Cleavage fracture of A 533 B pressure vessel steel in martensitic condition

AbstractMeasurements of microscopic cleavage fracture stress σF* and fracture toughness K 1C at low temperatures have been made on A 533 B, in an autotempered martensitic condition, to assess the effect of austenitizing temperature on fracture in a system where the fracture mode is transgranular quasicleavage for all austenitizing temperatures. A wide range of prior austenite grain sizes (and hence packet sizes) has been studied, and detailed microstructural information has been obtained in an attempt to gain a clear understanding of the mechanisms of cleavage fracture in this steel. The microscopic cleavage fracture stress is found to be independent of austenitizing temperature, and in the temperature range from −100 to −160°C it is also independent of temperature. At −196°C, the value of σF* falls slightly. The temperature independence of σF* strongly suggests a tensile stress controlled fracture criterion. The coarse grained condition exhibits higher strength, slightly higher fracture toughness, and a ...