Liquid zinc corrosion of steel welds

Abstract

Long term liquid zinc corrosion characteristics, up to 3000 h at 450°C, were investigated for the base metal and for multipass all weld metal deposits and weld joints produced via the gas shielded metal arc welding (GMAW and submerged arc welding (SAW) processes. The purpose of the present work was to determine the possibility of replacing the present shielded metal arc welding (SMAW) technique with the former two processes since they can offer demonstrably higher productivity than conventional SMAW in the fabrication process of hot dip galvanising baths. Regression analyses were also attempted to determine the corrosion rate quantitatively and thereby to establish a reasonable life prediction technique for such baths. It was found that the corrosion rate of the weld metal depends on the chemical composition, particularly on silicon concentration. Selection of low silicon (less than about 2.0 mass%) containing welding materials is thus vital to suppress the liquid zinc corrosion. Iron loss from the weld metal into the liquid zinc can be practically predicted with the selection of an appropriate magnitude of the parabolic rate constant. The information obtained in the present work confirmed that SMAW could safely be substituted by higher efficiency welding methods such as GMAW and SAW, subject to the restriction of the silicon concentration of the welding consumables.