Thermo-mechanical treatment of the C-Mn steel with Nb, Ti, V and B microadditions

Purpose: The paper presents the investigation results of the thermo-mechanical treatment parameters influence on the structure and mechanical properties of the low-carbon steel with Nb, Ti, V and B microadditions, destined for the weldable heavy plates production with the yield point above 960 MPa. Design/methodology/approach: Metallography, hot torsion test, tensile test, Charpy test have been used. Findings: It was found out that failing to attain the total static austenite recrystallization between the consecutive deformation stages results in a development of the segregation bands, causing the significant deterioration of the crack resistance of steel at the lowered temperature. Research limitations/implications: TEM investigations on structure of the steel after thermo-mechanical treatment were predicted. Practical implications: The investigation results obtained make it possible to work out the industrial scale technology for the weldable heavy plates with high strength and crack resistance at the lowered temperature, using the energy-saving thermo-mechanical method integrated with a ladle metallurgy of the molten steel and continuous slab casting. Originality/value: Adjusting the interval times between the deformation cycles in the multi-pass rolling process to the total recrystallization time of the plastically deformed austenite, by employing the retention shield, and the isothermal holding of the product at the temperature of the end of hot working for time t0.5 before quenching, offers the possibility of obtaining the homogenous austenite structure, and therefore, manufacturing the rolled products displaying high mechanical properties.