Relationship between yield strength and grain size for a bimodal structural ultrafine-grained ferrite/cementite steel

A bimodal ferrite grain size distribution was developed in the microstructure of a warm-rolled ultrafine-grained ferrite/cementite steel by annealing. The yield strength could be illustrated by the Hall–Petch relation, where the appropriate grain size was the average ferrite grain size determined from the area fraction of the inverse of the average grain size in both the large- and small-sized regions.