Strain rate sensitivity of nanocrystalline and ultrafine-grained steel obtained by mechanical attrition

High dense bulk specimens of 0.55% C steel with ferritic grain sizes within the nanocrystalline and ultrafine regimes have been produced from ball-milled iron powder through the warm consolidation process. The microstructure, the mechanical properties and the strain rate sensitivity parameter (m) were investigated for the different grain sizes obtained. A constant decrease of m was found as the grain size decreases within the ultrafine regime. In the nanocrystalline regime, on the contrary, as the grain size decreases a slight increase of m was observed.