The joining of wrought iron by fusion. Wrought iron can be welded using the arc, resistance, oxyfuel gas, and hammer welding processes.
In general, the procedure for welding wrought iron is the same as for welding mild steel, with slight modification. The fusion temperature of wrought iron is somewhat higher than that for mild steel. Fusion welding temperatures range between 1480 and 1540°C (2700 and 2800°F).
The shielded metal arc welding (SMAW), gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) processes can be used to weld wrought iron. The higher temperatures necessary for welding wrought iron are attainable by slightly decreasing the welding speed below that used for mild steel welding. At the reduced speed the pool of molten metal immediately following the arc remains molten for a longer period of time, which allows better degasification and affords removal of the entrained slag. This results in sound weld metal.
Oxyfuel Gas Welding
Wrought iron has inherently superior welding characteristics because of the self-fluxing action of the iron silicate, or slag. This self-fluxing action provides protection during heating, providing an environment conducive to a strong, uniform weld.
During the oxyfuel gas welding of most other ferrous metals, a fluxed or greasy-appearing surface occurs when the temperature is sufficiently high for fusion. In wrought iron, however, a greasy appearance occurs initially, due to the fluxing action of the slag, at temperatures between 1150 and 1200°C (2100 and 2200°F). These temperatures are below the fusion temperature of the base metal and are too low for the application of filler metal. After the “greasy” surface appears, therefore, the process requires continued heating to raise the base metal to fusion temperature.
Consistent maintenance of a puddle of molten metal is required for fusion welding. The end of the rod stays immersed as metal is deposited. The edges of the molten puddle and the surrounding colder metal fuse to form a solid joint. Metal deposition occurs only via the molten puddle, not directly from the rod. To obtain a sound weld without the oxides that produce porosity,the molten puddle must be undisturbed. Excessive puddling or agitation of the molten pool causes undue exposure of the molten metal to the atmosphere, resulting in the formation and entrapment of oxide in the weld.