Influence of the Bulk Concentration of Hydrogen in the Metal on the Specific Features of Deformation of Low-Alloy Pipe S
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INFLUENCE OF THE BULK CONCENTRATION OF HYDROGEN IN THE METAL ON THE SPECIFIC FEATURES OF DEFORMATION OF LOW-ALLOY PIPE STEEL І. M. Dmytrakh,1, 2 R. L. Leshchak,1 A. M. Syrotyuk,1 and О. L. Lutyts’kyi1
UDC 620.9:546.11
We establish the specific features of the process of deformation of low-alloy pipe steel in hydrogencontaining media depending on the bulk concentration of hydrogen in the metal. We determine a characteristic value of concentration for which the mechanism of the influence hydrogen of on the deformation of steel changes: Below this value, the material undergoes plasticization and, above this value,
* it suffers embrittlement. The value C H can be regarded as an important engineering parameter for
the evaluation of strength and the analysis of fracture processes in materials and structural elements in hydrogen-containing media and for the development of new technologies of hydrogen treatment of structural materials with an aim to optimize their operating characteristics. Keywords: pipe steel, hydrogen-containing media, hydrogenation of a metal, hydrogen absorption, hydrogen concentration, static load, mechanical characteristics.
At present, in the literature, one can find a large body of information about the influence of hydrogen on the mechanical properties of structural steels and alloys [1, 2]. However, quite often these data are contradictory. Thus, in some works, the hardening effect of hydrogen on the material was accompanied by the increase in its yield strength [3]. At the same, in some other experiments, on the contrary, the yield strength decreases under the action of hydrogen media [4]. This situation is most probably connected with the difficulty or impossibility of taking into account all available factors (sizes of the specimens, conditions of their hydrogenation, control over the concentration of hydrogen in the material, specific features of the applied loads, etc.) affecting the investigated phenomena. It should also be noted that the major part of investigations had a substantial disadvantage, namely, the actual values of hydrogen concentration in the metal were unknown, and the degree of hydrogenation of the material was taken into account indirectly. The results of the tests performed by the authors and presented in what follows remove this disadvantage. In our tests, the specimens were deformed for a known bulk concentration of hydrogen in the metal, and the behavior of the mechanical characteristics of the material was studied as a function of its concentration. Methods Used for the Investigation Tested Specimens. We studied 20 steel used for the production of pipeline systems. Its nominal chemical composition and standard mechanical characteristics are as follows: 0.17–0.24 wt.% C, 0.17–0.37 wt.% Si, 0.35–0.65 wt.% Mn, 0.04 wt.% S, and the balance is Fe; σ u = 440–540 MPa, σ y = 260 MPa, δ = 26%, HB = 156. 1 2
Karpenko Physicomechanical Institute, Ukrainian National Academy of Sciences, Lviv, Ukraine. Corresponding author; e-mail: [email protected].
Translated from Fizyko-Khi
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