Formation of Highly Misoriented Fragments at Hot Band Grain Boundaries During Cold Rolling of Interstitial-Free Steel
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DEFORMATION microstructures have a pronounced influence on recrystallization texture development and, hence, on the mechanical and physical properties of metals and alloys.[1–5] In the processing route to produce automotive sheet steels, such as interstitial-free (IF) steels, cold rolling is followed by static annealing to generate a fully recrystallized microstructure exhibiting the so-called c-fiber texture; this texture contributes to good drawability and enables complex-shaped car body parts to be produced. This cfiber texture is designated {111}huvwi, whereby a high fraction of recrystallized grains are oriented with their {111} planes parallel to the rolling plane.[2–4] It is generally accepted that the final recrystallization texture of IF sheet steels is generated in the early stages of annealing via the preferred nucleation of these coriented grains, and any further growth of these grains has only a minor effect on texture strengthening.[5,6] Hence, understanding the origin of recrystallization in
NASIMA AFRIN, PhD Student, Researcher, is with the School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia, MD. ZAKARIA QUADIR, Materials Manager, is with the Electron Microscope Unit, University of New South Wales, Sydney, NSW 2052, Australia, and also Lecturer with the School of Materials Science and Engineering, University of New South Wales. Contact e-mail: [email protected] MICHAEL FERRY, Professor, is with the School of Materials Science and Engineering, University of New South Wales, and also Deputy Director with the Australian Research Council Centre of Excellence for Design in Light Metals, Sydney, Australia. Manuscript submitted October 29, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
the deformation microstructure of these steels is important for improved drawability. It has been reported unanimously for IF steels that the nucleation of recrystallization takes place in the highly fragmented substructures of the c-fiber grains.[3,6] Subsequently, recrystallization progresses through the growth of these nuclei within the c-fiber grains followed by their propagation into another distinctive class of deformed grains, termed a-fiber grains.[7] These grains have their h110i directions aligned parallel to the rolling direction (RD) and exhibit a deformation substructure that is characteristically smooth in appearance.[2] Within the cfiber grains, shear bands[3,7] and deformation bands[4,6] form profusely and these are arguably the principal sites for recrystallization. Nevertheless, considerable nucleation also occurs at the prior high-angle boundaries (HABs) of the hot band.[8] For example, Inagaki[9] reported that 90 pct of recrystallization in a low-carbon steel occured within 2 lm of these boundaries and their origin was explained by the possible presence of local orientation curvatures near the grain boundary regions. Hawakawa and Szpunar[10] subsequently proposed a recrystallization model to illustrate how these grain boundary regions are effective si
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