INFLUENCE OF MICROSTRUCTURES OF EUTECTOIDSTEEL ON ROOM TEMPERATURE WORKHARDENING BEHAVIOR

Steels with ultrafine (α+θ) duplex structure, consisting of ferrite matrix (α) with average grain size of about 1 μm and dispersed cementite particles (θ), have been investigated widely in recent years for making better the work–hardening capability of ultrafine–grained steels. In fact, the ratio of yield strength to tensile strength for plain carbon steels with ultrafine (α+θ) duplex structure is commonly larger than 0.85. For structural material, the low ratio of yield strength to tensile strength is beneficial to absorb external energy and delay the occurrence of destruction. However, the ratio of yield strength to tensile strength is still relatively high for steels with ultrafine (α+θ) duplex structure to act as the structural material. Namely, the work–hardening capability of ultrafine (α+θ) duplex steel needs further improving. It could be feasible for improving the work–hardening capability of ultrafine (α+θ) duplex steel to change the form, size and distribution of the cementite. Therefore, it is necessary to investigate the work–hardening behavior of steel with different cementite states. In the present research, four different microstructures of eutectoid steel were obtained by different thermo–mechanical treatments, i.e., lamellar pearlite, spheroidized pearlite, ultrafine (α+θ) duplex structure and fine–grained (α+θ) duplex structure. The effect of different microstructures on the room– temperature work–hardening behavior of the eutectoid steel was analyzed using room temperature tensile tests, SEM and TEM. The results indicated that the work–hardening characters of lamellar pearlite, * FRF–TP–12–135A !" AE : 2012–08–24, !! AE : 2012–12–24 #$ : % , , 1986 !", #" DOI: 10.3724/SP.J.1037.2012.00503