Effects of Austenitising Conditions on the Microstructures and Mechanical Properties of Martensitic Steel with Dual Matrix Structure

A new high strength steel with dual matrix structure and exceptionally high toughness plus ductility have been produced by intermediate quenching of 0.22_wt % C microalloyed steel. The treatment consisted of initial austenitization and rapid quenching of the steel samples to achieve a fully martensitic state followed by annealing in the intercritical (α+γ) region of 730oC-810oC for the period of 30, 60 and 90_minutes. These samples were subsequently quenched to obtain dual phase microstructure containing varying proportions of ferrite and martensite constituents. The mechanical properties of the samples were measured according to ASTM standard and their microstructures were analyzed by optical microscopy. The experimental results show that martensitic dual phase (MDP) steel samples developed within the intercritical temperature range of 770–790oC revealed finer martensite and precipitate-free ferrite microstructure. The tensile and impact properties of the developed HMDP steels increased with intercritical annealing (ICA) temperatures, with an optimum properties obtained at 790oC mainly due to finer microstructure of the constituent phases and absence of carbide precipitate that permit ease of dislocation flow. A further increase in th