Effect of Intercritical Rolling on Microstructure, Mechanical and Corrosion Properties of the Dual Phase X70 American Petroleum Institute Pipeline Steel

The effect of intercritical annealing heat treatment on mechanical and corrosion properties of fer-rite/martensite dual-phase steels with and without deformation by rolling has been investigated in this study. The X70 steel was rolled at intercritical temperatures (760 and 800 °C) with 30% amount of reductions followed by water quenching in order to produce dual-phase microstructure. The experimental results show that microstructures, mechanical and corrosion properties and were strongly affected by intercritical rolling conditions. It is established that the intercritical rolling provides a fibrous structure, and improves the mechanical and corrosion properties of X70 dual phase steel. It was found that after intercritical rolling (DQR), grain refinement and hardness improved significantly compared to intercritical heat-treated steel without rolling (DQ). A carefully conducted comparison of resistance corrosion of the representative specimens obtained after (DQ) and (DQR) treatments has been studied. (DQR) treatment shows better corrosion resistance than (DQ) treatment. The microstructure, mechanical and corrosion properties of the rolled X70 dual phase steel were investigated by optical microscopy, scanning electron microscopy, hardness tests and electrochemical measurements.