Metallurgical investigations were carried out on a welded sample of 25% Cr super duplex stainless steel (UNS S32750) taken from a vessel that had been accidentally operated above 300-350°C (570-660°F) for at least six months, which had resulted in brittle fracture. As a result of microstructure observations, no abnormalities were found in the ferrite/austenite balance and no intermetallic phases were observed in the sample, while Charpy impact tests at room temperature revealed quite a low absorbed energy in both, the base metal and the weld metal. These results indicated the occurrence of 475°C (885°F) embrittlement in the steel. De-embrittlement heat treatment trials were also performed to find out the effective temperature range. The aim of this paper is to draw attention to the risk of in-service embrittlement of duplex stainless steels, highlighting the difference in susceptibility to 475°C (885°F) embrittlement of the base metal and the weld metal.

Subject
Embrittlement, Super duplex stainless steel, Materials, Intermetallic phases, Fracture surfaces, Base metals, Impact toughness, Steel, Duplex stainless steel, Ferrite, Hardness, Heat treatment, Weld metal
Keywords:
25% Cr super duplex stainless steels, 475°C (885°F) embrittlement, de-embrittlement heat treatment
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2018
Association for Materials Protection and Performance (AMPP)
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