Papers by Author: M.Z. Quadir

Abstract: The idea that a single subgrain is sufficient to produce a single recrystallised grain is the simplest explanation for the recrystallisation process. Likewise, a single Goss oriented grain arising from the primary recrystallisation process is the simplest unit which can give rise to a secondary Goss oriented grain. More complicated cluster models, for example subgrain coalescence is also considered feasible for primary recrystallisation, clusters of Goss oriented grains might be another mechanism for forming Goss oriented secondary grains. This paper examines the cluster theory using material which is produced by the ARMCO process which requires two stages of rolling. In order to achieve this aim it is necessary to destroy the connectivity between individual Goss oriented grains by using thin foils derived from sheet which gives a strong Goss texture on conventional annealing. The foils were sectioned from the subsurface which had a strong η fibre after primary recrystallisation, and ranged in thickness from 18μm (the average grain size after primary recrystallisation) up to 80μm, which is the approximate thickness of the η textured layer. The central layer, which had the classical {111} primary recrystallised texture, was similarly processed, but this did not produce secondary recrystallisation. The experiment followed the secondary recrystallisation process in the same area using sequential annealing in a vacuum furnace by a combination of EBSD and Channelling contrast microscopy. The data does not support the high energy boundary hypothesis nor the CSL explanation. But it is clear that connectivity is important, because when this is destroyed by the thin foil two dimensional morphology, as it is in the thinnest foil, secondary recrystallisation does not occur.

Abstract: The relationship between the deformation orientation distribution function (ODF) and the primary recrystallised ODF in cold and warm rolled metals, is not a simple mathematical transformation from one to the other, but is through thermally activated processes occurring in the deformation microstructure. In BCC metals the mature rolling microstructure consists of cells, microbands and shear bands on a length scale of fraction of a micron, to deformation and transition bands at the grain scale, when this is of the order of 10 or more microns. There is evidence that grain boundary regions are sometimes distinct from grain interiors. Wherever there is a relatively sharp change in either orientation or microstructure such locations are potential sites of recrystallisation nuclei. In this paper the results of a systematic investigation of the development of microstructure in rolled interstitial free (IF) steel using both transmission and scanning electron microscopy are presented. It is shown how the dislocation mesh structure, formed at the earliest stages of rolling, develops into the mature microstructure consisting of cells, microbands and shear bands. Deformation heterogeneities in the microstructure, known to be of vital significance in the recrystallisation process are associated with the α and γ fibre components of the rolling texture. Shear band thickening and α grain fragmentation are also considered, since both processes can produce recrystallisation nuclei, which in the α fibre case can reduce desirable mechanical properties.

Abstract: IF steel was homogeneously cold rolled between 30-95% reduction in thickness. The global cold rolling textures showed a gradual strengthening of both stable α and γ components with increasing reduction until ~80% after which γ remained effectively unchanged but α components intensified until 95% reduction of thickness. Deformation Banded (DB) and also fragmented microstructures were found exclusively in γ grains up until about 85% reduction after which DB was unexpectedly detected in α grains, becoming significant after 95% reduction. This is in sharp contrast with the rather undifferentiated microstructures found in α grains at low to medium levels of deformation. At lower reductions the annealing texture was a weak α, but the γ component increased with rolling strain and became dominant at ~80% rolling deformation. A peak type γ recrystallisation texture with orientations ranging from {554}<225> to {111}<123> was found in the 95% rolled sample. In addition to this a {411}<148> component began to intensify, reading 5R at 95% reduction. Microstructural analysis showed that DB provided the lattice curvature for nucleation in the α fibre.