Transformation textures in steels

Abstract

During the controlled rolling of steel, the parent γ phase develops a crystallographic texture which is later acquired by the material after transformation. The major components of the deformation texture of austenite are the {110} (112) and {112} (111) which give rise, respectively, to the {332} (113) and (113) (110) orientations in the transformation products. The recrystallisation texture of austenite, {1OO} (001), is similarly transformed into the {100} (011) component in the ferrite. The latter orientation can also be strengthened by ferrite rolling. During processing, the recrystallisation of γ should be avoided in order to prevent the formation of {100} (011) component, which has a deleterious effect on the delamination behaviour of steels. The {332} (113) is the most beneficial among the transformation texture components from the point of view of achieving good deep drawability and improved strength and toughness. The effects of compositional and processing variables, during controlled rolling, on the overall sharpness as well as on the relative intensities of the components of the transformation texture are described. While the {332}(113) component is significantly affected by some of these parameters, the {113} (110) remains relatively insensitive to these factors. Variant selection does not seem to occur during ferrite transformation. By contrast, martensite textures are generally much sharper than ferrite textures, and this is attributable to variant selection during transformation. Several analytical tools are available for the prediction of transformation textures. With the aid of information obtained in this way, suitable processing routes can be devised to produce desirable texture components in the γ, which are then inherited by the α. There is much scope for research along these lines.