MICROSTRUCTURAL EVENTS OF MACROSCOPIC STRAIN LOCALIZATION IN PRESTRAINED TENSILE SPECIMENS

Attempts have been made to correlate macroscopic strain localization with micro-mechanisms of deformation in low carbon steel. Particular attention was paid to the development of the internal structure of macroscopic deformation bands after a change of deformation path. The development of macroscopic strain localization was followed by the photographic technique. The mechanism of deformation was studied in terms of strain hardening rate and strain rate sensitivity along with structural SEM and TEM observations. The major conclusions are as follows: macroscopic strain localization is preceded by a microscopic flow instability (formation of course slip bands - (CSB's). CSBs start to form at an early stage of the deformation and they evolve into micro-shear bands - (MSBs), leading to the formation of a zone of macroscopic strain localization - (MSI). Within the MSL zone the deformation appears to be pseudo-homogeneous; it is composed of homogeneous and heterogeneous (CSBs, MSBs) components. The analysis of the shape of a load elongation curve shows that the corresponding stress-strain curve has a step-like character with plateaus representing nucleation and subsequent spreading of the deformation bands and a hardening region caused by the deformation within an already formed MSL zone.