抄録
Fracture toughness tests and unloading tests of C-1/2Mo steel and 21/4Cr-1Mo steel were conducted on CT specimens with different thickness at the ductile-brittle transition temperatures. According to fractographic examination of microscopic ductile tearing at the crack tip on the fracture surface of the specimens by a scanning electron microscope, the following two test procedures were proposed to estimate the plane strain fracture toughness KIc of small size specimens at the transition temperature; (1) The modified JIc test procedure to determine the value of J or KI at the initiation of microscopic ductile tearing at the midsection of the specimen which has critical volume as a trigger of cleavage fracture, and (2) the interpolation technique using the values of KIc which are determined by JIc test at the upper shelf temperature and KIc test at the lower shelf temperature.
