In this research, the effect of manganese content on the microstructure and tensile properties of dual-phase steels was studied. At first, three low-carbon steels with fixed carbon and silicon and variable amount of manganese (0.76-2.3wt.%) were produced by melting and casting method. Then the cast steels were hot rolled in several stages to create sheets with a thickness of 2 mm. To create dual-phase ferritic-martensitic structure in steels, they were subjected to intercritical annealing process at three different temperatures of 750, 775 and 800 ℃ for 20 minutes and then quenched in cold water. According to the variables of intercritical annealing temperature and manganese content, different ratios of volume fraction of ferrite and martensite phases were created in steels. In order to study the role of manganese in dual-phase steels, these steels were subjected to microstructure and tensile properties. The relationship between tensile properties and microstructure was cleared.

Increasing Mn at a constant intercritical annealing temperature significantly increased the martensite volume fraction. Meanwhile, the effect of annealing temperature on the volume fraction of martensite was less. The uniaxial tensile test on steels showed that manganese reduces the ductility of steels due to the increase of martensite volume fraction, while it increases their strength. The effectiveness of tensile strength was more than yield strength.