Abstract
This report describes the nanoscopic strength analysis of low carbon austenitic stainless steel 316NG pre-strained to ±10% and ±20% true strain under tension and compression loading. This strength analysis was conducted, using an ultra-micro, micro and Vickers hardness testers and TEM. TEM observations showed that the micro-structural parameters relevant the analysis are the dislocation cell size, dcel and the coarse slip band spacing, lcsl. 10dcel or 10lcsl shows the position where fine grain strengthening by dislocation cells or slip spacing saturates and the hardness becomes constant. The Vickers hardness, HV, corresponding to the micro strength was expressed as HV=Hv*bas+Hv*sol+Hv*dis+Hv*cel+Hv*csl. Hv*bas is the base hardness, Hv*sol is the solid solution strengthening hardness, Hv*dis is the dislocation strengthening hardness in the dislocation cell, and Hv*cel and Hv*csl are the fine grain strengthening hardness due to the dislocation cell and coarse slip band, respectively. Hv*bas, Hv*sol and Hv*dis were about 100, 50 and 0, respectively, independently of the pre-strain of ±10% and ±20%. Accordingly, the Vickers hardness increment corresponding to the work hardening was equal to the sum of Hv*cel and Hv*csl. In other words, the work hardening due to tension and compression pre-straining up to ±20% is dominated by fine grain strengthening due to the dislocation cell and coarse slip band. This behavior was similar to that obtained in SUS316NG steel pre-strained by cold rolling in the previous study. It is concluded from those results that the work hardening mechanisms in SUS316NG steel are independent of the pre-strain method.
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