Simultaneous increase of ultimate tensile strength and uniform elongation of 30Si2MnCrMoVE ultra-high strength steel by hot deformation direct quenching and partitioning

In order to further improve the combination of strength and ductility for 30Si2MnCrMoVE ultra-high strength steel (UHSS), a thermomechanical treatment, named deformation direct quenching and partitioning (DQ&P), was carried out on it. The microstructure evolutions and mechanical properties of 30Si2MnCrMoVE UHSS treated by DQ&P were compared with those treated by conventional off-line quenching and tempering (Q&T) through various microscopic characterization methods and uniaxial tensile tests. Moreover, the effects of austempering temperature on the microstructure evolutions and mechanical properties of the studied steel after DQ&P process were also investigated. The results show that the DQ&P samples, although lower or slightly lower yield strength, possess significantly higher ultimate tensile strength due to higher work-hardening rate caused by high density dislocations and fine dispersed carbides. Moreover, DQ&P310 sample exhibit apparently higher uniform elongation than Q&T sample despite of comparable content of retained austenite due to more prone to transformation induced plasticity (TRIP) effect. The DQ&P process can increase the ultimate tensile strength by 267 MPa~423 MPa and the uniform elongation by 78%~85%, respectively, as compared to Q&T process, which indicates that DQ&P process may be a promising thermomechanical treatment method to improve the comprehensive mechanical properties of the studied steel. The strengths and elongations of DQ&P samples do not vary monotonously with the increase of austempering temperature, which are both closely related to the content of retained austenite.(c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).