Abstract
Effect of cementite volume fraction on stress–strain relations in ultrafine-grained ferrite-cementite (FC) steels was studied. The ultrafine-grained FC steels with various cementite volume fractions between 0.3 and 13.7% and average ferrite grain size of about 0.25 μm were prepared by carbon steels. Lower yield stress, tensile strength and flow stress increased with increasing of the volume fraction of cementite. Effect of dispersed cementite on the work-hardening rate in the present ultrafine-grained FC steels was discussed by using Ashby's theory. It is very important for the work-hardening rate of the ultrafine-grained FC steels to control or maintain the size of finely dispersed cementite. By using the experimental results, true stress (σpdl) and true strain (εpdl) at plastic deformation limit were calculated. Effects of the volume fraction of cementite and the grain size on the σpdl−εpdl balance were summarized from the viewpoints of yield strength and the work-hardening rate at σpdl.
