Study on Extremely-Low-Cycle Fatigue of Fe–15Mn–10Cr–8Ni–4Si Alloy

Abstract

The extremely-low-cycle fatigue behavior and post-fatigue microstructure of an Fe–15Mn–10Cr–8Ni–4Si austenitic alloy were investigated under a strain rate and maximum strain amplitude of 0.5%/s and 10%, respectively, in the axial direction. The results can be summarized as follows. (1) A steel damper made of Fe–15Mn–10Cr–8Ni–4Si alloy can withstand approximately 15 swings back even if the structure is distorted by approximately 10% due to a large earthquake. (2) The εpa–Nf relationship of the Fe–15Mn–10Cr–8Ni–4Si alloy demonstrated a linear relationship, and it was confirmed that Manson-Coffin rule holds. (3) Even in an extremely-low-cycle fatigue test with a strain rate of 0.5%/s, the test specimen temperature did not exceed 40°C under all test conditions. Therefore, the ε phase was formed in the fatigue test under all test conditions. (4) Various facets and secondary cracks were observed in the fatigue propagation region of the fracture surface. Accordingly, it was inferred that most of the main cracks propagated at the γ/ε interface and the secondary cracks merged. Consequently, the fatigue crack could not propagate linearly, and the generation of the secondary cracks caused a decrease in the displacement at the tip of the crack when the stress was redistributed, thus extending the fatigue life.