Quenching and Partitioning (Q&P): A Modern Route to Strong, Ductile Sheet

Quenching and Partitioning (Q&P) is a heat treatment that produces a martensite + retained-austenite microstructure with tensile strengths of 800-1500 MPa and high ductility - the basis of 3rd-generation AHSS. Speer et al. (2003) described the principle: after an interrupted quench to a temperature above Ms, carbon partitions from supersaturated martensite into surrounding austenite, stabilising it against transformation during the quench to room temperature.

Edmonds et al. (2006) reviewed processing-microstructure-property links and showed that carbon-enriched retained austenite gives the TRIP-like ductility that makes Q&P sheet formable for automotive body structures. Because it avoids expensive alloying, Q&P is cheaper than TWIP while closing the strength-ductility gap. Clarke et al. (2004) modelled the carbon partitioning kinetics that set the process window.

For buyers of AHSS strip and pressings, Q&P grades (for example USIBOR-style and new QP980/QP1180) offer lightweighting with formability. JLHSteel can source Q&P and other 3rd-generation AHSS and advise on forming limits.

References
1. Speer, J.G., Edmonds, D.V., Rizzo, F.C., Matlock, D.K. (2003). Partitioning of carbon from supersaturated ferrite in low-alloy steels. Current Opinion in Solid State and Materials Science 7(3): 153-159. https://doi.org/10.1016/S1359-0286(03)00028-4
2. Edmonds, D.V., He, K., Rizzo, F.C., De Cooman, B.C., Matlock, D.K., Speer, J.G. (2006). Quenching and partitioning martensite - a novel steel heat treatment. Materials Science and Engineering A438-440: 25-34. https://doi.org/10.1016/j.msea.2006.02.133
3. Clarke, A.J., et al. (2004). Carbon partitioning to austenite during quenching and partitioning. Scripta Materialia 54(2): 279-283.