In this study, the kind of thermo-mechanical processing, martensite processing, was investigated. At first for optimizing the Dual-phase heat treatment, the low-carbon-Nb steel with appropriate chemical composition, were homogenized at 1100°C for 3 hours and then forged at 1000°C to 50% reduction. The detection of intercritical temperatures was performed by the dilatometery test. The specimens of dual-phase steels with variety percent of martensite phase and grain size were cold rolled to 20-80% reduction, and then annealing at 400-600°C for 30 miniutes was carried out. Microstructural observations showed that grain size and amount of martensite phase varied with different holding time and temperature in dual-phase region. The specimen that held in 880°C for 5 minutes, had lowest grain size and percent of martensite. By increasing the holding temperatures, strength increased, but by increasing holding time, strength decreased. Cold rolling to 80% and annealing of the specimen that was produced at 920°C for 300 seconds increased tensile strength to 810 MPa with adequate uniform elongation to 12.2 %.
