Search

A study has been made of the hydrogen absorbed by a high-strength steel during cathodic polarization in near-neutral solutions using rigidly controlled experimental conditions. Direct hydrogen analysis by the vacuum heating technique has been utilized and it has been established that use of high extraction temperatures (i.e. > 300°C) can lead to errors which are probably associated with a reaction between adsorbed water and the steel. Extraction at 200°C has been found to give satisfactory results free from this error. The linear relationship between hydrogen absorption and time observed during the early stages of polarization in solutions above pH 4.0 was considered to be characteristic of a rate-controlled slow discharge mechanism of hydrogen evolution. The relationship between hydrogen absorption and overvoltage has been studied in the range pH 4 - 10; the results were found to conform with those anticipated from the kinetics of hydrogen evolution. Metallurgical structure was found to exert a strong influence on the ability of the steel to absorb hydrogen, and a modification of previous theories on delayed failure due to hydrogen has been proposed on the basis of the present study. The influence of arsenic additions to the solution on hydrogen absorption during cathodic polarization have been studied. It has been found that there is a region of pH and overvoltage where hydrogen uptake is inhibited and these results have been correlated with sustained load experiments. The results of this study have been utilized in an attempt to establish whether delayed failure may result from galvanic action produced by discontinuous coatings of electronegative metals (Cd and Zn) on high-tensile steels.