Handbook-Welding Ferrous Metals

10 Wrought Iron Wrought iron, widely used a century ago, is no longer made in the U. S., but you may be called on to weld it, since a great deal of wrought iron piping is still in service. Wrought iron has properties much like those of mild steel, but is chemically and structurally much different. It is essentially a mixture of rather pure iron and a slag made up chiefly of iron oxides and iron silicates. The slag is distributed through the iron in the form of very fine particles which have been stretched, by rolling, into threads or fibers so small that there may be 250,000 or more per square inch of metal cross-section. This structure not only gives the metal high ductility, but also improves its corrosion resistance. You can weld wrought iron with any good low-carbon steel rod (such as OXWELD No. 1 H.T.) and without using flux. However, the iron component, which is virtually carbon-free, melts at a higher temperature than carbon steel, while the slag component melts at a much lower temperature. The slag will melt first and give the surface of the welding vee a greasy appearance. With most base metals, this greasy look is a signal that the metal is ready for fusion with the filler metal, but in the case of wrought iron this is not true. Considerably more heat must be applied before the metal really begins to melt. In welding wrought iron, you can concentrate the flame more on the rod than you should when welding steel, and let the puddle build up to a fair size before moving the flame from side to side to fuse the base metal with the puddle. Try to keep the motion of the rod to a minimum, and to melt as little of the base metal as possible.