Metal
Types
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 primarily 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
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 metals are iron-base alloys with small
percentages of carbon and other elements added to achieve desirable properties. Normally,
ferrous metals are magnetic and nonferrous metals are nonmagnetic.
Iron
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 manufactured 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
low-fatigue strength.
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. Alloying it with nickel, chromium, molybdenum, silicon,
or vanadium improves toughness, tensile strength, and.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.
Steel
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 Engineers (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:
- Low-Carbon Steel . . . . . . . . 0.05% to 0.30%
carbon
- Medium-Carbon Steel . . . . . . 0.30% to 0.45%
carbon
- High-Carbon Steel . . . . . . . . 0.45% to 0.75%
carbon
- Very High-Carbon Steel . . . . . 0.75% to 1.70%
carbon
LOW-CARBON STEEL.— Steel
in this classification is tough and ductile, easily machined, formed, and welded. It
does not respond to any form of heat-treating, except case hardening.
MEDIUM CARBON STEEL.—
These steels are strong and hard but cannot be welded or worked
HIGH-CARBON STEEL/VERY
HIGH-CARBON 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 specifications.
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 low-carbon steels.
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 are the most widely used and are normally
nonmagnetic.
The 400 series of steel is
subdivided according to their crystalline structure into two general groups. One
group is known as FERRITIC CHROMIUM and the other group as MARTENSITIC CHROMIUM.
Ferritic Chromium.— This
type of steel contains 12% to 27% chromium and 0.08% to 0.20% carbon. These alloys are the
straight chromium grades of stainless steel since they contain no nickel. They are nonhar-
denable by heat treatment and are normally used in the as annealed or soft
condition. Ferritic steels are magnetic and frequently used for decorative trim and
equipment subjected to high pressures and temperatures.
Martensitic
Chromium.— These steels are mag-netic and are readily hardened by heat treatment.
They contain 12% to 18% chromium, 0.15% to 1.2% carbon, and up to 2.5% nickel. This group
is used where high strength, corrosion resistance, and ductility are required.
ALLOY STEELS.— Steels
that derive their prop-erties primarily from the presence of some alloying element other
than carbon are called ALLOYS or ALLOY STEELS. Note, however, that alloy steels always
contain traces of other elements. Among the more common alloying elements are nickel,
chromium, vanadium, silicon, and tungsten. One or more of these elements may be added to
the steel during the manufac-turing process to produce the desired characteristics.
Alloy steels may be produced
in structural sections, sheets, plates, and bars for use in the “as-rolled”
condition. Better physical properties are obtained with these steels than are possible
with hot-rolled carbon steels.
These alloys are used in
structures where the strength of material is especially important. Bridge members,
rail-road cars, dump bodies, dozer blades, and crane booms are made from alloy steel. Some
of the common alloy steels are briefly described in the paragraphs below.
Nickel Steels.— These
steels contain from 3.5% nickel to 5% nickel. The nickel increases the strength and
toughness of these steels. Nickel steel containing more than 5% nickel has an increased
resistance to corrosion and scale. Nickel steel is used in the manufacture of aircraft
parts, such as propellers and airframe support members.
Chromium Steels.— These
steels have chromium added to improve hardening ability, wear resistance, and strength.
These steels contain between 0.20% to 0.75% chromium and 0.45% carbon or more. Some of
these steels are so highly resistant to wear that they are used for the races and balls in
antifriction bearings. Chromium steels are highly resistant to corrosion and to scale.
Chrome Vanadium
Steel.— This steel has the maximum amount of strength with the least amount of
weight. Steels of this type contain from 0.15% to 0.25% vanadium, 0.6% to 1.5% chromium,
and 0.1% to 0.6% carbon. Common uses are for crankshafts, gears, axles, and other items
that require high strength. This steel is also used in the manufacture of high-quality
hand tools, such as wrenches and sockets.
Tungsten Steel.— This
is a special alloy that has the property of red hardness. This is the ability to continue
to cut after it becomes red-hot. A good grade of this steel contains from 13% to 19%
tungsten, 1% to 2% vana-dium, 3% to 5% chromium, and 0.6% to 0.8% carbon. Because this
alloy is expensive to produce, its use is largely restricted to the manufacture of drills,
lathe tools, milling cutters, and similar cutting tools.
Molybdenum.— This
is often used as an alloying agent for steel in combination with chromium and nickel. The
molybdenum adds toughness to the steel. It can be used in place of tungsten to make the
cheaper grades of high-speed steel and in carbon molybdenum high-pressure tubing.
Manganese Steels.— The
amount of manganese used depends upon the properties desired in the finished product.
Small amounts of manganese produce strong, free-machining steels. Larger amounts (between
2% and 10%) produce a somewhat brittle steel, while still larger amounts (11% to 14%)
produce a steel that is tough and very resistant to wear after proper heat treat-ment.
NONFERROUS METALS
Nonferrous metals contain
either no iron or only insignificant amounts used as an alloy. Some of the more common
nonferrous metals steelworkers work with are as follows: copper, brass, bronze,
copper-nickel alloys, lead, zinc, tin, aluminum, and Duralumin.
NOTE: These metals are
nonmagnetic.
Copper
This metal and its alloys have many desirable properties. Among the commercial metals, it
is one of the most popular. Copper is ductile, malleable, hard, tough, strong, wear
resistant, machinable, weldable, and corrosion resistant. It also has high-tensile
strength, fatigue strength, and thermal and electrical conductivity. Copper is one of the
easier metals to work with but be careful because it easily becomes work-hardened;
however, this condition can be remedied by heating it to a cherry red and then letting it
cool. This process, called annealing, restores it to a softened condition. Annealing and
softening are the only heat-treating procedures that apply to copper. Seams in copper are
joined by riveting, silver brazing, bronze brazing, soft soldering, gas welding, or
electrical arc welding. Copper is frequently used to give a protective coating to sheets
and rods and to make ball floats, containers, and soldering coppers.
True Brass
This is an alloy of copper and zinc. Additional elements, such as aluminum, lead, tin,
iron, manganese or phosphorus, are added to give the alloy specific properties. Naval
rolled brass (Tobin bronze) contains about 60% copper, 39% zinc, and 0.75% tin. This brass
is highly corrosion-resistant and is practically impurity free.
Brass sheets and strips are
available in several grades: soft, 1/4 hard, 1/2 hard, full hard, and spring When working
with lead, you must take grades. Hardness is created by the process of cold roll- proper
precautions because the dust, fumes, or ing. All grades of brass can be softened by
annealing at a temperature of 550°F to 600°F then allowing it to cool by itself without
quenching. Overheating can destroy the zinc in the alloy.
Bronze
Bronze is a combination of 84% copper and 16% tin and was the best metal available before
steel-making techniques were developed. Many complex bronze alloys, containing such
elements as zinc, lead, iron, alu-minum, silicon, and phosphorus, are now available.
Today, the name bronze is applied to any copper-based alloy that looks like bronze. In
many cases, there is no real distinction between the composition of bronze and that of
brass.
CAUTION
When working with lead, you must take
proper precautions because the dust, fumes, or vapors
from it are highly poisonous.
Copper-Nickel Alloys
Nickel is used in these alloys to make them strong, tough, and resistant to wear and
corrosion. Because of their high resistance to corrosion, copper nickel alloys, containing
70% copper and 30% nickel or 90% copper and 10% nickel, are used for saltwater piping
systems. Small storage tanks and hot-water reservoirs are constructed of a copper-nickel
alloy that is available in sheet form. Copper-nickel alloys should be joined by
Lead
A heavy metal that weighs about 710 pounds per cubic foot. In spite of its weight, lead is
soft and malle-able and is available in pig and sheet form. In sheet form, it is rolled
upon a rod so the user can unroll it and cut off the desired amount. The surface of lead
is grayish in color; however, after scratching or scraping it, you can see that the actual
color of the metal is white. Because it is soft, lead is used as backing material when
punching holes with a hollow punch or when forming shapes by hammering copper sheets.
Sheet lead is also used to line sinks or protect bench tops where a large amount of acid
is used. Lead-lined pipes are used in systems that carry This is an alloy of copper and
zinc. Additional corrosive chemicals. Frequently, lead is used in alloyed elements, such
as aluminum, lead, tin, iron, manganese, form to increase its low-tensile strength.
Alloyed with or phosphorus, are added to give the alloy specific tin, lead produces a soft
solder. When added to metal properties. Naval rolled brass (Tobin bronze) contains alloys,
lead improves their machinability.
Zinc
You often see zinc used on iron or steel in the form of a protective coating called
galvanizing. Zinc is also used in soldering fluxes, die castings, and as an alloy in
making brass and bronze.
Tin
Tin has many important uses as an alloy. It can be alloyed with lead to produce softer
solders and with copper to produce bronze. Tin-based alloys have a high resistance to
corrosion, low-fatigue strength, and a com-pressive strength that accommodates light or
medium loads. Tin, like lead, has a good resistance to corrosion and has the added
advantage of not being poisonous; however, when subjected to extremely low tempera-tures,
it has a tendency to decompose.
Aluminum
This metal is easy to work with and has a good appearance. Aluminum is light in weight
and has a high arc welding or by brazing. strength per unit weight. A disadvantage is that
the tensile strength is only one third of that of iron and one fifth of that of annealed
mild steel.
Aluminum alloys usually
contain at least 90% aluminum. The addition of silicon, magnesium, copper, nickel, or
manganese can raise the strength of the alloy to that of mild steel. Aluminum, in its pure
state, is soft and has a strong affinity for gases. The use of alloying elements is used
to overcome these disadvantages; however, the alloys, unlike the pure aluminum, corrodes
unless given a protective coating. Threaded parts made of aluminum alloy should be coated
with an antiseize compound to prevent sticking caused by corrosion.
Duralumin
One of the first of the strong structural aluminum alloys developed is called Duralumin.
With the devel-opment of a variety of different wrought-aluminum alloys, a numbering
system was adopted. The digits indicate the major alloying element and the cold-worked or
heat-treated condition of the metal. The alloy, originally called Duralumin, is now
classified in the metal working industries as 2017-T. The letter T indicates that
the metal is heat-treated.
Alclad
This is a protective covering that consists of a thin sheet of pure aluminum rolled onto
the surface of an aluminum alloy during manufacture. Zinc chromate is a protective
covering that can be applied to an aluminum surface as needed. Zinc chromate is also used
as a primer on steel surfaces for a protective coating.
Monel
Monel is an alloy in which nickel is the major element. It contains from 64% to 68%
nickel, about 30% copper, and small percentages of iron, manganese, and cobalt. Monel is
harder and stronger than either nickel or copper and has high ductility. It resembles
stainless steel in appearance and has many of its qualities. The strength, combined with a
high resistance to corrosion, make Monel an acceptable substitute for steel in systems
where corrosion resistance is the primary concern. Nuts, bolts, screws, and various
fittings are made of Monel. This alloy can be worked cold and can be forged and welded. If
worked in the temperature range between 1200°F and 1600°F, it becomes “hot
short” or brittle.
K-Monel
This is a special type of alloy developed for greater strength and hardness than Monel. In
strength, it is comparable to heat-treated steel. K-monel is used for instrument parts
that must resist corrosion.
Inconel
This high-nickel alloy is often used in the exhaust systems of aircraft engines. Inconel
is composed of 78.5% nickel, 14% chromium, 6.5% iron, and 1% of other elements. It offers
good resistance to corrosion and retains its strength at high-operating temperatures. |
