抄録
The fracture toughness tests of ductile cast iron (JIS FCD 60) were conducted at ambient and low temperatures by using compact tension specimens and three-point bending specimens with fatigue pre-cracks. The distribution of the half-value breadth of X-ray diffraction profiles beneath the fracture surface was determined. Based on those results and electron fractographic observation, the mechanism of fracture in ductile cast iron was discussed as a function of test temperature. The main results are summarized as follows:
(1) The size of the plastic zone ωy determined from the half-value breadth distribution is related to the fracture toughness Ki through
ωy=0.13(Ki/σY)2
where σY is the yield stress.
(2) The fracture toughness decreased with lowering temperature and the fracture mode of the matrix changed from dimples to cleavage. The unique relation was established between the fracture surface strain and Ki2/σY.
