Effects of Heterogeneous and Homogenous Laves Phase Precipitation on Creep Rupture Strength of Fe-9Cr-3Co (wt.%) Alloys at 650 °C

The relationship between creep rupture strength and Laves phase precipitation and growth kinetics was investigated at 650 °C for two Fe-9Cr-3Co (wt.%) alloys differing mainly in the amounts of W and Mo added. In the alloy with 3.14 wt.% W added, Laves phase precipitated heterogeneously on grain boundaries and hence had little dispersion strengthening effect. Its stress exponent for rup-ture time became lower in the lower creep stress range tested. In the alloy with 1.31 wt.% W and 3.22 Mo added, Laves phase precipitated both heterogeneously on grain boundaries and homogenously within grains and there was no reduction in stress exponent for rupture time in the whole stress range tested. The Lave phase precipitation kinetics increased with increasing the total amount of W and Mo in the alloys. The differences in stress-rupture time relationship observed between the two alloys were discussed in relation to their differences in the Lave phase precipitation behaviour.