抄録
Thin wall ductile cast iron has many graphite nodules about 1000 counts/mm2 or more. Fracture toughness of cast iron is affected by graphite nodule counts. But it cannot be evaluated by usual testing because of its small thickness. The small punch test is a method which allows mechanical properties to be determined by small thickness specimens. Evaluation of fracture toughness was carried out using this test. The matrix of specimens was changed to 0 to 80% pearlite by heat treatment. Thin wall ductile cast iron with 50% pearlite or less showed lower fracture toughness than thick wall ductile cast iron, while the fracture toughness was the same for both cases having 50% pearlite or more. As a result of investigating the effects of nodule counts on fracture toughness in ductile cast iron with ferrite matrix, the fracture toughness was found to decrease with increasing nodule count until 600 counts/mm2, but remained nearly constant over 600 counts/mm2.
