A study has been made on the effects of inter-critical annealing temperature on the mechanical behavior of a low alloy dual phase Fe/0.083C/0.4Mn steel. Homogenization and normalization of the substrates via heat treatments were performed on low carbon-manganese steel. The direct annealing heat treatments were carried out at 735C, 755C, 795C and 830C, and suddenly quenched in cold water. Dual phase ferrite-martensite steel was obtained. Tensile and yield tests were determined through their relationship equation with hardness test at room temperature. Indentation analysis was carried out on the microstructure of each sample. The results revealed that the best mechanical properties in dual-phase steels, e.g., impact toughness and ductility, appear at the inter-critical temperature of 735C, highest strength at 755C, duplex microstructure were obtained when the temperature is higher than 800 C, with the highest ductility properties at 830C.