Mechanical properties of an ultrafine grained C-Mn steel

The mechanical properties of an ultrafine grained 0.2% C–Mn steel, processed by large strain warm deformation and subsequent annealing, have been investigated. The microstructure consists of spheroidized cementite particles in an ultrafine ferrite matrix (average grain diameter≈ 1.3 µm). The steel shows an improved combination of strength and toughness when compared with corresponding coarse grained specimens. The reasonable ductility of the steel can be attributed to finely dispersed cementite particles which effectively increase the work hardening rate by the accumulation of geometrically necessary dislocations in their vicinity. The lower shelf energy is significantly higher and the ductile-to-brittle transition temperature is lower in the ultrafine grained steel than in the comparable coarse grained specimens. This may be due to the joint effect of grain refinement and delaminations in the ultrafine grained