The creep rupture configuration of large welded specimens, having the shape as welded, was very different from that of conventional small welded specimens, cut off from the weld joint. The initiation of crack in rupture occurred at the toe of weld metal and the intersection of the bonds of both side weld metal. The crack propergated along the grain boundary of austenite of bond in the heat-affected zone of base metal.
The mechanism of creep rupture for large welded specimens was investigated with results of high temperature tensile test and creep rupture test at 500°C for synthetic HAZ specimens. The specimens were synthesized the coarse grain part near bond (max. heating temperature 1, 350°C), the fine grain part (max. heating temperature 900°C) and the intermediate part (max. heating temperature 1, 100°C) in the heat-affected zone of base metal.
By results of tests, high temperature tensile and creep rupture properties of the coarse grain part near bond were inferior to the other parts and the rupture occurred in austenite boundary. Especially, the absorbed energy to rupture of the coarse grain part near bond was smaller than that of the other parts above 400°C. Consequently, the creep rupture of large welded specimens may be occurred along the grain boundary of austenite of bond in the heat-affected zone of base metal.