Abstract
Four types of spheroidal graphite cast irons in which the pearlite ratio had been controlled from 0 to 94% were tested at −150 to 20°C. Fracture toughness JIC at 20°C lowers as the pearlite ratio increases. The lowering rate at the pearlite ratio 0 to 50% is smaller than that at 50 to 100% . All specimens show a transition behavior as temperature lowers that JIC greatly decreases by transition of fracture mode from ductile to brittle. The lowest temperature of the upper shelf region and the transition temperature in the relation between JIC and temperature rise as the pearlite ratio increases. The fractography well corresponds to these facts.
