High Temperature Low Cycle Fatigue Behavior and Life Prediction of N80Q Steel

The low cycle fatigue test of N80Q steel was carried out at 350℃ under the condition of strain amplitude of 0.5%, 0.7%, 1.0%, 1.5% and 2.0%, and the low cycle fatigue behavior was analyzed. The results show that the plastic strain amplitude and fatigue life, plastic strain amplitude and cyclic stress amplitude are in linear logarithmic coordinate system. The superposition of Manson coffin equation and basquin equation can well predict the relationship between strain and low cycle fatigue life of N80Q steel at 350 ℃. The main fracture mode of low cycle fatigue of N80Q steel is periodic cleavage fracture with alternate toughness and brittleness. The fatigue crack sources are all on the surface of the sample, and it is easier to form multiple crack sources under low strain condition. With the increase of the total strain amplitude, the length of the secondary crack in the crack growth zone increases significantly.