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Microstructure and Toughness of Heat-affected Zone of Weld Joint for Pipeline Steels with High Deformability |
JIA Shujun1,**( ), WANG Yuanfang2, TAN Fengliang3, LIU Qingyou1 |
1. China Iron & Steel Research Institute, Beijing 100081, China 2. Liaohe Oilfield Company, China National Petroleum Corporation, Panjin 124010, China 3. Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China |
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Cite this article:
JIA Shujun, WANG Yuanfang, TAN Fengliang, LIU Qingyou. Microstructure and Toughness of Heat-affected Zone of Weld Joint for Pipeline Steels with High Deformability. Chinese Journal of Materials Research, 2016, 30(7): 517-523.
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Abstract Welding thermal cycle process of test steels containing different Nb was investigated under different heat inputs with a Gleeble-3800 thermo-mechanical simulator. The microstructural characteristics of the coarse-grained heat-affected zone (CGHAZ) were observed by using optical microscope (OM), scanning electron microscope (SEM) and electron backscatter diffraction (EBSD), while their impact toughness was tested. The results indicate that with the increasing heat input, lath bainite transformed gradually into granular bainite, and the size and proportion of M/A islands increased, while the average grain size also increased. Under the same heat input, austenite in high Nb steel was refined obviously, with more dispersive and refined M/A islands distributed in the microstructure of high Nb steel, and the proportion of high angle boundaries was high. With the increasing heat input, the impact toughness of steels decreased sharply. The critical heat input value for a sharp decrease in impact toughness were approximately 35 kJ/cm for high Nb steel and 25 kJ/cm for low Nb steel. However, the impact toughness of the high Nb steel was significantly higher than that of the lower Nb steel in the range of experimental parameters.
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Received: 13 August 2015
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Fund: *Supported by National High Technology Researchand Development Program of China No.2013AA09A219 |
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