Combined effects of silicon content, prior deformation and partitioning conditions on retained austenite and mechanical properties of a quenched and partitioned 0.4% C advanced high-strength steel

Quenching and Partitioning (Q&P) has become one of the established processing routes for producing advanced high-strength steels (AHSS), owing to its ability to engineer microstructures that balance between high strength and ductility through retained austenite (RA) stabilization. However, the alternative Deformation–Quenching and Partitioning (DQ&P) pathway remains relatively underexplored. This study investigates the combined effects of silicon content, prior deformation, and partitioning parameters on RA stabilization and mechanical behavior in two medium-carbon steels (0.4C–2Mn–XSi–1Cr–0.02Al–0.49Ni, wt.%) with Si contents of X=0.25 wt.% (L-Si) and X=1.5 wt.% (H-Si). Three deformation passes (true strain ≈ 0.2/pass) were applied at 850 °C prior to quenching. Partitioning was performed at 250 °C and 300 °C for 1000 s, with additional holding times (10–10000 s) examined for selected conditions. Microstructural evolution was characterized using dilatometry, electron microscopy, and X-ray diffraction; mechanical behavior was evaluated via tensile testing. The high Si content effectively suppressed cementite precipitation and bainite formation, enabling higher RA fractions of ∼20 vol.% at 300 °C and ∼17 vol.% at 250 °C, with 1000 s identified as the optimal partitioning time. In the low-Si steel, ∼14 vol.% RA was obtained at 250 °C after 1000 s, and 17 vol.% after 10000 s. Applied deformation resulted in higher RA fractions compared to non-deformed Q&P steels. However, up to 23 vol.% bainite formed in the low-Si steel at 300 °C, consuming the available austenite. Both steels exhibited pronounced TRIP behavior. The high-Si steel partitioned at 300 °C (1000 s) achieved an excellent strength–ductility balance (1822 MPa and 9.3% elongation), while the low-Si steel partitioned at 250 °C also demonstrated competitive performance, highlighting the positive role of deformation. • DQ&P processing increases retained austenite stability compared with Q&P • High Si (1.5 wt.%) suppresses cementite and bainite, stabilizing up to ∼20 vol.% RA • Prior deformation refines austenite grains and enhances RA stability in low-Si steel • Optimal properties achieved: UTS ≈ 1.8–2.0 GPa with ∼8–9% elongation