Effect Of Nano-Oxide Addition On Microstructure And Performance Of X80High Level Pipeline Steel

With the oil and gas continuously exploit and utilize，as the most economic, stable andconvenient transportation means of transporting oil and gas-long distance pipeline project’sconstruction has been paid more and more people’s attention. Because the pipelineengineering’s vile environment decide pipeline steel must have good comprehensivemechanical properties as used in pipeline construction project, such as good and lowtemperature plastic toughness, good weldability and lower QuQiang ratio, etc. So this paperbased on X80pipeline steel as the research object, though conducting vacuum smelting, platehot rolling and welding thermal simulation and other related experiment, it analysis andstudies the influence that applied nano-calcium and magnesium oxide makes on X80pipelinesteel microstructure and mechanical performance, the main research results of the studyshows that:(1) Each experimental steel after adding nano-calcium magnesium oxide: castmicrostructure which is composed of ferrite and bainite; the microstructure After rollingwhich is composed of ferrite; Welding HAZ microstructure which is composed of battenbunchy bainite and granular bainite.(2) When the nano-magnesium or calcium oxide addition content is0.01%, cast grainsize presents decreased trend, but its refinement effect is not apparent, acicular ferrite’squantity is fewer in the microstructure. when its addition content is0.05%, cast microstructureis relatively bulky, and to a certain extent inclusion appeared gathered phenomenon. when itsaddition content is0.02%, the quantities of acicular ferrite and bainite are increased obviouslyand their distributions are more uniform in cast microstructure, inclusion size is small, the castmicrostructure’s refinement effect is remarkable, and it contrasts with without addingnano-oxide steel, cast grain size is drops respectively from0.644mm to0.438mm and0.389 mm, the grain size refinement is respectively improve1.47times and1.66times.(3) All experimental steel’s plate after rolling, their mechanical performance indexes canexactly conform to the GB requirements of X80pipeline steel. And they are higher than theminimum tensile performance requirements of national standard. The experimental steel afteradding0.02%nano-CaO plate after rolling which yield strength of transverse and longitudinaldirection respectively reached to596MPa and585MPa, its tensile strength of the transverseand longitudinal direction reached to792MPa and788MPa, it contrasts with without addingnano-oxide steel, yield strength were respectively increased by14MPa and10MPa, tensilestrength were respectively increased by12MPa and10MPa. And the experimental steel at0℃,-20℃and-40℃, its impact toughness data also had increased greatly.(4) In the case of big line energy welding, when adding0.02%nano-CaO in steel, CaOinduced nucleation and growth of the acicular ferrite in HAZ microstructure, and it finallypromotes the formation of the acicular ferrite. And it makes M-A distribute in matrix andpresents bended Rod-shape, it is not more easy to cause crack compared with long strip M-Aunit and they make X80high level pipeline steel’s welding HAZ toughness has improvedgreatly.