Annealing behaviour and mechanical properties of severely deformed interstitial free steel

The evolution of microstructure, micro-texture and mechanical properties during isothermal annealing of an ultrafine grained interstitial free (IF) steel processed by Equal Channel Angular Pressing (ECAP) followed by 95% cold rolling (CR) was studied. Microstructure and micro-texture changes were characterised by Electron Back-Scattering Diffraction while mechanical properties were assessed by shear punch and uniaxial tensile testing. During annealing, homogeneous coarsening via continuous recrystallisation is accompanied by the retention of a sharp α-fibre rolling texture and a decrease in area fraction of high angle grain boundaries from ∼80% to ∼40% due to texture clustering and orientation pinning. Failure during uniaxial tension occurred without post-necking elongation after CR. Upon annealing, an evolution from stress-drop soon after yielding to a return to continuous yielding and increased work hardening was observed. Good agreement is found between experimental and estimated strengths and total elongations derived from SPT and tensile data. Tensile characteristics and mechanical properties depend on both, grain size and area fraction of HAGBs.

► Microstructure and micro-texture evolution indicates continuous recrystallisation.
► HAGBs decrease from ∼80 to ∼40% due to texture clustering and orientation pinning.
► Characterisation of correlation between tensile and shear punch tests.
► Tensile behaviour evolves from stress drop to continuous yielding a work hardening.