolling, the number density of precipitates was increased and mean size was decreased along the processing route. High density of precipitates is attributed to severe inhomogeneous plastic deformation, which promoted the formation of high density in-grain shear bands during cold rolling and recrystallization Goss texture during annealing. Homogeneous microstructure with average grain size of ~ 11.6 μm, strong Goss texture with intensity of 2.5 multiples of random distribution, fine precipitates with number density of ~ 1.9 × 109 /cm2 and mean size of ~ 49 nm were formed after primary recrystallization annealing. Furthermore, grain-oriented electrical steel with Bi addition experienced complete secondary recrystallization of exact Goss grains during high-temperature annealing, which is attributed to beneficial optimization of Goss texture and strong inhibition effect, and superior magnetic induction B8 of 1.91 T was obtained. It is expected that this study paves a new way for fabrication of high-performance grain-oriented electrical steel.

Secondary recrystallization in grain-oriented silicon steel

Grain-oriented silicon steel is a soft magnetic material widely used for transformer cores. Magnetic properties are closely related to the sharpness of Goss texture, which is evolved by secondary recrystallization. An overview of our results will be presented; secondary recrystallization behaviour has been investigated by in situ observation utilizing synchrotron x-ray topography. The results support the selective growth mechanism. Migration of Goss grains is controlled by inhibitor and sharper Goss grains, which have higher frequency of CSL-boundaries to the matrix, start to grow preferentially while the other grains are stagnated by inhibitor. Secondary recrystallization behaviour can be explained based on this CSL-model. At the initial stage, inhibitor gradient through the thickness promotes Goss selective growth from the subsurface layer and at the later stage, inhibitor drop rate dominates the Goss selective growth. Inhibitor and CSL-boundaries synergistically affect Goss selective growth and Goss grain evolves to a coarse grain.

Secondary recrystallization behavior in magnetostrictive Fe-Ga thin sheets induced by nano-sized composite precipitates

Strengthening η texture (⟨001⟩//rolling direction) through secondary recrystallization can significantly improve the magnetostriction coefficient of Fe-Ga thin sheets and expand the use of Fe-Ga alloys in high-frequency applications. However, the secondary recrystallization of Goss texture in Fe-Ga thin sheets deteriorates significantly with the thinning of the sheet thickness under the current inhibitors of micron-sized NbC particles or precipitates. In this paper, a new composite inhibitor system, composed of nano-sized MnS and Nb(C,N) precipitates, is proposed to induce the secondary recrystallization Goss texture in Fe-Ga thin sheets with thicknesses less than 0.3 mm. The density and size of MnS and Nb(C,N) is designed based on the effect of alloy composition and hot rolling parameters on the precipitation kinetics of MnS and Nb(C,N), including the relative nucleation rate-temperature (NrT) and precipitation-time-temperature (PTT) curves. It is found that the stored deformation energy increases the maximum nucleation rate and the fastest precipitation temperature. A large number of lamellar and rectangular precipitates (MnS and Nb(C,N)) with a size of 5∼20 nm were precipitated after hot-rolling at a temperature of 800∼1,050 °C and a total thickness reduction of 80%. These nano-sized inhibitors provide a strong pinning effect for the primary recrystallized grains, and induce abnormal grain growth of Goss grains at an annealing temperature of 950∼1,050 °C. Resultingly, centimeter-sized Goss grains with a small deviation angle and maximum magnetostriction coefficient of 264 ppm are successfully achieved in Fe-Ga alloy thin sheets with a thickness of 0.25 mm.

The Origin of the Cube ({001}) Texture in Non-oriented Electrical Steel Sheets

Although cube ({001}<100>) is a preferred final texture in non-oriented electrical steel (NOES) sheets, this texture is rarely produced in commercial NOES products. The major texture of fully processed NOES is usually the unfavorable <111>//ND (normal direction) fibre, which originates from the deformed <111>//ND texture. To reduce/eliminate the <111>//ND texture and promote the cube texture, one method is to change the initial texture before cold rolling. In this research, two electrical steels containing 0.88 wt% and 2.8 wt% Si are cold rolled with the initial textures rotated by 60° around the ND before cold rolling. This rotation leads to the rotated Goss ({110}<110>) texture in the deformed microstructure. Within the shear bands of the rotated Goss grains, crystallites with cube orientation are formed. Regions of these crystallites may have lower stored energy than their neighboring areas. During annealing, these crystallites preferentially nucleate and grow, and form a strong cube texture in the final steel sheets.

Goss Texture Evolution in a Grain-Oriented Fe-6.5wt%Si Steel Processed by Strip-Casting

Fe-6.5wt%Si steel is an excellent soft magnetic material due to the near-zero magnetostriction and low core losses. In this study, a 0.3 mm-thick grain-oriented 6.5wt%Si steel sheet was produced by a novel strip casting and two-stage rolling. The microstructure and texture evolution were investigated with a special emphasis on the nucleation and growth of Goss grains. The thin normalized strip was composed of large columnar grains and small equiaxed grains. During intermediate annealing, Goss grains nucleated in the shear bands of the deformed &lt;111&gt;//ND grains, and the deformed {111}&lt;112&gt; grains provided most of the nucleation sites. After primary annealing, the Goss grains distributed across the entire thickness, which was different from the conventional rolling route. The fraction of high-angle boundaries (20°-45°) surrounding the Goss grains was apparently higher than those of the matrix grains, which promoted the abnormal growth of the Goss grains during secondary recrystallization.

Shear Banding in Rotated Goss Grains and its Effect on the Formation of Cube Texture in Non-Oriented Electrical Steel

Cube texture ({001}&lt;100&gt;) is a desired final texture in non-oriented electrical steel sheets used as magnetic cores because it contains two easy &lt;100&gt; axes in the sheet plane, which is beneficial to the magnetic properties. However, the cube texture is very difficult to form in non-oriented electrical steels through conventional rolling and annealing. It has been shown that after conventional rolling, the deformed &lt;111&gt;//ND (normal direction) grains provided nucleation sites for the unfavourable &lt;111&gt;//ND texture during recrystallization, leading to a final &lt;111&gt;//ND texture. To eliminate the &lt;111&gt;//ND texture and promote the {001}&lt;100&gt; texture, an uncommon rolling process, i.e. inclined rolling, was adopted in this study. By rotating the hot rolling direction by 60° around the ND, an uncommon initial texture, the rotated Goss ({110}&lt;110&gt;), was intentionally generated. This was intended to change the orientation flow during plastic deformation, and suppress the formation of the conventional &lt;111&gt;//ND texture in the deformed microstructure. Plane-strain compression (rolling) of the rotated Goss grains produced shear bands within these grains due to their large Taylor factor. Electron backscatter diffraction (EBSD) characterization of the shear bands illustrated that, crystallites with the cube orientation were formed within these shear bands. During recrystallization, the shear bands provided preferential nucleation sites, and the cube crystallites preferentially nucleate within the shear bands. These cube crystals can then grow into the deformed matrix, and lead to the formation of a strong cube texture in the final annealed steel sheets.

Unravelling the Role of Aging During Cold Rolling on the Primary Recrystallization of Grain-Oriented Electrical Steels Using a Robust EBSD-Based Analysis Approach

Aging during cold rolling improves the final magnetic properties of conventionally processed grain oriented electrical steels (GOES). In order to determine the influence of aging on the evolution of microstructure and texture during recrystallization, identical hot rolled GOES sheets, were cold rolled with and without aging, and examined by large-area electron backscatter diffraction (EBSD) investigations. Local misorientations were determined from the EBSD maps with a noise-correction technique and the statistical relevance of the EBSD-based texture measurements was examined and confirmed by a new approach. The most important effect of aging was found to be a significant modification of the deformation and recrystallization behaviour of the α-fiber components. In fact, the aging treatment resulted in more shear banding during cold rolling, which is attributed to dislocation pinning by carbon atoms. The dislocation pinning furthermore leads to significantly reduced recovery during annealing, which finally results in a higher remaining driving force for recrystallization and more nucleation sites in the otherwise sluggishly recrystallizing α-fiber grains. As a result the grain size of the aged material is significantly reduced. We assume that this smaller grain size provides a higher driving force for the subsequent growth of the Goss grains and leads to improved magnetic properties of the final processed GOES, although these relations have not been investigated here. In contrast, the α*-fiber, which is often suggested to be of importance for optimized Goss texture formation, was not found to be affected significantly by the aging treatment.

The role of grain colony on secondary recrystallization in grain-oriented electrical steel: New insights from an original tracking experiment

Secondary recrystallization is responsible for the sharp Goss texture ({110}<001>) of grain-oriented electrical steels. Many investigations have focused on establishing the relations between the sharpness of final Goss textures and primary recrystallization textures measured by the X-ray diffraction. However, the contributions of micro-texture characteristics to secondary recrystallization have not yet been well understood. Here, we report that the grain colonies composed of grains with similar orientations in the primary recrystallization matrix had a particular role on the development of secondary recrystallization via an original tracking experiment. We observe that the γ-grain (<111>//normal direction, ND) colonies facilitate the retention of primary recrystallization matrix grains (≤25µm) having 20-45° disorientation with {110}<001> and relatively large difference in the associated frequency with precise Goss orientation and that having deviation angle of 15°, promoting the abnormal growth of low-deviation-angle Goss grains especially after the onset of secondary recrystallization and leading to sharp final Goss texture. By contrast, the abnormal growth of high-deviation-angle Goss grains may be also promoted after the initiation of secondary recrystallization in case of randomly-distributed γ-grains in primary recrystallization matrix and thus resulted in deteriorated magnetic properties. In this way, we reveal the role of grain colony on secondary recrystallization and the underlying mechanism for the effect of primary recrystallization textures on the sharpness of final Goss texture. We also observe that the formation of grain colonies is mainly related to the initial solidification microstructure, processing route as well as the deformation and recrystallization features of γ-grains.

A quasi in-situ EBSD study of the nucleation and growth of Goss grains during primary and secondary recrystallization of a strip-cast Fe-6.5 wt% Si alloy

The nucleation and growth of Goss grains during primary and secondary recrystallization of a strip-cast grain-oriented Fe-6.5 wt% Si alloy were investigated using a quasi in-situ electron backscatter diffraction (EBSD) technique. During primary recrystallization at 700 °C, the Goss was found to nucleate from two locations in the deformed<111>//ND (normal direction) grains: in the shear bands and at the grain boundaries. However, only those nucleated from the shear bands tended to survive during the subsequent grain growth. Even the survived Goss grains would not develop as abnormal Goss grains during secondary recrystallization. Abnormally growing Goss grains were formed at the surfaces when the primary recrystallization temperature was 850 °C, which grew into the center and consumed the entire thickness during secondary recrystallization. The abnormal growth of the Goss grains was attributed to the large fraction of 20–45° grain boundaries at the growing front, which essentially did not change during secondary recrystallization. Using a classical grain growth model, the migration velocities of Goss grains during abnormal growth were calculated, which were compared to the experimental migration velocities obtained from the quasi in-situ EBSD data. It was shown that the model could roughly predict the abnormal growth of the Goss grains during secondary recrystallization.

Effect of Shear Bands Induced by Asymmetric Rolling on Microstructure and Texture Evolution of Non-Oriented 3.3% Si Steel.

In the present work, the microstructure and texture of non-oriented 3.3% Si steel processed by asymmetric rolling (ASR) and subsequent annealing at different temperatures were compared with those obtained when using traditional symmetric rolling (SR). This work aims to reveal the effect of shear bands introduced by the ASR on the microstructure and texture evolution. The ASR sample reaches a recrystallization fraction of 62% at an annealing temperature of 650 °C, which is 32% higher than that of the SR sample annealed at the same temperature. This can be attributed to the abundant shear bands introduced by the ASR, which serve as the heterogeneous nucleation sites for the recrystallized grains. When increasing the annealing temperature to 750 °C, complete recrystallization could be observed in both asymmetric- and symmetric-rolled samples. When using an annealing temperature of 650 °C, the γ-oriented grains were dominant in the surface layer, while strong Goss-oriented grains could be observed in the center in the ASR sample. This is due to the fragmented small subgrains with different orientations in the surface layer inhibiting the nucleation of Goss- and cube-oriented grains during the annealing. In contrast, numerous Goss- and cube-oriented grains were formed in the surface layer after complete recrystallization when the ASR sample was annealed at a temperature of 750 °C. This may be related to the higher thermal energy, which benefits the nucleation of the Goss- and cube-oriented grains. In addition, ASR significantly increased the strength of η-fiber after complete recrystallization when compared with SR. This work might be helpful to design the rolling and the subsequent annealing processes.

Simulation of recrystallization based on EBSD data using a modified Monte Carlo model that considers anisotropic effects in cold-rolled ultra-thin grain-oriented silicon steel

A Monte Carlo Potts model was developed to simulate the recrystallization process of a cold-rolled ultra-thin grain-oriented silicon steel. The orientation and image quality data from electron backscatter diffraction measurements were used as input information for simulation. Three types of nucleation mechanisms, namely, random nucleation, high-stored-energy site nucleation (HSEN), and high-angle boundary nucleation (HABN), were considered for simulation. In particular, the nucleation and growth behaviors of Goss-oriented ({011} ) grains were investigated. Results showed that Goss grains had a nucleation advantage in HSEN and HABN. The amount of Goss grains was the highest according to HABN, and it matched the experimental measurement. However, Goss grains lacked a size advantage across all mechanisms during the recrystallization process.

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

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

Evolutions of microstructure and magnetic properties of heatproof domain-refined silicon steel during annealing and its application

Heatproof domain-refined grain-oriented (DRGO) silicon steel is an ideal material for the manufacture of S15-type ultra-high efficiency transformer with three-dimensional wound-core (TDWC). In this paper, the microstructure, grain orientation, and magnetic performance of 23ZDMH80 heatproof silicon steel during stress-relief annealing were investigated by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) techniques. Based on heatproof DRGO steel, the Epstein-SST (single sheet tester) conversion factor and equivalent magnetic path length were calculated, and then an ultra-high energy efficiency transformer was developed. Results show that, the average size of micrograins in notched region increased from 42.3 μm to 68.2 μm after annealing at 850 ℃ for 0–8 h. The orientations of micrograins grown on large-size Goss grain included not only the non-〈0 0 1〉 orientations, such as {210} 〈−241〉, {215} < 1–20>, and {1 1 0} < 1–12}, which were harmful to the magnetic properties, but also the favorable {1 0 0} 〈0 0 1〉 and Goss. Correspondingly, the core loss of 5 pairs of Epstein specimens first decreased then increased slowly (the growth rates below 1.2%) during annealing. The Epstein-SST conversion factor δP for 23ZDMH80 heatproof steel was 8.6% (higher than 5.0% the value recommended by IEC standard), and the equivalent magnetic path length was 0.489 m. Finally, the developed 10 kV/400 kVA transformer with TDWC presented ultra low no-load loss of 289 W, load loss of 3072 W, and noise of 35.4 dB, it means significant advantage of energy conservation and environmental protection.

Texture evolution during inclined cold rolling of used non‐oriented silicon steel

AbstractWith the objective of optimizing the texture components and exploring a method to improve the magnetic properties of used silicon steel, the methods of one inclined rolling and two inclined rolling were applied. The result shows: the new Goss grains were nucleated except at {111} deformed grains, and also formed at the grain boundary between two deformed grains with {113} orientation, and at grains boundaries between {113} and {100} deformed grain. The grain size after one inclined rolling (57 %) was larger and more homogeneous than the grain size after the two inclined rolling. Although with different cold rolling methods (one and two inclined rolling), the resulted annealing textures all had similar features. The difference was the relative intensities between the main texture. A significant feature of one inclined rolling was the intensification of the η‐fiber and the Goss texture component and the weakening of γ‐fiber. At an inclination angle of 60°, a significantly strong Goss texture was produced, which was highest among all samples, and the maximum volume fraction of {110}+{100} texture can also be obtained. One inclined rolling can better improve the magnetic properties of used silicon steel (B50), and the magnetic induction is between 1.712 T and 1.742 T. The highest magnetic induction of 1.742 T can be obtained by one inclined rolling (at an inclination angle of 60°).

Origin of Goss (110)〈001〉 Grains in Hot-Worked Grain-Oriented Steel

This study involved hot working, mimicking the first strand of a compact strip production, of grain-oriented (GO) and non-grain-oriented (NGO) electrical steel. The as-cast microstructures, between the grades, were similar: large (~ 550 μm average diameter and 1 to 7 mm length) columnar grains with ND//〈001〉 fiber texture. However, the developments in hot-worked microstructures were remarkably different. Firstly, the GO had higher carbon (0.06 vs 0.003 weight pct)—which led to the presence of austenite phase at the hot working temperatures. The GO also showed dynamic recrystallization (DRx) and the presence of Goss (110)〈001〉 grains in the hot-worked state. These were absent in the NGO. Further, the majority (~ 95 pct) of the Goss grains, in the hot-worked GO, originated from dynamic recrystallization (DRx) in the ferrite phase, surrounding the harder prior austenite regions. This study thus identified DRx by particle-stimulated nucleation as the primary source of Goss orientation in the hot-worked GO.