Cast stainless steel may experience embrittlement when it is exposed approximately to 300degreesC for a long period. In the present investigation, the three classes of the thermally-aged CF8M specimen were prepared using an artificially-accelerated aging method. After the specimens were held for 300, 1800 and 3600hrs. at 430degreesC, respectively, the specimens were quenched in water which is at room temperature. Load versus load line displacement curves and J-R curves were obtained using the unloading compliance method. J(IC) values were obtained using the ASTM E 813-87 and ASTM E 813-81 methods. In addition to these methods, J(IC) values were obtained using the SZW(stretch zone width) method described in JSME S 001-1981. The results of the unloading compliance method are J(Q)=543.9kJ/m(2) for virgin materials. The values of J(IC) for the degraded materials at 300, 1800 and 3600hrs. are obtained 369.25kJ/m(2), 311.02kJ/m(2), 276.7kJ/m(2) respectively. The results obtained by the SZW method are compared with those obtained by the unloading compliance method. Both results are quite similar. Through the elastic-plastic fracture toughness test, it is found that the value of J(IC) is decreased with an increase of the aging time.
