FRACTURE BEHAVIOR OF ALLOY 600, ALLOY 690, EN82H WELDS AND EN52 WELDS IN WATER

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The cracking resistance of Alloy 600, Alloy 690 and their welds, EN82H and EN52, was characterized by conducting J{sub IC} rising load tests in air and hydrogenated water and cooldown testing in water under constant-displacement conditions. All test materials displayed excellent toughness in air and high temperature water, but Alloy 690 and the two welds were severely embrittled in low temperature water. In 54 C water with 150 cc H{sub 2}/kg H{sub 2}O, J{sub IC} values were reduced by 70% to 95%, relative to their air counterpart. The toughness degradation was associated with a fracture mechanism transition from microvoid coalescence ... continued below

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Mills, W.J., Brown, C.M. and Burke, M.G. January 11, 2000.

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  • Bettis Atomic Power Laboratory
    Publisher Info: Bettis Atomic Power Laboratory (BAPL), West Mifflin, PA
    Place of Publication: West Mifflin, Pennsylvania

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Description

The cracking resistance of Alloy 600, Alloy 690 and their welds, EN82H and EN52, was characterized by conducting J{sub IC} rising load tests in air and hydrogenated water and cooldown testing in water under constant-displacement conditions. All test materials displayed excellent toughness in air and high temperature water, but Alloy 690 and the two welds were severely embrittled in low temperature water. In 54 C water with 150 cc H{sub 2}/kg H{sub 2}O, J{sub IC} values were reduced by 70% to 95%, relative to their air counterpart. The toughness degradation was associated with a fracture mechanism transition from microvoid coalescence to intergranular fracture. Comparison of the cracking response in water with that for hydrogen-precharged specimens tested in air demonstrated that susceptibility to low temperature crack propagation (LTCP) is due to hydrogen embrittlement of grain boundaries. The effects of water temperature, hydrogen content and loading rate on LTCP were studied. In addition, testing of specimens containing natural weld defects and as-machined notches was performed to determine if low temperature cracking can initiate at these features. Unlike the other materials, Alloy 600 is not susceptible to LTCP as the toughness in 54 C water remained high and a microvoid coalescence mechanism was operative in both air and water. Cooldown testing of EN82H welds under constant-displacement conditions was performed to determine if LTCP data from rising load J{sub IC}/K{sub Pmax} tests predict the onset of LTCP for other load paths. In these tests, bolt-loaded CT specimens were subjected to 288 C water for up to 1 week, cooled to 54 C and held in 54 C hydrogenated water for 1 week. This cycle was repeated up to 6 times. For two of the three welds tested, critical K{sub I} levels for LTCP under constant-displacement conditions were much higher than rising load K{sub Pmax} values. Bolt-loaded specimens from a third weld were found to exhibit LTCP at K{sub I} levels comparable to K{sub Pmax} values. Although work to date indicates that rising load tests either accurately or conservatively predict the critical conditions for LTCP under constant displacement conditions, the potential for LTCP at K{sub I} levels less than K{sub Pmax} has not been fully evaluated. Annealing at 1093 C reduces or eliminates LTCP susceptibility. The microstructure and mechanical properties for susceptible and nonsusceptible EN82H welds were characterized to identify the key material parameters responsible for LTCP in the as-welded condition. The key microstructural feature associated with LTCP appears to be fine Nb- and Ti-rich carbonitrides decorating grain boundaries. In addition, the higher yield strength for the as-fabricated weld also promotes LTCP because it increases stresses and local hydrogen concentrations ahead of a crack.

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41 pgs / 11,404 KB

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  • Report No.: B-T-3303
  • Grant Number: DE-AC11-98-PN38206
  • DOI: 10.2172/940234 | External Link
  • Office of Scientific & Technical Information Report Number: 940234
  • Archival Resource Key: ark:/67531/metadc896758

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  • January 11, 2000

Added to The UNT Digital Library

  • Sept. 27, 2016, 1:39 a.m.

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  • Feb. 20, 2017, 2:54 p.m.

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Mills, W.J., Brown, C.M. and Burke, M.G. FRACTURE BEHAVIOR OF ALLOY 600, ALLOY 690, EN82H WELDS AND EN52 WELDS IN WATER, report, January 11, 2000; West Mifflin, Pennsylvania. (digital.library.unt.edu/ark:/67531/metadc896758/: accessed September 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.