Thermal Evolution Spectrum of Hydrogen from Low Carbon Steel Charged by Cathodic Polarization

Introduction of a large amount of hydrogen into specimens of a low carbon steel by cathodic polarization produces hydrogen damages such as blisters, microcracks, and dislocations. Hydrogen in the specimen exists as hydrogen atoms dissolved in iron lattice, atoms trapped at lattice defects such as dislocations, and gas precipitated in void-type defects such as blisters and microcracks. Hydrogen in the annealed specimens detected by the electrochemical permeation method was the lattice dissolved hydrogen, and the majority of hydrogen detected by the glycerol displacement method was the precipitated molecular hydrogen. In the case of the annealed specimens, one peak was observed in the thermal spectrum of hydrogen evolution rate. This peak originated in evolution of the precipitated hydrogen, and the peak temperature depended on specimen thickness, hydrogen concentration, and heating rate. In the case of cold-rolled specimens, two peaks were observed. The lower and higher temperature peaks originated in evolution of the precipitated hydrogen and the trapped hydrogen, respectively.