Alloy Steel
When classified according to the method of
manufacture, steels are known as (I) basic, open
An alloy metal may be defined as an intimate
hearth; (2) basic, electric; (3) acid, Bessemer; (4) acid,
mixture of two or more elements. Any ferrous or
electric; (5) acid, open hearth; or (6) basic, oxygen
nonferrous metal may be alloyed to form an alloy
furnace. The method of manufacture has a lot to do
metal with new and desirable characteristics.
with the properties of the finished steel, so these
A simple alloy consists of two metals in any
distinctions are important to metallurgists and to
proportion. An example of a simple alloy is the
design engineers. Since the method of manufacture is
combination of tin and lead, which is called solder.
not usually important to the HT, these processes will
The melting temperature of the lead is 621F (327C).
not be discussed in this training manual.
Tin has a melting temperature of 450F (232C).
When classified according to the method of
However, as the two metals are mixed, any
shaping, steels are often referred to as cold rolled steel,
combination of the two results in a lower melting
forged steel, drawn steel, and cast steel.
temperature than 621F (327C). At a certain
proportion of the metals, the lowest melting
Classifying steels according to the method or
temperature is reached. This point is called the
methods of heat treatment leads to such terms as
EUTECTIC POINT.
annealed steel, and casehardened steel.
Steel is a combination of iron and controlled
Classifying steels according to properties gives us
amounts of carbon. Alloy steels are created by adding
such classes as corrosion-resisting steels (CRES);
other elements to plain carbon steel. Alloy steels are
heat-resisting steels; low-expansion steels; free-
identified by the name of the alloying element or
machining or free-cutting steels; casehardening steels;
elements, usually without reference to the carbon that
high tensile steels (HTS); and special treatment steel
is present. Alloy steels are further identified as
(STS).
low-alloy steels or high-alloy steels, depending upon
the amount of alloying material that is present. Some
Probably the most reasonable way to classify
elements that are alloyed with carbon steel and the
steels is by their chemical composition. Steels that
qualities imparted to steel by each are as follows:
derive their properties primarily from the presence of
CHROMIUM--Increases resistance to corrosion
carbon are referred to merely as "steels" or sometimes
and improves hardness, toughness, wear resistance,
as "plain carbon steels." Steels that derive their
strength, and the responsiveness to heat treatment.
properties primarily from the presence of some
alloying element other than carbon are referred to as
M A N G A N E S E -- I n c r e a s e s strength and
"alloys" or "alloy steels." Note, however, that plain
responsiveness to heat treatment.
carbon steels always contain some carbon. Note, also,
MOLYBDENUM--Increases toughness and
that the use of the word alloy should not really be
improves the strength of steel at higher temperatures.
limited to mean an alloy steel, since there are many
NICKEL--Increases strength, ductility, and
alloys that contain no iron at all and are, therefore, not
toughness.
steels.
TUNGSTEN--Produces dense, fine grains; helps
steel to retain its hardness and strength at high
Plain Carbon Steel
temperatures.
SILICON--Improves the electrical quality of the
Plain carbon steels vary in carbon content from
steel.
about 0.05 percent to as much as 1.70 percent carbon.
VANADIUM--Retards grain growth and
The properties of the steel depend upon the amount of
improves toughness.
carbon present and the particular way in which the iron
and the carbon combine. The plain carbon steels are
NONFERROUS METALS
known (in increasing order of the amount of carbon
present) as mild steel, low-carbon steel, medium-
Although ferrous metals are used aboard ship
carbon steel, high-carbon steel, and very-high-carbon
in greater quantities than the nonferrous metals, the
nonferrous metals are nevertheless of great
steel.
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