B.J. Duggan

The effect of a deformation banding criterion on simulated b.c.c. rolling textures

Deformation Banding ( DB ) in cold rolled mild steel has been experimentally established by microstructure investigation and mis-orientation analysis using EBSP. Clearly this deformation banding mode must be included in modelling the deformation texture, and this has been attempted. The cause of deformation banding in all DB models is the reduction of the total work for plastic deformation through a relaxation of the deformation constraints. In the first DB model, all grains are assumed to band from the first deformation step. Such an unrealistic assumption has been eliminated in the new model by the introduction of a banding criterion which states that deformation will occur only if the energy for normal slip involved in the DB model is less than that for the RC model. The computer grains firstly deform according to conventional RC model before the DB criterion is satisfied and then deform according to DB model after the criterion is met at a specific step. If the ratio of critical resolved shear stresses for {110} and {112} slip planes is set at unity, the model overpopulates {111} component, but when the ratio is set at 0.85:1.0, the resulting ODF is closer to the measured textures.

Textures, models and experiments relating to drawable low carbon steels

This paper reports three distinct but related projects. In the first, an attempt is made to simulate BCC rolling textures by including a conditional deformation banding criterion modeled in a Taylor/Chin framework. The model is then run backwards to find the origins of the α and γ fibers. The practical importance of this work is to produce an ideal deformation texture from which it might be possible to maximise the development of {111} hkl and to minimise {100}hkl during rolling, since it is well known that {111} recrystallized components are associated with the γ fibre. The second investigation is concerned with the origins of the {111}hkl texture in a batch annealing steel. It is demonstrated that the γ fibre grains are heavily shear banded, and the nucleation of {111} grains occurs in these bands. The shear band material is a ND-rotated {111} component. Clearly, the condition leading to extreme strain localisation is determined by both the slip geometry and the solute/precipitate state. Finally an investigation into the origins of {111}hkl in IF steels using EBSP (Electron Back-Scattering Pattern) on longitudinal sections has failed to identify any sites of strain localisation for nucleation of these grains but it is shown that grain growth strengthens {111} components.

Microstructures of Heavily Deformed Continuously Cast 70/30 Brass and Copper

ABSTRACT The evolution of sub-structure and texture during the heavy cold rolling of coarse columnar grained continuously cast copper and 70/30 brass was examined. The copper is unusual in that it gives rise to a dominant {112} texture with other components being virtually absent. This texture is responsible for the unusually large amount of shear banding observed in the material. The formation of such a sharp texture is thought to be attributable to both the significant fiber texture in the cast material, and also to there being no relaxation of constraints at high deformations, a factor related to the shape of the grains. In 70/30 continuously cast brass the various stages of structural evolution were displaced to much higher levels of deformation compared with the behaviour of hot rolled stock. It was also shown that the brass continued to deform extensively by shear banding even when the areas of micro-twins prevalent at intermediate strains were completely destroyed. The persistence of brass texture at very high strains is viewed as a kind of dynamic equilibrium associated with repeated shear band operation.