Study On Rolling Processes On Microstructure And Performance Of X80 Pipeline Steel

In recent years,with the development of the economy the demand for energy has been increasing and oil and gas resources is increasingly scarce,and the development of oil and gas fields extends into the large displacement environment of frequent geological disasters,such as the polar,ocean and frozen soil.Traditional pipeline steel's ability of resisting to deformation is poor,and it is easy to bend,sway and even rupture,easy to cause significant loss and safety loophole.In order to overcome the potential threat caused by the large displacement of the environment,deformation pipeline steel was put forward in time.Different from traditional pipeline steel and dual phase steel,deformation pipeline steel is designed by multivariate microalloyed of low carbon and ultralow carbon and specially TMCP,and will obtain more uniform B + F or B + M/A.Soft phase ensures yield strength,and hard phase provides tensile strength.it will achieve excellent obdurability and good deformation ability to the tradition pipeline steel,and enhance the use safety.The deformation pipeline steel was studied in this paper.In order to obtain different volumes of F and B,some paramenters are controlled,including austenitizing temperature,initial rolling temperature,last rolling temperature,holding time and cooling method.Tensile test and hardness test are done to abtain the the mechanical performance indexes of different process such as yield strength,tensile strength and hardness.The influence of different paramenters to microstructures and deformantion is investigated by OM?SEM?TEM and so on.The microstructures show that: Lower Austenitizing temperature,lower initial rolling temperature,lower last rolling temperature,longer preservation time can promote ferrite transformation,increase the volume fraction of ferrite,and be good for the increase of Sv.The quicker cooling speed reduces the volume fraction of ferrite content,increases the volume fraction of bainite.The mechanics performance test show that:the strength,the yield ratio and the hardness of the testing is decreasing with the increase of the volume fraction of ferrite.Grain refinement can improve the yield strength,the tensile strength and hardness;Precipitation strengthening is one of the most effective ways of strengthening pipeline steel;the small and dispersed precipitation can improve the yield strength and tensile strength.