Comparative Study of Microstructure and Mechanical Properties of X80 SAW Welds Prepared Using Different Wires and Heat I
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JMEPEG https://doi.org/10.1007/s11665-020-04986-5
Comparative Study of Microstructure and Mechanical Properties of X80 SAW Welds Prepared Using Different Wires and Heat Inputs Qiaoling Chu, Shuai Xu, Xiongwei Tong, Jie Li, Min Zhang, Fuxue Yan, Wanpeng Zhang, Zongyue Bi, and Cheng Yan (Submitted April 25, 2020; in revised form June 22, 2020) The present work investigated the effect of weld composition and welding heat input on the microstructure and mechanical properties of two submerged arc welded (SAW) joints of API 5L-X80 pipeline steel. The weld metals were joined by two welding consumables (one is rich in C, Ni, Cr, Mo) under different welding heat inputs (20-22 and 34-36 kJ/cm for single-wire and triple-wire processes, respectively). The triple-wire welding procedure with less C, Ni, Cr, Mo alloy contents favors the formation of acicular ferrite (AF), whereas single-wire welding procedure with increased C, Ni, Cr, Mo contents promotes the formation of lath bainite (LB). Nanoindentation is used to evaluate the property of different microstructures. The hardness of lath bainite (LB), granular bainite (GB) and acicular ferrite (AF) is 8.0 GPa, 5.8 GPa and 3.0 GPa, respectively. The Charpy impact energy of weld metal with triple-wire welding procedure (136165 J) is much greater than that with single-wire welding procedure (15-44 J) at 2 45 °C. Larger cleavage facet size is observed in the fracture surface of single-wire weld metal. A computational procedure is developed to understand the temperature fields during the triple-wire welding. Combining the experiments and numerical simulation, simple models to predict the microstructure evolution through the weld thickness are established. Keywords
impact toughness, M/A, microstructure, X80 pipeline steel
1. Introduction The high-strength low alloy (HSLA) steels have a good combination of strength, toughness and weldability and have been widely used in the long-distance oil and gas transportation systems (Ref 1). The X80 pipeline steel is produced by thermomechanical controlled processing (TMCP), followed by accelerated cooling (ACC) to achieve excellent mechanical properties (Ref 2). An important consideration when preparing pipeline welded joints is to achieve equal or higher strength and toughness in weld metal than the base metal, to avoid fracture at the weld metal. Thus, it is imperative to have a desirable microstructure in the weld metal which depends largely on the electrode wire composition. The basic alloying elements such as Cu, Ni and Mo as well as micro-alloying
Qiaoling Chu, School of Materials and Engineering, Xian University of Technology, Xian 710048, China; and CGN-DELTA (Jiangsu) PLASTIC and CHEMICAL CO., LTD, Taicang 215421, China; Shuai Xu, Xiongwei Tong, Jie Li, Min Zhang, and Fuxue Yan, School of Materials and Engineering, Xian University of Technology, Xian 710048, China; Wanpeng Zhang and Zongyue Bi, Baoji Petroleum Steel Pipe Co., Ltd, Baoji 721008, China; Cheng Yan, School of Mechanical, Medical and Process Engineering, Science and E
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