Effect of microstructure on mechanical behavior for eutectoid steel with ultrafine- or fine-grained ferrite+cementite structure

A eutectoid steel with various ultrafine- or fine-grained ferrite matrix (α)+cementite particle (θ) structures was fabricated to explore the effects of the microstructural features on the mechanical behavior of hard particle-strengthened two-phase alloys. The effect of microstructure on the parameters of an analytical model and the mechanical behavior for the eutectoid steel with ultrafine- or fine-grained α+θ structure were analyzed basing on statistical data and physical metallurgy. The results showed that the rate of dislocation-storage caused by ferrite grain boundaries and cementite particles is approximately a microstructural constant and is proportional to the dislocation mean free path. The larger ferrite grains and the larger volume fraction of intragranular cementite particles are beneficial to obtaining a lower rate of dynamic recovery when ultrafine- or fine-grained α+θ structures with an equal dislocation mean free path, and the uniform elongation increases with the decrease in the rate of dynamic recovery. Moreover, the ultimate strength is closely related to the effective dislocation mean free path including both roles of the storage and the recovery of dislocations. It is feasible to design a microstructure consisting of ultrafine- or fine-grained ferrite matrix and tiny cementite particles mainly within grain interior to possess an enhanced strength-plasticity synergy for the eutectoid steel.