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We propose a new procedure for investigation of hydrogen embrittlement of steels. It is based on the use of a physically grounded quantitative criterion for reversible influence of hydrogen. This criterion is determined from the ratio between values of the actual fracture stress for a metal in hydrogenated and initial states. The procedure involves the use of standard cylindrical specimens, which are deformed by uniaxial tension in a prescribed temperature range. To illustrate the potentials of the new procedure, experimental results for hydrogen embrittlement of 09G2S steel are presented.Among the entire variety of manifestations of the deleterious effect of hydrogen on the operational properties of structural steels, reversible hydrogen brittleness is one of the most complex [1]. It can be observed at negligibly small concentrations of hydrogen, and the degree of hydrogen action depends on many factors: steel structure, temperature, kind of acting stresses, rate of deformation. It is just this form of hydrogen brittleness that attracts the most attention of investigators, since it creates serious technological problems in many cases and, at the same time, its mechanism has not yet been exhaustively studied. One of the reasons hampering the study of the influence of hydrogen is related to the necessity of selecting a quantitative criterion serving as a measure of sensitivity of steels to hydrogen brittleness.The goal of this work consists in the justification of a new criterion and a method of its establishment, making it possible to estimate quantitatively the degree of reduction in the brittle strength of metals under the conditions of reversible influence of hydrogen.As is known, most standard characteristics that are traditionally used for experimental determination of the mechanical properties of steels are not sensitive to variations in the concentration of dissolved hydrogen [2]. For this reason, a great number of various criteria and methodical schemes used for estimating the degree of influence of hydrogen can be found in the literature.The most simple method involves the determination of the number of bends that cause a specimen to fracture [3]. The influence of hydrogen was estimated by the time of transition from reversible hydrogen brittleness to irreversible [4] and also by the time to fracture of cylindrical specimens which were permanently hydrogenated under a tensile load [5]. We also mention other methods of estimating the influence of hydrogen: via the defect of the modulus of elasticity of specimens [6], separation stress of a hydrogenated specimen [7], ratio between the work of fracture under conditions of hydrogenation and in air [8], and the ultimate degree of shear deformation serving as a quantitative criterion [9].It is well known that in tests by the method of uniaxial tension the relative contraction of a specimen ~ is the most sensitive to the action of hydrogen. Therefore, the ratio lit H 8~r = --llt is used most often as a characteristic of hydrogen embrittlement [ 1 ]. Each of the...