Relationship between microstructure and yield strength for plain carbon steel with ultrafine or fine (ferrite+cementite) structure

Plain carbon steels with different ultrafine or fine-grained ferrite matrix (α)+cementite particle (θ) structures were formed through thermo-mechanical processes. Scanning electron microscopy was used to analyze the initial microstructural parameters, and the dislocation morphology was analyzed by transmission electron microscopy. A relationship between the microstructural parameters and yield strength was established for plain carbon steel with an ultrafine or fine (α+θ) structure. The results indicated that the yield strength of plain carbon steel with an ultrafine or fine (α+θ) structure had a direct relationship with the grain size of the ferrite matrix and the size, volume fraction and location of cementite particles, and the enhancement in yield strength caused by the cementite particles was improved with the increase in carbon content or the particle-refinement.