Hydrogen-assisted crack propagation in 304L/308L and 21Cr–6Ni–9Mn/308L austenitic stainless steel fusion welds

Elastic–plastic fracture mechanics methods were used to characterize hydrogen-assisted crack propagation in two austenitic stainless steel gas tungsten arc (GTA) welds. Thermally precharged hydrogen (140 wppm) degraded fracture initiation toughness and crack growth toughness and altered fracture mechanisms. Fracture initiation toughness in hydrogen-precharged welds represented a reduction of >67% from the estimated toughness of non-charged welds. In hydrogen-precharged welds, microcracks initiated at ferrite, and dendritic microstructure promoted crack propagation along ferrite. Deformation twinning in austenite interacts with ferrite, facilitating microcrack formation. While hydrogen altered fracture mechanisms similarly for both welds, the amount of ferrite governed the severity of hydrogen-assisted crack propagation.

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► Measured crack growth resistance of welds with 140 wppm H from gas charging.
► H reduced fracture initiation toughness by over 67% and altered fracture mode.
► With H, microcracks initiate at weld ferrite. Without H, fracture is uniformly ductile.
► With H, localized deformation in austenite creates stress concentrations at ferrite.
► In austenite/ferrite microstructures, JIC decreases with increasing vol.% ferrite.