Stress corrosion cracking susceptibility of nickel-molybdenum alloys by slow strain rate and immersion testing

Journal Article · Thu Aug 01 04:00:00 EDT 1996 · Corrosion

DOI:https://doi.org/10.5006/1.3292154· OSTI ID:276611

Nakahara, M ^[1]; Shoji, T ^[2]

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1. Asahi Chemical Industry Co., Ltd., Kawasaki (Japan)
2. Tohoku Univ., Sendai (Japan). Faculty of Engineering

Stress corrosion cracking characteristics of three commercially available nickel-molybdenum alloys (designated B, B2, and B3) in a reducing environment were investigated, with the alloys in their mill-annealed (MA) state and after heat treatment (HT) to simulate effects of welding and stress relief in clad vessel fabrication. Slow strain rate tests (SSRT) showed the cracking mode (intergranular [IG] or transgranular [TG]) varied with HT and electrochemical potential of the environment. At anodic potentials, Alloys B and B2 in the MA and HT states exhibited TGSCC, with a morphology that indicated an active path corrosion mechanism. At cathodic potentials with hydrogen (H{sub 2}) evolution on the specimen surfaces, all three alloys exhibited IGSCC on fracture surfaces in the HT state but not in the MA state. Alloys B2 and B3 showed greater susceptibility to IGSCC than Alloy B. Plant immersion tests showed generally the same results as SSRT at cathodic potentials, except Alloy B3 was similar to Alloy B in its low susceptibility of IGSCC and less susceptible than Alloy B2. Comparison of the SSRT, plant immersion, acid corrosion (20 wt% hydrochloric acid at 423 K for 100 h), and mechanical tensile test results indicated IGSCC susceptibility probably was attributable to phase transformations from {alpha} to {beta} and {gamma} during high-temperature HT and possibly to coherence, precipitation, segregation, and other grain-boundary characteristics. Results also indicated the presumable sensitization of the grain boundary by HT had no direct influence on IGSCC.

• Sponsoring Organization: USDOE
• OSTI ID: 276611
• Journal Information: Corrosion, Journal Name: Corrosion Journal Issue: 8 Vol. 52; ISSN 0010-9312; ISSN CORRAK
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANNEALING
CHROMIUM ADDITIONS
COMPARATIVE EVALUATIONS
CORROSION PRODUCTS
CRACK PROPAGATION
HEAT TREATMENTS
INTERGRANULAR CORROSION
IRON ADDITIONS
IRON ALLOYS
MANGANESE ADDITIONS
MECHANICAL TESTS
MICROSTRUCTURE
MOLYBDENUM ALLOYS
NICKEL BASE ALLOYS
STRESS CORROSION
STRESS RELAXATION