by J.M. Drew St. Paul Publishing Company
1918
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
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 molds 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 the
same 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 molds forming ingots. These ingots are afterwards heated and rolled the same as wrought
iron.
These processes have been so cheapened recently that soft steel is largely taking the place of wrought iron for many
use". It is now cheaper than the better grades of iron, and is taking the place of iron in almost all cases excepting
where extreme softness, (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.