Effect of the cyclic hydrogen charging and discharging on the mechanical properties of SUS304 steel

:Hydrogen effect on the mechanical properties in austenitic stainless steels has been studying(1-3)), using the hydrogen charging method with high temperature and high pressurized hydrogen atmosphere or electrochemical cathodic charging. In these methods, the mechanical testing must be done as soon as possible after charging or the test pieces must be kept soon in the box with dry ice or liquid nitrogen after the hydrogen charging until mechanical testing. So these methods are difficult to apply to the case which the mechanical testing can not be done soon after the hydrogen charging i.e. the case of handling the irradiated materials in the hot cell by the manipulator. Accordingly the repeating method of hydrogen charging and discharging was proposed. Namely soon after the hydrogen charging by electrochemical cathodic charging, the hydrogen discharging by heating is conducted and this process is repeated. After this method conducted the mechanical properties and the susceptibility of the intergranular cracking was investigated. The sensitized austenitic stainless steel showed the lower elongation and more average depth of intergranular cracking by the repeat of hydrogen charging and discharging than by the hydrogen charging only. Furthermore the mechanism of the intergranular cracking was investigated with measuring the hydrogen concentration and the martensite phase value in the test pieces. This mechanism seemed to be occurred by the hydrogen induced martensite phase made on the grain boundary with this repeating method of hydrogen charging and discharging.