Study on Crack Healing of Hydrogen Attack in Carbon Steel by Heat Treatment

The goal of the present experiments was to obtain crack healing of hydrogen attack (HA) in low-carbon steel by heat treatment. It was observed by scanning electron microscopy (SEM) that HA cracks experienced different healing effects. The results indicated that HA cracks ≤ 10 μm in length can be healed completely by cyclic heat treatment between room temperature and 1,000°C. Five cycles totaling 10 h were used. The studies performed showed that crack healing is controlled by diffusion and that the recovery kinetics depend on the plastic deforming energy, E_s, arising from the growth of HA bubbles or cracks. These findings led to the conclusion that the critical condition for healing of bubbles or cracks is E_s ≥ 2γ/r (where γ is the surface tension and r is the radius of bubbles or the half-length of cracks), provided the atoms of H, C, and Fe can diffuse rapidly.