Primary Recrystallization Research Articles

Simulation of the Evolution of Phase Composition and Austenite Grain Size upon Multi-Pass Hot Deformationof Low-Alloy Steels

The paper presents a model for predicting the structural characteristics and phase composition of low-alloy steels upon hot rolling in the multi-pass deformation mode. The model considers recovery, dynamic, primary, dynamic and static recrystallization of grains, and the normal grain growth, as well as nucleation (including accelerated nucleation during deformation), growth or dissolution, and coarsening of carbonitride particles. The comparison between the calculated results and the experimental data available in the publications shows a satisfactory agreement.

Grain Microstructure in Friction-Stir-Welded Dissimilar Al/Mg Joints of Thin Sheets with/without Ultrasonic Vibration.

Electron backscattered diffraction (EBSD) characterization was conducted on the typical regions in friction-stir-welded dissimilar Al/Mg joints of 2 mm thick sheets with/without ultrasonic assistance. The effects of ultrasonic vibration (UV) on the grain size, recrystallization mechanisms, and degree of recrystallization on both sides of the Al-Mg bonding interface and the intermetallic compounds (IMCs) were investigated. It was found that on the Mg side of the weld nugget zone (WNZ), the primary dynamic recrystallization (DRX) mechanisms were discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), with geometric dynamic recrystallization (GDRX) playing a secondary role. On the Al side of the WNZ, CDRX was identified as the primary mechanism, with GDRX as a secondary contributor. While UV did not significantly alter the DRX mechanisms in either alloy within the WNZ, it promoted the aggregation and rearrangement of dislocations. This led to an increase in high-angle grain boundaries (HAGBs) and an enhanced degree of recrystallization in the welds. The average grain size in both the Al and Mg alloys of the WNZ followed a pattern of initially increasing and then decreasing along the thickness direction, reaching a maximum in the upper-middle part and a minimum at the bottom. The influence of UV on the average grain size in the WNZ was minimal, with only slight grain refinement observed, and the minimum refinement degree was only 0.9%. The Schmid factor (SF) on the WNZ and thermo-mechanically affected zone (TMAZ) boundary regions of the advancing side (AS) indicates that the application of UV increased the likelihood of basal slip and extension twinning in the crystal structure. In addition, UV reduced the thickness of IMCs and improved the strength of the Al-Mg bonding interface. These results suggest a higher probability of fracture along the TMAZ and WNZ boundary on the AS when UV was applied.

Recent development of grain oriented electrical steel in Shougang steel

Shougang Steel has been pursuing the development of low iron loss and high permeability grain oriented electrical steels for more than a decade. Grain oriented electrical steel requires a very strong Goss {110}〈001〉 texture and as such a comprehensive control of thermo-mechanical processing parameters is required to achieve a strict control of texture. In this paper the key metallurgical problems associated with manufacture of grain oriented electrical steel are discussed, including the factors that affect both primary recrystallization and secondary recrystallization leading to the development of a strongly textured final sheet. The metallurgical factors affecting magnetostriction of electrical steels are also analyzed, and a technological approach for domain refinement, and its effect on magnetic properties, is described. Examples of magnetic properties under non-sinusoidal magnetization conditions are also reported and analyzed. As a result of continuous research and development efforts the high permeability low iron loss grain oriented electrical steel of thin gauge products of 0.2 mm/0.18 mm thickness have recently been developed to meet the requirements of the new China national standard of energy efficiency grades for power transformers.

Numerical modeling of shear band effect on Goss grain recrystallization in electrical steels: Crystal plasticity finite element and phase field modeling

This study investigates the effect of shear band evolution on the nucleation of Goss {110}<001> texture during the primary recrystallization of 3.24 wt% Si grain-oriented electrical steel. Nucleation at the early stage of primary recrystallization of the steel is explored both experimentally and numerically. The experimental approach involves cold rolling the steel specimens to obtain a thickness reduction ratio of 76 % and then applying heat treatment to them at 600 °C for less than 1 min. The numerical simulation employes crystal plasticity (CP) finite element model (FEM) to simulate the plastic deformation induced by the dislocation slips on predefined slip systems and non-crystallographic shear bands during cold rolling. Based on the CPFEM results, the generalized strain energy release maximization (GSERM) model is used to predict the preferential orientation probability of recrystallized nuclei for the steel by considering shear band formation. Subsequently, the microstructure evolution during the early stage of primary recrystallization of the steel is simulated using the phase field model (PFM). The developed CP model successfully predicted shear band activation and evolution in the γ-fibers centered on the {111}<112> texture component. The model also demonstrated that shear bands would be the preferred nucleation sites at the early stage of primary recrystallization because of their high stored energy. Moreover, by coupling with the GSERM model, the PFM could reproduce the nucleation of Goss grains at the beginning of primary recrystallization in shear bands.

Effects of normalizing process on microstructure, texture, and precipitates of Sn bearing oriented silicon steel

Low temperature heating process of the slab has become the mainstream process for producing high quality oriented silicon steel due to its environmental protection, low cost, and high yield. For this process, the number of inhibitors is less and the size is large, resulting in insufficient inhibition, coarsen grains during primary recrystallization, and insufficient driving force for secondary recrystallization, which reduces the magnetic properties of the product. These shortcomings can be improved by optimizing the inhibitors and normalizing processes. The effects of normalizing processes on the microstructure, texture, and precipitations of low-temperature oriented silicon steel containing Sn were studied by OM, SEM, TEM, and EBSD with Fe–3%Si hot-rolled plate as initial material. The experimental results show that the sample has the best performance in terms of microstructure, texture, and precipitations with the two-stage boiling water cooling normalizing process that the heating temperature is 1150 °C, and the normalizing intermediate temperature is 850 °C. With the above parameters, the microstructure is inhomogeneous along thickness. There are more {111}<112> textures, which are favorable to the growth of Goss texture. The proportion of high energy grain boundary reached 54.2%. The precipitates are significantly refined, which enhances the ability to inhibit primary recrystallization. The sub-surface thickness of the hot rolled plate increases from 40.6% to 62.1% with increasing Sn content from 0.01% to 0.11%. The degree of tin segregation at grain boundary increases with the increase of normalizing temperature and the decrease of medium soaking temperature.

Study on the texture evolution and mechanical properties of selective laser melting pure nickel

As a ductile and ferromagnetic transition metal, nickel possesses exgrainent metallurgical compatibility, corrosion resistance, high electrical conductivity and high temperature stability. This study investigates the influence of energy density on the microstructure and properties of laser powder bed fusion pure nickel. The research results demonstrate that: during the formation process of Ni, with the increase in energy density, the grain texture exhibits anisotropy. The surfaces parallel and perpendicular to the building direction demonstrate strong {111} and {220} textures respectively. Primary and secondary recrystallization leads to increase in texture strength, subsequently affecting the decrease in dislocation density. The {111} texture yields preferentially, while the {220} single-crystal-like microstructure (SCM) requires higher energy density to complete primary recrystallization and trigger the recovery and enhancement of {111} texture. The enhancement in tensile properties is mainly attributed to the improvement of unmelted defects and texture. With the loading of stress, the failure of the structure leads to a decrease in the strength of the optimal texture component. The {220} texture strengthens the bond between different cladding layers along the building direction, resulting in numerous epitaxial grains parallel to the building direction on the fracture surface, significantly increasing the elongation of the specimen.

Effect of abnormal grain refinement on synchronous strengthening behavior of Fe50Mn30Co10Cr10 high entropy alloys

Improving processing efficiency while obtaining excellent material formation and mechanical properties is the primary concern of the manufacturing industry. This study aims to refine the grains of Fe50Mn30Co10Cr10 high entropy alloy during friction stir processing, achieving exceptional tensile properties in the stir zone by increasing the rotational speed. The key driver behind grain refinement lies in the alloy's inherently low stacking fault energy, with the primary recrystallization mechanism being discontinuous dynamic recrystallization. The freshly recrystallized fine grains share analogous microstructures and energy levels during severe plastic deformation, which engenders a state of increased competition among them. This robust competitive dynamic impedes grain growth, thereby promoting the development of refined grains. This microstructure proves instrumental in avoiding premature microcracking during tensile loading by hindering martensite formation, consequently improving the UTS and EL of the material. Nevertheless, the high heat input and substantial strain result in an increase of temperature and strain energy in the system, eventually disrupting the high energy system and causing grain coarsening as the rotational speed continues to increase. This coarsened grain and high martensite fraction lead to premature initiation of cracks under tensile loading, which is not conducive to further improvement of tensile properties.

Special texture evolution behavior of strip-cast non-oriented electrical steel combined with in-situ experiment and CPFEM

The impact of shear deformation on texture evolution in strip-cast Fe-1.5%Si non-oriented electrical steel was studied combined with in-suit experiments and crystal plasticity finite element method (CPFEM). Throughout the deformation process, the texture evolution predominantly follows a traditional route: transitioning from {211}<036> and {411}<148> to {111}<112> orientation. In certain regions with specific stress conditions, orientation evolution shifts from {310}<236> to {411}<148>, {100}<021>, and finally to {100}<001> orientation. Crystal plasticity finite element (CPFE) simulation results show that the rotation of {310}<236> through {411}<148> to {100}<021> orientation, {211}<236> and {112}<110> orientations transition to {111} and {110} orientations, respectively, which is consistent with the experimental observations. Recrystallization texture mainly includes favorable λ and near-λ (<100>∥ND, normal direction) textures, with detrimental γ (<111>∥ND) texture essentially diminishing. In-situ heating experiments revealed {411}<148> as the primary recrystallization orientation, the mechanism involves both oriented nucleation and growth. In the edge region lacking stress constraints, the Schmid factor (SF) reaches up to 0.48, the (21-3)[111] slip system is preferentially activated, with shear bands appearing earlier in the same region. Indicating that when slip mechanism alone are inadequate for sustaining plastic deformation, the shear deformation becomes the favored mode of activation. {411}<148> orientation can serve as a transitional orientation for transitioning to {100} orientation, and further as an advantageous transitional orientation during the nucleation and growth of recrystallization. Due to the texture improvement, superior magnetic properties were achieved, with the average magnetic induction (B50) and iron loss (P1.5/50) being 1.77 T and 4.25 W/kg, respectively.

High-resolution simulating of grain substructure in cold rolling and its effects on primary recrystallization in annealing of ferritic stainless steel

In this study, an integrated crystal plasticity and cellular automaton (CA) model has been developed and employed to investigate the processes of cold rolling and annealing in ferritic stainless steel. Crystal plasticity simulates the deformation microstructure, deformation texture and corresponding dislocation density distribution in the cold rolled ferritic stainless steel. Meanwhile, CA predicts the microstructural evolution originating from nucleation and growth. The resolution of the crystal plasticity model has been improved using a newly developed remeshing technique, which allows for the capture of the grain substructure in the deformation microstructure. The developed model has been validated by experimental measurements with electron backscatter diffraction (EBSD) in terms of comparing the orientation distribution functions (ODFs), misorientation, local substructures, and grain size. The good agreement between simulations and experiments indicates that the developed crystal plasticity with CA model is reliable and efficient for predicting the microstructure and texture evolutions during cold rolling and subsequent annealing.

Advanced microstructural path modeling of primary recrystallization in aluminum alloys AA5182 and AA5657

AbstractWhen analyzing recrystallization kinetics data, it is extremely important to use a model, which has appropriate assumptions for nucleation and growth, including spatial distribution of nuclei, nucleation rate, growth rate, and directionality. In the present work, we reveal how advanced microstructural path modeling (MPM) can successfully fit kinetics data for the complex recrystallization of two different industrial aluminum alloys. Simpler models have failed to fit the data over the entire recrystallization period. The new model allows for spatially clustered nucleation and for different growth rates in different sample directions, whereby the grains evolve with an aspect ratio different from 1. Based on the MPM analysis, the specific nucleation and growth parameters as well as the recrystallized grain sizes are deduced, and the recrystallization characteristics of the two alloys are compared. The work demonstrates the power of quantitative metallography and the wealth of recrystallization information that may be obtained from MPM modeling of such stereological data.

The origin of {113}&lt;361&gt; grains and their impact on secondary recrystallization in producing ultra-thin grain-oriented electrical steel

Abstract Ultra-thin grain-oriented electrical steel with a thickness of 80 µm is produced by one-step-rolling with industrial grain-oriented electrical steel. The research employs electron back-scattering texture analysis technique to investigate the evolution of deformation and recrystallization textures in this specific steel. Emphasis is placed on examining the origin of {113}&lt;361&gt; grains and their consequential impact on secondary recrystallization. It is revealed that primary, secondary, and tertiary recrystallization phases are integral during the annealing process. The origin of surface {113}&lt;361&gt; grains were result of initial deviated Goss grains with specific shear deformation behavior in cold rolled ultra-thin strips. Additionally, the influence of these grains on texture evolution is predominantly evident during secondary recrystallization. These grains potentially undergo abnormal growth in secondary recrystallization, exploiting high-energy grain boundaries among Goss grains. This phenomenon consequently leads to the diminution of the sharp Goss texture formed during primary recrystallization. Given the magnetic properties and predominant applications of ultra-thin grain-oriented electrical steel in medium-frequency fields, it is recommended to prepare ultra-thin grain-oriented steel during primary recrystallization phase.

Primary recrystallization of a magnesium hybrid material fabricated by high-pressure torsion

The static recrystallization and grain growth of a hybrid AZ31/Mg-0.6Gd (wt%) material fabricated by high-pressure torsion (HPT) through 20 turns were explored after isochronal annealing at 150, 250, 350 and 450 °C for 1 h using electron backscatter diffraction, transmission electron microscopy and Vickers microhardness measurements. The results reveal heterogeneity in the grain size distributions of the AZ31 and Mg-0.6Gd regions after annealing at the lower temperatures of 150 and 250 °C leading to a clear AZ31/Mg-0.6Gd interfacial border. At the higher temperatures of 350 and 450 °C the AZ31/Mg-0.6Gd interfaces were not well-defined owing to the occurrence of grain growth. It is shown that grain growth is restricted in the AZ31 and Mg-0.6Gd regions due to the presence of stable nano-size Al8Mn5 particles and the precipitation of Mg17Al12 and Mg12Zn at 250 °C and of Mg5Gd and Mg12Gd phases at 350 and 450 °C. The distribution of the basal texture in both regions was strongly controlled by dynamic recrystallization, precipitation and grain growth. The values of the microhardness over the radial cross-sections of the hybrid discs decrease and become more uniform, in the range of ∼35–66 Hv, with increasing annealing temperature.

Coordinate regulation mechanism of primary recrystallization texture and microstructure of grain-oriented silicon steel

Texture control, which is affected by composition, hot rolling, cold rolling, and annealing, is the core element to improve the magnetic properties of grain-oriented silicon steel and is one of the key scientific problems in developing electrical steel technology. The research and control of first factors have been very mature, and the integrated regulation of upstream and downstream processes has become a breakthrough point for improving texture. For the common grain-oriented silicon steel based on the “two-stage cold rolling method”, primary recrystallization is the stage achievement of smelting, hot rolling, first cold rolling, and decarburization annealing. The grain size and texture characteristics of the primary recrystallization are the only standards to measure the pre-process technology and is the pointer of whether the secondary recrystallization can occur in the subsequent process or not, which are extremely important to improve the magnetic properties. This paper studied the hot rolling, the first cold rolling and decarburization annealing of grain-oriented silicon steel by using XRD, EBSD technologies. The results showed that the hot rolled plate is not as thinner as better, only the optimum ratio of the thickness of hot rolled plate and the first cold reduction rate can obtain optimal primary recrystallization. The minimum iron loss value and maximum magnetic induction intensity are obtained under the primary cold rolling reduction rate controlled at 77.27%, the average grain size of the primary recrystallization is 14 µm, the iron loss P1.7/50 is reduced to 1.02 W/Kg, and the magnetic induction intensity B8 can reach 1.910 T.

Investigation on deformation behaviors and dynamic recrystallization mechanism of spray formed Al–Zn–Mg–Cu alloy under hot compression

The thermal deformation behavior of spray formed Al–Zn–Mg–Cu alloy was investigated by the isothermal hot compression tests at the strain rates of 0.001–10 s−1 with the temperature range of 350–450 °C. An Arrhenius constitutive equation was established by the corrected strain-stress curves, and then the processing map was constructed based on the 3D instability map and 3D power dissipation map. The influence of strain rate and temperature on both flow stress and dynamic softening has been unveiled. The results show that dynamic recovery (DRV) is the primary softening mechanism and dynamic recrystallization (DRX) is substantively retarded due to the fine dispersed particles uniformly distributed in the spray formed alloy. Continuous dynamic recrystallization (CDRX) is the primary DRX mechanism at a low temperature or high strain rate. DRX grain was observed at the grain boundaries, especially at the triple junctions. The appropriate thermal deformation condition is recommended at the temperature range from 430 °C to 450 °C and strain rates from 0.003 s−1 to 0.1 s−1.

Influence of Fine Precipitates on Primary Recrystallization Mechanism and Texture Formation in Cold Rolled Fe-3%Si Alloy with Initial Coarse Goss Grains

Influence of Fine Precipitates on Primary Recrystallization Mechanism and Texture Formation in Cold Rolled Fe-3%Si Alloy with Initial Coarse Goss Grains

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.

Two-stage annealing-induced secondary grain growth for enhanced efficiency in CdTe solar cells on flexible polyimide foils

Flexible CdTe solar cells integrated onto polyimide foils are a promising renewable power generation technology. Optimizing crystal structure and reducing grain boundary recombination by CdCl2 annealing are the key approaches to increase carrier concentration and improve device performance. However, the inherent thermal constraints of polyimide substrates limit the feasibility of achieving full annealing. In response, we introduce a novel two-stage annealing process: a primary recrystallization at 350 °C followed by a secondary recrystallization at 380 °C. Employing a rigorous investigation of surface and interface energy minimization, strain energy minimization, and the growth kinetics of Cl drag phenomena, this method induces significant secondary grain growth, surpassing the film thickness itself. The culmination of these efforts yields an extraordinary power conversion efficiency (PCE) of 12.2 %, marking a historic achievement for sputtered CdTe solar cells on polyimide substrates. This study not only unveils a pioneering approach to grain boundary engineering but also offers insights into optimizing the CdCl2 annealing process for CdTe absorbers, ultimately facilitating the realization of high-efficiency, flexible CdTe solar cells.

Investigation of microstructure and texture as related to primary recrystallization of grain-oriented silicon steel

Grain-oriented silicon steel requires a very strong Goss {110}<001> texture and as such a comprehensive control of thermo-mechanical processing parameters is required to achieve a strict control of texture. In particular the cold rolling and decarburization annealing process parameters have a determining effect on the grain size, the grain size distribution and the crystal texture distribution. In this study, the effect of cold rolling reduction on texture distribution in cold-rolled sheet has been analyzed. Secondary recrystallization of grain-oriented silicon steel is also highly dependent on the microstructure and texture after primary recrystallization. The influence of annealing temperature and carbides on the primary recrystallization process has also been investigated by measurements of grain growth and texture following primary recrystallization. By optimizing the microstructure and the texture of primary recrystallization of grain-oriented silicon steel, it is shown that a grain-oriented silicon steel exhibiting high magnetic induction low iron loss has been developed at Shougang Steel.

The influence of deformation texture on nucleation and growth of cube grains in aluminium

The influence of deformation texture on the initial stages of recrystallization of deformed pure Al single crystals and commercial AA1050 alloy were characterized. To precisely quantify the orientation relationship between nuclei and simple deformation structures, single crystalline samples of stable Br(110) [1-1-2] and semi-stable S’(234) [20-28 11] orientations, were plane strain compressed (PSC) to 40% to develop a dominant homogeneous microstructure composed of two sets of microbands. The samples were then lightly annealed to reach the initial stage of primary recrystallization. The results on single crystals were related to the behaviour of the polycrystalline samples in state after hot-rolling then PSC to the same degree and lightly annealed. SEM/EBSD analyses of single crystalline samples demonstrate that the orientations of recrystallized grains are limited to a certain number of orientation groups. However, the orientations of the as-deformed state are not retained in the orientations of new grains. Deformed samples with Br orientation do not show the formation of cube grains during recrystallization, whereas strong nucleation of cube-oriented grains is observed in homogeneously and heterogeneously deformed areas in the semi-stable S’ orientation, despite the cube-oriented nuclei not present in the as-deformed structure. The recrystallization texture components of the AA1050 alloy were related to the standard β-fibre texture formed during the previous cold deformation. Cube grains formed intensively in PSC polycrystalline samples, primarily in association with as-deformed areas with near four variants of S(124) [21-1] and S’ orientations and were characterized by local misorientations around the <111> axes.

Microstructural path modeling of primary recrystallization

While the classic KJMA model is frequently used to fit experimental recrystallization kinetics data, the fitted values in most cases are inconsistent with the observed microstructural evolution. In this paper, we review the much more powerful microstructural path modeling (MPM) methodology. A basic assumption in this next generation of recrystallization models is related to the spatial distribution of nucleation sites, which may be uniform in the mathematical sense, i.e. randomly distributed in the sample volume, or clustered either along lines or on planes. For example nuclei are often observed to be linearly aligned because they have formed along original grain boundaries or stringers of second phase particles in the deformed matrix. In this paper, we present a new MPM, which is extending the former idealized linear MPM, allowing the recrystallizing grains to grow with different speeds in different directions, thus becoming prolate spheroid shaped. Finally issues concerning experimental determination and analysis of growth rates, are discussed.