Zasadnyi T. Estimation and ways of reduction of hydrogen permeability of low-activated reactor steels with welded joints

There are presented the results of theoretical and experimental researches, directed on the basis of investigations of the influence of complex doping (metals of IV-V group, silicon, carbon) on hydrogen permeability of the chrome-manganese steel Х12Г20В the optimal chemical composition of the steel, which allows minimizing the losses of hydrogen and its isotopes into environment, has been determined. The value of environmentally safe level of hydrogen permeation was calculated. This allows to determine a factor by which the hydrogen permeability of materials for reactor facilities should be reduced. The influence of hydrogenation on phase-structural state of the Х12Г20В steel has been studied. It is determined, that hydrogen induces redistribution of manganese atoms leading to the formation of the micro regions enriched by this element. Simultaneously, the steel ferritizing process accompanied by segregation -iron in austenitic matrix takes place. The new methodological approach to study the hydrogensolubility in steel welded joints has been proposed. This approach consist in measurement of hydrogen permeability Р by Berrer method and determination of this characteristic in the weld from the ratio of the parent metal area to the weld area, measurement of hydrogen diffusion coefficient D by electrical resistivity method in the specimens cut out of the weld, and calculation of hydrogen solubility in the weld by formula S=P/D. Values of P, D і S for welds obtained by laser welding of Х12Г20В and 10Х9ВФА steels have been determined for the first time. It is shown, that coating by protective oxide films with the spinel structure reduces the permeation value of hydrogen and its isotopes through reactor steels and their welded joints by 120-160 times, that is below environmentally safe level.