Investigation on processing for a titanium-microalloyed hot rolled dual phase steel

Continuous cooling transformation curves were established and the influence of finish rolling temperature on the microstructure was investigated for a titanium-microalloyed dual phase steel through simulation experiment. A feasible process based on simulation experiment was obtained and confirmatory experiment was performed. It was found that pro-eutectoid ferrite could form in the steel when the cooling rate was less than 5℃·s^-1 at a temperature of 625 to 725℃. The amount of ferrite and martensite increased firstly and then decreased slightly with the increasing of finishing rolling temperature. A higher hardness of ferrite was obtained at a higher finish rolling temperature because of precipitation strengthening. Better performance with a tensile strength of 672 MPa and a yield ratio of 0.61 was obtained for the steel when the finish rolling and slow cooling temperatures were 840℃ and 700℃,respectively. The amount of this precipitation strengthening was about 78.5 MPa based on calculations.