Lesson IV – Steel, Annealing, and Welding Cast Iron


There are many kinds of steel, but to the general blacksmith only two kinds are known,—”mild steel” and “tool steel.” The mild steel is fast taking the place of iron. In some instances it is cheaper, and it is certainly giving better results than iron. The mild steel is easily worked and welded, as it stands a higher heat than the harder steel. Sand is the only welding compound needed to weld mild steel.

The finer steel must be handled with great care, and few are the smiths who know how to heat highly carbonized steel. We often hear the remark, when a tool breaks, “He didn’t harden it right.” No hardening will prevail in an overheated tool, and the hardening and tempering of a tool is comparatively easy when the steel has not been overheated. The trouble begins when the smith places the steel in the fire. If it is a thin edge, the danger is greater than in a heavier piece. There is danger of overheating the outside edges before the center part is hot enough to work. High grade steel is also ruined by keeping it long in the fire at a high heat; thus the fiber of the steel is ruined and the carbon burned out. The higher the percentage of carbon, the more difficult is it to weld, and that for two reasons: First, such steel cannot be heated to a high heat; and second, there is less fusing material— slag and cinders—in this kind of steel, hence it is often necessary to use some kind of welding compound in welding it. Good steel breaks easily when cold, if cut into a little. It will also crumble under the hammer when white hot.

If the broken ends of a steel bar are of a fine grain and light color, the steel is good. Glistening and glittering coarse grains are a sign of poor steel. Alloy steel is used for crushing machinery, and for armor plate, and also for machinery where the friction is high. For alloy is used chromium, manganese, and tungsten.


Highly carbonized steel is often found too hard to file or drill without annealing. To reduce brittleness and increase flexibility, annealing must be resorted to. The simplest, yet most effective, method is to heat the steel slowly until red hot, then bury it in the cinders, and let it cool slowly. If a piece of fine steel is heated and exposed to the air in cooling, it will cool too fast, especially in cold weather, and contract what is termed “air temper.”

Cast iron is sometimes found to be too hard to drill before it is annealed; then a different method of annealing must be used. Heat to a low, red heat. Place a piece of brimstone just where the hole is to be; this will soften the iron if it is left to cool slowly, as in annealing steel.

Welding Cast Iron

I don’t believe I have met a blacksmith yet who could not weld cast iron, but I shall never meet the man who really can do it. There is no such thing as welding cast iron, and I offered $25 for a recipe to weld cast iron, in my book “Modern Blacksmithing,” but so far I have had no response. Cast iron will melt and crumble before a welding heat is attained. It might, however, be melted together; but if such a thing could be done, it would generally leave the casting so melted together shorter, and consequently leave it in a different shape, and then it would be of no value. When a smith tells you he welds cast iron, you need not say he is lying, for he has evidently succeeded in “sticking” a piece of malleable iron together, and imagined it was cast iron. The wish, in such a case, then, was the father of the thought. Fine malleable steel is sometimes a very good article, and can easily be welded.