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IN-SITU INVESTIGATION OF HEALING ON HYDROGEN-ATTACKEDCRACK IN STEEL BY HIGH-TEMPERATURE MICROSCOPE

The in-situ observation of hydrogen-attacked cracks healing in carbon steel had been done by high-temperature microscope.The whole cracks healing process was recorded at the same time.The results show that the cracks became obviously thinner when heated under 630℃.The escaping of methane and inner crack exposure on specimen surface make a certain difference between this experiment and true condition,the analysis indicates the cracks healing temperature in experiment is lower than actual system.The healing of hydrogen attacked cracks is closely related to heat diffusion of Fe and C atoms in steel.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 ≥2 γ/r (where γ is the surface tension, r is the radius of bubbles or half length of crack).