Effect of Fisheye on Fatigue Strength of Weld Metal

Using Titania type electrodes that are liable to develop fisheyes in the deposit metal, depending upon the test method adopted, two kinds of specimens were prepared : one as weld and the other subjected to a hydrogen-removing treatment (250°C, 8h). They were put to a fatigue test on the Ono's Repeated Bending Fatigue Testing Machine, with the following results :1) In the former specimen, fatigue cracks originate from micro-blowholes lying somewhat deep under the surface; while in the latter, they do so from micro-blowholes very close to the surface. These micro-blowholes correspond to the nuclei of fisheyes appearing in tension test pieces.2) In the former, nominal stress, namely, fatigue limit with no consideration made for the locations of these micro-blowholes, is about 2-3kg/mm2 lower than in the latter (Fig.3). When, however, the crack-developing stress is considered, the difference well be about 10kg/mm2 (Fig. 5) ; this is presumably due to the variance of hydrogen content between the two.