Austenitic stainless steels are used in hydrogen environments because of their generally accepted resistance to hydrogen embrittlement; however, hydrogen-assisted cracking can occur depending on the microstructures or composition of the stainless steel. One area that has not been well researched is welds and in particular heat affected zones. The goal of this work was to measure the subcritical cracking susceptibility of hydrogen precharged gas tungsten arc (GTA) welds in forged stainless steels (21Cr-6Ni-9Mn and 304L). Welds were fabricated using 308L filler metal to form 21-6-9/308L and 304L/308L weld rings, and subsequently three-point bend specimens were extracted from the fusion zone and heat affected zone and precharged in high-pressure hydrogen gas. Crack growth resistance curves were measured in air for the hydrogen precharged fusion zones and heat affected zones under rising-displacement loading, revealing significant susceptibility to subcritical cracking. Fracture thresholds of 304L/308L welds were lower than 21-6-9/308L welds which was attributed to higher ferrite fractions in 304L/308L since this phase governed the crack path. Fracture thresholds for the heat affected zone were greater than the fusion zone in 21-6-9/308L which is likely due to negligible ferrite in the heat affected zone. Modifications to the weld joint geometry through use of a single-J design were implemented to allow consistent testing of the heat affected zones by propagating the crack parallel to the fusion zone boundary. Despite low hydrogen diffusivity in the austenitic stainless steels, effects of displacement rates were observed and a critical rate was defined to yield lower-bound fracture thresholds.
Fracture Threshold Measurements of Hydrogen Precharged Stainless Steel Weld Fusion Zones and Heat Affected Zones
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Ronevich, JA, Somerday, BP, San Marchi, CW, & Balch, DK. "Fracture Threshold Measurements of Hydrogen Precharged Stainless Steel Weld Fusion Zones and Heat Affected Zones." Proceedings of the ASME 2015 Pressure Vessels and Piping Conference. Volume 6B: Materials and Fabrication. Boston, Massachusetts, USA. July 19–23, 2015. V06BT06A017. ASME. https://doi.org/10.1115/PVP2015-45432
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