Healing of Long Fatigue Cracks in Steel Plates by High-Density Current Pulses

Abstract

The healing of cracks in metals and alloys by means of exposure to strong pulsed electromagnetic fields is of considerable interest, since it allows to increase the reliability and service life of structural materials and products made of them. In spite of practical importance, the methodology of selection of the parameters of the electric pulse treatment, which would allow to heal the defects, has not been developed yet. Healing of long macrocracks in thin plates by welding of their edges under electric pulse action is of particular difficulty. The present work is devoted to the study of the possibility of selecting the parameters of electric pulse treatment for such a case. The mechanism of healing of macrocracks in flat specimens is considered. The proposed multistage method of electric pulse treatment allowed to heal a significant length of macrocrack in a steel plate. The conducted studies of microstructure of cross-sections of AISI201 stainless steel samples confirm that healing occurs by the mechanism of welding of crack edges by molten material. The electric pulse creates at the tip of the crack significant compressive stress and high temperature, causing the melting of steel. The experiments showed significant heterogeneity of healing along the macrocrack front and in depth, however, the quality of healing improved with increasing distance from the plate surface. In the healed region along the crack edges, a zone with elongated grains surrounding a central zone with equiaxed grains is observed, which reflects the kinetics of cooling of the molten region of the specimen exposed to the current pulse.