Abstract
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 10 000 h at 450700°C was conducted, and then toughness and microstructure were investigated. The results are summarized as follows.
(1) Heating embrittlement was significantly caused by heating at 550650°C 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= 823973 K and Si= 0.03 and 0.17 wt%.
