Experimental studies on liquid zinc induced cracking of high tensile strength steel tubes for tower structural purposes under hot-dip galvanizing

摘要

This paper describes the results of experiments and temperature analyses regarding the incidents of liquid zinc induced cracking of high tensile strength steel (590MPa) tubes under hot dip galvanizing The cracks were observed at the toes of fillet welds between the tubes and the ring plates which were different in thickness. It is well known that the cracking of steel tubes due to "Liquid Metal Embrittlement" can be induced under the following conditions, that is, high tensile stress exists at the toes of the welds, and the temperature of the tubes exceeds the melting point of zinc (420℃). Hot - dip galvanizing is composed of three processes, dipping into molten zinc, air cooling, and water - cooling. To identify when the cracks had been induced, the experiments of hot - dip galvanizing were performed and cracks were reproduced from dipping into molten zinc through air - cooling. The results of temperature measurement in the experiments and analyses show that some thermal tensile stress can be generated by the difference of temperature between the tube and the plates due to the difference of their thickness at each process, while the temperature of the tube is kept above the melting point of zinc.