Healing of hydrogen attacked crack in austenite stainless steel by heat treatment

The specimens of 304 austenite stainless steel with the hydrogen attacked bubbles or cracks were heat treated under 600°C for 6 h. The SEM and TEM observations on the specimens before and after the heat treatment show that the bubbles or cracks can be healed completely by heat treatment. The healing of hydrogen attacked bubbles or cracks is closely related to heat diffusion of Fe and C atoms in austenite. The driving force of crack healing results from the plastic deforming energy E_s induced by the growth of hydrogen attacked bubbles or cracks. The critical condition of healing of bubbles or cracks is E_s ≥ 2γ/r (where γ is the surface tension, r is the radius of bubbles or half length of crack). During healing of the hydrogen attacked bubbles or cracks, the recovery, polygonization and recrystallization of the sub-grain were also taken place.