Effect of Carbon Content in Filler Metal on J-R Characteristics of Weld Metal for Nuclear Power Plant Surge Line Piping

For the surge line piping in Korean standard nuclear power plants, SA312 TP347 stainless steel, which has excellent intergranular corrosion resistance, has been used. In order to apply Leak-Before-Break (LBB) design concept for the surge line piping, the piping material and its welding joint should have satisfactory fracture resistance. Thus, it is important to improve fracture toughness of its weld metal for ensuring sufficient quality. In this study, in order to examine the effect of carbon content in the filler metal on the fracture toughness of its weld metal, specimens were provided with 3 different filler metals, whose carbon contents were 0.025, 0.030 and 0.050%, respectively. In comparison with the J-R test results, better J-R fracture characteristics were shown as the carbon content of filler metal decreases. Meanwhile, the reduction in strength was very small as the carbon content decreases. Therefore, carbon content of filler metal should be restricted for its weld metal in order to apply LBB design concept to the surge line piping. For austenitic steel, the number of interstitial atoms increases as the carbon content increases. Due to these atoms, strength tends to increase, while ductility and toughness are reduced, in general. In SEM observation, the numbermore » of carbide increased with increasing carbon content of filler metal. The fracture toughness was reduced under the influence of carbide because Nb carbides play a role of the void nucleation site. (authors)« less