PSI - Issue 19

Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000 – 000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2019) 000 – 000 Available online at www.sciencedirect.com ScienceDirect

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Procedia Structural Integrity 19 (2019) 214–223

Fatigue Design 2019 Improved fatigue life of the newly developed Fe-15Mn-10Cr-8Ni-4Si seismic damping alloy Fumiyosi Yoshinaka a *, Takahiro Sawaguchi a , Nikulin Ilya a , Susumu Takamori a , Nobuo Nagashima a a National Insititute for Materials Science, 1-2-1, Sengen, Tsukuba, Ibaraki, 305-0047, Japan Fatigue Design 2019 Improved fatigue life of the newly developed Fe-15Mn-10Cr-8Ni-4Si seismic damping alloy Fumiyosi Yoshinaka a *, Takahiro Sawaguchi a , Nikulin Ilya a , Susumu Takamori a , Nobuo Nagashima a a National Insititute for Materials Science, 1-2-1, Sengen, Tsukuba, Ibaraki, 305-0047, Japan

Abstract Abstract

Fe-15Mn-10Cr-8Ni-4Si is a newly developed alloy for seismic damper applications. The low- and high-cycle fatigue (LCF and HCF) properties of this alloy was investigated in this study. The LCF resistance of this alloy was found to be superior to that of other materials. The inelastic component was established to be the main contributor to the superior fatigue life of Fe-15Mn-10Cr 8Ni-4Si, including at relatively low strain levels. This alloy demonstrated a gradual and mild cyclic hardening behavior at a wide range of strains. In terms of the HCF property, the fatigue limit was 262.5 MPa, which is 96% of 0.2% proof stress of 274 MPa. A surface observation of the post-fatigued specimen tested at a stress amplitude of 250 MPa for 10 7 cycles without failure showed that while surface relief developed, no cracks with a size of at least several grains were detected. Since Fe-high Mn alloys generally exhibit several unique deformation modes involving the deformation-induced phase transformation, the microstructure of Fe-15Mn-10Cr-8Ni-4Si after fatigue was investigated using electron-backscatter diffraction (EBSD) microscopy. As a result, ε -martensite formed via the deformation- induced γ→ε martensitic transformation was detected in all specimens tested under different conditions. Even at a stress level lower than the fatigue limit, ε -martensite formed while the amount of it was very limited. Except for the specimen tested at a low stress level of 275 MPa, a well-developed deformation induced microstructure was found near the crack; α′ -martensite formed by the two-stage phase transformation γ→ε→α′ was detected only in the region near the crack in a specimen tested at a total strain range of 2%. Fe-15Mn-10Cr-8Ni-4Si is a newly developed alloy for seismic damper applicati ns. The low- nd high-cycle fatigue (LCF and HCF) properties of this lloy was inv stigated in this study. The LCF resistance f this alloy was found to be sup rior to that of other materials. The in l stic component was established to b the main contributor to the superior fatigue life of Fe-15Mn-10Cr 8Ni-4Si, including at relatively low strain levels. This alloy demonstrated a gradual and mild cyclic hardening behavior at a wide range of strains. In terms of the HCF property, the fatigue limit was 262.5 MPa, which is 96% of 0.2% proof stress of 274 MPa. A surface observation of th post-fatigu specimen tested at a stress amplitude of 250 MPa for 10 7 cycles without failure sh wed that while surface relief develope , no cracks with a size of at least several grains wer detect d. Since Fe-high Mn alloys generally exhibit several unique deformation modes involvin the deformation-i duced phase transformation, the i r tructure of Fe-15Mn-10Cr-8Ni-4Si after fatigue w s investigated using lectron-backscatter diffraction (EBSD) microscopy. As a result, ε -martensite formed ia the deformation- induced γ→ε martensitic transformation was detected in all specimens tested under different conditions. Even at a stress level lo er than the fatigue limit, ε -martensite formed while the amount of it was very limited. Except for the specimen tested at a low stress level f 275 MP , a well-developed deformation induced microstructure was found near the crack; α′ -martensite f rmed by the two-stage phase transformation γ→ε→α′ was detected only in the region near the crack in a specimen tested at a total strain range of 2%.

© 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. Keywords: Low-cycle fatigue; High-cycle fatigue; High Mn steels; martensitic transformation Keywords: Low-cycle fatigue; High-cycle fatigue; High Mn steels; martensitic transformation

1. Introduction Countermeasures against earthquakes are being promoted, especially for high-rise buildings, in response to occurrences of giant earthquakes. During a giant earthquake, high-rise buildings resonate with long-period components of ground motion and vibrate for a long time. Seismic dampers are effective devices for controlling 1. Introduction Countermeasures against earthquakes are being promoted, especially for high-rise buildings, in response to occurrences of giant earthquakes. During a giant earthquake, high-rise buildings resonate with long-period components of ground motion and vibrate for a long time. Seismic dampers are effective devices for controlling

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers.

2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 10.1016/j.prostr.2019.12.023