Abstract: The process of aircooling followed by ultra fast cooling after hotrolling was used to investigate the effects of coiling temperature on the microstructure and mechanical properties of a ferrite/bainite (F/B) dual phase steel. The results show that the volume fraction and the grain size of ferrite are in the rage of 857%-878% and 36-37 μm， respectively， almost independent of the coiling temperature. Lowering coiling temperature from 504 ℃ to 250 ℃， the dominant hard phase was transformed from bainite to martensite， resulting in the ultimate strength up to 597 MPa from 510 MPa， the yield strength down to 389 MPa from 475 MPa， but the elongation without significant change (322%-350%). Besides， the deformation compatibility between ferrite and bainite or martensite is weakened with the decrease of the coiling temperature， which induces the nucleation in advance， accelerates growth and coalescence of microvoids， so the hole expansion property is deteriorated and the hole expansion ratio is reduced from 1014% to 524%.

Key words: hotrolled F/B dual phase steel, newgeneration thermomechanical control process (NGTMCP), ultra fast cooling, coiling temperature, microstructure evolution, mechanical property, hole expansion property