Specific Mechanism of Hydrogen Influence on Deformability and Fracture of Low-Alloyed Pipeline Steel

We have conducted the special tests of standard tensile specimens that were preliminary hydrogen charged to the low concentration about 0.23 wppm at which the mechanism of hydrogen influence changes, and then fully hydrogen discharged before testing. It has been found that increasing the number of cycles of charging-discharging leads to decreasing the value of yield stress, due to the appearance of the microstructural defects, which facilitate the deforming ability of steel. Thus, even a short-term presence of the diffusible hydrogen in the ferrite-pearlite pipeline steel leads to irreversible changes in the material’s microstructure increasing its defectiveness and, consequently, affects on the macroscopic mechanical behaviour of steel.