Abstract: Effects of two different quenching processes (delay quenching, intercritical quenching) on the microstructure and mechanical properties of a ferrite/martensite dual-phase steel after the same tempering treatment were studied by means of optical microscope, scanning electron microscope, transmission electron microscope and tensile and impact tests. The results show that the microstructure of the as-tempered steel quenched by the two different processes consists of ferrite, tempered martensite and M₂₃C₆ precipitates. Polygonal dual-phase structure is obtained by the delay quenching+tempering process, while fine lath structure is obtained by the intercritical quenching+tempering process. The yield strength and tensile strength of the as-tempered tested steel quenched by the two different processes decrease, while the yield ratio, elongation and impact absorbed energy increase. Compared with the delay quenching process, the yield strength and tensile strength of the as-tempered steel under intercritical quenching process are lower, while the yield ratio, elongation and impact absorbed energy are higher, which show that the intercritical quenching+tempering process can significantly improve the plasticity and toughness of the tested steel.

Key words: dual-phase steel, delay quenching, intercritical quenching, tempering, mechanical properties