This section discusses some of these processes.
The first three
paragraphs are introductory; they define an alloy, classify alloys,
and describe the ways of preparing alloys.
The paragraphs that
follow discuss, in more detail, the metal-working processes most
commonly used.
DEFINITION
An alloy is a metallic substance containing one or more metals and/or
elements.
If strictly applied, this definition would classify all
metals as alloys since no metal refinement can produce an absolutely
pure metal. The alloying of a metal is a concentrated effort to make
it gain certain qualities or properties. Some of the metals used in
alloying are nickle, chromium, molybdenum, aluminum, titanium,
copper, and manganese.
The alloying elements are silicon, sulfur,
and carbon. Each metal or element will cause the base metal to take
on different properties.
CLASSIFICATION
Industrial alloys are classed as ferrous (having an iron base) and
nonferrous; the ferrous alloys are the larger group.
The most
important ferrous alloys are those made with carbon. When the carbon
content is less than .13 percent by weight, the alloys are known as
steels. The terms, alloy steel and special steel, are descriptive of
steels with relatively large amounts of chromium and nickel.
An
example of such an alloy is stainless steel.
Aircraft industry
requirements have helped spur the development of important nonferrous
lightweight alloys such as aluminum and magnesium.
With increased
flight, speed, and payload, much use is being made of titanium and
titanium-based alloys.
These have much higher melting points and
strength-to-weight ratios than aluminum and its alloys.
ALLOY PREPARATION
The most common way to prepare alloys is to melt the constituent
metals together. If the melting points of the metals differ widely,
or if one is very reactive, it may be convenient to first prepare a
master alloy, portions of which are then melted with the remaining
metals. Depending upon the nature of the elements to be alloyed, the
melting process may be carried out in furnaces fired by gas, coke, or
oil.
Electrical heating, by resistance, induction, or arc melting
methods, is also used.
A few alloys are prepared directly by the process in which the
metals are extracted from their ores. For example, pig iron
is prepared by the reduction of iron ore in the blast furnace.
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