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 ÿ 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 ÿ 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 ÿ grain
interior at temperatures below 1100 K.