The changes in material properties caused by creep damage were observed with the test methods of electric resistance and hardness. The tested material was Cr-Mo-V steel for rotor in steam turbine.
The test specimens were subjected to long term heating and creep damage before testing. The prepared conditions were in the temperature range of 450∼650°C, and the heating or loading period of 160∼8000hours.
The results obtained are summarized as follows,
(1) Hardness and the ratio of electric resistivity decreased with increasing heating time or temperature.
(2) Hardness and the ratio of electric resistivity remarkably decreased by creep damage.
(3) Vickers hardness difference ΔHV (HV in the heated specimen-HV in the creep damaged specimen) increased according to the creep damage calculated by the strain fraction rule.
(4) Electric resistivity difference ΔRρ(Rρ in the heated specimen-Rρ in the creep damaged specimen) increased with increasing creep damage φCL up to φCL=0.5.
(5) It is possible to estimate the material life and creep damage by measuring hardness and electric resistance.