Duplex steel structure is mainly composed of ferrite and martensite, also known as martensitic duplex steel. With the characteristics of no yield extension, low yield strength, high tensile strength and good plasticity matching, it is expected to be the preferred material for the manufacture of expansion tubes in petroleum industry. The excellent properties of dual-phase steel are mainly determined by the morphology and quantity of martensite, and the quenching temperature has a decisive effect on the quantity of martensite in dual-phase steel.

The effect of quenching temperature on microstructure and mechanical properties of dual-phase steel was studied. The results show that with the increase of quenching temperature, the volume fraction of martensite increases gradually, resulting in the increase of yield strength and tensile strength. When quenching temperature is 820℃, duplex steel of expansion tube can obtain the best comprehensive properties.