Stress-assisted hydrogen attack cracking in 2.25Cr-1Mo steels at elevated temperatures

Journal Article · Fri Sep 01 04:00:00 EDT 1995 · Metallurgical Transactions, A

DOI:https://doi.org/10.1007/BF02671246· OSTI ID:116043

Chen, L C; Shewmon, P ^[1]

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1. Ohio State Univ., Columbus, OH (United States). Materials Science and Engineering Dept.

Crack growth in 2.25Cr-1Mo steels exposed to 3,000 psi hydrogen has been investigated in the temperature range 440 C to 500 C, using modified wedge-opening loaded specimens to vary stress intensity. Under conditions of temperature and hydrogen pressure, where general hydrogen attack does not occur, the crack propagated by the growth and coalescence of a high density of methane bubbles on grain boundaries, driven by the synergistic influence of internal methane pressure and applied stress. Crack growth rates were measured in base metal, and the heat-affected zones (HAZs) of welds were tempered to different strength levels. The crack growth rate increased with material strength. Above a threshold of about K{sub l} = 20 MPa{radical}m (at 480 C), the crack growth rate increased rapidly with stress intensity, increasing as roughly K{sub l}{sup 6.5}. Because of better creep resistance, stronger materials can sustain higher levels of stress intensity to drive crack growth and nucleate the high density of voids necessary for crack growth. Stress relaxation by creep reduces the stress intensity, and thus the growth rate, especially in weaker materials. The crack growth rate in the heat-affected zone was found to be substantially faster than in the base metal of the welds. Analysis indicates that K{sub l} rather than C* is the appropriate crack-tip loading parameter in the specimen used here and in a thick-walled pressure vessel. The DC potential drop technique met with limited success in this application due to the spatially discontinuous manner of crack growth and limited crack-tip opening displacement.

• Sponsoring Organization: USDOE
• OSTI ID: 116043
• Journal Information: Metallurgical Transactions, A, Journal Name: Metallurgical Transactions, A Journal Issue: 9 Vol. 26; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CHROMIUM ALLOYS
CRACK PROPAGATION
FRACTURE MECHANICS
GRAIN BOUNDARIES
HEAT AFFECTED ZONE
HYDROGEN EMBRITTLEMENT
MOLYBDENUM ALLOYS
NUCLEATION
PRESSURE DEPENDENCE
STEELS
STRESS RELAXATION
STRESSES
TEMPERATURE DEPENDENCE
VOIDS
WELDED JOINTS