Welding
Non-Ferrous
Metals
Treating
Welding
Cast Iron
Welding
Ferrous
Metals
Continued
on next page... HOW
STEELS ARE CLASSIFIED Steels
are classified in several different ways. The primary method of classification
is by carbon content, or by content
of alloying elements other than carbon (which is present in every steel); in short,
by chemical composition.
Let’s take a look at steels from
that standpoint first. Classification
by Composition Carbon
Steels. When we refer to ”carbon”
steel, we mean steel which contains iron, carbon, less than 1.65%
manganese, less than
0.6% copper, and small amounts of silicon, sulphur, and phosphorus. The
sulphur and phosphorus
are considered impurities, and not more than 0.05% of
either is allowed by specifications, except in the case
of some grades designated as ”free-machining”. The amount of manganese
may range from as little as .35%
to as much as 1.65%.
The family of carbon steels (it is
a large family, with nearly 50 standard grades) is usually sub-divided into four
sub- families:
the low-carbon steels, which contain no more than 0.30% carbon; the medium-carbon
steels, which range from
0.30 to 0.45% carbon*; the high-carbon steels, from 0.45 to 0.75% carbon;
and the very-high-carbon steels, which
range up to 1.50% carbon. The low-carbon steels, often termed ”mild”
steels, are more widely used than the grades
with higher carbon content. They are quite ductile, can be machined or formed
with relative ease, and can be
welded by any process. As the carbon content increases, tensile strength and hardness
increases, but ductility declines,
and machining of the steel may become more difficult. The very-high-carbon steels
are used principally for
springs and for tools which are used to cut or form metals. High-carbon and very-high-carbon
steels are seldom welded;
when welding must be used, the metal must be heat-treated before, during, and
after welding if sound welds
are to be obtained, and the desired mechanical properties of the steel retained.
Alloy Steels. Any
steel which contains more than 1.65% manganese, or 0.60% copper, or a guaranteed
minimum amount
of any other metal, is termed an ”alloy” steel. The metals most frequently
used for alloying purposes are nickel,
chromium, molybdenum, vanadium, and manganese. *Some
metallurgists refer to the medium-carbon range as ”0.25 to 0.50% ”.
1
