| Abstract Scope |
This study investigates the synergistic effects of Mn, Ni, and Cu co-precipitation in quenched and tempered (Q&T) steels. Homogenized and forged steel blocks underwent Q&T treatment at 920℃ (quenching) and 650℃ (tempering). Microstructural analysis using SEM, TEM, MatCalc, and Thermo-Calc revealed Cu-rich precipitates, enhancing hardness and toughness. JMatPro-simulated CCT curves showed increased hardenability with higher Cu content, correlating with a larger volume fraction of degenerate pearlite. After 45 minutes of tempering, the steel exhibited high strength (811 MPa), ductility (19.35%), hardness (267±4 HV), and tensile toughness (146×10⁵ kJ/m³). The improved toughness is attributed to grain refinement from complex carbides and nano-sized shearable-Cu precipitates. The study further explores how varying Cu content affects mechanical properties and details the transformation of Cu precipitates from BCC (coherent) → 9R (semi-coherent) → FCC (incoherent) structures. Fractography and misfit analysis link microstructural evolution to mechanical behaviour. |