Plasticity is the ability of a material to deform
permanently without breaking or rupturing. This prop-
erty is the opposite of strength. By careful alloying of
metals, the combination of plasticity and strength is used
to manufacture large structural members. For example,
should a member of a bridge structure become over-
loaded, plasticity allows the overloaded member to flow
allowing the distribution of the load to other parts of the
Brittleness is the opposite of the property of plastic-
ity. A brittle metal is one that breaks or shatters before
it deforms. White cast iron and glass are good examples
of brittle material. Generally, brittle metals are high in
compressive strength but low in tensile strength. As an
example, you would not choose cast iron for fabricating
support beams in a bridge.
Ductility and Malleability
Ductility is the property that enables a material to
stretch, bend, or twist without cracking or breaking. This
property makes it possible for a material to be drawn out
into a thin wire. In comparison, malleability is the
property that enables a material to deform by compres-
sive forces without developing defects. A malleable
material is one that can be stamped, hammered, forged,
pressed, or rolled into thin sheets.
Corrosion resistance, although not a mechanical
property, is important in the discussion of metals. Cor-
rosion resistance is the property of a metal that gives it
the ability to withstand attacks from atmospheric,
chemical, or electrochemical conditions. Corrosion,
sometimes called oxidation, is illustrated by the rusting
Table 1-2 lists four mechanical properties and the
corrosion resistance of various metals or alloys. The first
metal or alloy in each column exhibits the best charac-
teristics of that property. The last metal or alloy in each
column exhibits the least. In the column labeled Tough-
ness, note that iron is not as tough as copper or nickel;
however, it is tougher than magnesium, zinc, and alumi-
num. In the column labeled Ductility, iron exhibits a
reasonable amount of ductility; however, in the columns
labeled Malleability and Brittleness, it is last.
The metals that Steelworkers work with are divided
into two general classifications: ferrous and nonferrous.
Ferrous metals are those composed primarily of iron and
iron alloys. Nonferrous metals are those composed pri-
marily of some element or elements other than iron.
Nonferrous metals or alloys sometimes contain a small
amount of iron as an alloying element or as an impurity.
Ferrous metals include all forms of iron and steel
alloys. A few examples include wrought iron, cast iron,
carbon steels, alloy steels, and tool steels. Ferrous met-
als are iron-base alloys with small percentages of carbon
and other elements added to achieve desirable proper-
ties. Normally, ferrous metals are magnetic and nonfer-
rous metals are nonmagnetic.
Pure iron rarely exists outside of the laboratory. Iron
is produced by reducing iron ore to pig iron through the
use of a blast furnace. From pig iron many other types
of iron and steel are produced by the addition or deletion
of carbon and alloys. The following paragraphs discuss
the different types of iron and steel that can be made
from iron ore.
PIG IRON. Pig iron is composed of about 93%
iron, from 3% to 5% carbon, and various amounts of
other elements. Pig iron is comparatively weak and
brittle; therefore, it has a limited use and approximately
ninety percent produced is refined to produce steel.
Cast-iron pipe and some fittings and valves are manu-
factured from pig iron.
WROUGHT IRON. Wrought iron is made from
pig iron with some slag mixed in during manufacture.
Almost pure iron, the presence of slag enables wrought
iron to resist corrosion and oxidation. The chemical
analyses of wrought iron and mild steel are just about
the same. The difference comes from the properties
controlled during the manufacturing process. Wrought
iron can be gas and arc welded, machined, plated, and
easily formed; however, it has a low hardness and a
CAST IRON. Cast iron is any iron containing
greater than 2% carbon alloy. Cast iron has a high-com-
pressive strength and good wear resistance; however, it
lacks ductility, malleability, and impact strength. Alloy-
ing it with nickel, chromium, molybdenum, silicon, or
vanadium improves toughness, tensile strength, and