Cleavage fractures of ferritic structural steels were analyzed. A strong tendency to deformation twinning was observed in the vicinity of the main cleavage crack. Numerous cleavage nuclei were revealed on twins in the close vicinity of cleavage facets. It was concluded that deformation twinning was an integral feature of the deformation processes in the region of the propagating cleavage-crack tip and that deformation twins, which nucleated ahead of the crack tip, acted as nucleation sites for cleavage-fracture nuclei (pre-cleavage micro-cracks). The sizes of such cracks corresponded to that of the assumed inherent cleavage-crack nuclei which were predicted by brittle/cleavage fracture theory. Such nuclei had not previously been observed in ferritic materials.

Deformation Twins - Probable Inherent Nuclei of Cleavage Fracture in Ferritic Steels. J.Bošanský, T.Smida: Materials Science and Engineering A, 2002, 323[1-2], 198-205