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Sigma-phase Embrittlement. Embrittlement of iron-chromium alloys (most notably austenitic stainless steels Type 301,302, 303, 304, 308, 309, 316, 321) caused by precipitation at grain boundaries of the hard, brittle intermetallic sigma phase during long periods of exposure to temperatures between approximately 560 and 980 ºC ( 1050 and 1800 ºF). Sigma-phase embrittlement results in severe loss in toughness and ductility, and can make the embrittled material susceptible to intergranular corrosion.
