Materials Science Forum Vols. 467-470

Abstract: With the 3DXRD microscope it is now possible to follow in-situ the 3D shape of a recrystallizing grain in the bulk of a deformed microstructure. This opens up the possibility of making direct measurements of boundary migration through a deformed matrix. This paper focuses on recrystalliztion in a deformed Aluminum single crystal with initial orientation (112)<111> (Cu).

Abstract: In this work, it is shown that the contiquity ratio, Crr, defined as the fraction of the total grain boundary area of recrystallized grains shared by other recrystallized grains, is a useful experimental parameter for describing the clustering of recrystallization nuclei in partially recrystallized microstructures. Two experimental examples are presented where anisotropic impingement behavior, i.e. non random recrystallized grain distributions, is thought to be important. In the experimental examples, the deviation of Crr from Crr = Vv which is a characteristic of a random distribution, is clearly shown. The results justify the need for these cases to be modelled, as had been done, by impingement patterns other than the simple random nucleation behavior so often postulated without proof in recrystallization kinetics studies.

Abstract: New 3D X-ray diffraction microscopy (3DXRD) experiments on recrystallizing bulk grains that nucleated and grew in a 92% cold deformed pure copper during in situ annealing at both 150° C and 160° C are described. Nucleation times, growth velocities and apparent activation energies were determined for each grain. A wide range of apparent activation energies was observed but the average of 123 kJ/mol agreed well with earlier recrystallization experiments on a similar purity copper. It was clear that each recrystallized grain had its own individual characteristics; the grains do not all behave alike as various models would suppose.

Abstract: A Fe-2.8%Si single crystal was scratched in order to randomise the texture in the neighbourhood of the notch. Annealing resulted in recrystallization and grain growth starting from the deformed zone. Misorientations between the single crystal matrix and the grown grains were gathered and were studied in order to investigate the possibility for selective growth based on a specific misorientation. However, instead of studying the misorientation angle or axis profiles separately in a 1D or 2D projection a full misorientation analysis was carried out in the 3-dimensional Rodrigues-Frank misorientation space, which offers an unambiguous interpretation of the data because no features are hidden or masked by a projection. It is concluded that the selective growth phenomenon following the <110>26.5deg misorientation relationship is strongly supported by the gathered orientation data, after appropriately normalizing these data with respect to a random misorientation distribution.

Abstract: The microstructural evolution during annealing below the recrystallization temperature of a commercial purity aluminum (99wt.% purity) cold rolled to a true strain of 2 has been investigated by transmission electron microscopy concentrating on microstructural and orientational aspects. The deformation microstructure was a typical lamellar structure with extended lamellar boundaries, GNBs (geometrical necessary boundaries), and short interconnecting boundaries, IDBs (incidental dislocation boundaries). The microstructure was divided into regions representing typical rolling texture orientations and regions of other orientations. During annealing the structure coarsened towards an equiaxed structure and it was observed that this coarsening was significantly slower in regions of rolling texture orientations than in regions of other orientations. This difference was discussed based on the characteristics of the deformation structure.

Abstract: Duplex stainless steels 2205 are widely used in constructional and petrochemical applications because of their good mechanical and corrosion properties. The objective of this work was to study the influence of aging at high temperature on the austenite and d ferrite equilibrium. After welding by TIG process, duplex stainless steel was aged in the range of 800 – 1150 °C temperatures for 60 min. The microstructure was characterized by metallography and X-ray methods. The toughness of welded structure was also measured.

Abstract: Various microstructure models for Nb-bearing steels were tested under industrial strip rolling conditions to establish a relationship between grain size and toughness in Ti-Nb-V microalloyed steels. For similar Nb contents, microstructure models for Nb steels were found to adequately describe recrystallisation kinetics in more complex Ti-Nb-V steels. For thick-walled linepipe (11.6mm), a minimum of 0.04%Nb is required to achieve adequate toughness. Retained strain was the dominant processing parameter factor affecting ferrite grain size. The predicted minimum amount of retained strain after the last pass required for sufficient grain refinement concurred with laboratory simulation results. For the rolling schedules investigated, metadynamic recrystallisation was predicted to occur during roughing, whilst static recrystallisation was predominant during finishing.

Abstract: Several Fe – O samples containing different fractions of dispersed oxides were processed by mechanical milling followed by consolidating rolling. The samples were annealed at 1000oC and then compressed to strains of 0.35, 1.2, and 1.9 at an ambient temperature. Dispersed oxides with size of about 20 nm were homogeneously distributed throughout the ferrite matrix and their volume fractions varied from about 0.3% to 2.0%. To study the annealing softening mechanisms, the coldworked specimens were annealed for an hour at 700oC and 800oC. The fine dispersion of oxide particles was very effective to suppress any softening processes. Primary recrystallization fully developed in the samples with volume fraction of dispersed oxides of about 0.3%. Increase in the fraction of dispersed oxides resulted in decrease of the fraction recrystallized. In the samples containing 2.0 vol.% of dispersed oxides, only recovery was the annealing softening process irrespective of the preceding cold strain. The critical volume fraction of dispersed particles for development of the primary recrystallization is considered to range from 0.5 to 2.0%.

Abstract: The operation which allows reducing wire diameter is called wiredrawing. The wiredrawing principle is that of using the metal plasticity to reduce the wire diameter. Our study is based on wire steel containing 0.05 % carbon. The regular orientation of the grains (texture) caused by external stresses during the drawing process is observed. This texture causes a phenomenon of material consolidation. Two annealing temperatures were applied on deformed wires for modifying the structure and mechanical properties. The effects of drawing and thermal treatment on our material were studied by, scanning electron microscope, hardness measurements and X – ray diffraction.

Abstract: During annealing of cold rolled steel sheets, the evolution of the texture, to produce the characteristic texture of a recrystallised material, depends on a series of factors, including the starting deformation texture, composition and processing conditions. In the present work, electron backscattered diffraction (EBSD) techniques have been used to investigate the deformation substructures being developed by cold rolling into grains belonging to different texture components. The strain localisation, the deformation banding, the spread in orientation into grains with different orientations are some of the aspects that have been considered. Annealing cycles at different temperatures have also been carried out in order to promote recovery and initial stages of recrystallisation . The obtained substructures have been compared to the as-cold rolled ones. It has been observed that recovery induces the dislocation structures to arrange into subgrains. Associated to the ND fibre, a network of relatively high angle boundaries develop within the subgrain structure. The recrystallisation nuclei have been observed to evolve from such a network.