Evaluation of microcrack resistance curves by in-situ measurements

The paper deals with the influence of the microstructure on the crack resis tance behaviour of a bainitic pressure vessel steel. The size, shape, distr ibution and volume fraction of the carbides were changed by heat treatment. An in-situ electron microscopy technique allows the direct observation of the deformation process near the crack tip and the continuous measurement o f delta-Delta a curves under loading. These microcrack resistance curves ar e discussed in connection with sets of micrographs of the crack tip region for increasing load levels. It could be concluded, that both the crack tip blunting and the elastic-plastic fracture initiation parameter were determi ned by the microstructure. (C) 1998 Elsevier Science S.A. All rights reserv ed.