Aluminum, Chrome, Copper, Iron, Metal, Stainless Steel, Steal, Tin

Steel, The Strongest of All The Common Metals

Steel is composed of extremely minute particles of iron and carbon,
forming a network of layers and bands. This carbon is a smaller
proportion of the metal than found in cast iron, the percentage being from
3/10 to 2-1/2 per cent.

Carbon steel is specified according to the number of “points” of carbon, a
point being one one-hundredth of one per cent of the weight of the steel.
It may contain anywhere from 30 to 250 points, which is equivalent to
saying, anywhere from 3/10 to 2-1/2 per cent, as above. A 70-point steel
would contain 70/100 of one per cent or 7/10 of one per cent of carbon by
weight. The percentage of carbon determines the hardness of the steel, also
many other qualities, and its suitability for various kinds of work. The
more carbon contained in the steel, the harder the metal will be, and, of
course, its brittleness increases with the hardness. The smaller the grains
or particles of iron which are separated by the carbon, the stronger it
will be, and the control of the size of these particles is the object
of the science of heat treatment.

In addition to the carbon, steel may contain the following:

Silicon, which increases the hardness, brittleness, strength and difficulty
of working if from 2 to 3 per cent is present.

Phosphorus, which hardens and weakens the metal but makes it easier to
cast. Three-tenths per cent of phosphorus serves as a hardening agent and
may be present in good steel if the percentage of carbon is low. More
than this weakens the metal.

Sulphur, which tends to make the metal hard and filled with small holes.

Manganese, which makes the steel so hard and tough that it can with
difficulty be cut with regular tools. Its hardness is not lessened by
annealing, and it has great tensile strength.

Alloy steel has a varying but small percentage of other elements mixed with
it to give certain desired qualities. Silicon steel and manganese steel are
sometimes classed as alloy steels. This subject is taken up in the latter
part of this chapter under _Alloys_, where the various combinations
and their characteristics are given consideration.

Steel has a tensile strength varying from 50,000 to 300,000 pounds per
square inch, depending on the carbon percentage and the other alloys
present, as well as upon the texture of the grain. It is heavier than
cast iron and weighs about the same as wrought iron. It is about one-ninth
as good a conductor of electricity as copper.

Steel is made from cast iron by three principal processes: the crucible,
Bessemer and open hearth.

Crucible steel

Crucible steel is made by placing pieces of iron in a clay or
graphite crucible, mixed with charcoal and a small amount of any desired
alloy. The crucible is then heated with coal, oil or gas fires until the
iron melts, and, by absorbing the desired elements and giving up or
changing its percentage of carbon, becomes steel. The molten steel is then
poured from the crucible into moulds or bars for use. Crucible steel may
also be made by placing crude steel in the crucibles in place of the iron.
This last method gives the finest grade of metal and the crucible process
in general gives the best grades for mechanical use.

Bessemer steel

is made by heating iron until all the undesirable
elements are burned out by air blasts which furnish the necessary oxygen.
The iron is placed in a large retort called a converter, being poured,
while at a melting heat, directly from the blast furnace into the
converter. While the iron in the converter is molten, blasts of air are
forced through the liquid, making it still hotter and burning out the
impurities together with the carbon and manganese. These two elements are
then restored to the iron by adding spiegeleisen (an alloy of iron, carbon
and manganese). A converter holds from 5 to 25 tons of metal and requires
about 20 minutes to finish a charge. This makes the cheapest steel.

Open hearth steel is made by placing the molten iron in a receptacle
while currents of air pass over it, this air having itself been highly
heated by just passing over white hot brick. Open hearth steel is
considered more uniform and reliable than Bessemer, and is used for
springs, bar steel, tool steel, steel plates, etc.

Read more about steel here: Steel