The influence of grain size on brittle crack propagation

Abstract

Ferritic steels undergo a ductile to brittle transition as the temperature is progressively reduced. The strain annealing method has been developed to produce a microstructure in EN1A ferritic steel that contains a transition from a coarser grain size, ∼40 μm, to a finer grain size, ∼20 μm. Small pre-notched bend geometry specimens have been tested at -196°C to investigate crack propagation from the coarser to finer grain region and vice-versa. Details of the fracture path have been investigated using a combination of high resolution scanning electron microscopy, electron back scattered diffraction and ion milling and imaging. The results are considered with respect to the transgranular and intergranular modes observed.