Using the SM5OB(JIS) steel specimen cathodically charged with hydrogen, investigation of the mechanism of reversible hydrogen embrittlement of steel was carried out. To see the influence of defects on reduction of area, the steel was coldworked for four different amounts to give different concentration of defects and also to observe the effect of strain rate on reduction of area, tension tests were made at cross head speeds of 0.05 cm/min and 5cm/min at room temperature. The experimental results show that the larger amounts of cold work and the slower the cross head speed, the higher is the degree of hydrogen embrittlement.
These results agree well with the modified pressure theory that has been proposed by Tetelman to explain the mechanism of hydrogen embrittlement. To explain the low temperature anomalies in the hydrogen occulsive behavior of α-iron, Weiser proposed recently that the stable state of the absorbed hydrogen changed from atomic at high temperature to molecular as the temperature was lowered below critical value(about 200℃). Assuming that this theory is correct, it is most probable that the modified pressure theory is suitable for explanation of the mechanism of the hydrogen embrittlement of steel for this experimental results.
