炭素無添加Fe-Ni基合金HR6WにおけるFe₂Wラーベス相の析出挙動

抄録

The age-hardening behavior of the Fe-Ni-based alloy HR6W without carbon was investigated at temperatures between 973 and 1173 K for a maximum of 3000 h to clearly identify the nose temperature of the Fe₂W Laves phase. The microstructure observation was carried out for the aged alloys using field-emission scanning electron microscopy. One-step increase of hardness was detected for the alloy, which corresponds to the precipitation of Fe₂W phase. It was found that the Fe₂W phase precipitates with a flake-like morphology within γ grain interior and with a granular morphology at grain boundaries. The TTP (time-temperature-precipitation) diagram for the alloy is established based on the results of hardness measurements and microstructure observations, and the C curve representing the time required to initiate precipitation of the Fe₂W Laves phase within γ grain interior was determined. The nose temperature of the C curve was identified as 1100 K, and the precipitation starts at 20 h at the nose temperature. The precipitation of the Fe₂W phase at grain boundaries occurs for one order of magnitude earlier than that within γ grain interior at temperatures below 1100 K.

Fig. 3　TTP (time-temperature-precipitation) diagram of the HR6W without carbon within the γ grain interior. The C curve of the Fe₂W Laves phase for the conventional HR6W obtained in the previous paper is included (dashed line)¹⁰⁾.