Weld Cracking Behavior under Restraint (Part 2)

Abstract

Generally speaking, intensity of restraint in a weld joint increases according to the decrease of temperature. In many cases, however, the intensity of restraint is defined by the final value of it.In the present paper, considering the change of restraint during welding, relations between shrinkage speed and cracking during and after welding were investigated.In the previous report, experiments were conducted under the condition such that the speed of shrinkage is kept almost constant and it was reported that cracking is occurred in narrow range of temperature for both weldments of a mild steel and a high strength steel. However, in this report, the effects of shrinkage speed were investigated for both weldments of a mild steel and a high strength steel of 60 kg/mm2 strength level.The results obtained are as follows ;(1) Shrinkage speed and magnitude of reaction stress were widely changed by changing the gauge length of restraint, and weld cracking was occurred in wider range of temperature.(2) In mild steel weldments, weld crack is occurred only during cooling and crack intiation is not observed after cooled to room temperature.(3) However, in high strength steel weldments, crack initiation is observed during cooling and also after cooled to room temperature.(4) Especially the cracking after cooled to room temperature occures at a lower reaction stress range and the incubation period for these crack initiations (abont 20 hours after welded) was measured.The incubation time is insensitive to the applied reaction stress. Such cracking would be “Delayed failure” by hydrogen embrittlement.