Iron And Steel

It is necessary, or at least desirable, that the blacksmith should know something about the nature of the materials that are to be worked with.

One should, of course, know in a general way something about the different kinds of iron, (cast iron, wrought iron, malleable cast, etc.), which one sees all about; and has, as a rule, a general knowledge of steel and the uses to which it may be put. One should have heard of cast steel, tool steel, machine steel, and Bessemer steel, and have perhaps a somewhat dim idea of what is meant by each of these terms.

Let us in a few words define the different kinds of iron and steel, and show how each is made and for what it may be used.
Iron, as every school boy knows, is mined in many parts of the world where it is found mixed with stone and other materials. This mixture is called "ore," and may be in the form of solid rock or a brown powder or dust. Iron is seldom found in the pure state, but there is a great difference in the purity of the ores found in different parts of the world. This fact will be referred to later.

The iron is separated from the ore by a melting process called "smelting," which consists in melting the ore by great heat so that the iron will flow out in a liquid form. This liquid is not pure iron, but contains more or less impurities, depending upon the purity of the ore from which it is melted. From the smelter the liquid iron flows out in a trench in the earthen floor, and is led into little side trenches of the right size to make a lump of iron which may be handled by one man. These lumps are called "pig iron," from the fancies resemblance to a litter of pigs which a row of them presents when in the trenches. For a like reason the large trench is called the "sow."

Common cast iron is made by melting pig iron or a mixture of pig iron and old cast scrap iron and pouring it into moulds. The proper mixing of the materials is of great importance in making good castings.

Malleable cast iron, or, as it is more commonly called "malleable iron," is common cast iron from which the carbon has been baked by long-continued heating in red-hot ovens. It is the usual practice to bake it for seven days. By baking out the carbon the iron is made much less brittle, and hence is useful for a great many more purposes than the common cast iron.

Wrought iron, as we usually see it, is made of old wrought iron scrap, which is worked over by being done up in bundles held together by wire or band iron, heated to welding heat and run between rollers to give it the required shape and size. In reworking old scrap great care must be taken to use only wrought iron scrap, and pickers are employed to carefully exclude all pieces of cast iron and steel; for if any of these materials get into the bundles the result will be too much carbon, which will cause the iron to be harsh and brittle, instead of malleable and tough.

The best wrought iron for purposes where great toughness is required comes from Sweden, but is commonly known to the trade as "Norway iron." It is very tough, because it is free from carbon and other impurities. The ore from which it is made is the finest iron ore known, and for this reason is used for making the finest grades of tool steel. No scrap iron is used in making Swedish iron.

Steel is simply iron to which has been added a very small amount of carbon.
Carbon is one of the most common substances. We are most familiar with it in the form of charcoal. The diamond is almost pure carbon. There are other elements to be found in steel in very small amounts, but for all practical purposes if we take pure iron and add to it a small percentage of carbon we will have steel. Steel such as is used for making cold chisels contains less than 1 per cent of carbon.

In the usual process of making fine tool steel, rods of pure wrought iron are packed in charcoal in long iron troughs, or boxes, which are sealed with fire clay and placed in a furnace, where they are subjected to a high heat for several days. The heat is so regulated that the rods do not melt, but are kept near the melting point. During this process the iron absorbs some of the carbon from the charcoal, and is thus changed to steel.

The proper amount of carbon is determined by drawing out one of the rods occasionally and testing it.
The steel made by this process is called "blister steel," for the reason that the surface of the rods is covered with small blisters.
What is known as "shear steel" is made by heating these rods of blister steel and welding them together under a steam hammer, or by running them between rolls.

"Cast steel" is made by melting blister steel in earthen pots called "crucibles" and pouring into moulds forming ingots, which are afterwards heated and rolled or hammered out into bars.

It will easily be seen that cast steel is much better for all tools than blister steel or shear steel, because the melting insures a thorough mixture of the carbon so that all parts are sure to contain the same amount. In blister steel the outside portions of the rods contain a much greater percentage of carbon than the centers; and in the shear steel the welding process does not cause such a complete mixture as in the process of melting which cast steel undergoes.

What is known as "mild steel," or "machine steel,” is a steel which contains so little carbon that it is practically of thesame nature a good wrought iron, excepting that it is somewhat stiffer and more durable when subjected to wear. It is produced by several different processes, the most important of which are the Bessemer and the open hearth processes.

In the Bessemer process the pig iron is melted in a large crucible or converter, and air is forced through the molten metal from the bottom. This causes the carbon to burn out and leave a mass of nearly pure iron. Then a quantity of iron having a known percentage of carbon is added, thus giving any desired percentage of carbon to the steel.

The open hearth process consists in melting pig iron in large furnaces built of fire brick and keeping it at a very high temperature, until the impurities are practically all worked or burned out, leaving a liquid mass of nearly pure iron, which is then poured into moulds forming ingots. These ingots are afterwards heated and rolled the same as wrought iron.

Soft steel has largely taken the place of wrought iron for many uses. It is cheaper than the better grades of iron, and is taken the place of iron in almost all cases excepting where extreme softhess, (for example, the making of rivets), is required. For this purpose nothing is better than Norway iron.

Iron is the most useful of all the metals: First, because of its great strength; secondly, because it is so easily forged or changed in shape when hot, but becomes rigid, and at the same time tough, on being allowed to cool. Wrought iron and all the milder forms of steel may be readily welded below a burning temperature. Steels containing a high percentage of carbon (in general, all tool steels) may be welded if protected from the air by borax or other flux which will withstand a high heat.