On the Effect of Q&P Processing on the Stretch-flange-formability of 0.2C Ultra-high Strength Steel Sheets

Continuous weight reduction and increased safety requirements of vehicles have driven the automotive industry to design advanced high strength steels (AHSS) exhibiting high strength and good ductility.1) The first generation of AHSS refers to Dual-Phase (DP), Transformation Induced Plasticity (TRIP), and Martensitic (M) steels, and the second generation of AHSS consists of austenitic steels such as Twinning-Induced Plasticity (TWIP) steels.1,2) The third generation of AHSS, produced by Quenching and Partitioning (Q&P), is meant to provide a better strength-ductility compromise compared to the first generation, with lower cost than the second generation.3–5) The Q&P heat treatment, proposed by Speer et al. in 2003, consists of an interrupted quench between the martensite-start temperature (Ms) and the martensite-finish temperature (Mf) after full austenitization or intercritical annealing. The first quench is followed by a partitioning step aimed at stabilizing the austenite through carbon enrichment. In order to maximize carbon partitioning from martensite to austenite, competing mechaOn the Effect of Q&P Processing on the Stretch-flange-formability of 0.2C Ultra-high Strength Steel Sheets