Microstructure Features and Tensile Properties of a Recent Ultra-High-Strength Steel via Two-Step Quenching and Partitioning Process

The two-step quenching and partitioning process is an excellent heat treatment regime that improves the strength and toughness of various steel alloys. This study explores the potential of developing ultra-high-strength steel with good ductility from a novel 0.37C-3.65Mn-0.65Si-0.87Al-1.5Ni-0.05P, wt.% steel alloy through a two-step quenching and partitioning regime. The steel was produced by full austenitization followed by quenching to a temperature below the martensite start temperature (80 and 120 °C) and then partitioning at 450 °C for different durations (20 s to 180 s). The microstructure of all heat-treated specimens consisted of tempered primary martensite, bainite, retained austenite, and secondary martensite. Quenching at 80 °C for 140 s showed the highest elongation and strength elongation balance of 15% and 18.86 GPa.%, respectively, with a high ultimate tensile strength of 1245.3 MPa. The tensile properties of specimens quenched at 120 °C were lower than those quenched at 80 °C.