Creep characteristics in carbon free new martensitic alloys

A new attempt has been demonstrated using carbon free Fe-Ni-Co martensitic alloys strengthened by Laves phase, such as Fe2W or Fe2Mo, and μ phase, such as Fe7W6 or Fe7Mo3, 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 fine precipitates are found to be stable even at 973 K and effectively decrease the minimum creep rate much lower than that of the conventional high-Cr ferritic steels. Moreover, superior creep resistance is achieved by addition of Cr to the alloy.