  Metals are important structural materials for transport and the built
environment. Low carbon steels can fail through strain localisation due to the
role of interstitial solute atoms (such as carbon and nitrogen) interacting
with mobile dislocations, and this gives rise to the Portevin-Le Chatelier
effect and the formation of Luders bands. In this work, we use in-situ tensile
testing and observation with High Angular Resolution Electron Back Scatter
Diffraction (HR-EBSD) to explore deformation patterning in two Interstitial
Free (IF) steel samples. One of these steels was heat treated to trigger strain
localisation and Luders bands whilst the other was heat treated to homogenise
plastic strain and limit flow localisation. Our work reveals that flow
localisation at the macroscopic scale is closely correlated with differences in
the storage of dislocations at the microscale through analysis of the HR-EBSD
derived fields of stored Geometrically Necessary Dislocations (GNDs).
Homogeneous plastic flow correlates with more 'Face Centred Cubic (FCC)-like'
deformation patterning in these Body Centred Cubic (BCC) materials, where work
hardening is correlated with the association of dislocation networks which
interact with triple junctions and grain boundaries, and our in-situ tests
enable us to see how these fields develop. Our findings enable the modification
of steel processing routes, and micromechanical models, based upon information
obtained from these in-situ tests.
