Influence of rapid heating process on the microstructure and tensile properties of high-strength ferrite–martensite dual-phase steel

Three low-carbon dual-phase (DP) steels with almost constant martensite contents of 20vol% were produced by intercritical annealing at different heating rates and soaking temperatures. Microstructures prepared at low temperature (1043 K, FH1) with fast-heating (300 K/s) show banded ferrite/martensite structure, whereas those soaked at high temperature (1103 K, FH2) with fast heating reveal blocky martensite uniformly distributed in the fine-grained ferrite matrix. Their mechanical properties were tested under tensile conditions and compared to a slow-heated (5 K/s) reference material (SH0). The tensile tests indicate that for a given martensite volume fraction, the yield strength and total elongation values are noticeably affected by the refinement of ferrite grains and the martensite morphology. Metallographic observations reveal the formation of microvoids at the ferrite/martensite interface in the SH0 and FH2 samples, whereas microvoids nucleate via the fracture of banded martensite particles in the FH1 specimen. In addition, analyses of the work-hardening behaviors of the DP microstructures using the differential Crussard–Jaoul technique demonstrate two stages of work hardening for all samples.