Dual-phase steel

Dual-phase steel (DPS) is a high-strength steel that has a ferrite and martensitic microstructure. DPS starts as a low or medium carbon steel and is quenched from a temperature above A₁ but below A₃ on a continuous cooling transformation diagram. This results in a microstructure consisting of a soft ferrite matrix containing islands of martensite as the secondary phase (martensite increases the tensile strength). Therefore, the overall behavior of DPS is governed by the volume fraction, morpology (size, aspect ratio, interconnectivity, etc.), the grain size and the carbon content. For achieving these microstructures, DPS typically contain 0.06–0.15 wt.% C and 1.5-3% Mn (the former strengthens the martensite, and the latter causes solid solution strengthening in ferrite, while both stabilize the austenite), Cr & Mo (to retard pearlite or bainite formation), Si (to promote ferrite transformation), V and Nb (for precipitation strengthening and microstructure refinement). The desire to produce high strength steels with formability greater than microalloyed steel led the development of DPS in the 1970s.