Synchrotron analysis of toughness anomalies in nanostructured bainite

L. C. D. Fielding, N. G. Jones, J. Walsh, S. Van Boxel, M. S. Blackmur, P. D. Lee, P. J. Withers, H. J. Stone and H.K.D.H. Bhadeshia


High-resolution synchrotron X-ray diffraction has been used to characterise the notch root regions of Charpy impact test specimens of a superbainitic steel, both before and after loading. The changes in the volume fraction of austenite induced by the application of a three-point-bending load were quantified. Analysis of diffraction peak shifts revealed the extent of residual tensile and compressive strains present due to both machining and an applied load. The results lend support to the hypothesis that the comparatively low energies absorbed during Charpy impact testing of superbainitic steels, less than 7 J, are due to the formation of stress-induced martensite at the notch root, prior to crack initiation.

Acta Materialia 105 (2016) 52-58.

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