Microstructure and Properties of High Strength X100 Pipeline Steel with Dual Phase Through Controlled Rolling and Cotrolled Cooling

In order to improve the grade and ductility of pipeline steel in petroleum transportation,high grade pipeline steel X100 was trial-produced in lab using ultralow-carbon microalloy by cooling with three stages after controlled rolling.The microstructure and mechanical properties of the steel were analyzed.The results show that during tensile test the steel had high comprehensive mechanical properties as follows:the yield point was unconspicuous,yield strength was up to 770 MPa,yield-to-strength ratio was 0.80,elongation was up to 21.3% and impact energy at -20℃was 179 J.All the properties could meet standard requirements.Dislocation recovery, sub-grain formation,deformation-induced precipitation,acicular ferrite and lath bainite transformation,precipitation growth and carbide accumulation occurred in the steel during the cooling process.The microstructure was dualphase of acicular ferrite and lath bainite with a small amount of M-A islands and twins.