Correlation of Tensile Properties and Strain Hardening Behavior with Martensite Volume Fraction in Dual-Phase Steels

In the present study, tensile properties, strain hardening and fracture behavior of dual-phase (DP) steels were correlated with martensite volume fraction ( V M ). A series of DP steels with different amounts of V M (28–50 %) were produced by cold rolling and subsequent intercritical annealing of a ferrite-pearlite starting structure. Hardness and tensile tests results of DP steels showed that variation of hardness, uniform elongation and total elongation with V M was linear and obeyed the rule of mixtures, whereas yield strength and ultimate tensile strength exhibited a nonlinear variation with V M . Analysis of strain hardening behavior of DP steels by the Hollomon analysis showed two stages of strain hardening corresponding to ferrite deformation and co-deformation of ferrite and martensite, respectively. The strain hardening exponent of first stage ( n I ) increased with increasing V M , while the strain hardening exponent of second stage ( n II ) as well as transition strain between the deformation stages decreased.