Effect of carbon content on the martensite morphology, texture, and mechanical properties of dual-phase steels

In this study, the effect of carbon content on the grain size, martensite morphology, texture, and mechanical properties of dual-phase (DP) steels is investigated. Two plain low-carbon steels with different carbon (0.08 and 0.16 wt.%) were rolled (with 50% strain) and intercritical-annealed (at 770°C for 15 minutes). The results showed that the morphology of martensite in the DP1 (0.08 wt.% C) was elongated (lamellae); however, a chained network structure was formed in the DP2 (0.16 wt.% C). The main textures in the DP1 steel were Goss, Cube, and γ-fiber (<111>//ND), while the most important texture in the DP2 steel was Goss. The DP2 steel exhibited a higher yield strength (538 MPa vs. 437 MPa) and larger tensile strength (923 MPa vs. 704 MPa) compared to the DP1 sample due to its higher martensite fraction. On the other hand, the DP1 steel had a larger toughness (183 J/cm 3 vs. 126 J/cm 3 ) due to its deformable and elongated martensite. The true strain range for stage III in strain-hardening rate-true strain (Θ-ε) curves was much greater for the DP1 steel (0.148) compared to the DP2 sample (0.042), owing to the higher ductility and formability of martensite in the DP1 sample. Ductile fracture was dominant in both DP samples; however, some cleavage facets were observed in the DP2 steel due to the higher carbon content of the αʹ islands.