International Conference on Thermo Mechanical Processing - TMP 2026

Mechanical Property Comparison of Bainite-Based and Conventional Quenching and Partitioning (BQ&P vs Q&P) in a Medium-Carbon Steel

Not scheduled

20m

Austria Trend Parkhotel Schönbrunn

Oral Presentation Metallurgical Fundamentals of TMP

Speaker

Zeynab Aalipour Hafshejani (Materials and Mechanical Engineering, Centre for Advanced Steels Research, University of Oulu, Finland)

Description

Advanced high-strength steels are widely used in the automotive industry because of their excellent mechanical properties, which arise from their multiphase microstructure and the transformation-induced plasticity (TRIP) effect. Among advanced heat-treatment routes, quenching and partitioning (Q&P) has been extensively developed to produce retained austenite (RA)-containing microstructures with a favorable balance of strength and ductility. More recently, bainite-based quenching and partitioning (BQ&P) has attracted attention because bainitic ferrite may improve ductility while maintaining high strength. However, direct comparisons between conventional Q&P and BQ&P remain limited, particularly regarding RA fraction and mechanical performance.
In this study, the effects of bainite formation and partitioning temperature on mechanical properties (tensile and fracture toughness) were compared in a 0.4C–1.5Si–2Mn–1Cr–0.3Mo–0.2V (wt.%) steel, beside the microstructural characterization using FESEM-EBSD and TEM microscopies. Heat treatments were performed using a Gleeble thermomechanical simulator. For the Q&P route, a quench-stop temperature (QT) of 150°C was followed by partitioning (PT) at 200°C and 300°C for 1000 s. For the BQ&P route, samples were first held at 300°C for 400 s to allow bainitic transformation before quenching to 150°C, after which the same partitioning conditions were applied.
The results showed that the final RA fraction was similar in both routes. At 200°C partitioning, the RA fraction was 7.0% in Q&P and 7.5% in BQ&P, while at 300°C it increased to 17% in Q&P and 15% in BQ&P. BQ&P exhibited a higher yield strength than Q&P, increasing from 900 MPa to 1025 MPa at TP = 300°C and from 1229 MPa to 1294 MPa at TP = 200°C. However, ultimate tensile strength was slightly lower in BQ&P (1761 MPa) compared with Q&P (1804 MPa). Fracture toughness results showed no meaningful difference between the two routes. Overall, conventional Q&P provided comparable microstructural and mechanical performance with a simpler processing route.