Low-temperature fracture mechanisms in a spheroidised reactor pressure vessel steel

The micromechanisms of fracture of a spheroidised A533B reactor pressure vessel steel over the temperature range of −190◦C to +60◦C were investigated by performing uniaxial tensile tests on double-notched cylindrical specimens. Failure was by quasi-cleavage at temperatures between −190◦C and −145◦C. Quasi-cleavage fracture surfaces are characterised by clusters of planar facets that are separated from other facets either by large voids or by clusters of microvoids. At temperatures between −145◦C and −25◦C failure was by mixed microvoid coalescence and cleavage while complete microvoid coalescence was observed at temperatures higher than−25◦C. Over the whole temperature range studied, fracture nucleation was either from large single voids or localised regions of microvoids.