Effect Of Rare-earth Ce On The Microstructure And Properties Of X80Pipeline Steel

In this paper, based on the second line project of the “West-to-East Natural GasTransmission Project” are all made of X80pipeline steel, combined with abundant rare earthresources advantage, baotou area. With the different contents of rare earth in X80pipelinesteel have been smelted in the laboratory by vacuum induction furnace. We have studied theinfluence of the rare earth Ce on the microstructure, strength and toughness, and corrosionbehavior in saline soil of the X80pipeline steel by metallographic observation, mechanicalperformance experiment and the korla soil simulation solution soaking experiments. We canprovide the basis data for the development of rare earth steel, the improvement of theperformance of pipeline steel.The experimental results show that after adding rare earth Ce, microstructure of X80pipeline steel have been changed from polygonal ferrite to acicular ferrite, extended grainboundary, refined grains, inhibiting the formation of bainite at the same time, and made thegranular bainite more diffuse distribution at grain boundary and intracrystalline. At the sametime, the long strips sulfides and rod-shaped Al₂O₃inclusions have been changed intospherical or oval sulfur oxides of rare earth and rare earth compound inclusions by theinfluence of rare earth Ce. Sulfides size have been changed from11microns to5microns,rod-shaped Al₂O₃inclusions size have been down to2.5microns small globular. The size ofthe inclusion has been reduced greatly by rare earth Ce.With the increase of the content of rare earth Ce,-20℃low temperature performanceand room temperature mechanical properties of the X80pipeline steel increased gradually.Adding rare earth Ce in0.0093%, the low temperature impact toughness increased by27%,to349J; The yield strength increased by12%, to668.5Mpa; tensile strength increased by9%, to774.3MPa; Rare earth Ce content in0.0250%, the impact energy and strength weredecreased. A moderate amount of rare earth Ce can make greater depth and to distribute evenly of impact and tensile fracture morphology; Rare earth Ce content in0.0093%, X80pipeline steel have the best comprehensive mechanical properties.The corrosion potential of X80pipeline steel increased and the driving force of theelectrochemical reaction reduced with the adding of rare earth Ce, corrosion weightlessnessdecreased at the same time. General corrosion had taken place on the specimen with0.0093%rare earth Ce, without adding rare earth sample happened serious pitting. Analysisresults of rust layer show that after adding rare earth, the inner rust layer become dense, andclosely attached to the substrate. Corrosion products mainly composed of Fe2O3, FeOOHand Fe3O4. Rare earth has not changed the composition and phase of the rust layer. Theoptimum content of Ce is0.0093%in this experiment. Adding excessive amounts of rareearth, the corrosion resistance becomes worse.