Final Recrystallization Research Articles

A quasi-in-situ EBSD study on the formation and development of η-fiber in 0.15 mm ultra-thin Fe-4.5 wt. % Si sheet

Texture evolution of 0.15 mm ultra-thin Fe-4.5 wt. % Si sheet with strong η-fiber produced by two-stage rolling and final annealing was investigated using ex-situ and quasi-in situ electron backscatter diffraction (EBSD). The Goss grain of the hot-rolled plate was rotated to γ-fiber (<111>//ND) dominated by {111}<112> during one stage of moderate warm rolling reduction and then formed strong Goss after intermediate annealing. When the rolling reduction was slightly increased, the annealed strong Goss rotated to near {111}<112> and then formed strong {120}<001> after final annealing. The quasi-in-situ EBSD characterization of the intermediate and final recrystallization process indicated that the recrystallized Goss, {120}<001> and {111}<112> grains were nucleated and grown within the shear bands of deformed {111}<112>, near {111}<112>({223}<362>), and {111}<110> matrices respectively. The recrystallized strong η-fiber textures dominated by {120}<001> were dependent on the coarser Goss grains and suitable rolling reduction and could remain unchanged after considerable grain growth. The 0.15 mm specimen with superior magnetic properties and high strength achieved an iron loss (P10/400 =7.82 W/kg) improvement of 17 %, magnetic induction (B50 =1.65 T) improvement of 0.04 T, and yield strength (474 MPa) improvement of 61 MPa compared to commercial products with the same thickness.

Evolution of Recrystallization Texture in A286 Iron-Based Superalloy Thin Plates Rolled via Various Routes

The A286 iron-based superalloy has wide-ranging applications in replacing expensive nickel-based and cobalt-based superalloy to manufacture the turbine disk as well as the pipelines and valves of the fourth-generation supercritical water reactor (SCWR) working below 650 °C. The recrystallization texture importantly affects the mechanical properties and oxidation resistance of superalloys. However, very few investigations are available on the recrystallisation texture of A286 alloy. The current work reports the texture of A286 alloy fabrication using various rolling routes, including one-stage cold rolling with the rolling rates of 83% (Route I) and 91% (Route II), and two-stage cold rolling with the rolling rate of 83% + 50% (Route III). Route III is preferentially recommended to manufacture A286 alloy thin plates due to the obviously reduced work hardening as well as the weakened recrystallization texture and anisotropy; moreover, compared with other routes, the recrystallized grain size of Route III did not significantly coarsen. We also revealed the mechanism for the effect of cold rolling textures on the final recrystallization texture and the role of the deformation twin in {110} &lt;115&gt; grain. In this study, recrystallization texture develops through two independent mechanisms related to different deformation microstructures, including the recrystallization texture inherited from deformation texture and the recrystallization texture depended on deformation twins.

Comparative study on microstructure and texture evolution of low silicon non-oriented electrical steels along one-stage and two-stage cold rolling processes

Fe-0.9% Si-0.3% Al non-oriented electrical steels were fabricated by two-stage cold rolling process including hot rolling, first cold rolling, intermediate batch annealing, second cold rolling and final annealing, in which the first cold rolling reduction varied from 15% to 54%. One-stage cold rolling process with hot band normalization was also investigated for comparison. The findings revealed that, in two-stage cold rolling process, the final recrystallization texture and magnetic properties heavily relied on the rolling reduction schedule. As the first rolling reduction increased, the core loss increased and the magnetic induction decreased owing to the enhanced γ-fiber (〈111〉//ND) texture in the final annealed sheets. Relatively lower first cold rolling reduction (15%) was beneficial to generate coarse grains during intermediate annealing and led to large grains with weakened γ-fiber and enhanced Goss textures in final sheets. By contrast, relatively higher first cold rolling reduction (30% and 54%) caused small grains by promoting the occurrence of recrystallization during intermediate annealing and resulted in small grains with stronger γ-fiber texture after final annealing. The hot band normalization in one-stage cold rolling process could also effectively improve the grain size prior to cold rolling, though MnS precipitate and sharp γ-fiber recrystallization texture were promoted in the final sheets due to the high normalization temperature and much higher cold rolling reduction, respectively. Therefore, two-stage cold rolling process was propitious to reduce γ-fiber recrystallization texture and MnS precipitate compared with one-stage cold rolling process. The appropriate rolling reduction schedule (15%+75.6%) and suitable intermediate annealing process (750 °C for 1.5 h) were propitious to produce high-performance non-oriented silicon steel with lowest core loss and highest magnetic induction.

Enhanced grain refinement and texture weakening in Al–Mg–Si alloy through a novel thermomechanical processing

A novel thermomechanical processing including solution treatment, first rolling with large deformation and overaging based on particle-stimulated nucleation of recrystallization (PSN) was proposed to obtain an Al–Mg–Si alloy sheet with fine grain structure, weak texture and high plastic strain ratio. The difference between conventional thermomechanical processing and novel thermomechanical processing with two overaging time parameters was investigated by texture and microstructure characterization and tensile tests. The results show that the finest grain structure with an average size of 17 µm, the weakest recrystallization texture with a volume fraction of 8.4 %, the highest average plastic strain ratio r of 0.69 and the lowest planar anisotropy Δr of − 0.001 were acquired by the novel thermomechanical processing with a long overaging time. In comparison with conventional thermomechanical processing, the novel thermomechanical processing can generate completely different particle distributions and tends to develop a weak texture consisting of the CubeND {001}<310>orientation. Increasing the overaging time is effective in coarsening the particles and thus refining the grain structure, weakening the texture, and improving the average r and Δr values. The genetic characteristics of texture evolution and the particle distribution determine the final recrystallization texture.

Texture Development in Aluminum Alloys with High Magnesium Content

The evolution of texture in the AlMg6Mn0.7 (1565 ch) alloy throughout the entire cycle of its thermomechanical treatment has been studied. Using this alloy as an example, a new way is shown to control the texture development, which is applicable to alloys with high magnesium content. An integrated approach is applied, including optical and electron microscopy, as well as X-ray diffraction analysis, the determination of mechanical properties and texture modeling using algorithms of the crystallographic plasticity theory. All stages of the thermomechanical treatment have been studied, namely the development of the deformation structure out of the as-cast structure in the reversing hot-rolling stand, continuous hot rolling, cold rolling and final recrystallization annealing. The study showed that second phase particles are the main source of recrystallization nuclei at all stages of high temperature thermomechanical treatment. The importance of these particles increases when the Zener-Hollomon parameter increases. To obtain the maximum possible proportion of a random texture, thermomechanical processing must be carried out at high Zener-Hollomon parameters. However, the temperature should not interfere with the complete recrystallization process at the same time. After cold rolling and recrystallization annealing at temperatures equal or greater than 350 °C, a large proportion of random texture is formed, and the properties of the metal are almost isotropic.

Dependence of recrystallization behavior and magnetic properties on grain size prior to cold rolling in high silicon non-oriented electrical steel

The present work aimed to investigate the roles of prior grain size of the hot rolled sheets after normalization on final recrystallization behavior and magnetic properties in 3.1%Si + 0.9%Al non-oriented electrical steel. Bigger prior grain size produced coarser deformed grains and promoted the development of in-grain shear bands, which together resulted in distinct recrystallization behavior. The prior small-grained microstructure caused relatively slow kinetics at the early stage of recrystallization, while fast kinetics was displayed at the later stage due to the growth of new γ(<111>//normal direction (ND))-grains and led to strong γ-fiber recrystallization texture. By contrast, the prior big-grained microstructure gave rise to relatively fast recrystallization kinetics at the early stage due to the diversified nucleation orientation and rapid grain growth in the interior of coarse deformed γ-grains with the help of in-grain shear bands. However, relatively slow kinetics was displayed at the later stage because the coarse deformed λ(<001>//ND)-grains were sluggish to recrystallize. Hence, continuous recrystallization and shear bands induced nucleation contributed to strong λ-fiber texture. Magnetic induction B50 continuously improved as the prior grain size increased, while both the low-frequency core loss P15/50 and the high-frequency core loss P10/400 decreased firstly and then increased with different critical prior grain size.

Two-stage warm cross rolling and its effect on the microstructure, texture and magnetic properties of an Fe-6.5 wt% Si non-oriented electrical steel

Cross rolling is an effective processing technique used to optimize the crystallographic texture of electrical steel sheets. However, it is usually applied in cold rolling only. It is unknown how this rolling technique affects the microstructure and texture of electrical steels at elevated temperatures. In this study, a two-stage warm cross rolling scheme, i.e., rolling at elevated temperatures and in alternative directions with respect to the hot rolling direction (HRD), was applied to an Fe-6.5 wt% Si non-oriented electrical steel to produce thin steel sheets. The swapping of rolling direction between the two warm rolling stages significantly changed the deformation microstructure and texture, leading to different final recrystallization textures. These differences are attributed to the discrepancies in slip activities at elevated temperatures and to the different initial textures resulted from the change in rolling direction. The magnetic properties of the final steel sheets are evaluated by single sheet testing. Although the steel processed by warm rolling along HRD in the first stage and along HTD in the second stage exhibits a slightly higher magnetic flux density than other routes, it is shown that the magnetic flux density and core loss may have little relation to the crystallographic texture since the magnetocrystalline anisotropy caused by the texture is small.

Dynamic recrystallization behavior of the Ta-containing TiAl alloy in isothermal deformation

The dynamic recrystallization behavior of as-cast Ti-46.5Al-3Ta-2Cr-0.2W alloy during isothermal compression process with nominal deformation of 50% and strain rates from 0.01s to 1s was investigated by electron microscopy. The results showed that the deformation mechanism of this alloy can be concluded as grain boundary sliding and mechanical twins, which induce the final dynamic recrystallization. The phase boundary bulging was found to be the major nucleation mechanism responsible for the lamellar globularization and the formation of recrystallized γ grains inside the lamellar colony under the high strain rate. The recrystallized γ grains induced by the twinning is the main mechanism for refining α2 lamellar microstructures under low strain rate.

Investigation of microstructure and properties of strip-cast 4.5 wt% Si non-oriented electrical steel by different rolling processes

A 4.5 wt% Si as-cast strip with equiaxed grains microstructure fabricated by twin-roll caster was subjected to three different cold rolling and final recrystallization annealing processes. The results revealed that the rolling process has a significant effect on the evolution of microstructure and texture of the strip-cast 4.5 wt% Si non-oriented electrical steel. Moreover, both mechanical and magnetic properties of the steel exhibited various characteristics because of different rolling routes. After short-time annealing at high temperature, the steel sheet experienced one-step cold rolling exhibits the highest tensile strength. Regarding two-step cold rolling, better magnetic properties were obtained after a second cold rolling with a slight reduction. The excellent performance of mechanic and magnetic properties can be fabricated by two-step medium reduction cold rolling.

Retaining {100} fibre texture in electrical steel via strain-induced boundary migration recrystallisation.

In this paper, the feasibility of retaining the preferred {100} fibre texture for non-grain oriented (NGO) electrical steel from the as-cast columnar {100} grains by encouraging recrystallisation via the strain induced boundary migration (SIBM) mechanism was investigated. Rolling with intermediate annealing stages before the final anneal was used to reduce the stored energy through recovery before the final recrystallisation step. A strong {100} fibre recrystallisation texture, i.e. 32% area fraction, was seen in the sample which was warm deformed to 1.6 strain with 5 intermediate annealing stages then annealed at 950 °C for 5 minutes (to observe the early stages of recrystallisation) or 1 hour. Whereas only 12 - 14% {100} fibre component was observed after 1.2 strain with a single or with no intermediate annealing stage. It was found that the {100} fibre recrystallisation texture was formed in regions adjacent to parental deformed grains with {100} fibre texture due to the SIBM recrystallisation mechanism. EBSD imaging analysis was used to follow the recrystallisation process in the same microstructural region using interrupted heat treatments and it was seen that the {100} texture grains carried very low stored energy after deformation, which meant the subgrains in these grains bulged into the surrounding grains with higher stored energy. Due to its slow recrystallisation nucleation rate, a low overall stored energy is preferred to encourage {100} texture recrystallised grains to form via the SIBM recrystallisation mechanism.

Process Development toward a Pro-Drug of Buprenorphine

This paper describes the process development conducted toward the multi-kilogram synthesis of a hemiadipic acid pro-drug of buprenorphine. The major challenges were to control the levels of the dibuprenorphine monoadipate impurity and to improve the robustness of the final recrystallization. Modification of the reaction conditions limited the levels of the impurity formed during the reaction, and an additional point of control was introduced, a reslurry with dichloromethane. The solid-state properties of the pro-drug were fully investigated, and extensive polymorph screening was undertaken. An unusual low-temperature endothermic event was observed in the differential scanning calorimetry thermogram. This low-temperature event was further investigated using variable-temperature X-ray powder diffraction and variable-temperature solid-state nuclear magnetic resonance spectroscopy. It was concluded that this event was likely to be associated with a reversible, minor conformational change of the adipate side c...

On the influence of deformation mechanism during cold and warm rolling on annealing behavior of a 304 stainless steel

In the present study, a 304 stainless steel was deformed at different temperatures of room temperature (cold rolling) and 200 °C (warm rolling) for elucidating the distinct deformation mechanisms, and then, the influence of the deformed microstructures on the subsequent microstructural evolution and texture development during annealing treatments was studied. The results indicated that deformation-induced martensite transformation was the dominant deformation mechanism during cold rolling, and a mixed microstructure consisting of ~60% volume fraction of α'-martensite and deformed austenite was obtained. Deformation twinning of austenite dominated the deformation during warm rolling. The underlying reason was the increasing SFE with deformation temperature, which inhibited the martensitic transformation but promoted the formation of deformation twins. On annealing, the recrystallization of retained austenite in cold-rolled samples was retarded because of martensitic reversion compared to the warm-rolled samples. Completely recrystallized structure with average grain size of ~0.7 µm was obtained in both cold and warm-rolled samples after annealing at 800 °C. Texture evolution indicated that martensitic reversion enhanced the intensity of {110}< 112 > texture in cold-rolled and annealed samples. However, the final recrystallization texture components were consisted of {110}< 112 > and {113}< 211 > regardless of rolling process. Furthermore, structure-property relationship was established, and combination of high strength and excellent plasticity can be obtained in both cold and warm-rolled sheets by tuning the subsequent annealing parameters.

Asymmetric Synthesis of Netarsudil: A New Therapeutic for Open-Angle Glaucoma

The asymmetric synthesis of a Rho kinase/norepinephrine transport inhibitor, netarsudil, the active component in the recently FDA-approved product Rhopressa™, is described herein. This concise six-step synthetic route utilizes the 2,4-dimethylbenzoate ester of a phenylacetic acid as the backbone of the β-amino acid’s framework. A chiral enolate of the Evans auxiliary, (R)-4-benzyloxazolidin-2-one, is used to direct the formation of the (S)-stereocenter by incorporating the N-Boc-protected β-amino methyl arm with high diastereoselectivity (96:4 dr) using N-Boc-1-aminomethylbenzotriazole as the electrophile. Uniquely, 2,2,2-trichloro-1,1-dimethylethyl chloroformate is used as a non-racemizing activating agent for the coupling reaction between the chiral (S)-N-Boc-protected 2,4-dimethylbenzoyloxymethyl phenyl propanoic acid and 6-aminoisoquinoline to provide N-Boc-protected netarsudil in good yield and excellent enantiomeric purity (63%, 98% ee). Final acidic deprotection and recrystallization provides netarsudil (&gt;99% ee), an ophthalmic agent used for the treatment of patients with open-angle glaucoma.

Texture evolution behavior and anisotropy of 2A97 Al–Li alloy during recrystallization at elevated temperature

2A97 Al–Li alloy was cold-rolled to 2 mm and then thermally exposed at different temperatures for 1 h and at 723 K for different time, respectively. The texture evolution behavior and the anisotropy of 2A97 Al–Li alloy were investigated. The result shows that the {001} 〈120〉 and {011} 〈233〉 textures are the dominant recrystallization texture. The {124} 〈211〉 texture is the final recrystallization texture. In case of low-temperature thermal exposure (473, 573 K), the {011} 〈211〉 texture is aggregated to the {112} 〈111〉 and {123} 〈634〉 textures. During the recrystallization at 723 K, the {001} 〈110〉, {111} 〈112〉 and {011} 〈100〉 textures are the intermediate transition grain orientations. The concurrent precipitation of Al20Cu2Mn3 and Al3Zr results in the occurrence of unusually sharp {011} 〈233〉 and {001} 〈120〉 texture components during recrystallization. The alloy with both recrystallization and deformation texture possesses the smallest anisotropic, and the texture is the direct reason that results in the anisotropy.

Abating recrystallization inhomogeneity in twin-roll cast 3003 aluminum sheet by electromagnetic fields

Recrystallization inhomogeneity is a typical problem in twin-roll cast Al–Mn alloys. A compound field is applied during twin-roll casting of 3003 aluminum sheet to investigate its effects on the final recrystallization structure of the cold rolled and annealed sheet. Dendrite arms in the as-cast sheet are refined and become uniform after applying the field. The arm size range decreases from 5 to 15 μm to 5–8 μm. Two-step homogenization results in more nucleation particles and finer recrystallization structure than single-step routine does in both sheets. More nucleation particles are formed and evenly distributed in the field sheet under the same homogenization routine as a result of more uniformly distributed elements and grain size in the as-cast sheet. The recrystallization inhomogeneity is abated and eliminated by the compound field. Recrystallization grain size in the field sheet after 600 °C × 15 h + 500 °C × 15 h annealing is reduced to 30 μm × 60 μm and distributes evenly along sheet thickness.

Effect of Zn on microstructure, texture and mechanical properties of Al-Mg-Si-Cu alloys with a medium number of Fe-rich phase particles

The effect of Zn on the microstructure, texture evolution and mechanical properties of Al-Mg-Si-Cu alloys with a medium number of Fe-rich phase particles was investigated using tensile testing machine, optical microscopy (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffractometer (XRD) in the present study. The results show that Zn addition has a significant influence on the final mechanical properties, but a slight effect on microstructure and final recrystallization texture. Zn addition is favorable to increase yield strength, ultimate tensile strength and elongation, however it is detrimental to improve r value and reduce Δr value. During the thermomechanical processing, the microstructure almost has nothing to do with Zn addition. However, Zn could prevent the secondary phase particles from precipitating during intermediate annealing. In contrast to the alloy sheet without Zn, the alloy sheet with 1.0wt% Zn always has weaker textures before final cold rolling, but a stronger texture after experiencing final cold rolling. After solution treatment, they almost possess the same recrystallization texture. Finally, the effect of Zn addition on the recrystallization texture was discussed. Their similar recrystallization texture can be attributed to the similar microstructure, which was caused by the medium number of Fe-rich phase particles.

Texture evolution during skew cold rolling and annealing of a non-oriented electrical steel containing 0.9 wt% silicon

A novel rolling technique, i.e., skew rolling, was applied to a non-oriented electrical steel containing 0.9 wt% Si, aiming at altering the texture of the final sheets that usually contain the magnetically unfavorable //ND fiber after conventional rolling and annealing. The texture after skew cold rolling was compared to those obtained from conventional rolling and cross rolling and significantly different textures were observed. The cold-rolled steel sheets were then annealed and the texture evolution was investigated using a quasi in situ electron backscatter diffraction technique, i.e., tracking the microtexture of the same area at various holding times at the same temperature. The development of the recrystallization microstructure and microtexture (nucleation and grain growth) was characterized and the effect of skew rolling on the final texture was studied. The mechanisms governing the formation of the final recrystallization texture, e.g., preferential nucleation and selective growth, were elucidated.

Recrystallization Texture Transition in Fe-2.1 Wt Pct Si Steel by Different Cold Rolling Reduction

The competition dependent on cold rolling reduction among main recrystallization texture components in Fe-2.1 wt pct Si sheets was investigated from the hot band characterized by strong Cube ({001}〈100〉) at center layer and weak Goss ({110}〈001〉) at quarter layer. The deformation and recrystallization textures through thickness were both analyzed by X-ray diffraction technique. Goss, Cube, and {111}〈112〉 components dominate the recrystallization texture in sequence with the cold rolling reduction increasing from 60 to 90 pct. This recrystallization texture transition with cold rolling reduction can be explained in terms of the number and nature of nucleation sites for various texture components. A variety of final recrystallization textures are proposed for non-oriented silicon steel by designing texture and microstructure of hot band and cold rolling reduction.

Effects of rolling temperature on microstructure, texture, formability and magnetic properties in strip casting Fe-6.5 wt% Si non-oriented electrical steel

Fe-6.5wt% Si non-oriented electrical steel sheets with a thickness of 0.50mm were produced by using a new processing route: strip casting followed by hot rolling, intermediate temperature (150–850°C) rolling and final annealing. The present study focused on exploring the effects of rolling temperature varying from 150 to 850°C on the microstructure and texture evolution, the formability and final magnetic properties. The microstructure and texture evolution at the various processing steps were investigated in detail by using OM, XRD, EBSD and TEM. It was found that the formability during rolling, the microstructure and texture before and after annealing and final magnetic properties highly depended on rolling temperature. The formability during rolling was gradually improved with increasing rolling temperature due to the slipping of dislocation. In particular, the rolling temperature dominated the formation of in-grain shear bands in the rolled microstructure, which played an important role in the development of final recrystallization microstructure and texture. In the case of lower temperature (150–450°C) rolling, an inhomogeneous microstructure with a large amount of in-grain shear bands was formed in the rolled sheets, which finally resulted in a fine and inhomogeneous annealing microstructure dominated by mild λ-fiber texture composed of cube and {001}〈210〉 components and α*-fiber texture concentrated on {115}〈5–10 1〉 component. By contrast, in the case of higher temperature (650–850°C) rolling, a relatively homogeneous microstructure without in-grain shear bands was formed instead in the rolled sheets, which finally led to a coarse and relatively homogeneous annealing microstructure characterized by strong α-fiber and γ-fiber texture. Accordingly, on the whole, both the magnetic induction (B8 and B50) and iron loss (P15/50 and P10/400) decreased with raising rolling temperature.

Influence of the angle between cold rolling direction and hot rolling direction on the texture evolution of non-oriented electrical steels

In processing non-oriented electrical steel sheets using conventional rolling schemes, the most common texture components obtained after final annealing are the magnetically unfavourable <111>//ND (γ) and <110>//RD (α) fibres. A lot of researches have been carried out trying to optimize the processes to produce the favourable <001>//ND (θ) fibre. However, since the final texture is formed through a series of texture evolution steps during the solidification, hot rolling, cold rolling and annealing processes, it is quite challenging to tailor the texture of the final product. In this study, a new rolling scheme was examined, in which the cold rolling direction (CRD) was inclined to the hot rolling direction (HRD) at an angle from 0° to 90° (with a 15° increment). This was intended to alter the texture commonly produced by cold rolling along the HRD, and to optimize the final recrystallization texture. The cold rolling and recrystallization textures of two non-oriented electrical steels with 0.9% and 2.8% Si were measured. It was found that the inclination of CRD to HRD has a substantial effect on the cold rolling texture for both steels, but only in the low Si steel, does it lead to significantly different recrystallization textures. A strong cube texture was produced at an inclination angle of 60°, and the <111>//ND (γ) fibre was significantly weakened or essentially disappeared. The core losses of these steels were measured by Epstein frame method and the results showed a ∼10% difference among strips cold rolled at different angles. A minimum core loss occurred at a 45° inclination angle in the low Si steel.