Strain-hardening due to dispersed cementite for low carbon ultrafine-grained steels

摘要

Strain(work)-hardening in tensile tests was examined for low carbon steels with various ferrite grain sizes ranged from 0.4 to 16 mu m. The steels had microstructures composed of ferrite grains and dispersed cementite particles. They were fabricated through warm caliber bar-rollings with an accumulative area reduction of 93 percent. Strain-hardening rate at a given strain increased with an increase in volume fraction of cementite particles. The balance of yield strength and uniform elongation for ultrafine-grained structures could be improved by the dispersion of cementite particles. Effects of the cementite dispersion and the ferrite grain size on the strain-hardening rate can be roughly explained by the work-hardening model with GN-dislocation density. Strain-hardening design using dispersed cementites was proved to be effective in controlling ductility of the ultrafine-grained steels.