Orthogonal optimum design of parameters of flux used for low carbon bainitic steel
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Orthogonal optimum design of parameters of flux used for low carbon bainitic steel Liang Yang1 · Hong Wang2 Received: 6 April 2020 / Accepted: 15 June 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract L8 (27) orthogonal test table is applied to design eight kinds of flux, and arranged with SiO2, ZrO2 and TiO2 as three factors. The microstructure, morphology and mechanical properties of low carbon bainitic steels are investigated by means of optical microscope, scanning electron microscope, transmission electron microscope, tensile testing machine and instrumented drop weight impact tester with oscilloscope. The results indicate that the optimum composition rate is as follows: 20% S iO2, 10% ZrO2, and 6% TiO2, and the interaction between ZrO2 and TiO2 is obvious. The microstructure of deposited metal of low carbon bainitic steel is mainly formed by acicular ferrite and granular bainite. The acicular ferrite is paralleled distribution, and plenty of fine sheet Martensitic–Austenitic constituents are dispersing, which can hinder crack propagation and improve strength and toughness. The impact energy is up to 109.7 J at − 20 °C, and the ratio of brittle fracture termination load to maximum impact load is 0.378, ensuring excellent crack arrest toughness. Keywords Bainitic steel · Orthogonal design · Property · Deposited metal
1 Introduction The increasing demands of oil and gas need a great deal of steels for the installation of the pipeline. To improve operational efficiency and reduce construction cost, long-distance gas pipeline transportation system of large-diameter and high-pressure pipeline has become an inevitable development tendency [1]. Steels with high strength, toughness and good weldability are required for guaranteeing reliability and safety. At present, high grade pipeline steels are used in the project. One of the major goals for the steel industry is to develop steels with high performance [2–5]. Low carbon bainitic steels, as major pipeline steels, have the excellent comprehensive performance [6, 7]. Currently, due to simplicity, good protection, steady arc, high deposition efficiency and high-quality welding joints, submerged arc
welding (SAW) is the most common method for welding the pipeline steels [8]. Welding wire and welding flux belong to the SAW materials. For welding wire of low carbon bainitic steel, the research has achieved preliminary results [9, 10], but there are rare researches on the corresponding flux. The flux plays an important role in the process of SAW, while different components and proportions of flux have a great influence on the performance of SAW. To further reveal and characterize the influence law of flux, the principal components of flux are designed based on the orthogonal experiment, and the low carbon bainitic steels are welded through SAW technology. The effect of the flux composition on welding technology is studied, the microstructure and properties of welded joints are analyzed. The results provide an effective theoretical a
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