Abstract
The high-speed deformation behaviors of SUS316LN stainless steel, mainly comprised of deformation twin domains, ultrafine lamellae, and shear bands to form a heterogeneous-nano (HN) structure, were systematically investigated by means of Charpy impact tests and dynamic tensile tests. At the lowest applied impact velocity of v = 10−2 ms−1, the Charpy impact value increased with decreasing temperature from room temperature (RT) down to 173 K. Nevertheless, at the highest impact velocity of v = 100 ms−1, the impact values were approximately identical irrespective of temperature and were lower than those at 10−2 ms−1. Deformation-induced γ → α’ martensitic transformation was found to take place by the impact tests. The change in the volume fraction f of the α’ phase exhibited the same tendency as the impact value. That is, the value of f increased with decreasing temperature at v = 10−2 ms−1 and, however, it was almost identical regardless of the temperature at v = 100 ms−1. It was revealed by dynamic tensile tests that the temperature at the gauge section of the specimens increased abruptly with strain rate 
and reached approximately 720 K at = 103 s−1. The above experimental results can be reasonably understood from the suppression of the γ → α’ martensitic transformation by the increase in temperature during high-speed deformation. The above analyses strongly suggest that deformation-induced martensitic transformation plays an important role in the Charpy impact value via the transformation-induced plasticity effect.
