BRITTLE FRACTURE NUCLEATION IN SA 533B-1 STEEL.

Cleavage origins ahead of previous crack fronts have been identified and the cleavage nucleation distance measured on brittle fracture surfaces of CT specimens of A 533B-1 steel whose critical cleavage stress and plastic properties were also measured. Using these data, the RKR model allows to predict a toughness-temperature relationship in good agreement with experimental values. The critical nucleation distance, the cleavage stress and other secondary evidence point to the bainitic packet size as being the most probable structural parameter controlling brittle fracture. An active non-critical role of the carbides in the fracture process is however not excluded.