Abstract
Activities of Cryogenic Materials Working Group (Task 10) in the WE-NET program are introduced with emphasizing on mechanical properties of metallic structural materials used in liquid hydrogen and compressed gaseous hydrogen. Regarding the evaluation of properties in liquid hydrogen, mechanical tests were conducted mainly using the newly designed and installed facilities for mechanical testing in liquid hydrogen. Austenitic stainless steel plates of 5mm in thickness and their welds processed with TIG, MIG and FSW showed excellent mechanical properties at cryogenic temperatures, while the thicker weld metals processed with multi-layer deposition sometimes exhibited lower toughness in cryogenic circumstances. Regarding gaseous hydrogen, SUS304L showed clear hydrogen environmental embrittlement (HEE) even at room temperature, while SUS316L showed no HEE at room temperature although some ductility decrease was recognized at low temperatures. All kinds of steels tested, including plain steel, low-alloyed steels and stainless steels, exhibited considerable hydrogen absorption when the specimens were exposed at 54°C for 1000h in compressed hydrogen gas at 27MPa pressure. In case of stainless steels, plastic deformation at room temperature enhanced this tendency.
