Papers by Author: W. Bevis Hutchinson

Abstract: Primary recrystallised sheets of 3% silicon steel from two different industrial processing routes have been examined after laboratory annealing to initiate secondary recrystallisation. Metallography included etching to reveal individual dislocations and sub-boundaries as well as EBSD in scanning electron microscopy. Residual low angle boundaries are not normally observed inside the secondary grains. The growth of secondaries appears to occur in a jerky manner, associated with local intrusions into the primary matrix that destabilise the interface. The frequency of occurrence of special low energy grain boundaries such as 9 and 5 is believed to dictate the selectivity of the Goss orientation in both types of steel sheet.

Abstract: The paper surveys various types of dislocation substructure that are created by plastic deformation in metals. Special reference is made to those substructures that accommodate sharp misorientations as these are of fundamental importance to the nucleation of recrystallisation. Several different mechanisms can give rise to high misorientations; these are discussed in terms of the factors that control them and their relationships to orientation and texture. Different mechanisms for nucleation of recrystallisation may occur depending on the type of substructure, allowing some practical control over the final recrystallised texture.

Abstract: Work has been carried out at KIMAB to determine the best, industrially feasible, conditions for producing TRIP steel sheet with the aim of obtaining a tensile strength of 600 MPa and a ductility of 30% through a hot-dip galvanising process schedule. Two of the most promising steels were selected to study the microstructures and to follow the transformation from ferrite to austenite in more detail, as well as to examine the stability of the austenite during deformation. This investigation has been performed mainly with the aid of the EBSD technique.

Abstract: Possible effects of stress on the movement of grain boundaries and phase boundaries are considered in terms of available driving forces and mechanisms. Examples of some of these effects are presented from the literature and new experimental results. Stress may influence the kinetics of transformation and also the microstructure and texture of the product material.

Abstract: The mechanisms by which textures can be inherited in transformed phases are discussed in the light of different transformation mechanisms. Possible origins of variant selection in the different cases are reviewed and classified. Evidence is presented for a hitherto unsuspected source of variant selection that arises from the stresses which are generated during transformation due to the presence of micro-segregation. Some model predictions show the potential effect of this phenomenon on textures in bainite or martensite.

Abstract: Laser-Ultrasonics (LUS) provides a means of obtaining microstructure information continuously and non-destructively both in the laboratory and for quality control on-line in industry. Ultrasound is both generated and recorded using lasers which permits remote, non-contact operation with fast sampling and also the capability of working at high temperatures or at moving surfaces, for example during industrial continuous annealing. Examples of dynamic heating trials will be presented for samples of cold rolled steel sheets where primary recrystallisation and ferrite austenite transformation are monitored in-situ as a function of temperature. Examples are also presented where the grain size of low carbon steels have been quantitatively analysed and show very good agreement with microscopy methods.

Abstract: Island grains have been studied in iron samples that had been treated by critical-strainannealing and in commercial silicon iron alloy sheets after incomplete secondary recrystallisation. Such islands remain behind because their boundaries have such a low mobility that the grains cannot shrink away in the time available during annealing. Misorientations of these islands in relation to the grains surrounding them were measured using EBSD. Similar results were observed in both materials. A small number of low angle boundaries were found and also many twin boundaries. The most remarkable observation, however, was the presence of many general high angle boundaries that did not correspond to any evident coincidence relation.

Abstract: Conditions favouring spontaneous growth of whiskers from tin coatings are discussed. Observations are reported concerning orientations and geometry of whiskers. The driving force for growth arises from elastic stress in the coating and can be expressed as a Gibbs free energy in terms of the decrease in pressure. An analysis of diffusion-controlled growth based on grain boundary diffusion seems to be capable of accounting for the fast growth kinetics that are observed in practice at room temperature.