Separations in steels subjected to controlled rolling, followed by accelerated cooling

Zones on the fracture surfaces of Charpy specimens and profiles of the fractures of these specimens are examined using impact-bending tests carried out in the temperature range of +20 to–90°C and fractography. The specimens were cut out of hot-rolled plates produced from 05G2B super-low-carbon steels that contained Ti, Nb, V, and Cu microadditives using controlled rolling, followed by accelerated cooling. A detailed analysis of separations, including a study of the morphology, number, area of separations, and the surrounding stress-relaxation zones, and the structure of the walls, has allowed us to identify the mechanisms of the origination and growth of the separations. It has been found that the correlated changes in the length, width, and depth of the separations are accompanied by the formation and expansion of the stress-relaxation zones around the separations. The rate of expansion of the area of these zones is higher than that of the area of the separations, which favors the macroplastic fracture of the specimens.