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Materials and Fabrication

Microstructure and Mechanical Properties of Fiber Laser-Metal Active Gas Hybrid Weld of X80 Pipeline Steel

[+] Author and Article Information
Lei Zhenglong

e-mail:leizhenglong@hit.edu.cn

Chen Yanbin

State Key Laboratory of Advanced
Welding and Joining
Harbin Institute of Technology
Harbin 150001, China

Sun Zhongshao

Capital Aerospace Machinery Company
Beijing 100076, China

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received July 4, 2011; final manuscript received February 23, 2012; published online December 5, 2012. Assoc. Editor: Xian-Kui Zhu.

J. Pressure Vessel Technol 135(1), 011403 (Dec 05, 2012) (7 pages) Paper No: PVT-11-1151; doi: 10.1115/1.4006347 History: Received July 04, 2011; Revised February 23, 2012

Fiber laser-metal active gas (MAG) hybrid welding process was explored to join X80 pipeline steel to improve the efficiency and performance of pipeline welding. During the hybrid welding process, five different positions are applied to simulate the practical pipe girth welding. The weldability is evaluated concerning the bead shape, hardness, tensile, impact properties, and microstructures of welded joints. The results reveal that the tensile strength is higher than that of the base metal and the weld has a good impact ductility and an excellent bend performance. At the same time, the difference in microstructure between the laser zone and arc zone of laser-MAG hybrid welding of X80 pipeline steel is observed. Compared with the arc zone, the laser zone has finer weld grains and a narrower heat affected zone (HAZ). The fusion zone microstructure of the arc zone mainly consists of columnar proeutectoid ferrite (PF) and fine acicular ferrite (AF), whereas that of laser zone comprises acicular ferrite, upper bainite (Bu), and granular bainite (BG), which verifies technical feasibility of hybrid welding in pipeline steel and lays a good foundation for practical application.

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Figures

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Fig. 1

Schematic diagram of laser-MAG hybrid process

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Fig. 2

Five welding positions of X80 steel

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Fig. 3

Cross section of Yb fibre/MAG hybrid weld in X80 line pipe steel in five different positions: (a) PE, (b) PD, (c) PC, (d) PB, and (e) PA

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Fig. 4

Some defined parameters of hybrid welded joint

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Fig. 5

Hardness distribution of five positions: (a) arc zone and (b) laser zone

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Fig. 6

Fracture appearance of tensile specimen

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Fig. 7

The tensile strength of welded joints from five different positions

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Fig. 8

SEM of fracture surface of tensile specimen

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Fig. 9

The impact properties welded joints from five different positions

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Fig. 10

SEM of fracture surface of impact specimen in weld metal

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Fig. 11

The appearance of bent performance of five different positions: (a) PE, (b) PD, (c) PC, (d) PB, and (e) PA

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Fig. 12

Optical micrograph of base metal X80 steel

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Fig. 13

Optical micrograph of HAZ: (a) arc zone and (b) laser zone

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Fig. 14

Higher magnification of optical micrograph in HAZ of arc zone: (a) coarse grained zone, (b) fine grained zone, and (c) incomplete recrystallization zone

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Fig. 15

Positions for microstructure observation

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Fig. 16

Optical micrograph of microstructure in weld metal: (a) A region in arc zone and (b) B region in laser zone

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