Α-fiber Components Research Articles

Unravelling the Role of Aging During Cold Rolling on the Primary Recrystallization of Grain-Oriented Electrical Steels Using a Robust EBSD-Based Analysis Approach

Aging during cold rolling improves the final magnetic properties of conventionally processed grain oriented electrical steels (GOES). In order to determine the influence of aging on the evolution of microstructure and texture during recrystallization, identical hot rolled GOES sheets, were cold rolled with and without aging, and examined by large-area electron backscatter diffraction (EBSD) investigations. Local misorientations were determined from the EBSD maps with a noise-correction technique and the statistical relevance of the EBSD-based texture measurements was examined and confirmed by a new approach. The most important effect of aging was found to be a significant modification of the deformation and recrystallization behaviour of the α-fiber components. In fact, the aging treatment resulted in more shear banding during cold rolling, which is attributed to dislocation pinning by carbon atoms. The dislocation pinning furthermore leads to significantly reduced recovery during annealing, which finally results in a higher remaining driving force for recrystallization and more nucleation sites in the otherwise sluggishly recrystallizing α-fiber grains. As a result the grain size of the aged material is significantly reduced. We assume that this smaller grain size provides a higher driving force for the subsequent growth of the Goss grains and leads to improved magnetic properties of the final processed GOES, although these relations have not been investigated here. In contrast, the α*-fiber, which is often suggested to be of importance for optimized Goss texture formation, was not found to be affected significantly by the aging treatment.

Microstructure and texture evolution of thin-gauge non-oriented silicon steel with high permeability produced by twin-roll strip casting

A new method for producing high permeability thin-gauge non-oriented electrical steels with 2.3 mm thick Fe-3.2% Si steel as-cast strip was studied. The evolution of microstructure and texture was characterized during the entire processing route. Furthermore, the effects of cold-rolling with large reduction and intermediate annealing process on magnetic properties were studied. The results indicated that the as-cast strip with coarse grains exhibited strong λ-fiber. Coarse equiaxed grains with Cube texture were obtained after first-stage cold-rolling with a reduction of 71.74% and intermediate annealing at 900 °C, which promoted the formation of λ-fiber and α-fiber components in the final cold-rolled sheets. {100}⟨0vw⟩ texture was partially retained from the intermediate annealed grains, and new Cube and Goss components were nucleated within {110}〈110〉 shear bands. The magnetic properties of 0.2 mm final sheets were greatly improved by strengthening λ-fiber component with two-stage rolling process, and best magnetic properties were B50 = 1.758 T, P15/50 = 2.065 W/kg, P10/400 = 15.173 W/kg, P10/1k = 59.48 W/kg.

Development and homogeneity of microstructure and texture in a lamellar AlCoCrFeNi2.1eutectic high-entropy alloy severely strained in the warm-deformation regime

Abstract

Cold-rolling and recrystallization textures of a nano-lamellar AlCoCrFeNi2.1 eutectic high entropy alloy

The development of texture during cold-rolling and recrystallization was investigated in a AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA). For this purpose, the as-cast alloy was cold-rolled to 90% reduction in thickness and annealed at temperatures ranging from 800 °C to 1200 °C. The microstructure of the as-cast EHEA showed a nano-lamellar mixture of L12 and B2 phases. The B2 phase was significantly harder than the L12 phase. Development of an ultrafine microstructure was observed after 90% cold-rolling. During cold-rolling, progressive disordering of the L12 phase was observed while the B2 phase maintained the ordered structure. The progressive disordering and development of a predominantly brass type texture in the L12 phase correlated well with profuse shear band formation during cold-rolling. The B2 phase showed the presence of the {111}<110> component which was typical for cold-rolled B2 alloys. An ultrafine duplex structure of equiaxed L12 and B2 phases developed after complete recrystallization that showed significant resistance to grain growth up to very high annealing temperatures (∼1300 °C). The remarkable resistance to grain growth compared to conventional or even other single or dual phase HEAs was due to the formation of a homogeneous duplex structure where growth of one phase was effectively retarded by the other phase. The strong presence of the α-fiber components, but weak BR ({236}<385>) and D ({113}<332>) components in the recrystallization texture of the L12/FCC phase was due to the absence of strong preferential nucleation or growth. Presence of ND-fiber (ND//<111>) with strong {111}<011> component in the recrystallization texture of the B2 phase indicated ease of nucleation from similarly oriented regions in the deformed microstructure.

Microstructure evolution and their effects on the mechanical properties of TB8 titanium alloy

The effects of cold deformation on the microstructure, texture evolution and mechanical properties of TB8 alloy during cold rolling (CR) were investigated. The results show that grain size decreases with the increase in thickness reduction. Meanwhile, the textures change from initial {110}<001> and {113}<332> to α-fiber components ({112}<110>, {113}<110>) and {001}<110> orientation after cold rolling to a thickness reduction of 50%. Increasing the thickness reduction to 67%, α-fiber textures are enhanced along with the appearance of γ-fiber textures. Increasing the thickness reduction further to 83%, γ-fiber textures become dominated. Both grain refinement and texture components contribute to the enhancement of strength after cold rolling. The effect of textures on the mechanical properties are discussed briefly.

Microstructure characterization based on the type of deformed grains in cold-rolled, Cu-added, bake-hardenable steel

The electron backscatter diffraction technique has been used to characterize the microstructure of deformed grains in cold-rolled, Cu-added, bake-hardenable steel. A new scheme based on the kind and number of average orientations, as determined from a unique grain map of the deformed grains, was developed in order to classify deformed grains by type. The α-fiber components, γ-fiber components and random orientations, those which could not be assigned to either γ-fiber or α-fiber components, were used to define the average orientation of unique grains within individual deformed grains. The microstructures of deformed grains in as-rolled specimens were analyzed based on the Taylor factor, stored energy, and misorientation. The relative levels and distributions of the Taylor factor, the stored energy and the misorientation were examined in terms of the types of deformed grains.

A study on the annealing behavior of Cu-added bake-hardenable steel using an in situ EBSD technique

A combination of electron backscatter diffraction and in situ heating was used to study the annealing behavior of Cu-added bake-hardenable (BH) steel. The annealing behavior of cold-rolled, Cu-added BH steel was strongly dependent on the type and number of average orientations developed in the deformed grains. If deformed grains (type I) had a single γ-fiber component as the average orientation of a unique grain (UG), the density of the nuclei was very low and recrystallization began at a later stage of the in situ annealing. However, the average grain size of the recrystallized grains was drastically increased regardless of the deformed grain as soon as recrystallization had begun. If deformed grains (type II) had multiple γ-fiber components as the average orientation of a UG, the density of the nuclei steadily increased as the elapsed time of in situ annealing increased. The area fraction of the recrystallized grains in the partially recrystallized specimens gradually increased, but the kinetics depended on the deformed matrix. However, the average grain size of the recrystallized grains gradually increased in all deformed grains from the beginning of in situ annealing. If deformed grains (type III) had texture components which could not be assigned to either γ-fiber or α-fiber components as the average orientation of a UG, the number of the recrystallized grains was maximized, but the recrystallization kinetics based on a normalized number of recrystallized grains was similar to that of type II. Since type III was a minor deformed grain in the as-rolled Cu-added BH steel, the recrystallization in types I and II was identified as the principal feature determining the overall recrystallization phenomena of Cu-added BH steel.

Texture Evolution of a Cold-Rolled Fe-28Mn-0.28C TWIP Steel during Recrystallization

Texture evolution during static primary recrystallization of an austenitic Fe-28Mn-0.28C TWIP steel was analyzed. The cold-rolled material, which showed a Brass-type texture at medium (30% and 50%), and additionally a γ-fiber at high (80%) deformation degrees, was subjected to isothermal annealing at 700°C. The influence of rolling degree/starting texture on the development of particular texture components was studied. After recrystallization a weakened, retained rolling texture was observed for the examined reduction levels. In addition to the deformation components, Brass and Goss, further α-fiber components were formed mainly by annealing twinning leading to the development of this fiber.

Development of Texture, Microstructure, and Grain Boundary Character Distribution in a High-Strength Boron-Added Interstitial-Free Steel after Severe Cold Rolling and Annealing

A high-strength boron-added interstitial-free (IF) steel was subjected to cold rolling by 90 and 98 pct. Both these materials were subjected to annealing at 650 °C and 700 °C for various lengths of time. An in-depth thorough study has been carried out on the evolution of texture, microstructure, and grain boundary character distribution (GBCD), as a function of cold rolling and annealing. Formation of strain-free nanosize grains at few places has been observed in the severely cold-rolled (98 pct) steel. Ultrafine grains formed in this material at the early stages of annealing. The deformation texture sharpened and the high-angle grain boundary (HAGB) density increased with increasing amount of cold rolling. The intensity of α-fiber components increased at the early stages of annealing, while the γ-fiber components were found to predominate at the later stages. Selective growth of grains having orientations {111}\( \langle 123\rangle \) and {554}\( \langle 225\rangle \) occurred in the 98 pct cold-rolled and annealed material. The textural and microstructural results indicate that in these materials the recrystallization process may be of a continuous type.

Effect of cold rolling reduction and intercritical annealing temperature on the bulk texture of two TRIP-aided steel sheets

High strength TRIP-aided steel sheets with high formability and better ductility are of industrial interest. Texture control and retained austenite characterization are considered as the main factors with respect to the formability and ductility. Processing parameter such as initial conditions of hot rolling, cold rolling to final size of sheet, intercritical annealing after cold rolling and subsequent isothermal heat treatment to achieve TRIP specification in product, affect bulk texture of sheets. Moreover, chemical composition of steel should be noted especially because it can change the intensity of orientation and final macro texture of sheet. In this work, the effect of cold rolling and intercritical annealing on texture development has been investigated for two TRIP-aided steel sheets, which are different in C, Si and Al content. Results show that the cold rolling extends the γ-fiber on these grades of steel, whereas any intensive α-fiber components were not observed by change of cold rolling reduction. Also the effect of cold rolling on final texture of experimented materials is different and depends on chemical composition of steel. In contrary, intercritically annealing of cold rolled sheets decreases the intensity of γ-fiber so that the chemical composition of TRIP steel would influence effectively.