STUDY OF THE EFFECT OF DOUBLE ANNEALING ON THE QUALITY OF SPHEROIDAL GRAPHITE CAST IRONS

The study of the influence of double annealing on the structure and properties of rolled cast irons of the LShNM-58 design was carried out. As a result of the studies conducted using a complex plan obtained by combining plan 24 with a 4×4 Latin square, the optimal double annealing mode was selected: stage I - temperature 1000 °C, holding time 1 h; stage II - temperature 600 °C, holding time 3 h. Double annealing of cast irons of the working layer led to spheroidization of pearlite and graphitization of pearlite and eutectic cementite, in cast irons from the necks of the rolls - to a structure heterogeneous in morphology of eutectoid transformation products, which included graphite, ferrite, pearlite of different dispersion, bainite, martensite and phosphide eutectic. At the same time, the strength properties of heat-treated cast irons were higher than those of cast iron rolls by 8...96%. As a result of the research, a technology for high-temperature heat treatment of rolling rolls of the LShNM-58 design was developed, tested and recommended for implementation.