Abstract
It is well known that the ductility and notched tensile strength of steels are reduced in high pressure hydrogen gas. Since some high strength steels are used for the vessels to contain high pressure hydrogen gas, it is important to study this embrittlement phenomenon for the safety of the vessels. From this point of view, the steels generally used for vessels, AISI 4340, AISI 4130 and a high manganese steel were tested in hydrogen gas at 200kg/cm2 and their embrittlement phenomena were investigated by means of fracture mechanics. In addition, the fracture morphology was observed by the scanning electron microscope and the following results were obtained.
(1) Critiral stress intensity factor (KH) of the steels increases rapidly when the strengths become lower than 90kg/mm2 by tempering.
(2) The fracture morphology changes from hydrogen embrittlement quasi-cleavage fracture to intergranular fracture as the stress intensity factor decrases or the strength of the steels increases.
(3) From comparison with other environments to cause hydrogen embrittlement, it is realized that the high pressure (200kg/cm2) hydrogen gas is a severe emvironment almost corresponding to the pure water saturated with H2S.
