Effects of Crack Starter Bead Preparation in Drop-Weight Test on Nil-Ductility Transition Temperature

The procedure for making crack starter weld deposit on drop-weight test (DWT) specimens was altered from two passes to one pass in about 1990. The effects of some parameters of crack starter weld process on drop-weight test results were studied. Results of this study indicated that length of overlap of the second pass and height of crack starter beads were most effective on nil-ductility temperature (T_NDT). When overlap length and bead height of two-pass deposit were small enough, T_NDT obtained by two-pass deposit became lower than one-pass T_NDT, the discrepancy being by as much as 25°C. T_NDT values for 24 Japanese steels were determined using two different DWT methods, one-pass deposit and two-pass deposit having small overlap length and bead height. The difference of T_NDT depending on DWT method could be seen only for high-toughness low-alloy steel base metals. For other materials (i.e., low-to-medium-toughness low-alloy steel base metals, weld metals, and high-toughness carbon steels), T_NDTS by two-pass and one-pass deposits were essentially the same. For lower-toughness steels, T_NDT was frequently lower than the temperature of _vT_cv − 33°C), and thus, the reference nil-ductility temperature RT_NDT was determined from Charpy impact test results. These results can be taken as a way of interpreting the past toughness evaluations made for operating plants using the two-pass T_NDT.