The Stress-Controlled Low Cycle Fatigue Properties of HK40 and HP40 Heat-Resistant Fe–Ni Base Alloys

Abstract

The low cycle fatigue (LCF) properties of centrifugally cast Centralloy ET 45 MICRO (HK40 type) and Centralloy G 4852 MICRO (HP40 type) were quantified using fully reversed, stress-controlled fatigue tests at temperatures between 350 °C and 600 °C. Cast samples for both alloys were artificially aged to simulate the microstructure of alloys observed during service before assessing the LCF properties. Despite having a similar yield strength, the Centralloy ET 45 MICRO alloy was measured to exhibit reduced LCF properties when compared to Centralloy G 4852 MICRO specimen at elevated temperatures. The differences are largely attributed to variations in the size distribution of the primary Cr carbide clusters resulting from the solidification conditions. The ratio of stress amplitude over yield strength shows good agreement with the lifetime at every tested temperature as $\frac{{\sigma }_{a}}{{\sigma }_{Y}}=A{\left({N}_{f}\right)}^{C}$. At elevated temperatures and high stress amplitudes, plastic deformation and stress relaxation contribute to improving the overall LCF properties of both alloys. However, at smaller stress amplitudes where the test times are prolonged, elevated temperatures are responsible for deteriorating the LCF response of the alloys.