Effect of Surface Hydrogen Concentration on Hydrogen Embrittlement Properties of Stainless Steels and Ni Based Alloys

Hydrogen is a clean energy source, and has the potential to be widely used in various energy systems in the near future. Fuel cell vehicles equipped with cylinders containing hydrogen gas with high pressure up to 70 MPa are now being commercialized. Many hydrogen stations to supply fuel cell vehicles with gaseous hydrogen are under construction. For the safety and public acceptance of using hydrogen gas, it is important to investigate effects of hydrogen on reliability of structural materials used for the hydrogen systems. It is widely recognized that gaseous hydrogen decreases mechanical properties of steels and other kinds of metals. The environmental degradation caused by gaseous hydrogen is classified to following two types. One is hydrogen environment embrittlement (HEE) or hydrogen gas embrittlement (HGE), which occurs when a hydrogenfree material is mechanically tested in gaseous hydrogen near room temperatures.1–3) HGE susceptibility is evaluated by tensile tests4,5) or fatigue tests6) in highly pressurized gaseous hydrogen. The other is internal reversible hydrogen embrittlement (IRHE), which occurs when a hydrogen preEffect of Surface Hydrogen Concentration on Hydrogen Embrittlement Properties of Stainless Steels and Ni Based Alloys