The interfacial morphologies play a crucial role in mechanical properties of laminated/bimetal composite. This study investigates the effects of heat treatments on the interfacial characteristics, mechanical properties and fracture behaviour of a 2205 duplex stainless steel/AH36 carbon steel bimetal composite with varying interface situations fabricated by the hot-rolling and subsequent heat treatments. The bimetal composite was annealed from 850 °C to 1150 °C in steps of 100 °C with soaking 1 h. Heterogeneities of grain size and element concentration exist in the microstructural evolution of bonding zone adjacent to interface after annealing treatments, which were observed by the optical microscope and scanning electron microscope (SEM) coupled with the energy dispersive X-ray spectroscopy (EDS). It was found that the diffusion transition zone of Cr and Fe alloy elements between component 2205 and AH36 steel layers present an increasing trend with the rise of annealing temperature. The results of conventional, shear and compact tensile test indicate that the tensile strength of 2205/AH36 bimetal composite gradually decreases but the fracture elongation increases with the rising annealing temperature, the thicker alloy element diffusion zone results in the stronger interfacial shear strength and better ductility of bimetal composite, but the thick and strong interface has less positive effect than the mechanical properties of bimetal composite itself on preventing the fatigue crack growth across the interface.