The DP steel exhibits higher initial work hardening rate, higher ultimate tensile strength, and higher TS/YS ratio than a similar yield strength HSLA. Additional engineering and true stress-strain curves for DP steel grades are located in Figure 2-5 in the Advanced High-Strength Steels Application Guidelines.
DP and other AHSS also have a bake hardening effect that is an important benefit compared to conventional higher strength steels. The bake hardening effect is the increase in yield strength resulting from elevated temperature aging (created by the curing temperature of paint bake ovens) after prestraining (generated by the work hardening due to deformation during stamping or other manufacturing process). The extent of the bake hardening effect in AHSS depends on an adequate amount of forming strain for the specific chemistry and thermal history of the steel. Additional bake hardening information is located in Section 3.B.1.i. of the Advanced High-Strength Steels Application Guidelines.
In DP steels, carbon enables the formation of martensite at practical cooling rates by increasing the hardenability of the steel. Manganese, chromium, molybdenum, vanadium, and nickel, added individually or in combination, also help increase hardenability. Carbon also strengthens the martensite as a ferrite solute strengthener, as do silicon and phosphorus. These additions are carefully balanced, not only to produce unique mechanical properties, but also to maintain the generally good resistance spot welding capability. However, when welding the higher strength grades (DP 700/1000 and above) to themselves, the spot weldability may require adjustments to the welding practice. Current production grades of DP steels and example automotive applications:
- See more at: http://www.worldautosteel.org/steel-basics/steel-types/dual-phase-dp-steels/#sthash.gUsQmZy3.dpuf