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~6 s u m 6 -~' e f f e t r e n f o r c e de Snoek / DESE / dans du f e r i f a i b I e teneur en n i t r o g b e e s t d s c r i t .

The initial orientation has split into two equally strong symmetric orientations: (112)[111¯] and (112)[1¯1¯1]. Areas of identical orientation were band shaped and were called deformation bands. Up to 60% reduction, deformation occurs by slip on one plane (one from two possible) in two directions. This leads to the appearance of deformation bands with transition bands between them. Due to such deformation the initial orientation rotates around transverse direction towards the end-orientation {112}〈111〉. Due to rotation of the crystallographic lattice with deformation, the Taylor factor M changes as well, and it causes the activation of two not coplanar slip systems which stabilize the end-orientations {112}〈111〉. Such a sequence of the slip systems activation was concluded from the agreement of the calculated and experimental pole figures. The electron microscopy investigations showed that first shear bands formed due to the activation of these new slip systems.

The dislocation structure was free from inhomogeneities with high orientation changes normally observed in deformed materials. After reductions 20% and 40% against the background of cells there were sometimes observed bands (dislocation rich layers). With increasing strain the cell structure became faint and the dislocation rich layers became sharper (after 60% reduction no dislocation cells were revealed).It has been found, that in layers lying close to the rolled surface of the specimen the dislocation bands were nearly parallel to the RD and much thinner than those in further layers. SAD analysis indicate that in the surface layers the crystallographic orientation changed systematically with increasing distance from the surface to the center of the specimen (rotation around ND). In the intermediate layers the dislocation bands were curved and overlapped the other dislocation bands. Despite of detailed investigation shear bands were not observed even in specimens rolled to the 95% reduction.

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