Modern pipeline steels exhibit complex microstructures that cause mechanical anisotropy in various respects. For instance, strain path effects under non-monotonic loadings are exceptionally pronounced in these steels. Crystallographic texture and morphological anisotropy are the main contributors to strength and hardening directionality in pipeline steels under monotonic loading. In contrast, the dislocation substructure is seen as the primary source for Bauschinger and cross effects during complex non-monotonic loading, e.g. during pipe forming. The Bauschinger effect for example may arise from pile-ups formed at obstacles such as intragranular shear bands, and homo- or heterophase boundaries. The dislocation-based model by Peeters et al. [Acta Mater., 49 (2001), pp. 1607-1619] developed for coarse-grained ferritic steel allows for complex strain path effects through the accumulation of dislocations at micro-shear bands. However, it struggles to reproduce the large Bauschinger effect of ~250MPa in fine-grained bainitic pipeline steel [Bönisch et al., Procedia Manuf., 47 (2020), pp. 1434-1441]. Considering the microstructural differences between the two steel varieties, a promising way to improve the model predictions - especially for the Bauschinger effect - is to incorporate dislocation interactions with phase and/or grain boundaries. In the present work, we introduce this approach and demonstrate the basic capabilities of such a grain boundary-extended Peeters model. By accounting for the formation of pile-ups at grain boundaries the Bauschinger effect is enlarged. Furthermore, by explicitly considering the grain boundary spacing, the model can deliver grain size (Hall-Petch) strengthening.
M. Bönisch, M. Seefeldt, A. van Bael
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