Effect of prestraining on the behavior of hydrogen in structural steel
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EFFECT OF PRESTRAINING ON THE BEHAVIOR OF HYDROGEN IN STRUCTURAL STEEL E. Lunarska and K. Nikiforov We study the influence of cold working on the behavior of hydrogen in 0.25C–1Cr–1Mn–1Si–1Ni high-strength low-carbon low-alloy steel after various types of thermal treatment. The results of measuring the permeation of hydrogen are used to determine the lattice diffusion coefficient, the efficiency of trapping of hydrogen, and the formation of internal cracks for specimens deformed by shot peening, cyclic tension–compression, and uniform tension. The mode of deformation does not affect the value of the lattice diffusion coefficient for the bainite structure. All types of deformation increase the efficiency of traps corresponding to the deformation of the bainite lattice by cold working. The type of deformation specifies the morphology of internal hydrogen-induced cracks along the local slip strips in the metal.
Introduction The susceptibility of high-strength low-carbon low-alloy steels to hydrogen-induced cracking is affected by the hydrogen diffusivity specifying the rate of hydrogen access to the sites of its accumulation and by the hydrogen-entry flux responsible for the increase in the local concentrations of entrapped hydrogen up to certain critical level required for crack initiation and propagation [1, 2]. The cold working affects the susceptibility of steel to hydrogen-induced degradation due to the creation of hydrogen traps affecting the rate of hydrogen transport. Cold working also creates sites with local stress and dislocation concentrations that may serve as nuclei of cracks and, thus, affects the hydrogen-induced degradation. The dislocation structure and the distribution of stresses inside the plastically-deformed material may be different depending on the type of applied loading (tension, torsion, bending) and the mode of its application (static or cyclic). This should also modify the processes of hydrogen trapping and transport. Although the effect of cold working on the behavior of hydrogen is well-known (see, e.g., [3]), the effect of different types of deformation of the metal has not been fully explored [4]. In production, aircraft parts are commonly subjected to shot-peening treatment in order to decrease their susceptibility to fatigue failures. In the course of operation of highly-loaded aircraft parts, local plastic deformations can occur either due to stress concentration or as a result of fatigue. The indicated local changes in the structure of the metal and the stress and strain distribution affect the hydrogen transport and the susceptibility of the material to hydrogen embrittlement in the course of operation. In the present study, we examine the effect of deformation induced in the processes of production and/or operation (shot-peening, prefatigue, and uniform prestretching) on the behavior of hydrogen in low-alloy structural steel. Materials and Experimental Procedure Specimens were cut out from the slabs of the low-carbon low-alloy steel (0.253% C, 1.13% Cr, 1.04% Mn, 1.12% Ni, 1.65
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