hardness. A malleable cast iron is produced through a
easily as the low-carbon steels. They are used for crane
prolonged annealing process.
hooks, axles, shafts, setscrews, and so on.
INGOT IRON. Ingot iron is a commercially pure
iron (99.85% iron) that is easily formed and possesses
good ductility and corrosion resistance. The chemical
analysis and properties of this iron and the lowest carbon
steel are practically the same. The lowest carbon steel,
known as dead-soft, has about 0.06% more carbon than
ingot iron. In iron the carbon content is considered an
impurity and in steel it is considered an alloying ele-
ment. The primary use for ingot iron is for galvanized
and enameled sheet.
Of all the different metals and materials that we use
in our trade, steel is by far the most important. When
steel was developed, it revolutionized the American iron
industry. With it came skyscrapers, stronger and longer
bridges, and railroad tracks that did not collapse. Steel
is manufactured from pig iron by decreasing the amount
of carbon and other impurities and adding specific
amounts of alloying elements.
Do not confuse steel with the two general classes of
iron: cast iron (greater than 2% carbon) and pure iron
(less than 0.15% carbon). In steel manufacturing, con-
trolled amounts of alloying elements are added during
the molten stage to produce the desired composition.
The composition of a steel is determined by its applica-
tion and the specifications that were developed by the
following: American Society for Testing and Materials
(ASTM), the American Society of Mechanical Engi-
neers (ASME), the Society of Automotive Engineers
(SAE), and the American Iron and Steel Institute (AISI).
Carbon steel is a term applied to a broad range of
steel that falls between the commercially pure ingot iron
and the cast irons. This range of carbon steel may be
classified into four groups:
HIGH-CARBON STEEL/VERY HIGH-CAR-
BON STEEL. Steel in these classes respond well to
heat treatment and can be welded. When welding, spe-
cial electrodes must be used along with preheating and
stress-relieving procedures to prevent cracks in the weld
areas. These steels are used for dies, cutting tools, mill
tools, railroad car wheels, chisels, knives, and so on.
LOW-ALLOY, HIGH-STRENGTH, TEM-
PERED STRUCTURAL STEEL. A special low-
carbon steel, containing specific small amounts of
alloying elements, that is quenched and tempered to get
a yield strength of greater than 50,000 psi and tensile
strengths of 70,000 to 120,000 psi. Structural members
made from these high-strength steels may have smaller
cross-sectional areas than common structural steels
and still have equal or greater strength. Additionally,
these steels are normally more corrosion- and abrasion-
resistant. High-strength steels are covered by ASTM
NOTE: This type of steel is much tougher than
low-carbon steels. Shearing machines for this type of
steel must have twice the capacity than that required for
STAINLESS STEEL. This type of steel is clas-
sified by the American Iron and Steel Institute (AISI)
into two general series named the 200-300 series and
400 series. Each series includes several types of steel
with different characteristics.
The 200-300 series of stainless steel is known as
AUSTENITIC. This type of steel is very tough and
ductile in the as-welded condition; therefore, it is ideal
for welding and requires no annealing under normal
atmospheric conditions. The most well-known types of
steel in this series are the 302 and 304. They are com-
monly called 18-8 because they are composed of 18%
chromium and 8% nickel. The chromium nickel steels
Low-Carbon Steel . . . . . . . . 0.05% to 0.30% carbon
are the most widely used and are normally nonmagnetic.
Medium-Carbon Steel . . . . . . 0.30% to 0.45% carbon
The 400 series of steel is subdivided according to
High-Carbon Steel . . . . . . . . 0.45% to 0.75% carbon
their crystalline structure into two general groups. One
Very High-Carbon Steel . . . . . 0.75% to 1.70% carbon
group is known as FERRITIC CHROMIUM and the
other group as MARTENSITIC CHROMIUM.
LOW-CARBON STEEL. Steel in this classifi-
Ferritic Chromium. This type of steel contains
cation is tough and ductile, easily machined, formed,
12% to 27% chromium and 0.08% to 0.20% carbon.
and welded. It does not respond to any form of heat
These alloys are the straight chromium grades of stain-
treating, except case hardening.
less steel since they contain no nickel. They are nonhar-
MEDIUM-CARBON STEEL. These steels are
denable by heat treatment and are normally used in the
strong and hard but cannot be welded or worked as
annealed or soft condition. Ferritic steels are magnetic