Experimental Study of Low Concentration Diffusible Hydrogen Effect on Mechanical Behaviour of Carbon Steel

The presented work is dedicated to the evaluation of the mechanical behaviour of the ferrite-pearlite carbon steel under a low concentration of diffusible hydrogen in the bulk of the metal. Received standard stress-strain diagrams under different hydrogen concentration \( C_{H} \) in the specimens have shown on the existence of some specific value of the hydrogen concentration \( C_{H}^{ * } \) at which the mechanism of hydrogen influence changes, namely: below this value the enhanced plasticity (decreasing of the yield stress) takes places and above – the hydrogen embrittlement occurs. This phenomenon was explained based on the special tests of tensile specimens, which were preliminary charged by hydrogen to concentration \( C_{H}^{ * } \) and then discharged to the concentration \( C_{H} \approx 0 \). It has been found that increasing the number of cycles of charging-discharging leads to decreasing the value of yield stress. Thus, even a short-term presence of the hydrogen in the material leads to irreversible changes in the structure of the material, namely: the appearance of defects at the microlevel. This facilitates the deforming ability of steel and reduces the value of the plasticity limit.