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Research Papers: Materials and Fabrication

Sulfur Effects on High-Temperature Creep and Fracture Behavior of 25Cr35Ni–Nb Alloys

[+] Author and Article Information
Tao Chen, Xuedong Chen, Juan Ye

National Engineering & Technical Research
Center on Pressure Vessels and Piping Safety,
Hefei General Machinery Research Institute,
Hefei 230031, China

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received September 11, 2013; final manuscript received January 24, 2014; published online April 16, 2014. Assoc. Editor: Marina Ruggles-Wrenn.

J. Pressure Vessel Technol 136(4), 041407 (Apr 16, 2014) (7 pages) Paper No: PVT-13-1158; doi: 10.1115/1.4026597 History: Received September 11, 2013; Revised January 24, 2014

Centrifugal cast 25Cr35Ni–Nb alloy furnace tubes with different contents of S are selected to investigate effects of S addition on creep and fracture behavior. Rupture tests in air at 1100 °C and 17 MPa and slow rate tensile tests at 850 °C showed that the presence of S decreased the creep rupture life and elevated temperature ductility of 25Cr35Ni–Nb alloy obviously. Scanning electron micrographs (SEM) of the fracture and energy dispersive X-ray spectroscopy (EDS) analysis results indicated that S was the important element to control creep rupture life and elevated temperature ductility. S segregated to grain boundaries at elevated temperatures, and blocky fine sulfide particles with smooth surface distribute on the grain boundaries. The presence of sulfides became effective nucleation sites for intergranular creep cavities. Micro cracks occurred by linking up cavities at elevated temperatures due to local stress concentration. Eventually, early failure happened.

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Figures

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Fig. 1

The relationship between S content and rupture life of 25Cr35Ni–Nb alloy furnace tubes

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Fig. 2

The relationship between S content and average rupture life of 25Cr35Ni–Nb alloy furnace tubes

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Fig. 3

The relationship between S contents, loading rate, and percentage elongation after fracture

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Fig. 4

SEM photos and EDS pattern of fracture of 25Cr35Ni–Nb alloy with S content of 0.009 wt. % creep specimen tested at 1100 °C and 17 MPa for 30 h; (1) 2000×, (2) 2000×, (3) 15000×, (4) typical EDS patterns detected in areas of e and g.

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Fig. 5

SEM photos of fracture of 25Cr35Ni–Nb alloy with S content of 0.157 wt. % creep specimen tested at 1100 °C and 17 MPa for 30 h.

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Fig. 6

Line scanning map marked in Fig. 5(1). (1) Se image, (2) S element, (3) Mn element, (4) Cr element, and (5) Ni element.

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Fig. 7

S mappings of alloy with S content of 0.157 wt. % which was tested at 1100 °C and 17 MPa for 30 h

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Fig. 8

SEM photos of fracture surface of tubes tensiled at room temperature with S of 0.105 wt. % and 0.157 wt. % (1) 4000× and (2) 2000×

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Fig. 9

Line scanning results marked in Fig. 8(2). (1) Se image, (2) S element, (3) Mn element, (4) Cr element, (5) Ni element, and (6) Fe element.

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Fig. 10

The schematic interpretation of how S influencing the creep and fracture behaviour of 25Cr35Ni–Nb alloys

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