Abstract
A series of experiments under cyclic loads was carried out to propose the newly repair welding procedure under cyclic loads.
It was confirmed that the sound welded joints could be obtained by gouging hot crack from the reverse side and by performing multi-pass welding on it even if hot crack occurred in the first-pass of the multi-pass welding from the surface. The soundness of welded joints could be confirmed from the results of the fatigue test, too. From the results of the fractography, the cellular dendrite which is the characteristic of hot crack was observed on the first pass of the weld metal. And striations which are the characteristics of fatigue crack were observed after the second pass and at the root of the welds. It was confirmed that fatigue crack was generated from the starting point of hot crack and the root of welds and it was propagated to the thickness direction by cyclic loads. The size of hot crack was influenced by welded metal and the magnitude of Δδb (root gap displacement before welding). As the measure of monitoring the propagation of fatigue crack after welding, Δδa (root gap displacement after welding) was proposed and its usefulness was verified by comparing with macrograph of welded joints. As to propagation of crack due to cyclic loads, it was effective that Δδb was made to be small. From the result of the fatigue test, soundness of the welded joints repaired by the proposed procedure was confirmed.
