厚板80kg/mm<SUB>2</SUB>高張力鋼溶接部の脆性破壊発生特性(第3報)

Abstract

Effects of residual stress and repair welding on the brittle fracture initiation in weld fusion line of the manual arc welded joints for 80kg/mm2 high strength steel were investigated using the wide plate tension test specimen with an angular distortion and a surface notch. And the results were analyzed by application of the fracture mechanics. The main results are summarized as follow:(1) The maximum residual stress of T-shaped welded joints is about 50kg/mm2 in the direction of weld line. That of repair weld zone is about 35kg/mm2 in the direction of right angle with weld line and is about 50kg/mm2 in the direction of weld line.(2) The brittle fracture strength of the T-shaped welded wide plate specimen with a surface notch, is lower than that of the transversely welded W(1) specimen. The test results with the specimen in which residual stress is superimposed can be adjusted quantitatively by taking stress intensity factor KR of Eq. (4) into consideration. The fracture toughness obtained by the above procedure agrees with that of a transversely welded W(1) specimen without residual stress.(3) The fracture toughness of the repair welded wide plate specimen almost equals to the minimum values of stress relieved welded joints when the notch tip is heated to the temperature range, 300-550°C, in repair welding. Therefore, the fracture stress of the repair welded joints is extremely lowered if defects remain in the fusion line. But it is as high as the fracture stress of the transversely welded W(1) joints as welded, when the maximum temperature of notch tip is below 250°C in repair welding.(4) It is important that the maximum heat temperature of fusion line is below 250°C in repair welding. Removal ofhydrogen by heating is effective, but its temperature should be below 250°C.(5) We calculated relation between fracture stress and crack length of T-shaped welded joint and repair weld zone for welded structure.