Fatigue Life at 550 °C Temperature of Aged Martensitic Cast Steel

The paper presents the results of research on low cycle fatigue life of GX12CrMoVNbN9 – 1 (GP91) cast steel at the temperature of 550 °C. The cast steel under investigation was in the as-received condition (after heat treatment) and after 8000 hours of ageing at the temperature of 600 °C. Cyclic loads were realized at five levels of total strain amplitude ɛac amounting to: 0.25; 0.30; 0.35; 0.50 and 0.60%, respectively. Performed research has shown that GP91 cast steel is subject to strong cyclic softening within the entire experiment scope, and does not reveal any clear period of stabilization. Greater extent of softening was observed for the cast steel after the process of ageing. It has also been proved that the ageing process influences the basic parameters of hysteresis loop and fatigue life. Ageing in the case of the examined cast steel causes an evident decrease in its fatigue life which depends on the level of total strain.