Effect of tempering temperature on microstructure and properties of Ti-Mo-V microalloyed steel

Under the backdrop of the "dual carbon" goal, developing lightweight steel materials that combine high strength with excellent ductility and toughness is a key focus for the automotive industry. A combined process route of "low-temperature coiling + tempering" was employed to tailor the precipitation behavior of microalloying second phases. The effects of tempering temperature on the microstructural evolution, precipitation behavior, and mechani‑cal properties of Ti-Mo-V microalloyed steels were systematically studied. Results indicate that after tempering at 600,650,700,720 ℃, the microstructure of the experimental steel remains ferrite and granular bainite. Ferrite grain size shows no significant change, while granular bainite gradually decomposes. During tempering, a large number of V-enrich（Ti, Mo, V）C particles precipitate in the matrix, with their average size and volume fraction increasing from 4. 93 nm and 0. 205% at 600 ℃ to 8. 73 nm and 0. 517% at 720 ℃. Theoretical analysis indicates that elevated temperatures reduce interfacial energy between（Ti, Mo, V）C and ferrite matrix and enhance microalloying element diffusion rates, shortening the precipitation nucleation period of（Ti, Mo, V）C by approximately 3 orders of magni‑tude. However, this also accelerates（Ti, Mo, V）C coarsening, increasing its coarsening rate from 0. 088 nm³/s^1/3 at 600 ℃ to 0. 681 nm³/s^1/3 at 720 ℃, thereby diminishing the strengthening effect. At a tempering temperature of 700 ℃, the experimental steel achieves peak microhardness of 333 HV and maximum precipitation strengthening of 287 MPa, representing a 72 MPa improvement over the hot-rolled condition. This provides theoretical guidance for controlling the microstructure and properties of Ti-Mo-V microalloyed ultra-high-strength steels.