Enhancement of mechanical properties by changing microstructure in the eutectoid steel

The different microstructures of eutectoid steel were analyzed with SEM and its corresponding room-temperature tensile tests were carried out. The results show that the ultrafine (α+θ) duplex structure consisting of ferrite matrix (α) with grain size of about 1 μm and dual-size distributed cementite particles (θ) could be formed by hot deformation of undercooled austenite and subsequent annealing. Moreover, the mixed microstructures consisting of polygonal ferrite grains with size of about 2 μm and fine pearlite colonies could be also obtained by this process under different conditions. Although the yield strength and total elongation of ultrafine (α+θ) duplex structure increase markedly, its tensile strength decrease obviously comparing to that of lamellar pearlite. The lower work-hardening rate at the beginning of uniform plastic deformation is probably responsible for tensile strength decrease in the ultrafine (α+θ) duplex structure. Moreover, the tensile strengths and total elongations of mixed microstructures are both larger than that of ultrafine (α+θ) duplex structure and lamellar pearlite due to their well work-hardening capabilities.