Stress corrosion cracking of nickel-molybdenum alloys
- DuPont Co., Houston, TX (United States)
- Haynes International, Inc., Kokomo, IN (United States)
- DuPont Co., Wilmington, DE (United States)
Intergranular stress corrosion cracking (SCC) of alloy B-2 (UNS N10665) can occur in dilute acids at low temperatures if there is short range ordering and Ni{sub 4}Mo in its metallurgical structure. Certain chemistries of alloy B-2 are particularly susceptible to the rapid kinetics of the Ni{sub 4}Mo transformation, which can occur within minutes of exposure to temperatures of 650--750 C such as during welding. The severity of ordering is dependent on alloy chemistry and thermomechanical processing conditions, and can result in reduced ductility at 700 C, and subsequently to SCC. SCC in the heat-affected zones of welds of fabricated equipment of alloy B-2 have been found to be associated with the presence of Ni{sub 4}Mo and a short-range ordered structure. Laboratory tests confirmed that only a partially-ordered structure is needed for alloy B-2 to be highly susceptible to SCC in dilute sulfuric acid. A strong correlation was found between degree of ordering, and both susceptibility to SCC and reduced ductility at 700 C. Development of alloy B-3 (UNS N10675) overcomes this thermal instability of alloy B-2, and provides enhanced resistance to SCC in the as-welded condition. In addition to TEM evidence and ductility measurements at 700 C, a stress-corrosion cracking test in boiling 5 wt.% sulfuric acid has also been found useful in evaluating the susceptibility of Ni-Mo alloys to ordering, and to Ni{sub 4}Mo formation.
- OSTI ID:
- 382598
- Report Number(s):
- CONF-960389--
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AGING
CHEMICAL COMPOSITION
CHROMIUM ALLOYS
COBALT ADDITIONS
DUCTILITY
EXPERIMENTAL DATA
FRACTURE PROPERTIES
HARDNESS
HEAT AFFECTED ZONE
HEAT TREATMENTS
INTERMETALLIC COMPOUNDS
IRON ALLOYS
MANGANESE ADDITIONS
MECHANICAL PROPERTIES
MICROSTRUCTURE
MOLYBDENUM ALLOYS
NICKEL BASE ALLOYS
PHASE DIAGRAMS
SILICON ADDITIONS
STRESS CORROSION
SULFURIC ACID
TRANSMISSION ELECTRON MICROSCOPY
WELDED JOINTS