ASSESSMENT OF HYDROGEN EMBRITTLEMENT IN HIGH-ALLOY CHROMIUM-NICKEL STEELS AND ALLOYS IN HYDROGEN AT HIGH PRESSURES AND TEMPERATURES

The existence of two (low-and high-temperature) extremes of hydrogen embrittlement in heat-resistant austenitic steels and alloys with intermetallic hardening in the range of 293-1073 K was revealed. The low-temperature minimum of their properties in hydrogen is 250-300 degrees higher than that of martensitic and homogeneous austenitic steels. The high-temperature maximum of hydrogen embrittlement manifests itself at 1073 K in steels and alloys with intermetallic hardening and a small percentage of refractory elements (Mo, Nb, W), which retard phase transformations during tests. At 293 K, the action of the external hydrogen atmosphere and absorbed internal hydrogen is determined by the structural class and the nickel content of the material. The degree of brittleness of nickel-base alloys (56 and more wt.% Ni) and heat-resistant martensitic steels is determined by the gaseous hydrogen pressure, and the additional action of internal hydrogen is perceptible only at low pressures. The ductility and low-cycle life characteristics of austenitic steels (23 28 wt.% Ni) deteriorate only after hydrogen presaturation and change only slightly with increasing hydrogen atmosphere pressure, and iron-nickel alloy (43 wt.% Ni) is sensitive to the action of external and internal hydrogen. The existence of a hydrogen degradation limit, the limiting minimum values of the performance characteristics of steels and alloys (specific elongation and lateral contraction ratio, number of cycles to fracture), which do not decrease with increasing adsorbed hydrogen pressure and absorbed hydrogen content and with decreasing loading rate and frequency, has been established. Such values of the mechanical characteristics of martensitic steels and nickel-base alloys are achieved at hydrogen pressures of over 10 and 30 MPa and of dispersion-hardening austenitic steels and alloys at a hydrogen content of 15 and 30 ppm, respectively.