No abstract

Dual-phase (DP) steels offer an outstanding combination of strength and formability as a result of their microstructure, in which a hard martensitic or bainitic phase is dispersed in a soft ferritic matrix. DP steels have a high ultimate tensile strength combined with a low initial yielding stress. The yield strength of DP steels is further increased by the paint baking, also called bake hardening (BH), process. In the current research, the effect of BH parameters, namely pre-strain, baking temperature, and holding time, on yield strength increment of DP steels with different martensite volume fractions is investigated. DP steels with 20 and 30% martensite volume fraction are pre-strained up to 5%, then they are baked at 100, 170, and 300 8C for various times. The results show that maximum yield strength is obtained as optimum values of BH parameters are applied. It is also found that at high values of baking temperature and holding time, martensite tempering effects prevail and yield strength increment decreases. The results also indicate that the increment of pre-strain enhances the Lüders band and decreases the yield strength increment.