Effect of carbon on the low-cycle fatigue resistance and microstructure of the Fe–15Mn–10Cr–8Ni–4Si seismic damping alloy

Abstract

Fe–15Mn–10Cr–8Ni–4Si has been developed as a novel seismic damping alloy that absorbs seismic energy through elasto-plastic deformation and has an extraordinarily long low-cycle fatigue (LCF) life, Nf, owing to reversible dislocation motions in a dual austenite/ε-martensite phase developed under cyclic deformation. As carbon is an important interstitial element affecting mechanical properties of iron-based steels and alloys, the effect of the carbon concentration on the LCF properties and microstructures of Fe–15Mn–10Cr–8Ni–4Si–xC (x = 0, 0.1, 0.2, and 0.3 wt%) alloys was examined in the present study at total strain amplitudes, Δεt/2, of 0.005, 0.01, 0.02, and 0.03. Up to 0.1 wt% carbon, the Nf of the alloys was an order of magnitude greater than that of conventional steels, whereas carbon noticeably reduced the Nf at higher strain amplitudes and higher carbon concentrations (Δεt/2 ≥ 0.03 at 0.2 wt% and Δεt/2 ≥ 0.02 at 0.3 wt%). Microstructural observations revealed that the increase in carbon concentration decreased the ε-martensite fraction in fatigue-fractured specimens owing to an increase in the stacking fault energy of the austenite phase. Such an increase usually reduces the degree of slip reversibility, but the γ-slip mode in the carbon-added alloys exhibited planar characteristics, probably because the slip plane softened in the short-range ordering/softening zones to maintain a high Nf, unless the carbon content or strain amplitude exceeded certain levels.