高 Cr フェライト系耐熱鋼の長時間加熱脆化と Laves 相析出に及ぼす Si および Mo の影響

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Long-term heating embrittlement of high-chromium ferritic heat resistant steels was investigated. In this work, long-term heating of 9 wt%Cr ferritic steels with various amounts of molybdenum and silicon up to 10000h at 450∿700℃ was conducted, and then toughness and microstructure were investigated. The results are summarized as follows. (1) Heating embrittlement was significantly caused by heating at 550∿650℃ because of precipitation of the Laves phase mainly on the δ-ferrite/martensite boundaries and in δ-ferrite grains. (2) Decrease in the amount of silicon was effective in improving the embrittlement due to the decrease in the amount of precipitation of the Laves phase. Low-molybdenum steels with 0.7 wt%Mo was not caused the embrittlement because the Laves phase did not precipitate. (3) Relationship between molybdenum in solute, temperature and silicon content was given as folows ; log(Mo)_<sol.>=-1270/T+1.51-0.67・Si(wt%) Where, T=823∿973K and Si=0.03 and 0.17 wt%.
社団法人日本鉄鋼協会の論文
1990-12-01