New insights into the relationship between dynamic softening phenomena and efficiency of hot working domains of a nitrogen enhanced 316L(N) stainless steel

Abstract

In the present study, the dynamic recrystallization (DRX) behavior of a nitrogen enhanced 316L(N) stainless steel (with 0.14wt% N) has been studied in the temperature range of 1073–1423K and strain rate range of 0.001–10s−1 to understand the correlations between dynamic softening phenomena and efficiencies of hot working domains in the processing map. DRX fractions and the grain sizes in each condition were evaluated to develop DRX map and to study the grain growth. It was observed that the efficiency peaks of the stable domains are associated with increase in DRX fraction in the low temperature domain, increase in both DRX fraction and grain size at the medium temperature domain, and increase in grain size after saturation of DRX in the high temperature domain. Microstructures corresponding to high temperature unstable domain did not reveal any sign of conventional instabilities, instead show substantial amount of DRX grains. However, with increase in thermal energy neither a measurable increase in DRX fraction nor grain growth was observed. This mismatch between the energy input (through increase in temperature) and energy dissipation (through metallurgical phenomena) fulfills the instability criterion of dynamic materials model in this domain.