Using stress relaxation tests for evaluating and optimizing postweld heat treatments of alloy 625 welds
- Knolls Atomic Power Labs., Schenectady, NY (United States)
Alloy 625 (UNS N06625) is a solid-solution-strengthened, nickel based, chromium-molybdenum alloy used for its high strength and excellent corrosion resistance, Stress corrosion cracking (SCC) resistance and, to a lesser extent, strength can be enhanced by precipitation of intergranular carbides by appropriate heat treatment. In welded structures, dissolution of carbides near the fusion line in the heat-affected zone renders denuded regions susceptible to preferential SCC attack that is greatly aggravated by residual stresses. To reduce the propensity for SCC in weldments, manufacturing practice typically includes methods for reducing residual stresses, usually using postweld heat treatments (PWHT). With appropriate heat treatment, grain boundary carbides can be restored and welding-induced residual stresses can be reduced at the same time. A series of heat treatments was performed between 1,050 and 1,800 F (566 and 9826 C) to determine effectiveness in relieving welding-induced stresses. Stress relaxation testing of all-weld-metal specimens was compared to residual stress measurements in full-scale weldments using a hole-drilling strain gauge technique. The much simpler stress relaxation method provided an excellent measure of residual stresses and proved to be an expeditious way to select optimum postweld heat treatments for reducing those welding-induced stresses.
- OSTI ID:
- 42848
- Journal Information:
- Welding Journal, Vol. 74, Issue 4; Other Information: PBD: Apr 1995
- Country of Publication:
- United States
- Language:
- English
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