Abstract
Effects of testpiece size on the microscopic cleavage fracture stress, σF*, have been investigated for as-transformed, autotempered martensitic microstructures, by employing geometrically similar (scaled) testpieces. Both fine- and coarse-grained martensites have been examined. For a coarsegrained martensitic microstructure, significant effects on cr* attributable to sampling volume have been observed,i.e., reduced values of σF* are obtained as the testpiece size is increased. For a fine-grained martensitic microstructure the effects on σF* attributable to sampling volume are reduced, but significant reductions in σF* occur due to the lack of depth hardenability in large testpieces. The values of σF* observed are consistent with a micromechanism of failure involving the propagation of microcracks from autotempered carbides. For the coarse-grained condition the most potent autotempered carbides lie on embrittled prior austenite grain boundaries.
Published Version
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