2相ステンレス鋳鋼の相分離による引張特性の変化

抄録

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°C. The decomposition fraction of ferrite and the volume fraction (f_α') of Cr-rich phase were measured by Mösbauer spectroscopy as a function of aging time at 350°C. The result of f_α', was consistent with a result obtained by TEM for the specimen aged for 10016 h. 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 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.