It is known as “Liquid Metal Embrittlement (LME)” that elongation and reduction of area can be markedly reduced when a solid metal is coated with a certain liquid metal and then immediately deformed in tension. There are several reports on the LME cracking of steel structures by molten zinc occured while hot dip zinc galvanizing.
In this study, first of all, LME of SM 50 A and STK 55 steels contacting with molten zinc was examined by both tensile and bending tests using a special testing apparatus. The elongation and the reduction of area in molten zinc were reduced to 0.21 and 0.170.20 at the same temperature in air, respectively. However, the tensile strength was almost the same as that of in the air. LME of welded steel joints was also examined in molten zinc. In the second place, the thermal strain variations of a steel pipe which was dipping into molten zinc were measured by using capsule type high temperature strain gages, and the data obtained were converted into thermal stresses. On the other hand, the temperature distributions of the steel pipe which was dipping into molten zinc were analyzed sequentially by using heat equation, and quasi-static thermal stresses were analyzed sequentially by using “Finite Element Method (FEM)”. The thermal stresses measured by using capsule type high temperature strain gages were similar to the analyzed stresses by FEM. The higher the dipping speed in molten zinc becomes, the smaller the thermal stresses are, which occur in the steel pipe while dipping. Therefore, quick dipping is one of the useful countermeasures to prevent the crack occurence in the steel members which are galvanized.