Early Stages Of Recrystallization Research Articles

Exploring 4D microstructural evolution in a heavily deformed ferritic alloy

We present a multi-scale study of recrystallization annealing of an 85% cold rolled Fe-3%Si alloy using a combination of dark field X-ray microscopy (DFXM), synchrotron X-ray diffraction (SXRD), and electron backscatter diffraction (EBSD). The intra-granular structure of the as-deformed grain reveals deformation bands separated by ≈ 3–5°misorientation. We monitor the structural evolution of a recrystallized grain embedded in bulk, from the early stages of recrystallization to 65% overall recrystallization through isothermal annealing steps. Results show that the recrystallized grain of interest (GOI) grows much faster than its surroundings yet remains constant in size as the recrystallization proceeds. Isolated dislocations embedded within the volume of the recrystallized GOI are investigated.

Recrystallization and texture evolution of cold pilgered FeCrAl cladding tube during annealing at 700 °C∼1000 °C

FeCrAl alloys are being developed as potential accident-tolerant fuel cladding materials for the light water reactors due to significantly improved steam oxidation and good mechanical properties at high temperatures. In this study, the recrystallization and texture evolution of the cold pilgered FeCrAl cladding tube was investigated by means of hardness measurements and electron backscatter diffraction (EBSD) during annealing at 700∼1000 °C. The partially recrystallized maps were deconstructed into deformed, recovered, and recrystallized grain fractions based on the critical internal misorientation angle. In the early stages of recrystallization, cold pilgered cladding tubes contained a mixture of discontinuously recrystallized {111}<110> newly nucleated grains and heterogeneous deformed 〈110〉 orientation grains. The deformed microstructural inhomogeneity state could be explained based on the Taylor factor. The rate of recrystallization increased with increasing annealing temperature, which was described by the Johnson-Mehl-Avrami-Kolmogorov equation. The cladding tube showed slow recrystallization kinetics and thermally stable grains due to the pinning of the grain boundaries by the Laves precipitates. The dominant α-fiber decreased and γ-fiber increased with increasing recrystallization fraction in the cold pilgered tubes. The high area fraction and stable γ-fiber would be beneficial to the processability of the cladding tube.

Dual-effects of carbon doping on the recrystallization kinetics of the Cantor alloy during mid-temperature annealing

In this study, the comprehensive effects of carbon doping on the recrystallization process and the corresponding mechanical performance of the Cantor alloy during mid-temperature (700 °C) annealing were investigated. In the early stage of recrystallization, i.e., before 7 min annealing, abundant M23C6 carbides form preferentially along deformation bands and hence accelerate recrystallization process by providing dense heterogeneous nucleation sites. The fast consuming of the stored defects by recrystallization in this stage leads to the drastic decrease of strength but the regain of ductility. Detailed characterization on the precipitation behavior further shows that the initial fine carbide (≤10 nm in size) firstly enriches in carbon only, and then gradually grows to perfect M23C6 as controlled by the diffusion of Cr. In the later stage of recrystallization, e.g., after 7 min annealing, these carbides coarsen and Zener-pin grain boundaries from further migration, which in turn suppress the overall recrystallization process. In this stage the mechanical properties vary slightly as a result of the balance between the slowly deceased amount of hard non-recrystallized regions and the slowly increased carbide volume fraction.

Formation of η-oriented shear bands and its significant impact on recrystallization texture in strip-cast electrical steel

The evolution of shear band (SB) and texture in strip-cast electrical steel was studied in order to investigate the crystallographic character of SB and its influence on recrystallization texture. Shear deformation in the form of SB played an effective role in tailoring the local lattice rotation to accommodate heavy deformation in the case of inhomogeneous deformation under conditions of initial coarse grain in strip-cast electrical steel. During rolling process, η-oriented SBs appeared at different stages of deformation as a result of geometric softening. Cube-oriented SB was mainly retained from initial exact Cube grain at early stage of shear deformation and Goss-oriented SB was newly developed during the formation of γ-fiber matrix after heavy deformation. {210}<001> SB formed as a transition form among different SBs. Crystal rotation inside SB, SB dimension and SB boundary misorientation progressed in proportion to cold rolling reduction. It is demonstrated that crystallographic direction of SBs tended to be parallel to <001> under the driving force of reduction in stored energy to maintain relatively quasi-stable state. Low orientation gradient as well as relatively low density of dislocations was developed within SB region, while high orientation gradient formed between SB region and surrounding matrix. Interestingly, the η-oriented cell blocks inside SBs provided preferential nucleation sites for Goss and Cube texture at early stage of recrystallization, which significantly contributed to beneficial recrystallization texture in a manner of texture inheritance and superior magnetic properties (B50 was as high as 1.81 T, and P1.5/50 was as low as 4.0 W/kg).

Microstructure and texture evolution of ultra-thin high grade non-oriented silicon steel used in new energy vehicle

The evolutions of microstructure and texture of ultra-thin high-grade non-oriented silicon steel for new energy vehicles were investigated in this paper, and the formation mechanism of typical recrystallized α*-fiber texture was described. The results show that: The microstructure of the hot rolled plate was inhomogeneous along the thickness direction because of the shear force and temperature gradient, resulting in the texture in each layer of the hot rolled plate appearing rotational distribution around the Goss orientation. After normalizing, the fully recrystallized microstructure was obtained, and α*-fiber texture was formed. Banded structure was obtained in the cold rolled sheet, with α-fiber texture {114}〈110〉 dominated. The typical α*-fiber texture was formed after annealing recrystallization, which mainly consist of {114}<481 > and {113}<361>. The {114}<481 > oriented grains were mainly nucleated within the deformed {114}<110 > grains and at the grain boundaries of α-fiber deformed grains, and without size, quantity and strength advantages. {111}<112 > is dominated in the early stage of recrystallization, but {114}<481 > became the main texture with size, strength and quantitative advantages in the late stage of recrystallization.

Effects of thermomechanical processes on grain boundary characteristics and plasticization mechanism of micro nickel wires

“Tensile and annealing” grain boundary (GB) modification is carried out on micro nickel wires to investigate the influence of thermomechanical parameters on the microstructure and plasticity, and to clarify the relationship between GB evolution and plasticity. A high proportion of special boundaries (SBs), the optimized GB characteristic distribution (GBCD) and a 9% reduction in hardness can be achieved by stretching the sample by 10% and then annealing at 900 °C for 5 min. Microstructure analysis indicates that numerous SBs formed in the early stage of recrystallization. Such SBs especially Σ3 boundaries contribute the most to the plasticization of nickel wires. The grains with high Schmid factor always have 〈001〉 orientation, which is conductive to the formation of Σ3 boundaries. What's more, a microscopic indicator concerning incoherent Σ3 boundaries that can quantitatively characterize the macroscopic hardness is presented, and thus the plasticization mechanism is analyzed accordingly.

On the thermal coarsening and transformation of nanoscale oxide inclusions in 316L stainless steel manufactured by laser powder bed fusion and its influence on impact toughness

The thermal evolution of nanoscale oxide inclusions in 316L stainless steel (SS) manufactured by laser powder bed fusion additive manufacturing (AM) was explored. The size, chemical composition, morphology, and distribution of the oxides were characterized as the function of heat treatment conditions. The study revealed the mechanistic driving force of the rapid oxide coarsening during recrystallization. Ostwald ripening governs oxide coarsening. The active grain boundary-oxide interaction at the early stage of recrystallization accelerated oxide coarsening via enhanced solute diffusion along grain boundaries. Pipe diffusion along dislocation cellular boundaries has a negligible contribution to oxide coarsening. At high temperatures (T > 1065 °C), although lattice diffusion primarily controlled the oxide growth, the contribution from the grain-boundary diffusion was necessary. The transformation from MnSiO3 to CrMn2O4 took place in the un-recrystallized grains but was not observed when recrystallization started. The interaction of grain boundary and oxides during recrystallization resulted in a high fraction of oxides accumulated at grain boundaries. While oxide coarsening does not significantly alter the toughness value, grain-boundary oxides promote microvoid formation and intergranular fracture under Charpy impact in the recrystallized AM 316L SS.

The Research on Recrystallization Behaviors and Mechanism of a Medium-Density Ni-Based Alloy

Revealing the recrystallization behavior and mechanism of this new alloy is of great significance to subsequent research. In this study, the Ni-36.6W-15Co ternary medium heavy alloy was solution-treated at 1100–1200 °C for different lengths of time. The grain size change, microstructure and texture evolution as well as twin development during recrystallization annealing were analyzed using SEM, EBSD and TEM techniques. The study found that complete recrystallization occurs at 1150 °C/60 min. In addition, it takes a longer amount of time for complete recrystallization to occur at 1100 °C. The value of the activation energy Q1 of the studied alloys is 701 kJ/mol and the recrystallization process is relatively slow. By comparing the changes of microstructure and texture with superalloys, it is found that the recrystallization mechanism of the studied alloy is different from that of the superalloy. The development of annealing twins has a great influence on the recrystallization behavior and mechanism. The results show that the twin mechanism is considered as the dominant recrystallization mechanism of the studied alloy, although the formation and development of sub-grains appear in the early stage of recrystallization.

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.

Impurity effect on recrystallization and grain growth in severe plastically deformed copper

The impurity effect on commercial purity copper (4 N and 3 N) was investigated by comparing their annealing induced recrystallization and grain growth behavior after severe plastic deformation. Equal channel angular pressing (ECAP) with additional cryogenic rolling was applied to produce equiaxed ultra-fine grained (UFG) and nano-laminated (NL) coppers with high stored excess energy. The stored excess energy increased with decreasing purity from 4 N to 3 N, whereas the grain boundary velocity and recrystallized grain size decreased for both UFG and NL Cu. In particular, the NL structures were found to be more sensitive to impurities than equiaxed ultra-fine grained ones, and consequently the abnormal grain growth at the early stages of recrystallization in NL 4 N Cu was effectively suppressed in NL 3 N Cu. The analysis of the grain growth rate during recrystallization, using the microstructural path methodology (MPM), demonstrates that the correlation between the abnormal grain growth and the significantly enhanced grain boundary mobility cannot be solely explained by the high stored excess energy. Under all conditions, the impurity drag effect poses a kinetic constraint on the rate-controlling mechanism for grain boundary migration.

Topological aspects responsible for recrystallization evolution in an IF-steel sheet – Investigation with cellular-automaton simulations

A cellular automaton algorithm for curvature-driven coarsening is applied to a cold-rolled interstitial-free steel’s microstructure - obtained through electron backscatter diffraction (EBSD). Recrystallization nucleation occurs naturally during the simulation, due to the highly heterogeneous and hence competitive growth among pre-existing (sub) grains. The spatial inhomogeneity of the subgrain growth that takes place derives from the large local variations of subgrain sizes and misorientations that comprise the prior deformed state. The results show that capillary-driven selective growth takes place to the extent that the prior elongated and deformed grains are replaced by equiaxed grains with no interior small-angle boundaries. Additionally, during the simulation certain texture components intensify and others vanish, which indicates that preferential growth occurs in a fashion that relates to the crystal orientations’ topology. The study of the early stages of recrystallization (i.e. nucleation) shows that the pre-existing subgrains that eventually recrystallize, exhibit certain topological characteristics at the prior deformed state. Successful nucleation occurs mostly for pre-existing matrix subgrains abutting shear bands or narrow deformation bands and particularly at regions where the latter intersect.

Evolution of recrystallization texture for Cu-30% Zn alloy sheets with high Young’s modulus in the transverse direction

Miniaturization of electric connecters with higher stability in the coupling force is demanded as components of electric vehicles. Copper alloys are attractive materials from the perspective of electric conductivity. It is considered that Brass orientations {110}<112> has high Young’s modulus along the transverse direction (TD) since the Young’s moduli of copper single crystals show a maximum value at the <111> direction. The authors could successfully develop the near-Brass orientation in TD of the annealed sheets by performing additional warm rolling at a low reduction in thickness for cold rolled Cu-30% Zn alloy (brass) sheets with material cost lower than pure copper. The near-Brass recrystallization texture with a main component {110}<223> showed maximum orientation density after annealing at 723 K when warm rolling was performed at 623 K. In addition, we discussed the mechanism of the recrystallization texture evolution for Cu-30% Zn alloy sheets, which were subjected to the combined rolling consisting of cold and warm rolling using a conventional rolling mill and subsequently annealed at 723 K, in view of annealing twinning in the early stage of recrystallization.

Texture Selection Mechanisms during Recrystallization and Grain Growth of a Magnesium-Erbium-Zinc Alloy

Binary and ternary Mg-1%Er/Mg-1%Er-1%Zn alloys were rolled and subsequently subjected to various heat treatments to study texture selection during recrystallization and following grain growth. The results revealed favorable texture alterations in both alloys and the formation of a unique ±40° transvers direction (TD) recrystallization texture in the ternary alloy. While the binary alloy underwent a continuous alteration of its texture and grain size throughout recrystallization and grain growth, the ternary alloy showed a rapid rolling (RD) to transvers direction (TD) texture transition occurring during early stages of recrystallization. Targeted electron back scatter diffraction (EBSD) analysis of the recrystallized fraction unraveled a selective growth behavior of recrystallization nuclei with TD tilted orientations that is likely attributed to solute drag effect on the mobility of specific grain boundaries. Mg-1%Er-1%Zn additionally exhibited a stunning microstructural stability during grain growth annealing. This was attributed to a fine dispersion of dense nanosized particles in the matrix that impeded grain growth by Zener drag. The mechanical properties of both alloys were determined by uniaxial tensile tests combined with EBSD assisted slip trace analysis at 5% tensile strain to investigate non-basal slip behavior. Owing to synergic alloying effects on solid solution strengthening and slip activation, as well as precipitation hardening, the ternary Mg-1%Er-1%Zn alloy demonstrated a remarkable enhancement in the yield strength, strain hardening capability, and failure ductility, compared with the Mg-1%Er alloy.

Effect of solution treatment on mechanical properties and microstructure of welded joints of Fe-29Mn-9Al-0.9C low-density steel

In recent years, Fe–Mn–Al–C steel has been widely regarded as a promising lightweight material due to its excellent specific strength and good balance of strength and toughness. However, the performance of welded joints is crucial for the application of Fe–Mn–Al–C low-density steel. This paper aims to study the effect of different solution treatment times on the mechanical properties and microstructure of tungsten inert gas (TIG) welding of Fe-29Mn-9Al-0.9C low-density steel. After solution treatment, the phase types of the weld change and the granular ferrite transforms into austenite. Electron backscattered diffraction (EBSD) results show that with the increase of solution treatment time, dislocation density decreases, recrystallized grains grow, and the texture changes from uniform distribution to cubic texture again. It is concluded that in the early stage of recrystallization, dislocation walls are formed due to dislocation slip, which impedes dislocation movement in the process of stretching and thus improves the tensile strength. By controlling the time of solution treatment, the maximum tensile strength can be increased to 845.05[Formula: see text]MPa and the maximum elongation can be increased to 38.21%, which are all higher than for the welded joints without solution treatment.

Formation of Recrystallization Cube Texture in Highly Rolled Ni–9.3 at % W

In this work the formation of strong recrystallization cube texture in heavily rolled Ni–9.3 at % W has been studied. During the cold rolling (also known as recovery-rolling) process the deformation texture of Ni–9.3 at % W alloy (further notated as Ni9W) transforms to Copper-type rolling texture, and after annealing, a sharp cube texture is generated. It is remarkably strong recrystallization cube texture, as high as 93 vol %, in metallic materials with low stacking fault energy. The formation mechanism of the cube texture is adopted for the rapid recovery of cube nuclei at the early stage of recrystallization as well as fast migration rate of high angle boundaries between cube grains and deformed microstructure at high temperature. Considering the cold rolling texture of Ni9W, oriented nucleation seems to play more important role in the cube texture formation process. In this article, the relationship between the deformation texture and recrystallization cube texture is discussed.

Recrystallization Behavior and Formation of {411}&lt;148&gt; Grain from α-fiber Grains in Heavily Cold-rolled Fe-3%Si Alloy

Recrystallization texture is essential to control the mechanical and magnetic properties of steels. Both γ-fiber (ND//<111>) and α-fiber (RD//<011>) textures are known to develop during the rolling process of bcc iron. Recrystallization behavior from γ-fiber has been extensively studied. On the other hand, recrystallization behavior from α-fiber, in particular after heavy cold rolling reduction, has not been sufficiently clarified. In this study, recrystallization behavior from α-fiber, focusing on the formation of {411}<148> recrystallized grain, was investigated by means of EBSD and TEM. {411}<148> region already existed in the vicinity of deformed grains having upper α-fiber orientation ({100}<011> ~ {211}<011>). TEM observation revealed the existence of the lamellar structure with {411}<148> relatively fine dislocation cells in the {211}<011> deformed grains. With the progress of the recovery, {411}<148> subgrains (dislocation cells) are postulated to easily form and are surrounded by the deformed matrix grains with high angle interface. Thus, it is easy to form the recrystallization nuclei having the potential to grow with the sake of both high driving force and high interface mobility. At the early stage of recrystallization, {411}<148> recrystallized grains developed in {211}<011> deformed grains. At the later stage, {411}<148> recrystallized grains from {211}<011> deformed grains encroach {100}<011> deformed grains and new {411}<148> recrystallized grains developed in {100}<011> deformed grains.

Strong {1 0 0}〈0 1 2〉-{4 1 1}〈1 4 8〉 recrystallization textures in heavily hot-rolled non-oriented electrical steels

Strong {1 0 0}〈0 1 2〉-{4 1 1}〈1 4 8〉 recrystallization textures were obtained in heavily hot-rolled non-oriented electrical steels by increasing the normalization temperature and holding time. After cold-rolling at medium reduction and annealing, a strong {1 0 0} texture and a weak γ-fiber texture were finally acquired. The magnetic properties of final sheets were obviously improved compared with commercial ones. In the early stages of recrystallization, the {4 1 1}〈1 4 8〉 recrystallization nuclei formed by subgrain coalescence, which mainly nucleated in the vicinity of the grain boundaries of α-fiber deformed grains and the nucleation sites evenly distributed. The {4 1 1}〈1 4 8〉 grains selectively grew due to the higher mobility and the advantages of size and quantity.

Texture and Microstructure Development of Tensile Deformed High-Mn Steel during Early Stage of Recrystallization

The early stages of annealing behavior of a high-Mn steel were studied at 750°C for 120 and 300 seconds after straining to 30 and 60% (true strain). Different characterization methods comprising optical microscopy, X-ray diffraction (XRD) and electron backscattered diffraction (EBSD) were employed to study the macro-texture and microstructural evolutions. EBSD examination revealed that the products of γ‒e–α' transformation nucleate within deformation twins during deformation. Annealing of a specimen strained to 30% resulted in almost complete reversion of martensite to austenite, re-appearing of deformation twinning as well as partial static recrystallization with a weak texture. The recrystallized grains were formed from untwined parent orientations. Moreover, the nucleation of annealing twinning with a weak texture was observed in high kernel average misorientation area. A fine-grained structure with a weak texture (Copper, S, and Goss) was achieved at 750°C for 300 seconds after straining to 60%.

Unraveling Recrystallization Mechanisms Governing Texture Development from Rare-Earth Element Additions to Magnesium

The origin of texture components often associated with rare-earth element (REE) additions in wrought magnesium alloys is a long-standing problem in magnesium technology. While their influence on the texture is unquestionable, it is not yet clear why certain texture components, such as $$ \langle 11\bar{2}1 \rangle ||{\text{extrusion}}\;{\text{direction}}, $$ are favored over other components typically observed in traditional magnesium alloys. The objective of this research is to identify the mechanisms accountable for these RE textures during early stages of recrystallization. Electron backscattered diffraction and transmission electron microscopy analyses reveal that REEs in zinc-containing magnesium alloys corroborate discontinuous dynamic recrystallization. REEs promote isotropic growth for all nuclei generated through the bulging mechanism. During nucleation, the effect of REEs on orientation selection was explained by the diversified activity of both $$ \langle 10\bar{1}0 \rangle $$ and [0001] Taylor axes in the same grain with a marked preference for [0001] rotations to occur first. During nuclei growth, no growth preference was observed when sufficient REEs are added in the zinc-containing magnesium alloys, instead isotropic nuclei growth across all grain orientations occurs. This phenomenon is attributed to REEs segregating to grain boundaries (GBs), in agreement with prior computational and theoretical results (Barrett et al., Scripta Mater 146:46–50, 2018) that show a more isotropic GB energy and mobility after segregation.

Modeling the viscoplastic behavior and grain size in a hot worked Nb-bearing high-Mn steel

In this study, hot compression tests were performed on a Nb-containing high-Mn steel at temperatures in range of 850–1150°C and strain rates of 0.001–1s−1. The stacking fault energy of the material at different conditions, i.e. without Nb, with Nb and C in solution and with Nb and C as NbC, was calculated by JMat Pro software as 10.9, 10.15 and 10mJ/m2. The software predicted that the stacking fault energy reaches 200–250mJ/m2 as temperature rises to the deformation range. A new model with interactive effects of temperature, strain and strain rate was constructed on the basis of Johnson-Cook equation to predict the experimental flow curves satisfactorily. Optical microscopy and SEM-EBSD observations showed that strain-induced boundary migration (SIBM) is the major mechanism of dynamic recrystallization giving rise to a necklace structure at the early stages of recrystallization. It was found that very fine layers of lath martensite form within the large austenitic grains during post-deformation quenching. However, the martensite layers were less discernible in the small DRX grains. The dynamically recrystallized grain size decreased with increase in strain rate or decrease in temperature. The model developed based on Bate and Hutchinton approach showed that the recrystallized grain size has an indirect relationship with the flow stress level.