Stretching the mechanical properties in a 590MPa ferrite-martensite dual-phase steel through rapid heating

In the study described here, rapid heating was adopted to obtain ferrite/martensite dual-phase (DP) steels. An understanding of structure-property relationship was obtained through electron microscopy. The average ferrite grain size of steel with heating rate of 300 degrees C/s (HRA) was refined from 10.2 mu m to 4.3 mu m as compared to the conventional heating rate of 5 degrees C/s (CA) during continuous annealing. The morphology of martensite was changed from network-type along the ferrite grain boundaries to uniform distribution in the final DP microstructure. The HRA steel exhibited excellent mechanical properties, R-m - 712MPa, R-p0.2 - 438MPa, UEL - 15.7% and TEL - 23.3% and the product of strength and ductility (R-m x TEL) is 17,650MPa %. In comparison to the conventional continuous annealed steel (CA), there was 8.4% increase in ultimate tensile strength and 10.4% increase in total elongation. The variations of strength, elongation, strain hardening behavior and fracture mechanism for steel subject to different heating route are discussed in relation to the microstructure.