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In this work, the precipitates in Ti−Mo−V steel were systematically characterized by high-resolution transmission electron microscopy (HRTEM). The thermodynamics and kinetics of precipitates in Ti−Mo and Ti−Mo−V steels were theoretically analyzed, and the effect of vanadium on the precipitation behavior was clarified. The results showed that the precipitation volume fraction of the Ti−Mo−V steel was significantly higher than that of Ti−Mo steel. The randomly dispersed precipitation and interphase precipitation (Ti, Mo, V)C particles coexisted in the Ti−Mo−V steel. When the temperature was higher than 872 °C, the addition of vanadium could increase the driving force for (Ti, Mo, V)C precipitation in austenite, resulting in an increased nucleation rate and shortened incubation period, promoting the (Ti, Mo, V)C precipitation. When the temperature was lower than 872 °C, the driving force for (Ti, Mo, V)C precipitation in austenite was lower than that for (Ti, Mo)C precipitation, and the incubation period of (Ti, Mo, V)C precipitation was increased. Moreover, it was also found that the precipitated-time-temperature curve of (Ti, Mo, V)C precipitated in the ferrite region was "C" shaped, but that of (Ti, Mo)C was "ε" shaped, and the incubation period of (Ti, Mo, V)C was significantly shorter than that of (Ti, Mo)C. [ABSTRACT FROM AUTHOR]

In this paper, the low-temperature hot rolling was conducted on air-cooled medium manganese martensitic steel, utilizing a finishing rolling temperature (FRT) that was significantly lower than the conventional used temperature. The effect of FRT on the microstructure, mechanical properties and wear resistance was systematically investigated. The results revealed that the pancaked austenite grain formed after low-temperature hot rolling could still be completely transformed into martensite structure under air-cooled condition. The lower FRT significantly refined the martensite multi-level microstructures, increased the grain boundaries density and dislocations density, and promoted the nano-scaled V(C, N) precipitation. These resulted in enhanced refinement strengthening, dislocation strengthening and precipitation strengthening. Compared to the FRT-900 sample, the FRT-700 sample exhibited increased yield strength, tensile strength, and Brinell hardness, with values rising from 973 MPa, 1526 MPa, and 454 HB to 1174 MPa, 1701 MPa, and 482 HB, respectively. In addition, the refined microstructure effectively increased the dimple region in the fractography of impact samples, preventing the propagation of crack and thereby enhancing the impact absorbing energy. Consequently, the impact absorbed energy at −40 °C of experimental steel was increased from 28 J to 38 J, while also increasing strength. Moreover, the low-temperature hot rolling effectively increased the surface hardness of the experimental steel, inhibited abrasive embedding and improved impact wear resistance. The mass loss rates of low-temperature hot rolling samples were 0.052 mg/s and 0.063 mg/s under the impact energy of 1 J and 2.5 J, respectively. • The low-temperature hot rolling was conducted on air-cooled medium manganese martensitic steel, and its finishing rolling temperature was substantially lower than the temperature commonly used. The pancaked austenite grain formed after low-temperature hot rolling could still be completely transformed into martensite structure under air cooling condition. • The low-temperature hot rolling significantly can refine the martensite multi-level microstructures, increase the grain boundaries density and dislocations density. Meanwhile, it can promote the nano-scaled V(C, N) precipitation and inhibit Fe 2 C carbides. • The low temperature hot rolling can improve impact absorbed energy (−40 °C) while increasing the strength and hardness of the experimental steel. And The effect of finishing rolling temperature on the strengthening, toughening mechanism and wear resistance was systematically investigated. [ABSTRACT FROM AUTHOR]