Effect of Mo and W on Creep Characteristics of Precipitation Hardened Carbon Free Martensitic Alloys

Abstract

A new attempt has been demonstrated using carbon free Fe-Ni-Co martensitic alloys strengthened by μ-phase and Laves phase to achieve homogeneous creep deformation at high temperatures under low stress levels. Creep behavior of the alloys is found to be completely different from that of the conventional high-Cr ferritic steels. The alloys exhibit gradual change in the creep rate with strain both in the transient and acceleration creep regions, and give a larger strain for the minimum creep rate. In these alloys the creep deformation takes place very homogeneously and no heterogeneous creep deformation is enhanced even at low stress levels. The minimum creep rates of the Fe-Ni-Co alloys at 700°C are found to be much lower than that of the conventional steel, which is due to fine dispersion strengthening useful even at 700°C in these alloys. It is thus concluded that the Fe-Ni-Co martensitic matrix strengthened by μ and Laves phases is very useful to increase the creep resistance at elevated temperatures over 650°C.