Restoration of impact properties of internal crack healing in a low carbon steel

In this paper, a new model of internal crack presetting was presented via a butt-joint and compression method. Restoration of impact properties of internal crack healing in a low carbon steel was investigated using a 300 J pendulum impact testing machine. The results show that impact properties of crack healing zone dramatically increase from 900 ℃ to 1000 ℃. Recrystallization in the crack healing zone promotes the rapid restoration of impact properties of internal crack healing. Percentage recovery of impact properties after crack healing treatment increases with increasing healing temperature and holding time in the temperature range 900-1100 ℃, while impact properties deteriorate at 1200 ℃ due to the formation of reticular ferrite and grain coarsening near the crack healing zone. Additionally, a new phenomenon is discovered: when internal cracks are disappeared completely, tensile properties of crack healing zones can be restored completely but their impact properties are only partially achieved. Post-fracture analysis indicates that in the initial healing stage the Charpy fracture exhibits massive brittle dimples and unhealed regions, and the ultimate fracture mode of the center region presents cleavage and ductile dimple mixed fracture.