On the Fillet Weld Cracking of 50kg/mm^2 Grade High Strength Steels : On the Heel-Crack

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It is generally known that the majority of fillet weld cracks are toe cracks underbead cracks and so on. But we have found unusual crack in the fillet welds of 50kg/mm^2 grade high strength steels. The crack occurred at the heel-opposite side of the toe-of fillet weld. Therefore we refer to them by the name of "Heel-Crack" in this paper. We have carried out various experiments to make clear the characteristics of the crack and the causes of the crack formation, and also we have established a practical preventive method for the crack which based on these test results. The test results are summarized here as follows: (1) Heel-cracks are located at the heel of fillet welds and they are hardly detectable by inspection methods such as visual observation and magnetic particle inspection. (2) It has been difficult to reproduce the heel-cracks by well known weld cracking tests such as C. T. S. test and Reeve cracking test. But we have developed Non-restraint T type Cracking Test which can reproduce heel-cracks succssfully. (3) Heel-crack is a low temperature crack which occurs at temperature below 100℃. (4) Main factors which affect the heel-crack formation are the cooling process of the weld, rigidity and hydrogen in the weld. (5) Many 50kg/mm^2 grade high strength steels are susceptible to the formation of heel-cracks. But semi-killed steels seem somewhat less susceptible to heel-cracks than killed steels. (6) Crack sensitivity is increased by increasing the carbon equivalent and/or the maximum hardness at underbead. (7) Heel-crack could be prevented by preheating or controlling the bead length. To prevent the heel-crack, higher preheating temperature and longer weld bead are preferable.
大阪大学の論文

On the Fillet Weld Cracking of 50kg/mm^2 Grade High Strength Steels : On the Heel-Crack

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