Effects of the Cr and Ni concentrations on the fatigue and corrosion resistances of Fe−Mn−Cr−Ni−Si alloys for seismic damping applications

Previous research has shown that Fe–Mn–Cr–Ni–Si alloys offer excellent low-cycle fatigue resistance via reversible bidirectional transformation between face-centered cubic (FCC) γ-austenite and hexagonal closed-packed (HCP) ε-martensite. The alloy shows superior low-cycle fatigue life and is used for seismic damping applications, but there have been concerns over their resistance to highly corrosive environments. In this study, Fe–15Mn–aCr–bNi–4Si alloys were prepared with different Cr and Ni concentrations to evaluate the effects on the fatigue and corrosion resistances: Z1 with (a, b) = (14, 10.1), Z2 with (a, b) = (12.5, 8.8), Z3 with (a, b) = (11, 7.5), Z4 with (a, b) = (9.5, 6.1), and Z5 with (a, b) = (8, 4.8). Z2 had the longest fatigue life. The alloy showed Gibbs free energy difference between γ-austenite and ε-martensite phases close to the ideal of zero and the α′-martensitic transformation was suppressed well, which agreed with the design criteria for achieving bidirectional transformation-induced plasticity. The developed alloys showed superior corrosion resistance in seawater. Local pitting corrosion was observed that was attributed to the high Mn concentration of the alloys, although this was greatly mitigated by adjusting the Cr and Ni concentrations, especially with Z1 and Z2.