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 modern 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.