Effect Of Trace Ce On Microstructures And Mechanical Properties Of High-level Pipeline Steel

With the increase of the worldwide total energy and clean energy needs, oil, natural gas has become to affect the world economic development can not be missing important resources; people want to adopt a high efficiency (high pressure, high flow), high-level (X100X120) pipeline steel to reduce oil and gas pipeline construction costs and improve transmission efficiency. Therefore, the development, manufacture of high strength, high toughness of oil, natural gas transmission pipeline steel, meet the needs of energy supply"has become one of the development of this century Pipeline.We all know, oil, natural gas from the producer to the consumer end to the seismic zone, discontinuous permafrost, deep sea and other severe environments, high-speed conveying high-pressure corrosive fluids containing H2S, requires pipeline steel with high strength and toughness, high-deformation energy, anti-the HIC and anti-the SSCC capacity and high heat input welding performance. To this end, the basic research aspects of the development of high-level (X120) pipeline steel in the development of the brief high-level pipeline steel background, production process, there is the problem on the basis of consolidation, summarized, summarizes the nature of the rare earth elements and the mechanism of steel. In order to improve the robust performance of pipeline steel, deformation capacity and anti-the HIC anti-the SSCC ability to solve the steel substrate clean, refine and change the steel inclusion morphology in these two key scientific issues.In this study, complete the following four tasks.1.The use of metallurgical thermodynamics theory to estimate the Ce content on the undercooling of liquid steel, the calculation of the thermodynamic formation conditions of Ce, O, S inclusions in the steel;2.In vacuum induction furnace, at8X102Pa Ar atmosphere, put the3kg Industrial pure iron and accessories into0.05%C-0.3%Si-2.0Mn%steel melting liquid, and then added Ce element, while the refining temperature was1873K (analog RH vacuum refining process for refining). And then4groups of pipeline steel were prepared by the no oxidation of gravity casting and forging method;3.Composition analysis, metallographic examination, SEM and EDS analysis, tensile and impact testing, testing methods, research, and characterization of Ce on the composition of the high-level pipeline steel, inclusion morphology, the influence of microstructure and mechanical properties;4.Analysis study on Ce to improve the microstructure of steel, steel tensile and impact properties of the mechanism. By theoretical calculation, experimental characterization and analysis, the following conclusions: The experimental results show that:When the steel content of Ce is0.0374%mass, the oxygen content decreased from0.0036%mass to0.0008%mass, sulfur content decreased from0.0065%mass to0.0010%mass.Description of the Ce element has deep deoxidation and desulphurization of molten steel, realizes the purification effect.At the same time, Ce elements can improve the liquid steel degree of supercooling, increase matrix organization of the nucleation coagulation of quantity, makes the acicular ferrite, granular ferrite and the M/A increasing number and small even uniform, so that the matrix organization get refined.Study found that:In liquid steel by adding element Ce,1873K high-temperature refining, the steel O mainly in the form of Ce2O3; in S content under the conditions of Ce and O, S generate Ce2O2S. With the increase of Ce content, the original volume, irregular morphology of MnS, SiO2inclusion into1μm, even nanoscale spherical Ce oxygen sulfur inclusions; with a corner of large complex inclusion into Ce inclusions, its scale is reduced by a factor of10or so; steel is smaller than2μm inclusion accounted for80%, more than10μm inclusions almost disappeared.Ce elements in the steel, the original large size, irregular morphology of MnS, SiO2inclusions into about1μm, and even nanoscale spherical Ce oxygen and sulfur inclusions. Large complex inclusions with sharp corners is reduced to the small size of Ce composite inclusions, its scale is reduced by about10times; with increasing Ce content, accounted for80%less than2μm inclusions, inclusions larger than10μm were almost disappeared;Finally the steel comprehensive mechanical performance improved, Ce content in0-0.0374%range, the comprehensive mechanical properties of pipeline steel appeared to improve after a slight downward trend; when the Ce is0.0167%, yield strengthRp0.2, tensile strength Rm, elongation at break of A section respectively,710MPa,764MPa,24%; Compared with the steel in which the content of Ce was0, Rp0.2, Rm and A were increased33.1%,24.8%,54.9%; Meanwhile, the impact energy AK reached276J,which also increased57.7%than the steel without Ce concent.