Low-Alloy Ultra-High Strength Cast Steels Prepared by a Quenching–Partitioning–Tempering Treatment

To synergistically enhance the strength and toughness of low-alloy cast steels, a quenching–partitioning–tempering (Q-P-T) heat treatment process was specifically performed based on the “Constrained Carbon Equilibrium” thermodynamic model. The effects of partitioning temperature on microstructure and mechanical properties were examined. The Q-P(210)-T approach successfully produced an ultra-high strength cast steel (48SiNiMnCrMoAl6-4-4-3-8-14) with a tensile strength exceeding 2000 MPa and an elongation greater than 19.0%. The microstructure of this cast steel consists of tempered martensite (TM), bainite, ferrite, and retained austenite (RA). During tensile deformation, dislocations from adjacent martensite are absorbed by the film-like RA, thereby alleviating stress concentration induced by dislocations. Meanwhile, the transformation-induced plasticity (TRIP) effect of the RA significantly enhances the toughness of the cast steel. Furthermore, the ultra-high strength of the cast steel is jointly ensured by the fine crystalline strengthening of the martensite and the precipitation strengthening of the transitional carbides in the microstructure of the cast steel. This work provides a good reference for the development of high-performance cast steels.