著者

松本 和久 秦野 正治 大宮 慎一 藤井 秀樹

出版者

一般社団法人 日本鉄鋼協会

雑誌

鉄と鋼 (ISSN:00211575)

巻号頁・発行日

vol.103, no.1, pp.54-63, 2017 (Released:2016-12-31)

参考文献数

40

被引用文献数

4 5

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To investigate an effect of internal hydrogen on mechanical properties of a new austenitic stainless steel “STH2” having a nominal composition of Fe-15%Cr-9%Mn-6%Ni-2.5%Cu-0.15~0.2%N, tensile tests and fatigue crack growth tests were conducted for the specimens containing around 80 ppm hydrogen charged by the exposure in 45 MPa hydrogen gas at 300˚C for 200 h and the ones heat treated in air with the same heat pattern.At room temperature and –40˚C, no significant ductility drop by hydrogen charging was observed and about 80% of relative reduction of area was obtained, which is the same as that of JIS SUS316L with the same amount of internal hydrogen. In the specimens tensile tested at –40˚C, a small quantity of quasicleavage fracture surfaces were observed. In the banded areas in which Mn, Ni and Cu were negatively segregated, some relatively coarse voids coalesced with cracks extended along the maximum shear stress plane, which is similar to what is called void-sheet type of fracture. It is quite different from the case for tensile tests in 90 MPa hydrogen gas, in which coarse longitudinal cracks form, suggesting that the concentration of hydrogen at crack tips in 90 MPa hydrogen gas is higher than 80 ppm. It was also confirmed that fatigue crack growth rates were not accelerated by 80 ppm internal hydrogen although some faceted fracture surfaces composed of (111) γ formed.It is confirmed that STH2 has excellent properties not only in high pressure hydrogen gas but also in the circumstance of internal hydrogen of around 80 ppm.

著者

久保田 佳基 秦野 正治 菖蒲 敬久 森 茂生

出版者

日本結晶学会

雑誌

日本結晶学会誌 (ISSN:03694585)

巻号頁・発行日

vol.58, no.6, pp.273-278, 2016-12-31 (Released:2017-01-06)

参考文献数

15

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In-situ synchrotron diffraction experiments were conducted in order to clarify the formation process of α'-martensite from the γ-phase induced by external strain, combined with Lorentz transmission electron microscopy (TEM) and high-resolution TEM observations. Lorentz TEM observation revealed that α'-martensite exist near the defect structures such as dislocations and stacking faults in the parent γ-phase. In addition, it is clearly demonstrated that ε-martensite with hexagonal symmetry appears as an intermediate phase during the plastic deformation of SUS304 stainless steel. Our experimental results suggested that the interfaces between twin structures of the γ-phase presumably play a crucial role in the formation of ε-martensite.