伊藤吾朗, 倉本 繁, 車田 亮, 小林純也, 浅見重則, 小川武史
Effects of Alloying Elements Addition on Delayed Fracture Properties of Ultra High-Strength TRIP-Aided Martensitic Steels
Tomohiko Hojo, Junya Kobayashi, Koh-ichi Sugimoto, Akihiko Nagasaka and Eiji Akiyama
Open Journal of Metals
Effects of Cr and Mo on Mechanical Properties of Hot-Forged Medium Carbon TRIP-Aided Bainitic Ferrite Steels
Koh-ichi Sugimoto, Sho-hei Sato, Junya Kobayashi and Ashok Kumar Srivastava
Open Journal of Metals
Hot spinning formability of aluminum alloy tube
Shunichiro Nakasato, Junya Kobayashi, Goroh Itoh
Spinning is a forming method which forms the flat disk metal into cylindrical metal. Spinning is also used to neck-form the tube end，such as the high-pressure hydrogen storage container．The 6061 aluminum alloy is used as a liner material of the container．The tube end of the liner is neck-formed by spinning without forming die．In this case， there is an issue that the forming defect may be introduced at the inner surface of container after neck-forming．It is considered that the defect in the forming is suppressed by spinning with forming die．However, such as a shape like a high-pressure hydrogen storage container, the mold can not be removed from the container after spinning. Therefor spinning is usually carried out without the mold. In this study, a removable mold which can be taken out after spinning applies for production of a shape like a high-pressure hydrogen storage container.
Now, saving energy and effective utilization of resources are demanded from environmental problems, such as global warming and the depletion of the resources. Magnesium is expected as a promising structural material of next-generation since they are lightweight and excellent in recyclability. In recent years, flame-resistant magnesium alloys which have been developed as a candidates of the body structure in high speed railways. However, several important mechanical properties other than tensile properties, such as fatigue and resistance to hydrogen embrittlement (HE) have not been assessed in detail in these alloys so far. With respect to the HE of conventional alloys, HE has been reported to occur in an AZ31 alloy. In this study, the newly developed flame-resistant alloys, AX81 and AZX611 were subjected to slow strain rate technique tensile test in moist air and dry nitrogen gas environments to examine whether HE takes place in these alloys.
Hydrogen embrittlement (HE) significantly reduces the ductility of metals and its mechanism has not been elucidated. Hydrogen embrittlement is caused by diffusible hydrogen but it is difficult to be observed. Tensile test was conducted on a ferritic stainless steel both with and without simultaneous cathodic hydrogen charging to examine the effect of hydrogen on the elongation to failure. About 35% of elongation to failure was obtained in the uncharged specimen with a dimpletype fracture surface. In contrast, when specimen was tested with simultaneous charging, the elongation decreased to about 8%, with a quasi-cleavage fracture surface. Thus, it was confirmed that HE takes place in this steel. In addition, a test piece was subjected to a tensile plastic deformation of 7% with simultaneous charging, aged at 25℃ for 168h, and then tensile-tested without hydrogen charging. By this treatment, the total plastic strain to failure was recovered to almost the original value, i.e., 35%. Hence, it is deduced that no undiffusible defect remains in the specimen after the tensile deformation of 7%.
Recently, the fuel cell vehicle which uses the hydrogen energy has been attracting attention because of environmental problems such as global warming and depletion of fossil fuel. With the spread of fuel cell vehicles, lower cost of each component is required. High-pressure hydrogen container for fuel cell vehicle is composed of a liner of 6000 series aluminum alloy and shell of carbon-fiber-reinforced plastic（CFRP）. Higher strength aluminum is demanded to decrease the cost of the hydrogen container by reducing the amount of the expensive CFRP. Humid gas stress corrosion cracking test is one of the ways to examine the safety of aluminum alloys. However, the effect of the main alloying elements （Mg, Si, Cu） on the humid gas stress corrosion cracking behavior is not clear. In this study, using aluminum samples of various compositions, we investigated the effect of alloying elements on the humid gas stress corrosion cracking behavior in 6000 series aluminum alloys.
Gilbert R. Speich Award for Best Paper(AIST)
Advanced Ultrahigh-Strength TRIP-Aided Martensite Steels for Automotive Applications