Microstructural effects and mechanical response of microalloyed ferrite and austenite subjected to metal forming at extremely different rates of deformation

Abstract

The mechanical behaviors and microstructures of severely deformed microalloyed austenitic M_A and ferritic M_F steels were analyzed in wires drawn from wire rods (6.5 mm in diameter) down to the final diameter of 0.75 mm. The deformation induced microstructures in the cold drawn wires under “static” (low speed wire drawing) and “dynamic” (high speed wire drawing) conditions were compared and analyzed. The analysis has been focused on a detailed characterization of the effects of microalloying on the dislocation substructure development and the in-situ recrystallization. The correlations between mechanical behavior and dislocation substructure development with increasing deformation reveals that precipitation strengthening and microstructure refinement are the dominating mechanisms that control the mechanical behaviors of wires, especially in those subjected to deformation under dynamic loading conditions. An approach has been presented to model the evolution of work hardening process during complex deformation. Additional advantage of the presented approach is its capability of tracking evolution of dislocation density during the deformation process. The changes of dislocation density calculated for both materials show similar behaviour, but higher values of the dislocation densities were observed in the specimens of M_F than in the case of M_A.