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Abstract
X-ray diffraction, positron annihilation Doppler broadening spectroscopy and magnetic measurements have been used to investigate the effect of deep drawing on the generation of structural defects in austenitic Mn-based twinning induced plasticity steels. The effects of plastic deformation and hydrogen on structural defects in austenitic Mn-based twinning induced plasticity steels have not extensively been investigated, leaving the understanding of the effect of the deformation mechanisms involving twinning or plasticity induced transformation on the structural defects incomplete. X-ray diffraction measurements show an initial increase in defect concentration with increasing equivalent strain. Positron annihilation Doppler broadening revealed the existence of two defect types with a different degree of open volume. The interpretation in terms of dislocations, stacking faults and/or twins corroborated with the line broadening results from X-ray diffraction measurements. Magnetisation measurements revealed the formation of α′ martensite, which was related to the fraction of positrons annihilating at smaller structural defects. The presented findings attribute the larger defect type to dislocations, whereas the smaller defect type is attributed to partial dislocations and is consequently related to twinning or plasticity induced transformation.
This research was carried out under project no. MC5·07292 in the framework of the Research Program of the Materials Innovation Institute (M2i) (http://www.m2i.nl). The support of M2i, Tata and SKF is gratefully acknowledged. The authors want to thank M. de Bruine (Tata) and M. Faid (SKF) for their technical support in the deep drawing and H charging experiments respectively. The authors also want to thank P. Kömmelt for performing the FEM simulations.