抄録
Critical COD values of weld metal obtained by standard bending COD test are often scattered widely. One of the causes of the scattering will be local embrittlement-zones in weld metal which are inevitable in multi-pass welding. In the present study, statistic investigations of the critical COD δc obtained by both bending tests and tensile tests are made. Standard bending COD specimens and notched-welded tensile specimens are cut from weldments of a steel for low temperature use, 22 mm thick. Weld metal of each specimen includes artificial embrittlement zones of different sizes ranging between 4 mm and 22 mm in depth. Tensile tests are made by a 600 tons testing machine with a coned disc spring.
It is demonstrated that the standard bending COD test is much sensitive to existence of local embrittle-ment-zone in weld metal than notched tensile test: Cumulative frequency of the δc values in bending test is almost the same independent to the depth of embrittlement zone. On the other hand, the δc values in tensile test are increased with decrease of the depth, and in the tensile specimens with an embrittlement zone of 4-5 mm in depth, final fracture is occurred at net stress level as high as yield stress of the material, although in some specimens the first fracture is observed as pop-in at lower COD level. Statistic study reveals that the δc values of the tensile specimens with an embrittlement zone ranging 4 mm-18 mm in depth are 1.5-2 times the δc values of the bending specimens.
