Complete Secondary Recrystallization Research Articles

Evolution of Microstructure and Texture in Grain-Oriented 6.5% Si Steel Processed by Rolling with Intrinsic Inhibitors and Additional Inhibitors.

A grain-oriented steel containing 6.5% Si, characterized by a notable Goss texture, was effectively manufactured through the rolling technique, incorporating both intrinsic inhibitors and additional inhibitors. This investigation focuses on tracking the development of texture and magnetic properties during the manufacturing process and delineates the mechanism underlying secondary recrystallization. The empirical findings clearly demonstrated the significant influence of nitriding duration and quantity on the secondary recrystallization process. In instances where additional nitrogen is absent, the intrinsic inhibitors alone do not lead to secondary recrystallization. However, when the nitriding duration is 90 s and the nitriding amount is 185 ppm, a complete secondary recrystallization structure with a strong Goss texture enables the finished products have excellent magnetic properties. The preferential growth of Goss grains is mainly governed by the enhanced mobility of high-energy (HE) grain boundaries. With the increase in annealing temperature, the occurrence of 20°-45° HE grain boundaries with Goss grains becomes more progressively frequent. At the secondary recrystallization temperature of 1000 °C, the frequency of 20°-45° HE grain boundaries with Goss grains reaches 62.7%, providing favorable conditions for the abnormal growth of Goss grains. This results in a secondary recrystallization structure predominantly characterized by a strong Goss texture. In light of these observations, the present study provides fundamental theoretical insights and serves as a valuable procedural guideline for the industrial manufacturing of 6.5% Si grain-oriented electrical steels.

Effects of primary recrystallization texture and inhibitor characteristic on the secondary recrystallization of Fe-Ga alloy thin sheet induced by nano-sized inhibitor

Sharp Goss texture and excellent magnetostriction coefficient were successfully developed in Fe–Ga alloy thin sheet by composite nano-sized inhibitor. Various primary recrystallization textures in Fe–Ga alloy thin sheets were produced by different cold rolling reductions. The effect of primary recrystallization texture and inhibitor characteristics on the secondary recrystallization of Fe-Ga alloy thin sheet was investigated. The results show that the nano-sized sulfide provides a sufficient pinning force to the normal grain growth of primary grains. The increase in size and distribution width of precipitation during high-temperature annealing indicates the preferentially weakened pinning force. Goss grains in the primary recrystallization do not predominate in number and grain size, but it is surrounded by a higher fraction of high energy grain boundaries (HEGBs). Complete secondary recrystallization of Goss grains can be induced by the preferentially weakened inhibitor and the priority of grain boundary energy and mobility around Goss grains. The cold-rolling reductions have a significant influence on the secondary recrystallization by changing the primary recrystallization texture and the grain boundary characteristics. Based on the relationship between the anisotropic grain boundary energy and mobility and the misorientation angle, a multi-parameter interaction model is proposed to explain the nucleation and development of secondary recrystallization Goss texture under the pinning force.

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

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

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.

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.

Comparison of Precipitates and Texture Evolution in Nb-Bearing Grain-Oriented Silicon Steel Produced by Conventional Processing and Novel Twin-Roll Casting

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} &lt;110&gt;, together with very few Goss components. While in the case of twin-roll casting specimens, the strongest primary recrystallized texture was {111} &lt;112&gt; 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.

Secondary recrystallization induced by composite precipitates in magnetostrictive Fe-Ga alloy thin sheet

Secondary recrystallization of Goss ({110} < 001>) texture is successfully produced by using nanometer-sized composite inhibitor in primary cold rolled Fe81Ga19 alloy sheet. Nanometer-sized sulfides consisting of MnS and Cu2S are dispersedly precipitated during hot rolling and normalization as inhibitors for secondary recrystallization. Strong γ texture with peak at {111} < 112> and weak Goss texture distributed through the sheet thickness in primarily annealed sheets can provide favorable environment for the secondary recrystallization. The higher onset and finishing temperatures of secondary recrystallization confirm the stronger inhibition and driving force originated from the composite inhibitors. Centimeter-sized Goss grains and large magnetostriction coefficient are obtained by primary cold rolling methods without surface energy effect. The result indicates that complete secondary recrystallization in Fe-Ga alloy can be realized by precisely controlling inhibitor characteristic and primary recrystallization texture.

Sharp secondary recrystallization and large magnetostriction in Fe81Ga19 sheet induced by composite nanometer-sized inhibitors

Abstract Strong Goss texture ({1 1 0}〈0 0 1〉) in Fe81Ga19 thin sheet is successfully produced by secondary recrystallization process based on the precise control of inhibitor and primary recrystallization texture. Nanometer-sized sulfides of MnS and Cu2S are dispersedly precipitated during hot rolling as inhibitors for secondary recrystallization. Primary recrystallization texture is characteristic of weak Goss and strong γ textures distributed through sheet thickness by appropriate rolling and annealing schedule. The composite nanometer-sized inhibitors accompanied with the primary recrystallization texture can provide a well-matched pinning effect on normal grain growth of matrix grains and induce abnormal grain growth of exact Goss grains in final annealing process. The magnetostriction coefficient as high as 285 ppm is obtained in Fe81Ga19 sheet after complete secondary recrystallization. Thus, an efficient method is proposed for developing sharp Goss texture and upgrading magnetostriction coefficient in Fe-Ga sheet.

Cube texture evolution and magnetic properties of 6.5 wt% Si electrical steel fabricated by surface energy and three-stage rolling method

0.1 mm-thick 6.5 wt% Si electrical steel sheets with strong cube texture were successfully produced by surface energy effect and three-stage rolling method. The texture evolution and magnetic properties during the processing were briefly investigated, special attention was paid on the development of cube texture. The study shows that cube texture component was originated from the deformed cube grains existed in center layer of hot rolled sheet. During three-stage rolling and intermediate annealing, the cube texture component was enhanced. Attributed to the frequencies as well as size advantages of cube recrystallized grains during nucleation, a homogeneous microstructure associated with cube texture was produced after primary recrystallization. The mechanism responsible for the microstructure and texture of primary recrystallization was explained by strain induced boundary migration. After high temperature annealing for a long time, complete secondary recrystallization microstructure consisting of entirely large cube grains was produced by means of the surface energy effect. Both the strong cube texture and proper grain size enable final annealed sheets have excellent magnetic properties. The present study provides a new efficient way to optimize the recrystallization texture and improve the magnetic properties of double grain-oriented 6.5 wt% Si electrical steel.

Secondary recrystallization behavior in a twin-roll cast grain-oriented electrical steel

The microstructure and texture evolution along the processing was investigated with a particular focus on the secondary recrystallization behavior in a 0.23mm-thick twin-roll cast grain-oriented electrical steel. A striking feature is that Goss orientation originated during twin-roll casting as a result of shear deformation and it was further enhanced during hot rolling and normalizing. After primary recrystallization annealing, a homogeneous microstructure associated with a sharp γ-fiber texture was produced. During secondary recrystallization annealing, the γ-fiber texture was first strengthened and weakened with increasing temperature prior to the onset of secondary recrystallization. Goss grains always exhibited more 20–45° misoriented boundaries than the matrix. The matrix was quite stable during secondary recrystallization with the aid of dense inhibitors. Finally, a complete secondary recrystallization microstructure consisting of large Goss grains was produced. The grain boundary characteristics distribution indicated that the high energy model was responsible for the abnormal growth of Goss grains under the present conditions.

Microstructure and texture evolution of ultra-thin grain-oriented silicon steel sheet fabricated using strip casting and three-stage cold rolling method

A 0.1mm-thick grain-oriented silicon steel sheet was successfully produced using strip casting and three-stage cold rolling method. The microstructure, texture and inhibitor evolution during the processing was briefly analyzed. It was found that Goss texture was absent in the hot rolled sheet because of the lack of shear deformation. After normalizing, a large number of dispersed MnS precipitates with the size range of 15–90nm were produced. During first cold rolling, dense shear bands were generated in the deformed ferrite grains, resulting in the intense Goss texture after first intermediate annealing. The microstructure was further refined and homogenized during the subsequent cold rolling and annealing processes. After primary recrystallization annealing, a homogeneous microstructure consisting of fine and equiaxed grains was produced while the associated texture was characterized by a strong γ-fiber texture. Finally, a complete secondary recrystallization microstructure consisting of entirely large Goss grains was produced. The magnetic induction B8 and iron loss P10/400 was 1.79T and 6.9W/kg, respectively.

Inhibitor induced secondary recrystallization in thin-gauge grain oriented silicon steel with high permeability

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=0.7W/kg).

Oriented Nucleation and Selective Growth during Secondary Recrystallization in Ultra Low Carbon Steels

After primary recrystallization, on further annealing, abnormal grain growth occurred in ultra low carbon steel. Texture evolution was studied by comparing the orientations after complete secondary recrystallization, with on one hand the nuclei for abnormal grain growth and on the other hand the selective growth products of the primary recrystallized matrix. The influence of both mechanisms could be identified in the final texture.

Secondary recrystallization behavior in grain-oriented 2.3% Si-1.7% Mn steel

The secondary recrystallization behavior in 2.3% Si-1.7% Mn steel containing 0.012% sol.Al has been investigated under the conditions of slab soaking at 1150°C and secondary recrystallization annealing at 950°C. Complete secondary recrystallization and good magnetic properties, equivalent to those of regular grade for grain-oriented electrical steel, have been obtained using an N 2-containing atmosphere during the heating stage of secondary recrystallization annealing.

Effect of Annealing Atmosphere on Secondary Recrystallization in 2.3% Si-1.7% Mn Steel

The effect of the N2 content in secondary recrystallization annealing atmosphere on magnetic properties and secondary recrystallization behavior in 2.3% Si-1.7% Mn steel containing 0.008% sol.Al was investigated from the viewpoint of inhibitor nitride precipitation. The specimens were secondary recrystallization annealed with two stage heat cycle, in which first stage was the 875°C soaking in 5, 25 and 50 vol% N2 - H2 gases for nitrogenizing and second stage was the 950 °C soaking in 100vol% H2 gas for purification. 25vol% N2 gas of the 875 °C soaking leads to the best magnetic properties and complete secondary recrystallization after full annealing. On the other hand, other N2 contents result in poor magnetic properties and incomplete secondary recrystallization. Complete secondary recrystallization of 25vol% N2 annealing is explained by the appropriate inhibitor effect of the nitrides through the nitrogenizing. This appropriate inhibitor effect is considered to result when the product of R and Z, which are average grain radius and Zener term respectively, is situated in the range of 0.8 to 1.0 after the heating stage of the 875°C soaking.

Effect of thickness on secondary recrystallization of Fe-3%Si

A study was made on the effect of the final thickness (0.60-0.18 mm) on the secondary recrystallization of Fe-3%Si using MnS and AlN as inhibitors. When heated in hydrogen during final annealing, the 0.60 mm thick specimen underwent a complete secondary recrystallization, but the 0.36 mm and thinner specimens did an incomplete secondary recrystallization. When heated in a mixture gas of hydrogen and nitrogen during final annealing, all specimens underwent a complete secondary recrystallization, but the thinner the specimen, the lower the magnetic flux densities were. The reduction of final thickness makes the specimen too sensitive to the atmosphere during final annealing to get a precisely Goss-oriented secondary-recrystallized texture.

焼結タングステン線材の再結晶過程

The time law of primary grain growth and the effect of doping agent, annealing temperature and heating rate on the shape of secondary recrystallized grains and the orientation distribution of the wire axis for them are investigated using sintered tungsten wires. The rate of primary grain growth is obtained from an increase in mean thickness of fibers, showing that the rate is fairly smaller in the doped wire than in the non-doped wire. Doping has another effect on retarding the start of secondary recrystallization from the surface and also its completion at the central part of the wire. The grains of the doped wire are much more elongated in a longitudinal direction than those of the non-doped wire after a complete secondary recrystallization. However, there is the tendency that the grains of both materials become more equiaxed in shape and are distributed near 〈011〉 in the wire axis as the annealing temperature and the rate of heating increase. It is concluded that the appearance of large elongated secondary recrystallized grains with a wire axis near 〈011〉-〈135〉 is directly due to the bubble effect and the large driving force of grain growth inherent in their orientations.

Magnetic properties of boron-silicon-iron alloys decarburized at the hot-band stage

Magnetic properties of boron-silicon-iron alloys with various amounts of carbon have been investigated by the measurement of magnetic induction at a magnetizing force of 800 Am−1. The amount of carbon was varied before and after hot rolling by adding carbon to the melts and by decarburization of hot bands at 700‡ C. Results show that high magnetic inductions are obtained from heats with 0.043 to 0.070 wt% carbon but that the heat with 0.024 wt% carbon does not result in high induction. Results also show that complete secondary recrystallization and high induction are obtained from heats whose hot bands have been decarburized to a level of 30 p.p.m. provided that the heat contained 0.043 to 0.070 wt% carbon during heating for hot rolling. From these results it can be said that carbon plays a significant role during heating for hot rolling in determining the texture and magnetic induction of boron-silicon-iron alloys.

Effects of decarburization and normalizing heat treatment in boron-silicon iron alloys

Effects of carbon content and various heat treatments on the secondary recrystallization in boronsilicon iron have been studied by measurement of induction at a magnetizing force of 800 A/m and examination of microstructures at various stages of sample preparation process. Carbon was varied before and after hot rolling by adding carbon to the melts and by oxide decarburization of hot bands at 700 °C. Results show that complete secondary recrystallization and high induction (1.92 Tesla) are obtained from heats whose hot bands have been decarburized at 700 °C to a level of 30 to 40 ppm provided the heats contained 0.039 to 0.049 wt Pct carbon during heating for hot rolling. From these facts and analysis of microstructures of cross-sectional area of specimens at various stages of process it can be said that one of the major roles that carbon plays is to introduce, through transformation of austenite, a nonuniform layer-like microstructure during hot rolling and during the normalizing heat treatment of the hot band. This structure continues to exist in the final cold rolled sheet and results in anisotropic growth of secondary grains, and plays a significant role in the secondary recrystallization of boron-silicon iron.

The relation between carbon content and hot rolling temperature in developing high induction in boron silicon–iron

The development of high induction in boron silicon-iron involves satisfying both composition and processing requirements. One requirement for high induction, which necessitates complete secondary recrystallization to a strong (110) [001] texture, is sufficient carbon to assure the presence of some austenite at the hot rolling temperature. A related requirement is that a minimum of 3–4 ppm boron must be dissolved at the rolling temperature for the subsequent development of high induction. The objective of the work to be reported was to determine whether it would be beneficial to magnetic properties to raise the hot rolling temperature, thereby dissolving more boron, providing the carbon content was also raised to maintain the austenite content. Two sets of laboratory alloys, one with 30 ppm nitrogen and the other with 50 ppm nitrogen, and with carbon contents ranging 0.025% to 0.050%, were hot rolled from 1200, 1250, and 1300 °C. The highest inductions were obtained by hot rolling the 0.050% carbon alloys, whether with 30 or 50 ppm nitrogen, from 1250 or 1300 °C, with the higher rolling temperature giving the higher induction. It was concluded that increasing the hot rolling temperature, thereby dissolving more boron, is beneficial provided the carbon level is increased to maintain the austenite content around 5 volume percent. The major limitation of high austenite contents is severe edge cracking, as was encountered with about 20 volume percent.