Secondary Recrystallization Temperature Research Articles

In-situ observation of recrystallization of K-doped tungsten sheets using laser reflection

The microstructure of (doped) tungsten sheets is crucial for their mechanical behavior. Within this study, a new method, based on laser reflection, is proposed to in-situ determine the process of (secondary) recrystallization and the resulting grain size of (doped) tungsten sheets under ultra high vacuum conditions. The system introduced here allows to position the reflection setup at a reasonable distance from the sample to further observe the sample temperature via a pyrometer. The main signals of interest are the reflection intensity, the resulting distribution, and changes thereof. Furthermore, the proposed method can be carried out on polished and as rolled surfaces likewise. This novel method makes it possible to determine the secondary recrystallization temperature (TRx) in rolled (K-)doped tungsten sheets within a single non-isothermal annealing procedure. The average surface grain size during isothermal annealing procedures can be evaluated as well. Even though the observations are generally restricted to the surface, in the case of tungsten sheets a sufficient determination of bulk recrystallization kinetics is possible as well. Furthermore, the obtained results show, that the recrystallization temperature can serve as a sufficient measure to describe the recrystallized microstructure. Even for different sample strains, TRx correctly predicts the average grain size resulting for various temperature increase rates. The proposed method provides a simple, coherent, and robust method to evaluate the recrystallization properties of (doped) tungsten sheets within a single measurement.

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.

Characteristic of Precipitate Evolution during High Temperature Annealing in Grain-Oriented Silicon Steel

Precipitate evolution during high temperature annealing plays an important role in the magnetic property of grain-oriented silicon steel but was rarely studied. Aluminum was one of the important components of precipitates. Grain-oriented silicon steels with three levels of aluminum content were prepared and the interrupted extraction experiments were carried out. The results showed that during high temperature annealing, the precipitates were polygonal with the main composition of (Al,Si)N. Both the distribution density and volume fraction of precipitates showed first increasing and then decreasing tendencies, while the precipitate size remained approximately constant at first and then increased. Aluminum had a significant effect on the density and volume fraction of precipitates, which resulted in different secondary recrystallization structures. A small amount of aluminum with 0.015 wt.% led to low precipitate density, resulting in a low onset secondary recrystallization temperature as well as a Goss texture with large deviation angles. With the aluminum content of 0.025 wt.%, the secondary recrystallization was developed exactly right in the optimum temperature range, resulting in a perfect magnetic property. When the aluminum content was overcommitted to 0.035 wt.%, Goss grains could not show the preferential growth advantage and the secondary recrystallization structure could not be well developed.

Effect of aluminum on secondary recrystallization texture and magnetic properties of grain-oriented silicon steel

The slab low-temperature reheating grain-oriented silicon steel was prepared in the laboratory, and the high-temperature annealing interruption tests were carried out. The effects of aluminum (which meant acid-soluble aluminum) on the grain size texture, precipitate, magnetic properties and their correlations were studied. The results showed that with the increase in aluminum element, the grain size decreased, while the intensity of {114} and {111} textures increased in the primary recrystallization structure. Meanwhile, the pinning force during the secondary recrystallization and the onset secondary recrystallization temperature were increased. The precipitates were concluded to have a more important role on determining the onset secondary recrystallization temperature than the primary grain size. The higher onset temperature resulted in sharper Goss texture and the better magnetic properties, but when the aluminum content came up to a certain extent, a fine-grain structure was developed. The most suitable aluminum content for present study was 0.025 wt.%, while the onset secondary recrystallization temperature and the primary texture were considered to be conducive to the sharpness of Goss texture.

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 Cr on secondary recrystallization behaviors in high permeability grain oriented silicon steel manufactured by low-temperature slab reheating

Abstract The effect of Cr on secondary recrystallization behaviors of high permeability grain oriented silicon steel manufactured by low-temperature reheating was studied by transmission electron microscopy (TEM), electron back-scattered diffraction (EBSD) and magnetic properties measurement. The results show that Cr containing silicon nitride (Cr, Si) N precipitates after nitriding with the size below 150 nm and regular shaped. Furthermore, primary grain size becomes smaller and more uniform; In the heating stage of purification annealing, precipitates turn into composite silicon nitride (Cr, Al, Si) N. Due to the number of inhibitors is larger and the size is smaller, the pinning effect is stronger. So the starting temperature of secondary recrystallization increases 20 K, the analysis of Zener factor is in agreement with experiment results. With the addition of 0.145 wt% Cr, final grains become smaller and the iron loss (P17/50) could be significantly reduced by nearly 5.4%.

Secondary recrystallization characteristics of 3%Si grain-oriented electrical steel

A secondary recrystallization Lab study focusing on the secondary recrystallization temperature and magnetic properties was carried out on cold rolling industrial samples of 3%Si grain-oriented electrical steel produced by low slab reheating temperature technology. The results showed a secondary recrystallization temperature, determined by the observed grain size change, of 1080°C with annealing interruption and of 1060°C in annealing for 50h at constant temperature. In addition, the best set of magnetic properties, the higher induction and the lower core loss values, was achieved by annealing the samples during 50h at 1070°C constant temperature.

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.

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.

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.

Shot Peening Characteristics of Cold-Rolled Mo Sheet

The commercial pure Mo sheet was shot peened to increase high-temperature mechanical and thermal resistance. Shot peenining was conducted on the surface of cold-rolled Mo sheet with 0.4MPa of shot pressure. The hardness of bcc Mo sheet was increased with increase of shot peening time. Surface hardenss is gradually increased to 120s at the 0.4MPa pressure, but the profiles become almost flat at the prolonged time. The grains were deformed and work hardened in the surface layer. The surface roughness was also increased with peening time. The grain size of shot-peened Mo sheet was smaller than that of cold-rolled Mo sheet in the all recrystallization temperature range. The reason for this could be a larger density of nucleation sites caused by the higher surface deformation of shot-peened Mo sheet. Mo2C carbide phase was analyzed on the surface of recrystallized Mo sheet at the secondary recrystallization temperature range. It was considered that molybdenum carbide was formed due to the evaporation of graphite heating element in the hot-zone furnace. From this study, shot peening of Mo sheet could be a good cold work hardening method to improve high-temperature mechanical and thermal resistance properties.

Activated sintering of refractory borides

The interaction of titanium, zirconium, and tungsten borides with chromium is studied. It is shown that the process is induced by contact melting involving intensive wetting of borides with interaction products at temperatures much lower than the melting points of components. The temperature dependences of contact angles and the phase constitution of interaction products are analyzed. Chromium vapors that reduce the strength of chemical bonds in the lattice lead to a liquid eutectic phase with low contact angles to the surface of borides and promote the activated sintering of boride systems. It is demonstrated that low-porous (1–2%) borides can form at sintering temperatures lower than the temperature of secondary recrystallization. The dependence of bending and compressive strength on sintering temperature is examined. Conditions for producing low-porous fine-grained materials are determined.

Grain Boundary Characteristics of Isolated Grains in Conventional Grain Oriented Silicon Steel

During the secondary recrystallization of GO, isolated grains are often observed in secondary-recrystallized Goss grains (matrix). In an extraction experiment, the crystallographic relations between single isolated grains and matrix grains respectively were investigated in the case of CGO. Although the Σ5 grain boundary to the Goss orientation was the most frequent in the primary recrystallization texture, no Σ5 boundary could be observed at the onset temperature of secondary recrystallization; hence it was concluded that the Σ5 boundary was most mobile in this case. On the other hand, in the case of HGO, it has already been reported that the Σ9 is most mobile. The reason why the dominant grain boundary may differ for the same Goss orientation could be the temperature dependency of the grain boundary features, i.e., mobility and/or grain boundary energy. Furthermore, the Σ3 was more mobile than GGB (general grain boundary) at the higher temperature, which corresponded to the lower temperature range of HGO.

Microstructure and texture development of Fe–3%Si GO steel during high temperature annealing

The one- and two-stage cold rolled Fe–3%Si grain-oriented electrotechnical steels were used as experimental material. Investigated steels were treated according to 6 different high-temperature annealing schedules. The relations between the regime of high-temperature annealing, state of secondary particles system at the onset temperature of secondary recrystallization and development of microstructure and texture during high-temperature annealing were investigated.

Secondary recrystallization and high temperature compressive properties of ODS MA NiAl

A NiAl based oxide dispersion strengthened alloy has been produced by mechanical alloying and consolidated by hot extrusion. Thermo-mechanical treatments have been performed to induce secondary recrystallization (SRx). SRx leads to a pronounced grain coarsening without concurrent dispersoid coarsening, resulting in improved high temperature mechanical properties.

Influence of heat cycling on microstructural parameters of Fe–3%Si grain oriented steel

The influence of heat cycling before the onset temperature of secondary recrystallization during high temperature annealing on the microstructure and texture development of Fe–3%Si two-stage cold rolled grain oriented electrical steel is described.

Reduction of porosity in oxide dispersion-strengthened alloys produced by powder metallurgy

In this work, the porosity in a iron-based oxide dispersion-strengthened (ODS) alloy, namely, PM2000, has been studied together with its recrystallization behavior. It has been found that pores are only found in coarse secondary recrystallized grains formed at the early stage of recrystallization. It is suggested that a lack of fast diffusion paths, particularly grain boundaries, will prevent gas trapped in the materials during mechanical alloying (MA) from diffusing away, and porosity is formed as a result. Thus, it is proposed that an extended anneal below the secondary recrystallization temperature will help to reduce the subsequent evolution of porosity in these materials, and the method has been demonstrated to work successfully in PM2000.

Microstructure and texture in secondary recrystallized silicon steel

Characteristic features of microstructure in secondary recrystallized grain oriented silicon steel containing MnS and AIN have been investigated. Since secondary recrystallization is markedly influenced by inhibitors and a small amount of solute elements, transmission electron microscopy has been used to characterize changes of the morphology of inhibitors by tin addition. The onset temperature of secondary recrystallization of the silicon steel is shown to be decreased by tin addition. Also tin addition tends to reduce the size of inhibitors, MnS and AIN, and thereby appears to reduce the size of primary recrystallized grains. These effects of tin addition on microstructure are consistent with the fundamental idea that reduction of the size of primary recrystallized grains generally decreases the onset temperature of the secondary recrystallization. Electron back scattering pattern measurement was also conducted to characterize microscopic texture of recrystallized grains. Clear {110} texture evolution is confirmed in this silicon steel.

Influence of the Secondary Recrystallization Temperature on the Sharpness of Goss Secondary Recrystallization Texture

Primary recrystallized Fe–3%Si specimens containing AI and nitrided were annealed intermittently with the heating rate of 15℃/h in 100% N2 atmosphere. The magnetic induction B8 was measured after each annealing. The onset of secondary recrystallization was detected by the rapid rise of B8. The maximum B8 obtained was about 1.94 T when the onset temperature of the secondary recrystallization was around 1075℃ regardless of the initial grain size or nitrogen content.The same primary specimens were coated with MgO and annealed with the same heating rate in 5% H2–N2. The maximum B8 obtained was nearly same as with the above annealing condition, however, the initial grain size and nitrogen content was quite contrary in this annealing. The difference in the optimum grain size and nitrogen content for obtaining the highest B8 between both annealings was explained on the assumption that ∑9 boundaries become most mobile at 1075℃ regardless of the annealing methods. Based on this finding, the possibility of producing grain oriented silicon steel without hot band annealing and nitriding treatment was shown.

Mechanism of Orientation Selectivity During Grain Growth of Secondary Recrystallization in Fe-3%Si Alloy

Selective growth of {110}〈001〉 grains in the temperature gradient annealing has been studied in Fe–3%Si alloy. As grains grow, the average deviation angle from the ideal {110}〈001〉 orientation becomes smaller and orientation distribution changes corresponding to that of coincidence grains in the matrix. Secondary recrystallization temperature depends on the orientation of secondary recrystallized grain and sharper {110} 〈001〉 grains grow preferentially at lower temperatures.These phenomena are explained by modified Hillert's model of grain growth. Interfacial energy of coincidence boundary is lower than that of general boundary. Therefore, sharper {110}〈001〉 grains, which have higher frequency of coincidence grains in the primary recrystallized matrix, suffer lower pinning effect from the second phase particles and thus grow preferentially at lower temperatures.