Fragmentation of Orientation within Grains of a Cold-rolled Interstitial-free Steel

Abstract

The formation of a favourable recrystallization texture in interstitial-free (IF) steels depends on the availability and activation of particular nucleation sites in the deformed microstructure. This paper presents a description of the deformed microstructure of a commercially cold-rolled IF steel, with particular emphasis on the microstructural inhomogeneities and short-range orientational variation that provide suitable nucleation sites during recrystallization. RD-fibre regions deform relatively homogeneously and exhibit little short-range orientational variation. ND-fibre regions are heavily banded and exhibit considerable short-range orientational variation associated with the bands. While the overall orientational spread of ND-fibre grains frequently is about the ND-axis, the short-range orientational variation often involves rotation about axes in the TD-ND plane that are nearer to the TD than the ND.KEY WORDS: steel; IF steel; cold rolling; texture; misorientation; electron backscatter diffraction; EBSD; shear bands.scope (FEG-SEM) were used to investigate the microstructural and orientational fragmentation of grains in a commercially cold-rolled (75 % reduction) titanium-stabilized interstitial-free steel. The composition of the steel is listed in Table 1. The steel was prepared by standard metallographic techniques and the final polishing step was with colloidal silica. Both EBSD mapping and forescatter imaging were conducted using the same microscope settings: an accelerating voltage of 20 kV and a 60 mm aperture. The specimen was positioned at a working distance of 25 mm and at a tilt of 70°. An EBSD map covering a 360ϫ360 mm area (1 200ϫ1 200 pixel array, 0.3 mm pixel spacing) was taken on each of the RD-ND and RD-TD sections. Forescatter images were taken of selected regions within the areas covered by the EBSD maps.In order to save space when describing the microstructural and orientational characteristics of grains having various orientations (and for convenience of labelling on figures) the nomenclature adopted by Samajdar et al. 3) is used. The classification scheme is shown in Table 2. Letters represent the main texture components occurring in cold-rolled steel (H, I, E, F) as well as a minor component of interest (designated J in this paper). It may be noted that there is some overlap between the I and E classes, since an orientation was considered to belong to a particular orientation class if it was within 15°of the ideal orientation corresponding to that class. A grain or region was considered to belong to a particular orientation class if the majority of orientations within it belonged to that class. However, when selecting grains or regions belonging to each class for further analysis, preference was given to grains or regions in which a high proportion of orientations were quite close to the ideal orientation for that class. While using this method carries some risk of favouring grains or regions having a lower overall orientational spread, it was felt that this effect was likely to b...

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