Dynamic strain aging in DP1000: Effect of temperature and strain rate

Abstract

The present study reports on an extensive experimental campaign performed to identify the occurrence of dynamic strain aging (DSA) in a fine-grained DP1000 steel. Tensile tests are performed covering 7 orders of strain rate, i.e., 0.0001 s-1 to 1080 s-1, and temperatures ranging from −40 °C to 400 °C. The test results are thoroughly analysed with particular attention to typical features of DSA, such as serrated flow, thermal hardening, negative strain rate sensitivity and blue brittleness. In addition to the plastic strain, DSA is sensitive to both temperature and strain rate. DSA effects are most dominant at higher temperatures and lower strain rates. However, even at the highest strain rate, traces of DSA are found in DP1000. At temperatures below 100 °C, no DSA is observed. The way and extent to which DSA manifests itself depend on the specific combination of temperature and strain rate. Analysis of the serrations stimulate the hypothesis that quasi-periodic dislocation cells might lie at their origin. In addition, scanning electron microscopy images of the fracture surfaces reveal finer and shallower dimples with flat features in the dynamic strain aging regime.