The main points of the present work are the solution kinetics and the alterations of the mechanical properties of Cr-Ni steels and alloys as well as pure nickel at 300-900 °C and hydrogen pressures of 30 and 80 MPa. The data on the hydrogen solution kinetics, the alterations in strength and plastic properties, the long-term strength and the microstructure of metal after the long-term exposure in Ar and hydrogen are presented. It is demonstrated that the decrease in the grain-boundary-controlled strength for nickel and nickel-containing materials occurs at the concentration of nickel higher than 50%. The main mechanisms of this decrease are the formation of the brittle hydride phase and the high pressure of hydrogen in the pores and defects, both effects mainly took place at the grain boundaries. The obtained results on the behavior of the various steels and alloys at the hydrogen exposure allow us to suggest the mechanisms of the alterations of the alloys mechanical properties. It was determined that the decrease in the mechanical properties, both reversible and irreversible, is associated by the early break of the steel at grain boundaries. That is that the decrease in the intercrystalline strength of metal is a result of the hydrogen exposure. On the basis of the obtained experimental data the mechanism of the hydrogen brittleness of Cr-Ni austenitic steels is discussed.
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