The term “dual-phase steel” refers to a group of steels consisting of a soft ferrite matrix and 3–30 vol.% of hard martensite islands. These steels are widely used for automotive applications. DP
steels have a number of
unique properties, which include a low elastic limit, high initial strain-hardening rate, continuous yielding, high tensile strength and high uniform and total elongation. Moreover, DP steels exhibit
a bake-hardening (BH) effect, i.e.
the yield strength increases upon aging at paint-baking temperatures (ca. 170 °C) after forming, giving rise to improved dent and crush resistance. The austenite-to-martensite phase transformation
bears the main influence on the
mechanical properties of dual-phase steels. This phase transformation involves a volume expansion of 2–4%, causing an elastically and plastically deformed zone in the ferrite adjacent to
martensite.