摘要：UNI C 15, C 45, and C 85 pla.in carbon steel specimens were prepared for J-integrat testing in the furnace-annealed, normalized, conditions and spheroidized at an upper-shelf temperature of 225'C. Furnace-anniealed and normiafizea steéts aóÀur" o-iturú1, regards to tougihness,' ùh,"r"u, spheroidized steels exhibit higher levels of toughness and ductitity. Since fracture in low and medium C lamblar péarlite steelé occurred predominantly in the ferrite, fracture toughnesies were associated wtth the distribution of pearlite colonies withiin the ferrite and the resulting contained plastic deformation, which grows as the average free ferrite parth decreases. Also J1. values in sphetroidized structures resulted depended mainlv on the mean free path between carbidés with a decrease in spacing resiliiií iiti*éiti|giÈness values.
