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Research Papers: Materials and Fabrication

# Effect of High-Pressure Hydrogen Gas on Fracture of Austenitic Steels

[+] Author and Article Information
C. San Marchi, D. K. Balch, K. Nibur, B. P. Somerday

Sandia National Laboratories, Livermore, CA 94550

J. Pressure Vessel Technol 130(4), 041401 (Aug 20, 2008) (9 pages) doi:10.1115/1.2967833 History: Received February 28, 2006; Revised April 24, 2007; Published August 20, 2008

## Abstract

Applications requiring the containment and transportation of hydrogen gas at pressures greater than $70MPa$ are anticipated in the evolving hydrogen economy infrastructure. Since hydrogen is known to alter the mechanical properties of materials, data are needed to guide the selection of materials for structural components. The objective of this study is to characterize the role of yield strength, microstructural orientation, and small concentrations of ferrite on hydrogen-assisted fracture in two austenitic stainless steels: 21Cr–6Ni–9Mn (21-6-9) and 22Cr–13Ni–5Mn (22-13-5). The testing methodology involves exposure of tensile specimens to high-pressure hydrogen gas at elevated temperature in order to precharge the specimens with hydrogen, and subsequently testing the specimens in laboratory air to measure strength and ductility. In all cases, the alloys remain ductile despite precharging to hydrogen concentrations of $∼1at.%$, as demonstrated by reduction in area values between 30% and 60% and fracture modes dominated by microvoid processes. Low concentrations of ferrite and moderate increases in yield strength do not exacerbate hydrogen-assisted fracture in 21-6-9 and 22-13-5, respectively. Microstructural orientation has a pronounced effect on ductility in 22-13-5 due to the presence of aligned second-phase particles.

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## Figures

Figure 6

Scanning electron microscope images of fracture surfaces from high-strength 22-13-5 tested with precharged hydrogen: (a) L-orientation and (b) C-orientation. The arrows indicate Z-phase particles.

Figure 7

Scanning electron microscope images of fracture surfaces from 21-6-9 Heat B tested with precharged hydrogen: (a) L-orientation and (b) C-orientation

Figure 4

Scanning electron microscope images of fracture surfaces from low-strength 22-13-5 tested in C-orientation: (a) noncharged condition and (b) hydrogen-precharged condition

Figure 5

Scanning electron microscope images of fracture surfaces from 21-6-9 Heat A tested in L-orientation: (a) noncharged condition and (b) hydrogen-precharged condition. The arrows indicate elongated dimples in (b).

Figure 1

Optical micrographs of (a) 21-6-9 Heat A, (b) 21-6-9 Heat B, (c) low-strength 22-13-5, and (d) high-strength 22-13-5. The longitudinal axis of the forging is parallel to the horizontal edges of these micrographs, and taken near the middle of the length and toward the outside diameter of the forging. Note the magnification is different between the 21-6-9 and the 22-13-5 micrographs.

Figure 2

Micrographs of as-received 22-13-5 bar stock showing distribution of Z-phase; (a) backscattered scanning electron microscope image, bright phase is Z-phase; (b) transmission electron microscope image, dark precipitates are Z-phase

Figure 3

Stress-strain curves of noncharged and hydrogen-precharged (a) 21-6-9 Heat A, L-orientation and (b) high-strength 22-13-5, C-orientation

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