Microstructure and mechanical properties after annealing of equal-channel angular pressed interstitial-free steel

The evolution of microstructure, microtexture and mechanical properties during isothermal annealing of an ultrafine-grained interstitial-free steel after eight passes of route BC room temperature equal-channel angular pressing (ECAP) was studied. The microstructure and microtexture were characterized by electron back-scattering diffraction, and mechanical properties were assessed by shear punch and uniaxial tensile testing. Homogeneous coarsening via continuous recrystallization of the ECAP microstructure is accompanied by minor changes in the ∼63% high-angle boundary population and a sharpening of the original ECAP texture. This is followed by abnormal growth during the final stages of softening due to local growth advantages. Linear correlations between shear and tensile data were established for yield, ultimate strength and total elongation. After yield, the changes in uniaxial tensile behaviour from geometrical softening after ECAP to load drop, Lüders banding and continuous yielding after annealing is attributable to a coarsening of the microstructure.