Materials Reports  2019, Vol. 33 Issue (z1): 428-431 |
| METALS AND METAL MATRIX COMPOSITES |
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| Analysis of Softening Cause of TIG Welding Heat Affected Zone in Low Carbon Microalloyed Tube |
| ZHOU Yong1, FENG Xuenan1, BI Zongyue2, TIAN Xiaojiang2, WANG Lei1, LI Bofeng2
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1 School of Material Science and Engineering, Xi’an Shiyou University, Xi’an 710065
2 Steel Pipe Research Institute of Baoji Petroleum Steel Pipe Co., Ltd., Baoji 721008 |
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Abstract With aim to solve the softening problem of heat affected zone (HAZ) in girth welding of low carbon microalloyed tube, the microstructure of plate, tube and HAZ was analyzed by optical microscope (OM), EBSD and transmission electron microscope (TEM).The results show that the grain size of the plate is between 12 and 13 grade which belongs to ultrafine grain range, and the microstructure is granular bainite. Due to the deformation strengthening during the process of tubulation,the fraction of the low-angle grain boundary increase by 27.5% compared with plate metal. The fraction of the deformed grain increase from 8.75% to 78.75% after deformation. The dislocation density rise from the original 4.2×1013 /m2 to 1.9×1014 /m2 after deformation. With influence of the thermal cycle of girth welding, the hardness in the part of HAZ is greatly reduced, and softening occurs. Furthermore, in the softening region, the low angle grain boundary decreases by 11.8%, and the dislocation density decreases to 3.9×1013 /m2, at the same level of plate. Therefore, the grain growth, the dislocation density decrease, and the recrystallization ratio increase are main reasons for the softening of girth welding joint of low carbon microalloyed tube.
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Published: 05 July 2019
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| About author:: Yong Zhou is mainly engaged in the research of petro-leum engineering materials welding and surface engineering technology. He has held and participated in more than 20 scientific research projects, and has participated in compilation of one textbook. Furthermore, he gained the second prize of Shaanxi Provincial Science and Technology Progress Award, the third prize of China National Petroleum and Natural Gas Corporation Science and Technology Progress Award. He also published more than 50 academic papers in domestic and international public journals. |
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