Secondary Recrystallization Behavior Research Articles

The role of primary recrystallization microstructure in secondary recrystallization of Goss grain in industrial low-temperature grain-oriented silicon steel

Low-temperature grain-oriented silicon steel has very excellent magnetic properties along the rolling direction. During industrial mass production, slight process fluctuations can directly lead to variations in the primary recrystallization microstructure, which in turn can have a dramatic effect on the magnetic properties of the final product. However, it is unclear how different primary recrystallization microstructures influence the magnetic properties of the industrial final products, making it difficult to further optimize the production process of industrial low-temperature grain-oriented silicon steel. Therefore, it is very important to clarify the transformation behavior of different primary recrystallization microstructures and their influences on the transformation behavior of inhibitors during the high-temperature annealing process. Here, we analyzed the differences between two primary recrystallization microstructures in terms of microstructure homogeneity, Goss grain characteristics and texture characteristics and investigated the secondary recrystallization behavior of Goss grains and the dissolution behavior of inhibitors in these two primary recrystallization microstructures during high-temperature annealing. Based on the results of this work, it was found that a finer primary recrystallization microstructure could be more favorable to the formation of a sharp Goss texture, which in turn could significantly improve the magnetic properties, and in addition, new insights into the transformation behavior and the grain boundary pinning behavior of inhibitors during high-temperature annealing process were established. The results of this work could help to further improve the understanding of the actual role of inhibitors during high-temperature annealing and could also provide new ideas for further improving the industrial production process.

Effect of Secondary Cold Rolling Reduction Rate on Secondary Recrystallization Behavior of CGO Steel

With the implementation of the “double carbon” policy in various countries in the world, the demand for grain-oriented electrical steel with low iron loss and high magnetic induction is increasing. Reducing the thickness of the steel sheets is an effective method to reduce the iron loss.The sheet thickness reduction means the increasing cold rolling reduction rate, especially the secondary cold rolling reduction rate, will directly affect the texture evolution of the secondary recrystallization process. In this paper, the secondary cold rolling reduction rate of commercial grain-oriented silicon steel was studied by means of X-Ray Diffraction, Electron Backscatter Diffraction. The results showed that Ultra-thin oriented silicon steel cannot be obtained by increasing the secondary cold rolling reduction rate alone; the optimum secondary cold rolling reduction rate was 59.2%. The grain size increased as the secondary cold rolling reduction rate increased and favorable texture content decreased, which was disadvantage to obtain a secondary recrystallization environment.

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.

Secondary Recrystallization Behavior in Fe-3%Si Grain-oriented Silicon Steel Produced by Twin-roll Casting and Simplified Secondary Annealing

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 °C. The corresponding growth rates were in the range of 60–1400 μm/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 γ- 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.

Effect of Wire-Drawing Process Conditions on Secondary Recrystallization Behavior During Annealing in High-Purity Copper Wires

The relationship between the process condition of wire-drawing and the microstructural evolution during the subsequent annealing was investigated for the production of high-purity copper wires. Three wire-drawing process conditions were considered according to the reduction in the area per pass and the die angle, and their effects on the evolution of the grain structure and texture during annealing were investigated. Strain distributions, calculated using the finite element method, showed that the shear strain near the wire surface varies according to the process condition. The electron backscatter diffraction results indicate that the location on the cross-section of the wire, where secondary recrystallization initiates during annealing, is closely related to the shear strain during wire-drawing. Meanwhile, the effect of shear deformation on the grain structure and texture after primary recrystallization is insignificant. Drawing process conditions with a small reduction in the area per pass and die angle resulted in a relatively small shear strain and gave rise to the onset of secondary recrystallization at the central region of the wires. In contrast, the condition with a large reduction in the area per pass and die angle led to a high shear strain and the onset of secondary recrystallization at the peripheral region of the wire. The observed primary and secondary recrystallization behavior during annealing was explained from the viewpoint of dynamic material phenomena and inhomogeneity in the local recrystallization texture, regulated by the extent of shear deformation during wire-drawing.

Secondary recrystallization behavior in strip-cast grain-oriented silicon steel processed by isothermal secondary annealing

The primary annealed sheets of strip-cast grain-oriented silicon steel were isothermally secondary annealed for 15 min under 100% H2 atmosphere. The microstructure and crystallographic orientation at different annealing temperatures were characterized and the secondary recrystallization behavior was elucidated. It was observed that relatively complete abnormal grain growth occurred at 1025 °C. Incomplete abnormal grain growth developed when the temperature was lower than 1025 °C, and normal grain growth occurred when the temperature was higher than 1025 °C. During the abnormal grain growth, both of the Goss and {110}⟨227⟩ grains developed because of the rapid decrease of the inhibiting force and the limited annealing time. Considering the high energy boundary (HE), coincidence site lattice boundary (CSL) and solid-state wetting (SSW) models for abnormal grain growth, the first one explained the development of the Goss and {110}⟨227⟩ grains. Another result was that several matrix grain colonies were observed in the interior or at the boundaries of secondary grains after abnormal grain growth. The grains at the periphery of these colonies showed a large fraction of high energy boundaries (20–45° misorientation) with the surrounding secondary grain and similar grain size with the unconsumed matrix grains. Therefore, these colonies were expected to be consumed by prolonging the annealing time and thus the limited annealing time was responsible for their occurrence. A possible explanation for the dominated high energy boundaries instead of low energy boundaries at the periphery of these colonies was proposed. All of these behaviors promoted the understanding of abnormal grain growth.

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.

Secondary Recrystallization Behaviors of Grain-Oriented 6.5 wt% Silicon Steel Sheets Produced by Rolling and Nitriding Processes

By rolling and nitriding processes, 0.23- to 0.3-mm-thick grain-oriented 6.5 wt% silicon steel sheets were produced. The core losses of grain-oriented 6.5 wt% silicon steel at frequencies ranging from 400 Hz to 20 kHz were lower than that of the grain-oriented 3 wt% silicon steel with the same thickness by 16.6–35.8%. The secondary recrystallization behavior was investigated by scanning electron microscopy, energy-dispersive spectroscopy, and electron backscattered diffraction. The results show that the secondary recrystallization in high-silicon steel sheets develops more completely as the nitrogen content increases after nitriding, secondary recrystallized grain sizes become larger, and the sharpness of Goss texture increases. Because more \(\left\{ {110} \right\}\left\langle {116} \right\rangle\) grains in the subsurface and the central layer of the sheets have a lot of 20°–45° high-energy boundaries in addition to Goss grains, \(\left\{ {110} \right\}\left\langle {116} \right\rangle\) can be the main component through selective growth during secondary recrystallization when the inhibitor quantity is not enough and inhibitor intensity is weaker. The increases in nitrogen content can increase the inhibitor intensity and hinder abnormal growth of a mount of \(\left\{ {110} \right\}\left\langle {116} \right\rangle\) grains and therefore enhance the sharpness of Goss texture.

Influence of cold rolling on the precipitation in an Al–Mn–Zr alloy

Abstract The aim of the experiments was to study the influence of the rolling reduction (39, 87, and 96%) on the size and distribution of secondary particles and recrystallization behaviour of Al–Mn sheets with Zr addition prepared by twin-roll casting (TRC) in the industrial conditions. Samples, cold rolled on a laboratory mill, were subjected to a two-step precipitation annealing. Their microstructure (grain structure, substructure, particle analysis) as well as mechanical and physical properties (microhardness, electrical conductivity, resisitivity) were then characterized. The material cold worked with 39% reduction shows a moderate decrease of microhardness due to recovery, while sheets cold worked with 87 and 96% reduction soften more due to recrystallization. Regardless of the cold rolling reduction, the highest density of precipitates of α-Al(Mn,Fe)Si phase form during heating to 450 °C in the temperature range from 350 °C to 450 °C. Quantitative particle analysis of the sheets after the whole annealing cycle indicate that the alloy deformed 96% shows the highest density of particles in the size range from 50 to 140 nm. In addition, many spherical particles up to 15 nm were observed by transmission electron microscopy, some of them were identified by electron diffraction as Al 3 Zr phase with L1 2 crystal structure.

The Relationship Between Hot and Cold Rolling Parameters and Secondary Recrystallization Behavior in Silicon Steel Sheets

The effect of different hot and cold rolling process variables was evaluated for the secondary recrystallization behavior of silicon steel sheets, and a simple model was developed. On the basis of the model, the following results can be drawn: (a) for complete secondary recrystallization of silicon steel sheets, rolling of cast ingots must precede MnS precipitation start; (b) if it is necessitated, intermediate annealing during hot rolling passes must be carried out in the temperature of about 1000 °C; (c) during hot rolling, the amount of initial strain before the intermediate annealing of rolled strips at 1000 °C must be >70% reduction in thickness; (d) in the two-stage cold rolling method, the thickness reduction in the second cold rolling stage must be <61%; and (e) secondary recrystallization is encouraged by using the non-conventional three-stage cold rolling method with two intermediate anneals.

Secondary recrystallization behavior in the rolled columnar-grained Fe–Ga alloys

The secondary recrystallization behavior with temperature increasing from 900 to 1080°C was investigated in the rolled columnar-grained magnetostrictive Fe–Ga alloy sheets. The abnormal Goss grain growth occurred due to the inhibitory action of NbC in the Fe–Ga–0.1at%NbC sheets. With the temperature increasing at a rate of 0.25°C/min, the secondary recrystallization started below 950°C. In addition to the S-induced surface energy effect, sulfur annealing also introduced a large number of S-rich and Nb-rich precipitates, which retarded the grain boundary migration on the surface. The abnormal grain growth was found to be restricted inside the sheet during the sulfur annealing process when the temperature was below 1000°C, and a large amount of small island-like grains was remained on S-annealed sheets. After final Ar/H2 annealing processes, the S-rich precipitates and small island-like grains were eliminated, and sharp Goss orientation and high magnetostriction of 245ppm were obtained in the final S-annealed sheets.

Microstructure and Mechanical Properties of Al-Mn Sheets with Zr Addition

The aim of the experiments was to study the influence of the rolling reduction in thickness on the size and distribution of secondary particles and recrystallization behaviour of Al-Mn sheets with Zr addition prepared by twin-roll casting (TRC) in the industrial conditions. Samples, cold rolled on a laboratory mill, were subjected to a one and two-step precipitation annealing. Their microstructure (grain structure, phase composition, particle analysis) and mechanical and physical properties (microhardness, electrical conductivity) were then characterized. Quantitative particle analysis was carried out on field-emission gun scanning electron microscope (FEG-SEM) micrographs.

The Relationship Between Inhibitors and Secondary Recrystallization Characteristics of High Permeability Grain-Oriented Electrical Steel

In order to understand the secondary recrystallization characteristics of high-permeability grain-oriented electrical steel, we studied microstructure, Goss orientation, onset secondary recrystallization temperature and Σ3, Σ5 and Σ9 grain boundaries during high temperature annealing. In particular, we examined the effect of different amounts of AlN inhibitors on the secondary recrystallization behavior. First, with the increase of AlN amount, the onset secondary recrystallization temperature and magnetic properties increase. Second, when the inhibitory ability is weak, the fraction of grains that have Goss±5, Goss±10, and Goss±15 keep constant before secondary recrystallization; with the increase of AlN amount, the fraction of grains that have Goss±15 keep almost constant, but the Goss±5 and Goss±10 grains increase obviously with the increase of temperature. Third, the frequency of Σ3, Σ5, Σ9 grain boundaries around Goss grains and general grains keeps almost constant with the increase of temperature before secondary recrystallization when having enough AlN inhibitors; however, when the content of AlN is very low, the frequency of Σ3, Σ5 and Σ9 grain boundaries around Goss grains will decrease to the level of that around general grains, which eventually leads to unsuccessful secondary recrystallization.

Influence of Si and Fe on the distribution of intermetallic compounds in twin-roll cast Al–Mn–Zr alloys

The aim of the experiments was to study the influence of Si and Fe on size and formation of secondary phases and recrystallization behavior of Al–Mn–Zr alloys prepared by twin-roll casting (TRC) in the industrial conditions. Microstructure (grain structure, phase composition, particle analysis) of these alloys was characterized during downstream processing. Quantitative particle analysis was carried out on FEG–SEM micrographs at both high and low magnifications. The phases were examined by light metallography, energy dispersive X-ray spectroscopy (EDXS) and by means of electron back-scattering diffraction (EBSD) according to their crystallographic structure. The microstructure at the final gauge was also observed by transmission electron microscope (TEM). A relatively high (0.5 wt.%) Si content and low (0.2 wt.%) Fe content in one of the alloys resulted in balancing of nucleation and dissolution rate for small particles. Hence a higher density of small particles was stable during the downstream processing, and this alloy showed improved recrystallization resistance.

Effect of Hot Band Annealing on Magnetic Properties in 3% Si Grain-oriented Electrical Steels

Hot band annealing is known to be a prerequisite for good magnetic properties irrespective of manufacturing methods in grain-oriented Fe-3 wt.% Si electrical steels. In this study, the effects of hot band annealing on magnetic properties were investigated in 3% grain-oriented electrical steels of low soluble Al contents and one-stage cold rolling. Microstructure and precipitate distribution were compared with hot band annealing conditions. Secondary recrystallization behaviour with hot band annealing condition was also discussed.

Secondary Recrystallization Behavior in 3% Si Grain Oriented Steels

The effects of primary recrystallization on secondary recrystallization in grain oriented 3% Si steels were experimentally clarified and unidentified microstructural behavior in the incubation stage of secondary recrystallization was verified. A secondary recrystallization mechanism from the incubation period to the growth stage is suggested by identifying microstructural changes based on grain orientation, texture, and misorientation.

分散強化型Ｍｏ板の２次再結晶粒成長挙動

In order to understand in detail the secondary recrystallization behavior of dispersion strengthened molybdenum sheet made by adding a certain amount of La2O3 the influence of La2O3 additives on the secondary grain growth behavior was investigated by use of EPMA and chemical analyses. The results obtained were as follows:(1) Second phase, which are dispersed in the form of La2O3 as a stable oxide at the primary grain boundaries and matrices, plays an important role as inhibitors to the normal grain growth and conversely as promoters of the secondary grain growth at higher temperatures.(2) At higher temperatures the dissociation and dissolution of second phase consisting of La2O3 are taken place, resulting in development of secondary grain growth.(3) A single crystal sheet can be easily prepared from La2O3 dispersion strengthened molybdenum sheet.

Effect of hydrogen content in the final annealing atmosphere on secondary recrystallization of grain-oriented Si steel

Secondary recrystallization behavior of the grain-oriented silicon steel utilizing MnSe, AlN and Sb as inhibitors was investigated through the observation of the specimens secondary recrystallized partially during the final annealing. The atmosphere of higher hydrogen content accelerated primary grain growth and enhanced {1 1 1} and {1 1 0} texture in the surface region at the early stage of the final annealing. Consequently, iron loss was reduced due to smaller grains after secondary recrystallization. The best value of the material of 0.23 mm thickness without domain refining was 0.82 W/kg as W 17/50 and 1.95 T as B 8. The fact that hysteresis loss was reduced as well as eddy current loss, makes it evident that many secondary grains having sharp {1 1 0}〈0 0 1〉 texture developed under the atmosphere of high hydrogen content.

ＴｉＣ，ＨｆＣ分散強化型Ｍｏ合金板の結晶粒成長および焼鈍集合組織

In order to understand in detail the secondary recrystallization behavior of fine-grained molybdenum alloy sheets dispersed with TiC and HfC particles of 0.8mol%, the effects of kinds of dispersed particle on the secondary grain growth behavior and annealing textures in hot-rolled dispersion strengthened molybdenum sheets were investigated. First, it was recognized that dispersed particles, which are present in the form of Ti (Ox, C) and Hf (Ox, C) as complicated oxides and carbides at the primary recrystallized grain boundaries, play an important role as inhibitors to the normal grain growth and conversely as promoters of the abnormal grain growth at higher temperatures in both molybdenum alloy sheets. Moreover, the temperature at which secondary recrystallization commences from both molybdenum alloy sheets is strongly dependent on the kinds of dispersed particle and is correspondent to their dissociation and dissolution. Secondary, it was found that most components of secondary textures correspond to very weak components in the primary recrystallization textures and are related by a rotation of approximately 20°-30° about the <110> axis of the strong primary recrystallized {111} (<112>+<110>) matrice in both molybdenum alloy sheets.