A Study on the Defects in Seam Welds of Metal Coated Steel Sheets

概要

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Investigations were carried out on the defects which appear in the seam welds of zinc-coated and terne-coated steel sheets. It was revealed that some copper alloys of low melting point, which are formed by the reaction between electrode and coated metal, penetrate into the grain boundaries of the steel and that the alloy penetration causes fine cracks on the surface. The penetration takes place within a second and the penetration depth increases with the degree of plastic deformation of the material to be welded prior to welding. Higher welding current and longer current duration, both of which are related to the generation of heat, tend to increase the defects. Increasing of the flow rate of cooling water and immediate removing of deposit on electrodes decrease the defects. Thus the causes of the defects were clarified, and procedures to prevent the formation of defects and to improve weld quality were proposed. It was also confirmed that the same kind of defects would appear in spot welds as well as in seam welds of zinc-coated steel.
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