Effects of coiling temperature on microstructure and mechanical properties of Ti microalloyed steel

Compared with Nb and V microalloyed steel,Ti microalloyed steel has the lowest cost,so a lowcarbon Ti microalloyed hot roll strip steel has been designed. The microstructure and mechanical properties of the steels with different coiling temperature were investigated by utilizing SEM and TEM. The results show that the coiling temperature has a considerable influence on both the microstructure and mechanical properties. The microstructure was lath bainite and granular bainite when coiled at 300 ℃,and was granular bainite when coiled at 400 and 470 ℃. The yield strength and the tensile strength of the steel decrease first,and then increase with the increasing of coiling temperature,while the elongation appears opposite law. The changes of the mechanical properties were mainly depended on the phase transformation strengthening,precipitation hardening,as well as the size and shape of the M-A island. When the steel was coiled at 470 ℃,the yield strength and tensile strength reached 700 and 865 MPa respectively,and the elongation reached 18. 9%.