Wrought iron and steel will fuse when the proper temperature and the right quality of the temperature is attained. We often read in the trade journals and in books, “Iron or steel will weld when hot enough;” but the metal may be hot enough, be of the proper heat, and still it will refuse to fuse. Then there must be something besides the degree of heat to consider, and that is the ingredients or quality of the heat. Such as the fire is, such the heat. If the fire is full of small cinders and sulphur, you try any degree of heat you wish, and there will be no weld; and if, perchance, you will be able to make it “stick,” it will be a poor weld, that will break at the first strain. Iron as well as steel will burn, and if overheated will make a poor weld. The heat at which iron will weld is the melting heat. When the scales which are formed on the iron melts, the pieces will stick together. But the scales or oxide may not melt even at a high heat. For instance, if the iron is held too close to the tuyer, and the blast strikes directly on the iron, or the coal or coke may have burned out, so you have a hollow fire, then the air will also strike the iron and form black scales, preventing the scales from melting. Too much blast may be the cause in some instances. A trained eye will tell at a glance whether the fire is a fire for welding or not. If the iron is burnt, there will be a lot of sizzling sparks issuing from it, and the surface is rough and dry. In this kind of a heat there is no fusing quality. Sand is the best welding flux for iron. It will form a glue-like coating, and promote the dissolution of the oxide. If the parts—iron or steel—that are to be welded together be of a large dimension, it is best to heat slowly, for otherwise the outside might be too hot while the center is still too cold. This lower temperature in the center will chill the outside when the iron is placed on the anvil, and thus spoil the weld.
Not only in welding, but for all kinds of forging, it is important to have all tools in their proper places, and the apprentice should be taught to be careful not to take any tools away from the forge’s tool bench. This often happens in a repair- shop, and it is very annoying to have taken much pains in producing a good weld, and then, when you place it on the anvil, you find that the hammer has been used by some one and left somewhere in the shop.
Steel of a high percent of carbon is more difficult to weld than iron or mild steel. If fine steel is heated until the sparks appear, it is ruined and the best thing to do is to cut the burnt part off. Highly carbonized steel cannot be welded without a flux, because it cannot be heated to a heat to melt the scales without burning, if no fluid is used. In welding steel, beware of the oxidizing fire. That does not necessarily mean too much blast; it may mean too little blast, or it may mean a hollow, dirty fire also. Borax is the most used flux for welding fine steel. It has two offices: First, to help melt the scales; second, it prevents burning and oxidizing, by covering the steel with a glue-like coating. This coating keeps the air from coming in contact with the steel, and thus much mischief is prevented. The flux does not act as a glue; it promotes the melting of the oxide. And although an oxidizing fire is a bad fire, there could be no weld without it, for this oxide is simply a thin coat of iron; and when this iron is melted, that, and that alone, is the cement that has the power to unite the two pieces, as it is “flesh of the same flesh.”
Steel borings are often used in welding steel. If these borings can be placed between, it will aid materially in making the two pieces stick, as it will not slip so easily when these chips grip in the steel. All kinds of welding would be easy if we could find coal free from sulphur.