Goss Grains Research Articles

Effect of the Number of Cold Rolling Passes on the Formation of {110}<001> Goss-Oriented Grains in Fe-3.2 wt% Si Electrical Steel

Effect of the Number of Cold Rolling Passes on the Formation of {110}<001> Goss-Oriented Grains in Fe-3.2 wt% Si Electrical Steel

Secondary recrystallisation behaviours of grain-orientated silicon steel produced by TSCR process

ABSTRACTGrain-oriented electrical steel is mainly used as the core material in electrical transformers, and its magnetic properties are closely related to the sharpness of Goss texture formed by secondary recrystallisation during high-temperature annealing. However, the mechanisms of abnormal Goss grain growth are still disputed in the literature. In this paper, grain-oriented silicon steel strips with AlN as main inhibitor were produced by thin slab casting and rolling process, and the evolution of microstructure and texture during high-temperature annealing was investigated. Moreover, the mechanisms of secondary recrystallisation were further discussed. The results show that secondary recrystallisation is actually a multi-stage process, and different mechanisms are at work at different stages. Coincident site lattice grain boundaries play an important role at the early stage of secondary recrystallisation, however, the role of high-energy grain boundaries and solid-state wetting should be more important at the later stage of secondary recrystallisation.

Ultra-thin grain-oriented silicon steel sheet fabricated by a novel way: Twin-roll strip casting and two-stage cold rolling

0.05–0.15 mm-thick ultra-thin grain-oriented silicon steel sheets were successfully produced by a novel processing route including strip casting, hot rolling, normalizing, two-stage cold rolling with intermediate annealing, primary recrystallization annealing and secondary recrystallization annealing. The evolutions of microstructure, texture and inhibitor along the processing were briefly investigated. The results showed that the initial Goss orientation originated due to the heterogenous nucleation of δ-ferrite grains during solidification. Because of the lack of shear deformation, only a few Goss grains were observed in the hot rolled sheet. After the first cold rolling and intermediate annealing, Goss texture was enhanced and distributed in the whole thickness. A small number of Goss grains having a high fraction of high energy boundaries exhibited in the primary recrystallization annealed sheet. A large number of fine and dispersed MnS and AlN and a few co-precipitates MnS and AlN with the size range of 10–70 nm were also observed. Interestingly, a well-developed secondary recrystallization microstructure characterized by 10–60 mm grains and a sharp Goss texture were finally produced in the 0.05–0.15 mm-thick ultra-thin sheets. A magnetic induction B8 of 1.72–1.84 T was obtained. Another new finding was that a few {2 3 0}〈0 0 1〉 and {2 1 0}〈1 2 7〉 grains also can grow up abnormally because of the high fraction of high energy boundaries and the size and number advantage, respectively. These non-Goss grains finally deteriorated the magnetic properties of the ultra-thin sheets. In addition, low surface energies of {hk0} planes may also contribute to the abnormal growth of Goss, {2 3 0}〈0 0 1〉 and {2 1 0}〈1 2 7〉 grains.

Effect of typical elements on the heredity of hot-rolled and annealed texture in non-oriented electrical steel

Macroscopic texture and microscopic orientation in hot-rolled and annealed sheets of non-oriented electrical steel were studied by XRD and EBSD techniques. The microstructure of hot-rolled and annealed samples was studied by OM. Experimental results indicate that a strong heredity is observed in texture evolution between hot-rolled texture and annealed texture. Typical elements have a large effect on the recrystallization microstructure and texture distribution. The texture distribution through thickness is highly affected by recrystallization in hot rolled sheets. The recrystallization is boosted by Si and Al. Goss grains originate from cracked initial columnar grains. {110} , {112} and {111} grains are related to Goss grains. In subsurface lay of hot rolled sheets, Al can strengthen Goss texture and weaken copper-type texture. {112} texture and {110} texture are strengthened by Si. In the central layers, {100} texture and {111} texture are weakened by Al. {100} texture is increased by Al. Si can increase the proportion of γ-fiber texture and decrease that of {100} texture. In annealed texture, {100} texture and Goss texture are decreased by Al and Si. γ-fiber texture is increased by Si and {111} texture is preferentially increased by Al. The recrystallized grain size is increased and iron loss of annealed sheets is reduced by Al and Si, which means that the magnetic properties are optimized by the Al and Si content.

Three-Dimensional Morphologies of Abnormally Grown Goss Oriented Grains in Hi-B Steel During Secondary Recrystallization Annealing

Three-Dimensional Morphologies of Abnormally Grown Goss Oriented Grains in Hi-B Steel During Secondary Recrystallization Annealing

Final thickness reduction and development of Goss texture in C- and Al-free Fe-3%Si-0.1%Mn-0.012%S electrical steel

The correlation between final thickness reduction and development of Goss texture has been investigated in a C- and Al-free Fe-3%Si electrical steel. During final annealing, the annealing texture is transited from {110}⊥ND to {100}⊥ND texture with increasing final thickness reduction. This is due to the decrease in primary grain size after pre-annealing with increasing final thickness reduction which accelerates the selective growth rate of the {100} grains at the expense of the other {hkl} grains. At an optimal final thickness reduction of 75.8%, the high magnetic induction of 1.95 Tesla, which arises from the sharp {110} Goss texture and is comparable to that of conventional grain-oriented electrical steels, is obtained from the C- and Al-free Fe-3%Si-0.1%Mn electrical steel. Such a high magnetic property is produced through the surface-energy-induced selective grain growth of the Goss grains under the lower surface-segregated condition of sulfur which makes the surface energy of the {110} plane lowest among the {hkl} planes.

Mechanism of Texture and Precipitates Evolution in CGO Silicon Steel During High-Temperature Annealing Process

Grain-oriented silicon steel is an important soft magnetic material for electrical applications. A conventional grain-oriented silicon steel with final thicknesses of 0.27, 0.23 and 0.20 mm was prepared separately by a two-stage cold rolling process. Texture evolution, precipitates distribution and Goss textures formed during secondary recrystallization were analyzed by electron backscattered diffraction and field emission scanning electron microscopy. The results show that plate thickness influences the distribution density of secondary phase particles and the content of favorable texture components such as {111} , {111} and {112} texture. Decreasing plate thickness increases the areal density of secondary phase particles, the temperature of secondary recrystallization, which also increases the content of favorable texture component, and the strength of Goss texture in secondary recrystallization. Goss grains have higher particle density than the grains with other orientations, which facilitates their abnormal growth by swallowing surrounding grains with lower particle density.

Inhibition force of precipitates for promoting abnormal grain growth in magnetostrictive Fe83Ga17-(B,NbC) alloy sheets

Inhibition force of precipitate particles for promoting abnormal grain growth in magnetostrictive Fe83Ga17-(B,NbC) alloy sheets was investigated in this study. After a continuous heating and a high-temperature annealing, the Fe83Ga17 + 0.5 at% B alloy sheets do not occur significant abnormal grain growth. Correspondingly, textures of {111} and {100} in addition to the Goss texture are obtained in the final annealed alloy sheets. By contrast, after the same annealing processes, the size of {110} textured grains is very large in the final annealed Fe83Ga17 + 0.5 at% NbC alloy sheets due to the abnormal grain growth, which results in a sharp Goss texture. BN precipitates were introduced into Fe83Ga17 + 0.2 at% B alloy sheets by nitriding annealing at 800 °C for 2 min under NH3 atmosphere. The abnormal grain growth of Goss grains is achieved in 0.2 at% B-doped Fe83Ga17 alloy sheets after a high-temperature annealing, which is attributed to the enhanced inhibition force by introducing BN precipitates. During the recrystallization annealing process, Fe2B precipitates is easy to coarsen and decompose at high temperature due to the low thermal stability, resulting in a decrease or even disappearance of the inhibition force. For NbC and BN precipitates, the thermal stability and hardness of particles are both better than those of Fe2B precipitates, leading to strong inhibition force. Because of the preferred Goss texture, the magnetostriction of 2.05 × 10−4 and 1.81 × 10−4 is obtained in the secondary recrystallized Fe83Ga17 + 0.5 at% NbC and Fe83Ga17 + 0.2 at% B alloy sheets, respectively.

Strong NbC particle pinning for promoting abnormal growth of Goss grain in Fe82Ga4.5Al13.5 rolled sheets

A great number of fine and dispersive NbC precipitates were obtained in Fe82Ga4.5Al13.5 sheets by rolling process consisting of hot rolling at 900°C, warm rolling at 500°C and intermediate annealing at 650°C for 15min. The mean size of precipitates in primarily recrystallized sheets is ∼45nm. Grain growth in final sheets was investigated to study the influence of fine precipitates on the promotion of abnormal grain growth (AGG). Fully developed AGG of Goss grain was observed in samples with the heating rate during continuous process of 0.5°C/min, 1°C/min and 2°C/min. In contrast, AGG in samples of 0.25°C/min and 4°C/min were partially developed. The influence of heating rate on the development of AGG was examined by the investigation of precipitates and grain configurations during continuous heating process. With the fine precipitates, sharp Goss orientation was developed in Fe82Ga4.5Al13.5 sheets annealed at Ar atmosphere. A maximum saturation magnetostriction of 170ppm was obtained in sample of 2°C/min.

The impact of niobium on the microstructure, texture and magnetic properties of strip-cast grain oriented silicon steel

We elucidate here the impact of niobium in ultra-low carbon grain oriented electrical steel (GOES) in terms of microstructure, texture, precipitation and magnetic properties that was processed by twin roll strip casting. Coarse and complex MnS+NbN precipitates, and fine NbN were nucleated at the grain boundaries and in the interior of the grain in the as-cast strip, which contributed to a small degree of grain refinement together with relatively random texture, and AlN precipitation was suppressed during the strip casting process. NbN continuously precipitated during the entire process and exhibited high stability during the reheating cycle, which provided stronger inhibiting force in comparison to AlN precipitates. As a consequence, fine and homogeneous inhibitors were obtained in the primary annealed sheet in the presence of Nb under cold rolling and annealing parameters used in the present study. On considering the effect of NbN particles or Nb in solution on the deformation and recrystallization behavior, the primary annealed Nb-containing sheet exhibited significantly more homogeneous microstructure in relation to Nb-free GOES, with grain size in the range of ∼8–12μm, and was characterized by relatively more pronounced γ-fiber and weak Goss texture, beneficial for the abnormal growth of Goss grains. Furthermore, Nb-containing GOES experienced complete abnormal growth during secondary recrystallization annealing, such that the enhanced magnetic induction (B8 as high as 1.88T) was obtained. In summary, the present study underscores that NbN can be used as an effective inhibitor in ultra-low carbon grain oriented electrical steel using strip casting technology.

Effect of primary recrystallization microstructure on abnormal growth of Goss grains in a twin-roll cast grain-oriented electrical steel

Various primary recrystallization microstructures and textures were produced in a twin-roll cast grain-oriented electrical steel by employing different routes. The relationship between the primary recrystallization microstructure and texture and the abnormal growth of secondary Goss grains was investigated. The results show that the cold rolling reductions have a significant influence on secondary recrystallization by changing the primary recrystallization microstructure. Sheet processed by single-stage cold rolling with 88.3% reduction displayed the poorest secondary recrystallization microstructure as it contained many small equiaxed grains. By contrast, the employment of two-stage cold rolling markedly improved the secondary recrystallization microstructure. In the case of two moderate reductions of 65.2% and 66.3%, dense deformation substructures formed during both the first and second cold rolling, leading to a homogeneous primary recrystallization microstructure together with a strong γ-fiber texture. In this way, a suitable secondary recrystallization microstructure consisting of large Goss grains was produced. In the case of the inappropriate reductions, many large λ- and α-grains in the primary recrystallization matrix blocked the growth of secondary Goss grains along the transverse direction, resulting in a poor secondary recrystallization microstructure.

Influence of intermediate annealing on abnormal Goss grain growth in the rolled columnar-grained Fe-Ga-Al alloys

Magnetostrictive Fe82Ga4.5Al13.5 sheets with 0.1at% NbC were prepared from directional solidified alloys with <001> preferred orientation. The slabs were hot rolled at 650°C and warm rolled at 500°C. Then some warm-rolled sheets were annealed intermediately at 850°C for 5min but the others not. After that, all the sheets were cold rolled to a final thickness of ∼0.3mm. The microstructures, the textures and the distributions of second phase particles in the primary recrystallized samples were investigated. With intermediate annealing, the inhomogeneous microstructure was improved remarkably and strong Goss ({110}<001>) and γ-fiber (<111>//normal direction [ND]) textures were produced in the primary recrystallized samples. But, an evident disadvantage in size and quantity was observed for Goss grains in the primary recrystallized sample without intermediate annealing. After a final annealing, the final textures and magnetostrictions of samples with and without intermediate annealing were characterized. For samples without intermediate annealing, abnormal growth of {113} grains occurred and deteriorated the magnetostriction. In contrast, abnormal Goss grain growth occurred completely in samples with intermediate annealing and led to saturation magnetostriction as high as 156ppm.

Effect of Normalizing Cooling Process and Cold-Rolling Reduction Ratio on the Microstructure and Macro-texture in Hi–B Steel

Microstructure and macro-texture with different normalizing processes for Hi–B steel were analyzed and compared with the non-normalizing cold-rolled steel by optical microscopy, X-ray diffractometer. The results show that the degree of the elongated grain is small after normalizing, and through the normalizing and cold-rolling process, the tissue of cold-rolled sheet is more uniform, the content of the beneficial {111}〈112〉 texture is relatively higher, and the intensity of α fiber texture is weakened and the intensity of γ fiber texture is gradually enhanced. When the reduction ratio is 88%, the content of {111}〈112〉 texture is the maximum and the intensity of γ fiber texture is the strongest, which is beneficial to the improvement of the {111}〈112〉 texture during the primary recrystallization and the growth of the Goss grains.

Development of Secondary Recrystallization in high permeability grain oriented Silicon steel produced by Thin Slab Casting and Rolling process

Texture evolution during high temperature annealing process in high permeability grain oriented(Hi-B)silicon steel, produced by Thin Slab Casting and Rolling(TSCR) process, was investigated using macro-/microtexture analysis. Goss texture appears in ODF at 800°C, the intensity of Goss texture is very weak until 950°C;Goss grains grow abnormally during 980°C∼1000°C, grain size reached centimeter level at 1000°C; instead of Primary Grains, Goss grains were obtained fully at 1020°C, Secondary recrystallization completed at 1040°C; The deviation angle of Goss grain orientation decreases gradually with increasing temperature, and it reached the minimum at 1040°C.

Effect of Initial Oriented Columnar Grains on the Texture Evolution and Magnetostriction in Fe–Ga Rolled Sheets

The effects of initial oriented columnar grains on the texture evolution and magnetostriction in (Fe83Ga17)99.9(NbC)0.1 rolled sheets were investigated. The recrystallization texture evolution exhibited the heredity of initial orientations, concerning the formation of cube and Goss textures in the primary recrystallized sheet for the columnar-grained sample. Moreover, the growth advantage of Goss grains was more obvious than that of cube grains during the secondary recrystallization process. Because of the combined effect of this and Nb-rich precipitates as inhibitors, a sharp Goss texture and very large Goss grains were achieved in the secondary recrystallized sheet for the columnar-grained sample. For comparison, the secondary recrystallization in the equiaxed-grained sample was not fully developed although there were Nb-rich precipitates as inhibitors. We think this could be ascribed to the large particle size and premature coarsening of precipitates. Magnetostriction of the secondary recrystallized columnar-grained sheet was up to 232 ppm owing to the ideal Goss texture and quite large grain size. As for the equiaxed-grained sample, the magnetostriction was only 163 ppm in the secondary recrystallized sheet.

Effect of annealing atmosphere on secondary recrystallization in thin-gauge grain-oriented silicon steel: evolution of inhibitors

Thin-gauge cold-rolled grain-oriented (TG-CRGO) silicon steels were fabricated using the acquired inhibitor method, in which the behaviors of inhibitor are strongly influenced by the final annealing atmosphere and differ from that of the TG-CRGO silicon steel. In this study, macrostructures, grain orientations, and evolution of inhibitors in two gauges of thickness (0.23 and 0.18mm) of steels were studied and compared in five different annealing atmospheres. The second-phase particles in samples were observed by field-emission scanning electron microscopy. Distribution densities and mean diameter of particles were statistically calculated to illustrate the effect of Zener factor. Results indicated that the inhibitor behaviors in the two thickness samples are similar with the change of N2 proportion in annealing atmosphere, i.e., nitrogen loss, decomposition, coalescence, and ripening of particles would be strongly suppressed with the increase of N2 content. However, in comparison with the 0.23-mm samples, the nitride precipitation, decomposition and inhibitor coarsening of the 0.18-mm specimens are more likely to occur at a lower temperature because of the thinner thickness. Furthermore, the value of Zener factor implies that for thinner samples, more N2 should be employed when nitrides are used the main inhibitor; this condition would inhibit the development of undesirable deviated Goss grains. This study showed that the 0.23-mm sample could achieve the best magnetic properties (B8) at 1.92T in the atmosphere containing 25% N2. The 0.18-mm sample could achieve the best magnetic properties (B8) at 1.93T in the atmosphere containing 75% N2.

Effect of annealing atmospheres on secondary recrystallization in thin-gauge grain-oriented silicon steel: Microstructures and textures

By controlling the onset temperature of secondary recrystallization and the temperature interval for grain growth, the annealing atmosphere is the key factor affecting the grain size and texture of grain-oriented silicon steel. The thin-gauge cold-rolled grain-oriented silicon steel (TG-CRGO) is not only more sensitive to annealing atmosphere than the thick-gauge grain-oriented silicon steel, but also requires a different annealing atmosphere. In this paper, the evolution of microstructures and textures in 0.18mm TG-CRGO steel during high-temperature annealing in five different annealing atmospheres are detected through EBSD technique. The results show that excellent magnetic properties (B8=1.93 T) can be obtained when annealing atmosphere as 75%N2+25%H2 (volume ratio). Secondary recrystallization occurs in all the specimens that were prepared in five different annealing atmospheres, which causes significant differences in secondary recrystallized microstructures and textures. As N2 content rises, the average secondary recrystallized grain sizes increased and reaches a maximum average grain size in 75%N2 atmosphere and then decreases along with N2 content over 75%. When N2 content is 75%, Goss grains show preferential abnormal growth at 1050–1055°C, which is a very narrow temperature range for secondary recrystallization. In conclusion, proper annealing atmosphere is one of the important measures to control and enable the grain-oriented silicon steel to get the sharp Goss texture.

Investigation on the Early Stages of Growth of Secondary Grains in a Grain Oriented Silicon Steel

A sequence of cyclic annealing experiments was performed to trace the growth of secondary grains after primary recrystallization in a two-pass cold rolled Fe-3.5%Si steel. By using electron backscattered diffraction (EBSD), the development of grain growth and texture in the early stages of secondary growth in as-received and annealed samples was examined. Annealing was performed at 900°C for 3, 6 and 15min. During the early stages of secondary growth, it was observed that Goss grains and other oriented grains can grow at the expense of their surrounding matrix grains. This growth is likely to be determined by particle dissolution at their boundaries which, hence, affects their ability to break away from pinning. It is shown that the presence of Σ5 and Σ9 CSL boundaries that surround Goss grains, size advantage in the as-received sample, texture sharpness and the presence of Goss grain colonies do not guarantee Goss grains to successfully grow at this stage of annealing.

Effect of Heating Rate and Annealing Temperature on Secondary Recrystallization of Goss Grains in a Grain Orientated Silicon Steel

Effect of Heating Rate and Annealing Temperature on Secondary Recrystallization of Goss Grains in a Grain Orientated Silicon Steel

Grain Boundary Deformation Phenomena and Secondary Growth of Goss Grains in a Fe-3.5%Si Steel

Grain Boundary Deformation Phenomena and Secondary Growth of Goss Grains in a Fe-3.5%Si Steel