Abstract
The dependence of fracture toughness (K//i//c) on the area fraction of transgranular fracture was investigated on four alloys aged at 393 K. The fracture toughness of transgranular fracture is affected by Fe content and has minus 1/6 power dependence on the volume fraction of Fe rich inclusions. The fracture toughness of intergranular fracture has about minus 1/20 power dependence.