EFFECT OF CREEP FRACTURE TOUGHNESS ON CRACK INITIATION AND PROPAGATION UNDER CREEP-FATIGUE INTERACTION.

Effect of creep fracture toughness on crack initiation and propagation under creep-fatigue interaction for three low alloying Cr-Mo-V steels and their micro-fracture processes has been investigated. It showed that the toughness of the material plays an important role in crack initiation and propagation. In the brittle state, crack initiation under creep-fatigue interaction is faster than that subjected to creep, and there is no marked difference in the crack growth rate between them. In the ductile state, not only is the crack initiation time shorter, but also is its crack growth rate much faster. On the other hand, creep-fatigue interaction tends to embrittle the steel, which depends on the original toughness value of the steel. All three Cr-Mo-V steels can be transformed from the state of toughness into the state of brittleness when they are in the ductile state. However in the brittle state, this transformation is not marked.