Thermal fatigue crack nucleation in ferritic-martensitic steels before and after neutron irradiation

Thermal fatigue behaviour of the ferritic-martensitic steels MANET-II, 12Cr-1.5NiMo and F82H-mod. have been investigated in the temperature range from 50 deg. C to 350 deg. C and total strain range ≤0.33%. Crack appearance has been checked after 3x103, 6x103 and 104 cycles and has been successively detected in these steels. The thermal fatigue cracks have a transgranular character; sometimes, intergranular cracks are observed in the F82H-mod. steel. A certain correlation of grain size and ferrite content with the thermal fatigue crack peculiarities has been noted. Specimens of MANET-II and 12Cr-1.5NiMo have been irradiated in a WWR-M reactor with a fluence of 1x1025 n m-2 at a temperature of 300 deg. C and then subjected to thermocyclic loading. It has been established that the neutron irradiation does not significantly affect fatigue crack nucleation in both materials