Materials Science Forum Vols. 702-703

Abstract: An experimental study of the microstructural and texture evolution attending recrystallization of Nb-Ti stabilized ferritic stainless steel is presented. Two specimens with different Nb-Ti compositions, TCS345 and B4003, have been selected for comparison. The result shows that, after annealing at 750 °C for 5min, the major orientation in the TCS345 specimen locates at {111}, microstructures presents an equiaxed grain morphology, whereas the texture in the B4003 is not typical recrystallization texture and remains weak, indicating recrystallization occur preferentially to the TCS345 sheet. And after continuous annealing at 850°C for 5 min, the texture in TCS345 remains stronger than in the B4003, indicating that the additional amount of Nb-Ti acts to significantly hinder the recrystallization process.

Abstract: One-pass hot rolling in the ferrite region was conducted at higher temperatures, using various rolling temperatures and rolling reductions, with two types of ULC steels, 0.016% Nb and 0.023% Ti, and recrystallization behaviors immediately after hot rolling were investigated. The γ-fiber strength reached its maximum at around 50% rolling reduction at 1273K with the Nb-added steel and 1323K with the Ti-added steel. On the other hand, in high temperature rolling of the Ti-added steel, the γ-fiber did not develop, independent of rolling reduction. These changes corresponded to the recrystallized fraction, in that the strength of the γ-fiber decreased when recrystallization occurred immediately after rolling. New recrystallized-like grains were produced in the domain where distortions were particularly concentrated. Recrystallization seemed to be the result of various mechanisms, as some recrystallized grains were formed by a bulging mechanism, whilst others were surrounded by high angle grain boundaries.

Abstract: The present study aims to understand the evolution of microstructure leading to nano/ultrafine grain formation during cyclic thermal process. A commercial grade of AISI 304L austenitic SS was cold rolled which resulted in a creation of a dual microstructure having strain induced martensite (43%) and heavily deformed retained austenite. The dual phase microstructure was subjected to cyclic thermal annealing process at 825 °C. The events occurring in; a) retained austenite and b) reverted austenite formed by phase reversion of strain induced martensite, during annealing treatment, were studied by the Electron backscattered diffraction (EBSD). The study revealed recrystallisation process of the two austenite grains, which resulted into ultrafine grain formation during cyclic thermal process.

Abstract: The Nb-1%Zr-0.1%C (wt%) alloy is one of the most promising refractory metal alloys having an excellent combination of high temperature properties. Such a combination of properties makes it suitable for several structural applications in the Compact High Temperature Reactor (CHTR). In order to produce the alloy in different shape and sizes a new thermo-mechanical route has been established. The central idea behind the development of such thermo-mechanical route is to reduce the working temperature and provide suitable intermediate annealing treatments to develop desired microstructures. The present paper reports about the application of orientation imaging microscopy in optimizing annealing parameters like temperature and time as a function of the extent of deformation. Samples were also characterized by optical microscopy and transmission electron microscopy techniques. It has been shown that a heat treatment of 1300°C for 3 hour could produce nearly full-recrystallized microstructure. This paper also discusses about the carbide precipitation, their morphologies, chemical compositions and orientations with the matrix phase.

Abstract: The magnetically driven motion of planar symmetrical and asymmetrical <> tilt grain boundaries in high purity (99,995%) zinc bicrystals was measured in-situ by means of a po­la­rization microscopy probe in the temperature range between 330°C and 415°C and the corres­pon­ding migration activation parameters were obtained. The results revealed that grain boundary mobi­lity essentially depends on the misorientation angle and the inclination of the boundary plane. The magnetic annealing of the cold rolled (90%) Zn-1.1%Al sheet specimens resulted in an asymmetry of the two major texture components. This effect is attributed to a magnetic driving force for grain growth. The grain microstructure evolution was also essentially affected by a magnetic field.

Abstract: A 2-dimensional vertex dynamics simulation is applied to the annealing behaviour of deformed Aluminium single crystals having different orientations. It is observed in experiments that deformed single crystals of different orientations - typically the common rolling textures like Goss (110)[001], Brass (110)[1-12], Cube (001)[100] – exhibit remarkably different rates of recovery. It is suggested that this difference arises from the deformation microstructures, with sub-grain boundaries of various misorientation values. The sub-grain boundary mobilities and energies, being strong functions of the boundary misorientation, thus affect the recovery rates. This effect is illustrated using vertex dynamics simulation on the same orientations and schematic deformation substructures as above. Good agreement is obtained for the orientation dependency of recovery.

Abstract: This study investigates the changes in radial micro-texture via Kearn’s f-factors during single cold pilger reduction of a titanium Ti-3-2.5 alloy as a result of strain path changes from tooling modifications. EBSD results confirm that the texture intensity as well as the radial f-factors can be increased by modifications of pilgering tooling. In addition a switch between the secondary prism planes which lie normal to the pilger direction in the starting tube to primary prism planes after pilgering has been observed.

Abstract: A TWinning Induced Plasticity (TWIP) steel was cold rolled to 42% thickness reduction followed by isochronal annealing for 300 s between 600-850 °C. Bulk texture evolution during recrystallisation was investigated by X-Ray Diffraction. While the development of the α-fibre after cold rolling is typical of low stacking fault energy materials, anomalously higher intensities were noted for the Goss ({110}) compared to Brass ({110}) orientations. Upon recrystallisation, the main rolling texture components were retained and ascribed to nucleation at orientations close to those of the deformed matrix followed by annealing twinning which leads to crystallographically identical variants. Unlike previous texture investigations on austenitic steels, the relatively homogeneous deformation microstructure and uniform distribution of subsequent nucleation sites led to the retention of the F ({111}) orientation. Moreover, the firsthand observation of the Rotated Copper ({112}) orientation in TWIP steel is attributed to the second order twinning of the A ({110}) orientation.

Abstract: The role of rare earth addition on the microstructure and texture during recrystallization of cold rolled sheets is investigated by a comparative study of pure Mg, Mg-3Y and Mg1.5Nd sheets. In pure Mg, nucleation occurs mainly at shear bands which results in a texture weakening. The basal-type texture re-strengthens rapidly during grain growth of the pure Mg sheet. In contrast, in the Mg-RE alloys the weaker texture formed during early recrystallization strage is retained during further annealing due to retarded grain growth. Uni-axial tensile and Erichsen tests show that ductility and sheet formability are significantly improved by addition of rare earth elements.

Abstract: The migration rates of C->Si, Si->C, and Si->Sj were assumed to be high and those of Si->Si and all other rates to be low. Here Si(i=1,2,3,4) is a variant of S orientation and C->Si means the growth of a cube grain into an Si grain. The textural development through grain coarsening was simulated as a function of the ratio of the high rate to the low one. The compromising effect surely promotes the development of the cube texture but its decisive development requires any asymmetry between C->Si and Si->C migration processes.