Browsing by Author "Akiyama, Eiji"

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High-concentration carbon assists plasticity-driven hydrogen embrittlement in a Fe-high Mn steel with a relatively high stacking fault energy
(ELSEVIER SCIENCE SA, PO BOX 564, 1001 LAUSANNE, SWITZERLAND, 2018) Tugluca, Ibrahim Burkay; Koyama, Motomichi; Bal, Burak; Canadinc, Demircan; Akiyama, Eiji; Tsuzaki, Kaneaki; 0000-0001-6916-3703; 0000-0002-5006-9976; 0000-0002-7389-9155; 0000-0001-9961-7702; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
We investigated the effects of electrochemical hydrogen charging on the mechanical properties of a Fe-33Mn-1.1C austenitic steel with high carbon concentration and relatively high stacking fault energy. Hydrogen pre charging increased the yield strength and degraded the elongation and work-hardening capability. The increase in yield strength is a result of the solution hardening of hydrogen. A reduction in the cross-sectional area by subcrack formation is the primary factor causing reduction in work-hardening ability. Fracture modes were detected to be both intergranular and transgranular regionally. Neither intergranular nor transgranular cracking modes are related to deformation twinning or simple decohesion in contrast to conventional Fe-Mn-C twinning induced plasticity steels. The hydrogen-assisted crack initiation and subsequent propagation are attributed to plasticity-dominated mechanisms associated with strain localization. The occurrence of dynamic strain aging by the high carbon content and ease of cross slip owing to the high stacking fault energy can cause strain/damage localization, which assists hydrogen embrittlement associated with the hydrogen-enhanced localized plasticity mechanism.
Lowering Strain Rate Simultaneously Enhances Carbon- and Hydrogen-Induced Mechanical Degradation in an Fe-33Mn-1.1C Steel
(SPRINGER, 233 SPRING ST, NEW YORK, NY 10013 USA, 2019) Tugluca, Ibrahim Burkay; Koyama, Motomichi; Shimomura, Yusaku; Bal, Burak; Canadinc, Demircan); Akiyama, Eiji; Tsuzaki, Kaneaki; 0000-0002-5006-9976; 0000-0002-7389-9155; 0000-0001-6916-3703; 0000-0001-9961-7702; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü
We investigated the strain rate dependency of the hydrogen-induced mechanical degradation of Fe-33Mn-1.1C steel at 303K within the strain rate range of 10(-2) to 10(-5)s(-1). In the presence of hydrogen, lowering the strain rate monotonically decreased the work hardening rate, elongation, and tensile strength and increased the yield strength. Lowering the strain rate simultaneously enhanced the plasticity-related effects of hydrogen and carbon, leading to the observed degradation of the ductility.
Potential Effects of Short-Range Order on Hydrogen Embrittlement of Stable Austenitic Steels—A Review
(Springer Science and Business Media Deutschland GmbH, 2021) Koyama, Motomichi; Bal, Burak; Canadinc, Dermican; Habib, Kishan; Tsuchiyama, Toshihiro; Tsuzaki, Kaneaki; Akiyama, Eiji; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü; Bal, Burak
Here, we present a review of the hydrogen embrittlement behavior of face-centered cubic (FCC) alloys with short-range order (SRO) of solute atoms. In this paper, three types of FCC alloys are introduced: Fe–Mn–C austenitic steels, high-nitrogen steels, and CoCrFeMnNi high-entropy alloys. The Fe–Mn–C austenitic steels show dynamic strain aging associated with Mn–C SRO, which causes deformation localization and acceleration of premature fracture even without hydrogen effects. The disadvantageous effect of dynamic strain aging on ductility, which is associated with the deformation localization, amplify plasticity-assisted hydrogen embrittlement. Cr–N and Co–Cr–Ni SRO effects in high-nitrogen austenitic steels and high-entropy alloys enhance the dislocation planarity, which causes stress concentration in the grain interior and near the grain boundaries. The stress concentration coupled with hydrogen effects causes quasi-cleavage and intergranular fractures. © 2020, The Author(s), under exclusive license to Springer Nature Switzerland AG.
Strain rate and hydrogen effects on crack growth from a notch in a Fe-high-Mn steel containing 1.1 wt% solute carbon
(Elsevier Ltd, 2020) Najam, Hina; Koyama, Motomichi; Bal, Burak; Akiyama, Eiji; Tsuzaki, Kaneaki; AGÜ, Mühendislik Fakültesi, Makine Mühendisliği Bölümü;
Effects of strain rate and hydrogen on crack propagation from a notch were investigated using a Fe-33Mn-1.1C steel by tension tests conducted at a cross head displacement speeds of 10-2 and 10-4 mm/s. Decreasing cross head displacement speed reduced the elongation by promoting intergranular crack initiation at the notch tip, whereas the crack propagation path was unaffected by the strain rate. Intergranular cracking in the studied steel was mainly caused by plasticity-driven mechanism of dynamic strain aging (DSA) and plasticity-driven damage along grain boundaries. With the introduction of hydrogen, decrease in yield strength due to cracking at the notch tip before yielding as well as reduction in elongation were observed. Coexistence of several hydrogen embrittlement mechanisms, such as hydrogen enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) were observed at and further away from the notch tip resulting in hydrogen assisted intergranular fracture and cracking which was the key reason behind the ductility reduction. © 2019 Hydrogen Energy Publications LLC