316系ステンレス鋼の高圧水素環境脆化特性におよぼすNiおよびCr量の影響

抄録

To accelerate the construction of hydrogen energy society featuring fuel cell vehicles by enlarging the kinds of materials safely used in hydrogen circumstances in addition to JIS SUS316L, several steels having Ni contents lower than SUS316L and Cr contents equivalent to SUS316L are prepared and their tensile properties in high pressure gaseous hydrogen are investigated at room temperature and -40°C. [Ni]+0. 35[Cr] ([Ni] and [Cr] are their concentrations in mass%) is proposed as an indicator to properly indicate whether hydrogen environmental embrittlement (HEE) occurs or not in45MPa hydrogen gas at both temperatures. HEE is basically related to strain-induced martensite having bcc crystallographic structure. However, there are some steels which do not exhibit any significant HEE although noticeable amount of martensite phase forms. In this case, HEE mainly occurs at the later stage of deformation just before fracture. Steels containing more than 12mass% Ni including SUS316L do not show HEE if there is not serious segregation of alloying elements such as Ni, Cr, Mo. It is also indicated that SUS316 probably do not show HEE if more than 12mass% Ni is contained. Furthermore, steels having Ni content close to 10mass%, which corresponds to the lower limit of the standard of JIS SUS316 and AISI 316L, have considerably higher resistance against HEE compared to SUS304 based steels although HEE occurs at the late stage of deformation. It may be possible for them to be used in high pressure hydrogen circumstances if temperature range at which they are used is fully taken into account and small level of HEE is acceptable.