Effect of Annealing Time on Microstructure Stability and Mechanical Behavior of Ferrite-Cementite Steel with Multiscale Lamellar Structure

Plain medium carbon steel with multiscale ferrite (α) + cementite (θ) lamellar structure was produced by warm rolling and subsequently annealing. The effect of annealing time on microstructural evolution was studied via scanning electron microscope and electron backscatter diffraction. The obtained results showed that the feature of multiscale lamellar microstructure remained virtually the same with annealing times from 10 to 60 minutes, while the increase of annealing time destabilizes the stability of the microstructure. The specimen annealed for 30 minutes demonstrated good combination of strength and ductility because of the improvement of strain strengthening ability. The strain hardening behavior was described by instantaneous strain hardening exponent ( $$ n_{i} $$ ) and modified Crussard–Jaoul (C–J) model. Furthermore, the respective strengthening contribution of grain refinement, sub-grain strengthening and cementite particles to the yield strength was investigated in detail.