Reversible hydrogen embrittlement of steels as a physical phenomenon

Abstract

Reversible hydrogen embrittlement of structural steels results in serious technological problems, but the physical nature of this complex phenomenon has been insufficiently studied. We present new ideas on its mechanism and use fundamental concepts of the modem physics of metals, literature data, and results of our experiments with specimens made of St3 steel, 09G2S low-carbon steel, and a low-alloyed high-strength steel of type AB to substantiate these ideas. We show that plastic strain causing the appearance of incipient cracks in a metal is a necessary condition for development of reversible hydrogen embrittlement. Hydrogen, having a high diffusive mobility, is transported by moving dislocations to the places of crack initiation in the course of plastic deformation. The physical reason for the embrittling influence of hydrogen consists in the decrease in the critical stress necessary for the loss of stability of incipient microcracks and the transition to their autocatalytic propagation. The new ideas enable us to explain the established regularities of reversible hydrogen embrittlement and can also serve as a basis for further investigations of this phenomenon and the development of methods for its prevention.The harmful action of hydrogen on the mechanical properties of steels is well known [1][2][3][4][5][6][7][8]. At present, anxiety is caused by the formation of flakes and exfbliations in forgings and profile forge-rollings, welding cold cracks induced by hydrogen, development of hydrogen stress corrosion of main pipelines, and hydrogen fracture of equipment in chemical and petrochemical industry and other branches of modem and future engineering. Even a simple enumeration of the existing problems related to hydrogen demonstrates that the investigation of its effect on steel remains topical [9].The forms of manifestation of the negative action of hydrogen on properties of steel are very diverse. In [8], Kolachev proposed a classification of the types of hydrogen embrittlement. Among them, reversible hydrogen embrittlement attracts the highest attention from the scientific and applied viewpoints. Only reversible hydrogen embrittlement is considered to be "true" [10], and, therefore, it was studied in most detail. Various hypotheses and theoretical concepts of the mechanism of reversible hydrogen embrittlement have been proposed and analyzed in numerous works (see, e.g., [2,5,6,8]).The very fact of existence of numerous hypotheses shows that this phenomenon has not yet obtained a convincing and complete explanation. "White spots" in the mechanism of the action of hydrogen complicate the study, prediction, and development of methods for prevention of this process. For this reason, it is necessary to further investigate reversible hydrogen embrittlement, in order to understand it completely, from the beginning to the end [11].In this work, we describe new ideas on the physical nature of reversible hydrogen embrittlement. They are based on fundamental concepts of the modem physics of metals, which describe mec...

Speed of metal deformation of welded pipe sections in the process of natural tests

“…Відомо [1][2][3][4][5][6], що середня швидкість розповсюдження хвилі пониженого тиску вздовж осі трубопроводу складає для природного газу приблизно 400 м/с. А тому це значення приймають при визначенні оптимальної довжини випробуваних секцій.…”