Fatigue Resistance of GX12CrMoVNbN9-1 Cast Steel after Ageing Process

Abstract

In the present paper, low cycle fatigue behaviour of GX12CrMoVNbN9-1 (GP91) cast steel is presented. Fatigue tests were performed under isothermal conditions at room temperature and at 550 and 600^oC, on five levels of total strain amplitude value ɛ_ac = 0.25÷0.60%. The cast steel subject to investigation was in the as-received condition (after heat treatment) and after 8000 hours of ageing at the temperature of 600^oC. Performed research has shown an insignificant influence of the ageing process on mechanical properties of GP91 cast steel, determined with the static test of tension. Analysis of the performed tests has proved that GP91 cast steel in the as-received condition and after ageing process was characterized by strong cyclic softening without a clear period of stabilization of the hysteresis loop parameters. The fatigue lifetime curves at each temperature were obtained based on Basquin and Coffin – Manson equations. The process of ageing of GP91 cast steel contributed to a decrease in its fatigue life N_f from a few to a few dozen percent, and the level of fatigue life was dependent on the value of strain amplitude ɛ_ac. It has also been stated that the fatigue life N_f of GP91 cast steel is determined by its plastic properties, and the degree of changes in fatigue life N_f was dependent not only on the temperature of testing, but also on the value of strain amplitude ɛ_ac.

DOI: http://dx.doi.org/10.5755/j01.ms.20.4.6077