Morphology Evolution and Mechanisms of Crack Healing in a Low-Carbon Steel During Isothermal Heat Treatment

Crack healing in metallic materials has significant economic, ecological, and social benefits. However, the morphological evolution and mechanism of crack healing have no clear consensus. Therefore, in this study, isothermal heat treatment was applied to heal internal cracks at temperatures of 900 °C to 1200 °C for 15 to 120 minutes. Subsequently, microhardness and tensile tests were performed on the specimen to evaluate the reliability of the healed specimens. The results show that the morphology evolution in crack healing can be divided into three stages. Both atomic diffusion and recrystallization dominate crack healing. Atomic diffusion and recrystallization work together to heal cracks in the first stage. Atomic diffusion allows the recrystallization of materials, and recrystallization accelerates the processes of atomic diffusion. In the second and third stages, atomic diffusion controls crack healing on its own. In addition, with increasing healing time, the ultimate tensile strength and microhardness of the crack healing zone decrease due to the difference in the healing mechanism.