Evaluation of microcrack resistance curves by in-situ measurements Original Research Article

The paper deals with the influence of the microstructure on the crack resistance behaviour of a bainitic pressure vessel steel. The size, shape, distribution 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 of δ–Δa curves under loading. These microcrack resistance curves are 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 determined by the microstructure.