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.