Abstract
The fracture toughness of the welded joint measured by three point bending COD test usually results in unignorable variation. Especially low critical COD value is often obtained when the fatigue crack tip of COD test specimen is located at the coarse grain region i.e. partially embrittled region. In this paper, the reason to obtain such low critical COD value and fracture behavior of the COD test specimen are investigated in view of welded joints of low temperature service steels. To make examination into this subject, welded joints furnished with embrittled regions artificially are prepared. Welded joints with partially embrittled regions are reproduced in the following two types, which are welded joints contained regions of hot straining embrittlement and mixed with low toughness material. As a result, it was evidenced that critical COD value obtained by COD test specimen depended on the partially embrittled region, and that a crack initiation in any embrittled region had potential to lead to a fracture, but there was a tendency of fracture behavior showing not a one-step fracture but a multi-step fracture.
