The drop-weight test plays an important role in determining the reference nil-ductility transition temperature (RT_NDT), which indicates the fracture toughness characteristics of ferritic steels in the design of nuclear power plant components. In recent years, however, it has been shown by various papers that the nil-ductility transition temperature (NDTT) obtained by this test depends on such parameters as the welding conditions of the crack-starter bead, notch location, and other factors.

In this paper, the authors have investigated the scattering of NDTT and discuss the necessity of revising Japan Electric Association Code 4202, The Method of Drop-Weight Testing of Ferritic Steels, under the auspices of the Japan Electric Association; this standard refers to the practical welding conditions employed by many research organizations in Japan.

From the results of this study on the effects of such parameters as the welding current, preheating, interpass temperature, shape of bead, welding speed, and notch location on NDTT, the authors conclude that the most influential factor to be determined for prevention of wide scattering of NDTT is the welding current. Based upon these results, standard JEAC 4202 was revised on 20 March 1984.