An evaluation of cast stainless steel (CF8M) fracture toughness caused by thermal aging at 430°C

Cast stainless steel may experience embrittlement when it is exposed approximately to 300°C 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 430°C, respectively, the specimens were quenched in water which is at room temperature. Load versus load line displacement curves andJ- 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 areJ Q = 543.9kj/m2 for virgin materials. The values ofJ IC for the degraded materials at 300, 1800 and 3600hrs. are obtained 369.25kJ/m2, 311.02kJ/2, 276.7kJ/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 ofJ IC is decreased with an increase of the aging time.