A multiple-pass gas tungsten arc weld in 22Cr - 13Ni - 5Mn austenitic stainless steel with matching filler exhibited dramatically reduced fracture toughness relative to the base material. This reduction in toughness was exacerbated by 6500 appm of thermally charged hydrogen. Optical and scanning electron microscopy revealed that significant amounts of the ferrite present in the weld deposit had transformed to the brittle intermetallic sigma phase as a result of the heat input of successive weld passes. Examination of the fracture surfaces and sub-surface regions showed that the lower fracture toughness of the uncharged weld could be attributed primarily to microvoid nucleation, growth, and coalescence associated with both manganese sulfide inclusions and cracking of the sigma phase particles. The presence of hydrogen increased the propensity for low-plasticity fracture, and it is proposed that this increase may be due to enhanced fracture along austenite – ferrite interfaces and through the ferrite dendritic structure, followed by linking of damage sites ahead of the crack tip by hydrogen-enhanced shear failure.

Subject
Scanning electron microscopy, Steel structures, Materials, Fracture toughness, Imaging, Crack initiation, Fracture surfaces, Crack propagation, Micrography, Ferrite, Fracture, Toughness, Hydrogen
Keywords:
hydrogen embrittlement, austenitic stainless steel, GTA weld, sigma phase
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2004
Association for Materials Protection and Performance (AMPP)
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