2相ステンレス鋳鋼の相分離による引張特性の変化

概要

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Duplex stainless steels are subject to embrittlement due to the phase decomposition of ferrite to form Fe-rich phase and Cr-rich phases during thermal aging about 300℃. The decomposition fraction of ferrite and the volume fraction (f_α′) of Cr-rich phase were measured by Mosbauer spectroscopy as a function of aging time at 350℃. The result of f_α′ was consistent with a result obtained by TEM for the specimen aged for 10016h. The phase decomposition was accompanied by the increase in hardness of ferrite and 0.2% proof stress, contrary to the decrease in fracture elongation. The origin of the strength change can be fully explained by a model proposed by a model proposed by Williams for f_α′<12%, but partly for f_α′>12%. Initiation of crack was observed near the ferrite boundary adjacent to arrested slip bands in the deformed austenite by the in-situ observation under tensile test. The crack nucleation is discussed on the basis of the Stroh's model.
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