９％Ｎｉ鋼溶接継手の応力・ひずみ挙動と破壊特性の考察

Abstract

Concentrations of stress/strain at the notch tip of notched-wide plate specimens of undermatching and evenmatching welded joints are investigated by elasto-plastic FEM analyses. In the undermatching weld specimen in which notch is located at weld fusion line, magnitude of stresses/plastic strains in an area of heat-affected zone side adjacent to the notch tip is released by plastic deformations of weld metal of which yield strength is lower than base metal, and as the results the stress/strain concentration is quite smaller than those in evenmatching weld specimen. This leads us to the conclusion that 9% Ni steel weldments of undermatching austenitic 70%Ni-alloy weld metal will be much insensitive to brittle crack initiation at HAZs than those of evenmatching ferritic weld metal. The local COD δBep values which should control stresses/strains at embrittled HAZs are also considerably smaller in undermatching specimens than in evenmatching specimen. Based on expected joint strength of 9%Ni steel weldments, discussions are made on fracture toughness requirement for both undermatching and evenmatching weld HAZs. Carck path observed in notched-wide plate tension tests at LNG temperatures that brittle crack initiated from the pre-existing notch at HAZ goes into austenitic weld metal and is often arrested is understood by the change of principal stress directions resulted from the difference in Young's modulus between weld metal and base metal.