Thermal Healing of Hydrogen Attacked Cracks in Steels

摘要

The specimens of carbon steel and 304 austenite stainless steel with the hydrogen attack bubbles or cracks were chosen for testing of thermal healing of hydrogen attack cracks. The hydrogen attacked carbon steel were circle annealed under 1000°C for 10 h and the hydrogen attacked 304 were heat treatment 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 could be healed completely by heat treatment. The healing of hydrogen attack bubbles or cracks was closely related to heat diffusion of Fe and C atoms. The driving force of crack healing resulted from the plastic deforming energy E_s induced by the growth of hydrogen attack bubbles or cracks. The critical condition of healing of bubbles or cracks is E_s ≥ 2 γ /r (where γ is the surface tension, r is the radius of bubbles or half length of crack). During healing of the hydrogen attack bubbles or cracks, the dense of dislocation around grain boundaries decreased and the dislocation type transformed from tangly dislocation with high energy to vertical and regular dislocation with low energy.