**5.2 Quenched and partitioned (Q&P) steels**

Quenched and partitioned (Q&P) steels are the result of the recent developments of third-generation AHSS steels. The elaboration of Q&P steels is partly based on the knowledge of duplex stainless steels and the quenching and partitioning process [44], as well as on the properties of medium manganese steels [45]. The Q&P steels usually contain carbon, manganese, silicon, nickel, and molybdenum alloying elements. The amount of alloying elements can be around 4%, which is much lower than that of in the second-generation AHSS. During heat treatment of Q&P steel, quenching is interrupted and is reheated for partitioning. With this reheating process, a unique microstructure is created containing 5–12% stable retained austenite, 20–40% ferrite, and 50–80% martensite.

Baosteel was one of the first companies to apply Q&P steels, initially with 980 MPa and later 1180 MPa strength [46]. It was demonstrated that a B-pillar reinforcement could be cold-formed using Q&P 1180. Auto/Steel Partnership (A/SP) also has tested Q&P 980 using GM's B-pillar die, proving that this steel has better formability and is less prone to edge cracking than DP 980.

Recently, Q&P steels were developed up to 2100 MPa tensile strength with 9% uniform elongation and about 13% total elongation. The elongation level of this steel is comparable to DP 980, which is a cold-formable grade.
