| With the development of production technology of pipeline steel, X80 pipeline steel has become a priority in the use of high-level pipeline steel at home and abroad. China is a country with a vast territory, which brings great difference in climate and geological conditions, so it puts forward higher requirements on the pipeline’s corrosion resistance.Rare earths (RE) is the characteristic resources of China. The functions of RE in steel are purifying molten steel, modifying inclusions and micro-alloying. The investigation and exploitation of high added value RE steel have great economic benefits and strategic meaning. At present, it is founded that weathering steel products (as 09CuPTiRE steel, B450NbRE steel) and heavy rail steel products (as BNbRE steel, BVRE steel) with our country’s resources characteristic have realized batch production. But the research and development of RE pipeline steel have not reported.In this paper, X80 pipeline steel was chosen as the research subject. Corrosion resistance of RE pipeline steel in Kuerla (alkaline) and Yingtan (acidic) soil simulation solution was systematically studied by corrosion weight loss test and electrochemical experiments, combining with phase analysis and component analysis of the rust layer. And the effects of RE, molybdenum (Mo), niobium (Nb) content on the corrosion resistant mechanism in pipeline steel were thoroughly investigated. The research results have theoretical significance for the research and development of RE pipeline steel. The following results were obtained:(1) RE can improve the corrosion resistance of pipeline steel obviously. In present study, when RE content is 0.018%, the corrosion rate of RE pipeline steel in Kuerle and Yingtan simulated solution is lower than that of pipeline steel without RE, which is 3.883g·(dm2·a)-1and 5.474g·(dm2·a)-1, respectively.(2) Increasing Nb content is beneficial to improve the corrosion resistance of RE pipeline steel, and then the corrosion rate of RE pipeline steel in Kuerle simulated solution and Yingtan simulated solution is decreased to some extent. In present study, Mo has no notable effect on the corrosion resistance of RE pipeline steel.(3) In Kuerle simulated solution, adding RE can accelerate the corrosion reaction of pipeline steel matrix at initial stage. When the steel matrix forms rust layer, RE can improve the corrosion resistance of pipeline steel through decreasing corrosion current and raising corrosion potential of pipeline steel, increasing resistance of corrosion reaction. In Yingtan simulated solution, adding RE can decrease corrosion current of pipeline steel and increase resistance of corrosion reaction, so the corrosion resistance of the pipeline steel is improved obviously.(4) Increasing Nb content can accelerate the corrosion reaction of RE pipeline steel matrix at initial stage. When the steel matrix forms rust layer, increasing Nb content can decrease the corrosion current and raise corrosion potential of RE pipeline steel, increase resistance of corrosion reaction, thus the corrosion resistance of the pipeline steel is improved in Kuerle and Yingtan simulated solution.(5) The corrosion products which are formed on RE pipeline steel surface after immersing 45 days can be divided into two layers. The corrosion products of outer rust layer are reddish brown Fe2O3 and γ-FeOOH. The corrosion products of inner rust layer are black Fe3O4, which can combine matrix more closely. RE and Nb can improve the corrosion resistance of pipeline steel through increasing the density, continuity and adhesive ability of rust.(6) Compared to Kuerle simulated solution, capacitance arc of RE pipeline steel in Yingtan simulated solution decrease obviously. It indicates that the corrosion resistance of RE pipeline steel in Kuerle simulated solution is better than that in Yingtan simulated solution. |
