Retaining {100} fibre texture in electrical steel via strain-induced boundary migration recrystallisation.

Abstract

In this paper, the feasibility of retaining the preferred {100} fibre texture for non-grain oriented (NGO) electrical steel from the as-cast columnar {100} grains by encouraging recrystallisation via the strain induced boundary migration (SIBM) mechanism was investigated. Rolling with intermediate annealing stages before the final anneal was used to reduce the stored energy through recovery before the final recrystallisation step. A strong {100} fibre recrystallisation texture, i.e. 32% area fraction, was seen in the sample which was warm deformed to 1.6 strain with 5 intermediate annealing stages then annealed at 950 °C for 5 minutes (to observe the early stages of recrystallisation) or 1 hour. Whereas only 12 - 14% {100} fibre component was observed after 1.2 strain with a single or with no intermediate annealing stage. It was found that the {100} fibre recrystallisation texture was formed in regions adjacent to parental deformed grains with {100} fibre texture due to the SIBM recrystallisation mechanism. EBSD imaging analysis was used to follow the recrystallisation process in the same microstructural region using interrupted heat treatments and it was seen that the {100} texture grains carried very low stored energy after deformation, which meant the subgrains in these grains bulged into the surrounding grains with higher stored energy. Due to its slow recrystallisation nucleation rate, a low overall stored energy is preferred to encourage {100} texture recrystallised grains to form via the SIBM recrystallisation mechanism.