Identifying Metals and Their Physical...

Identifying Metals andTheir Physical Properties

METALS are used to make

agricultural machines and

equipment, tools, structures, vehicles,

and even electronics. Many products

rely on steel and other metals for proper

assembly. Just think what life would be

like without metal?

Objective:

� Describe the properties, structures, and characteristics of metals.

Key Terms:

�

Properties of Metals

Metal is an element. There are more than 100 known elements, and about 75 percent of

them are classified as metals. The most common metal elements are iron, copper, aluminum,

chromium, gold, tin, zinc, and silver.

By using a combination of metals, mostly iron, steel is created. The different types of steel

include stainless steel, galvanized steel, and carbon steel. Steel is used in making knives,

machines, rails, cars, motors, and wire.

TERMS ASSOCIATED WITH METALS

Because of the widespread use of metals and the necessity for them in agriculture, it is

important for the worker to have a basic understanding of metals and metallurgy when fabri-

cating metals and making repairs to them.

E-unit: Identifying Metals and Their Physical Properties

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adhesion

alloy

annealing

casting

compressive strength

crystal structure

fatigue strength

flexure strength

hardening

hardness

high-temperature creep

impact strength

malleable

shear strength

space lattice

steel

tempering

tensile strength

TABLE 1. Terms Associated with Metals

Term Meaning

alloy A mixture of two or more metals or of metals and one or more nonmetals.

high-temperature

creep

The slow stretching of steel under stress at high temperatures.

adhesion The sticking together of two unlike metals involving a mechanical bond. The

mechanical bond involves the flowing of a metal in a liquid form into the

pores of a metal in a solid form.

annealing The softening of metal and removing of the brittleness. The annealing

process is done by heating the metal to a cherry red and then allowing it to

cool slowly in vermiculite, dry hot sand, or a furnace.

tempering Obtaining the desired hardness and toughness in metal.

hardening The process of making steel harder. This is done by heating the steel to a

cherry red, then cooling it quickly in water. Hardened steel is not only

extremely hard but also brittle. Hardening is the first step in tempering.

hardness The ability of a material to resist being indented.

casting Pouring melted metal into a mold so that it will be a certain shape after

cooling.

malleable The capability of being extended or shaped by being beaten with a hammer

or by being pressed by rollers.


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FIGURE 1. Periodic table of the elements.

PROPERTIES AND STRUCTURES OF METALS

The distinct characteristics used to help identify a given metal are referred to as its proper-

ties. These characteristics include brittleness, color, corrosion resistance, ductility, malleability,

and strength.

Mechanical Properties

Mechanical properties are hardness, brittleness, ductility, percent elongation, toughness,

wear, and strength. There are different types of strength.

1. Tensile strength is the

ability of a metal to resist

being pulled apart.

2. Compressive strength

is the ability of a metal to

resist deformation by

forces pushing it together.

3. Shear strength is the


forces acting in opposite

directions.

4. Fatigue strength is the

ability of a metal to take

repeated loads without

deforming.

5. Impact strength is the


shock.

6. Flexure strength is the ability of a metal to bend without deforming or breaking.

Chemical Properties

Chemical properties refer to the chemical make-up of a metal and its ability to resist reac-

tion with the environment. Chemical properties are oxide or compound composition; acidity

or alkalinity of the metal; corrosion resistance; resistance to acids and salts; and resistance to

other chemicals. Corrosion-resistant metal will resist deterioration from heat, sunlight, water,

and humidity.

Other Properties

Physical properties relate to the dimensions, shape, specific gravity, and weight of a metal.


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Tensile StrengthCompressive Strength

Sheer Strength Fatigue Strength

FIGURE 2. Some types of strength a metal may possess.

Thermal properties are characteristics such as expansion, contraction, thermal conductivity,

and specific heat.

Optical properties are luster, color, light transmission, and light reflection.

Electromagnetic properties are electrical conductivity, magnetic permeability, and galvanic

action.

Acoustical properties relate to the ability of a metal to transmit and reflect sound.

Crystal Structure

The crystal structure of a metal is the way molecules of a substance are arranged or how

they are packed or fitted together. The pattern these atoms make is called a space lattice.

Most metals are arranged in simple patterns.

STEEL

Steel is an alloy of iron and carbon and usually other metals. There are hundreds of differ-

ent steels, ranging in composition from 99 percent iron and very small amounts of carbon to

less than 55 percent iron and a large percentage of other metals.

There are four major steel-making processes: the Bessemer furnace, the open-hearth fur-

nace, the electric furnace, and the oxygen furnace. All four processes are similar in principle in

that pig iron is treated with an oxygen-bearing material to burn out the carbon and impurities.

Alloying metals are then added.

Approximately 80 to 90 percent of steel produced is carbon steel. Carbon steel contains 0.05

to 1 percent carbon and less than 1.5 percent other elements. The strength of steel increases as

the carbon content increases, but the hardness, brittleness, and difficulty of fabrication also

increase. There are hundreds of alloy steels. The effects of additives vary.


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Cubic body centered (bcc)

Fe, V, Nb, Cr

Cubic face centered (fcc)

Al, Ni, Ag, Cu, Au

Hexagonal

Ti, Zn, Mg, Cd

FIGURE 3. Crystal structures of commonly used metals.

TABLE 2. Examples of Additives to Steel and the Associated Effects

Additives Effects

Chromium Makes the alloy hard and increases the wear and corrosion resistance of steel.

Steels containing more than 4 percent chromium are called stainless steels.

Sulfur Added to aid in machinability of the steel.

Silicon Added to improve the electrical, mechanical, and thermal characteristics.

Nickel Added to increase the toughness and strength.

Vanadium Added to increase the strength.

Tungsten Used to produce tool steels that will maintain a cutting edge at high heat.

Aluminum Helps to provide a hardened surface.

Molybdenum Added to increase the hardness and the endurance limits of steel.

Oxygen Forms iron oxide, which is not desirable.

Phosphorus At high percentages, considered an impurity; at low percentages, improves

machinability.

Carbon Changes the physical properties.

CLASSIFYING METALS

Of the known elements, about 80 to 90 are technically considered metals. Of these, 10 to 15

are considered important in agricultural mechanics. These metals can be broken down into

four groups.

Ferrous Metals

The main ingredient of these types of metals is iron. Pig iron, or cured iron, is iron ore

changed to pig iron by a blast furnace. Cast iron is a product of pig iron and contains a consid-


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FURTHER EXPLORATION…ONLINE CONNECTION: Blast Furnace

A blast furnace is used to produce pig iron from iron ore. But, how does a blast furnace

work? How long does it take the raw materials to form molten pig iron? How big is a blast fur-

nace? Learn more about the process of converting iron oxides into liquid iron by visiting the fol-

lowing website:

http://www.steel.org/AM/Template.cfm?Section=How_Steel_is_Made&CONTENTID

=25317&TEMPLATE=/CM/ContentDisplay.cfm

erable amount of carbon and some impurities. It is brittle and granular in structure. It is

formed by pouring into special castings.

Wrought iron, a product of pig iron that has had most of the carbon removed, is a two-com-

ponent metal consisting of high-purity iron and iron silicate. Wrought iron is the only ferrous

metal that contains siliceous slag. The slag is responsible for the desirable properties of

wrought iron, particularly its resistance to corrosion and fatigue. Wrought iron is used for riv-

ets, porch furniture, and decorative roof supports.

Steel is iron characterized chiefly by its carbon content. Types of steels include mild, tool,

stainless, galvanized, and plated.

Non-ferrous Metals

A non-ferrous metal has no iron and is made up of a single element. Non-ferrous metals

are aluminum, copper, lead, magnesium, nickel, tin, tungsten, zinc, silver, and gold.

Aluminum is a silver-white, malleable, ductile metal. It is known for its electrical conduc-

tivity, heat conductivity, and rust resistance and for being lightweight. Aluminum is commonly

used in the manufacturing of truck bodies, aircrafts, ladders, roofing, and siding.

Copper, reddish-brown in color, is used for tubes, wire, sheets, and plates. It has excellent

workability, either hot or cold, and the highest electrical and heat conductivity of all commer-

cial metals. Cooper is mainly used in electrical wiring, electric motors, and plumbing systems.

Lead has a bluish-white color and a bright luster. It is soft, highly malleable, and ductile; has

slight tenacity; and is a poor conductor of electricity. It is used in batteries, lead pipe, and con-

tainers for corrosive liquids.

Magnesium is a very lightweight, silver-white metal that is malleable and ductile and burns

in air. It is usually found in the alloy known as Dowmetal. It is useful for airplane bodies, truck

and auto wheels, ladders, lawnmower frames, and other items for which weight reduction is

important.

Nickel is a hard, malleable, ductile, tenacious white metal that is somewhat magnetic. It is

valuable for the alloys it forms with other metals.


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DIGGING DEEPER…

UNCOVERING ADDITIONAL FACTS: Dowmetal

Dowmetal was developed by The Dow Chemical Company in late 1930s. It was designed to

be the lightest metal and to improve the manufacturing of all transportation items from railroads

to buses and from trucks to tractors. The aviation industries were interested in its use in attain-

ing greater speed and eliminating needless weight. Dig a little deeper as you discover how

Dowmetal made a difference:

https://kb.osu.edu/dspace/bitstream/1811/35668/1/OS_ENG_v23_i03_000.pdf

Tin does not corrode in humid conditions, adheres tenaciously to iron, has a low melting

point, and is used extensively in solder, brass, bronze, and pewter.

Tungsten, one of the heaviest metals, is used for making filaments for incandescent lamps.

Tungsten carbide is almost as hard as diamond and is used extensively for cutting tools.

Zinc, a bluish-white metal at ordinary temperatures, is brittle but malleable at high temper-

atures and is used as a galvanizing metal coating to prevent corrosion.

Silver is a shiny, white metal used mostly for ornamental work, jewelry, and tableware. Sil-

ver is the best conductor of electricity.

Gold is most often used for ornamental jewelry.

Ferrous Alloys

Ferrous alloys are metals made up largely of ferrous materials but having other elements in

sufficient quantities to change the ferrous characteristics.

TABLE 3. Types of Ferrous Alloys

Type of Steel Advantages Uses

Manganese steel Can stand strain, hammering, shock,

and hard wear

Used for the ore-crusher jaws, power

shovels, chains, gears, and safes

Chromium steel Resists rust, shock, scratches, and

stains

Used for bearings, safes, and ore

crushers and is the basis for high-

quality stainless steel

Nickel steel Is strong, hard, elastic, tough, and

durable

Does not rust easily and is used for

springs, cables, axles, shafts, and

armor plate

Stainless steel Seldom rusts Used for cutlery, precision measuring

instruments, dentistry supplies, auto

parts, and engine valves

Tungsten steel Adds hardness to steel and allows it

to withstand heat

Used for various cutting surfaces; is

the hardest metal known

Molybdenum steels Have strength and hardness Used for hack-saw blades, high-

grade machinery parts, bearings,

and auto parts

Vanadium steel Is tough and can withstand great

shocks and corrosion

Used for springs, gears, and

vibrating parts of machinery

Non-ferrous Alloys

Non-ferrous alloys are made up of two or more non-ferrous elements.


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TABLE 4. Types of Non-ferrous Alloys

Type Consists of

Brass Copper and zinc

Bronze Copper and tin

Solder Lead and tin, copper and zinc alloy, and silver and copper alloy

Pewter 92 percent tin, 5 percent antimony, and 3 percent copper

Monel 60 percent nickel and 40 percent copper

Grading and Classifying Steel

Because steel varies in carbon content

and alloying elements, a system for grad-

ing and classifying it was developed using

standards established by the Society of

Automotive Engineers (SAE). In the SAE

numbering system, the first digit indicates

the general type of steel. The second digit

indicates the percentage of the main alloy

in the steel. The third and fourth digits

show the percentage of carbon in the steel

in hundredths of 1 percent.

IDENTIFYING METALS

Physical and chemical tests are used to determine types of metals. Because so many kinds of

metals are used in agriculture, learning to identify them is important.

The Appearance Test involves identification of a metal by its appearance and use. Color and

appearance make certain metals, such as copper, brass, and bronze, easy to identify.

The Magnetic Test involves identification of a metal by the use of a magnet.

The Chisel Test involves identification of a metal by the use of a hammer and cold chisel.

The Fracture Test involves identification of a metal by fracturing the metal and observing

the grain.

The Flame Test involves identification of a metal by applying a flame to it and watching

what occurs.

The Spark Test involves identification of a metal by applying it to a grinding wheel and

observing the spark generated. The color, shape, average length, and activity of the sparks are

characteristics of the material being tested.


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4 6 O 2Molybdenum

Steel PercentMolybdenum

PercentCarbon

FIGURE 4. SAE grading and classifying system.


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AppearanceMetal

Low-carbon steel

Medium-carbon steel

High-carbon steel

High-sulphur steel

Manganese steel

Stainless steel

Cast iron

Wrought iron

Dark grey

Dark grey

Dark grey

Dark grey

Dull castsurface

Bright,silvery smooth

Dull grey,evidence ofsand mold

Light grey,smooth

Stronglymagnetic

Stronglymagnetic

Stronglymagnetic

Stronglymagnetic

Non-magnetic

Dependson exactanalysis

Stronglymagnetic

Stronglymagnetic

Continuous chip,smooth edges,

chips easily


chips easily

Hard to chip,can be

continuous


chips easily

Extremely hardto chisel

Continuous chip;smooth, bright

color

Small chips,about 1/8 in.;

not easy to chip;brittle

Continuous chip,smooth edges,soft and easily

cut and chipped

Bright grey

Very light grey

Very light grey

Bright grey,fine grain

Coarsegrained

Depends ontype, bright

Brittle

Bright grey,fibrous

appearance

Melts fast,becomes bright

red before melting


red before melting


red before melting


red before melting


red before melting


red before melting

Melts slowly,becomes dull

red before melting


red before melting

Long yellowcarrier lines

(0.05% to 0.30% carbon)

Yellow lines, sprigsvery plain now

(0.3% to 0.6% carbon)

Yellow lines, brightbursts very clear,

numerous star bursts(0.6% to 1.0% carbon)

Swelling carrierlines, cigar shaped

Bright, whitefan-shaped bursts

1. Nickel—black shapeclose to wheel.

2. Moly.—short arrow-shaped tongue.

3. Vanadium—longspearpoint tongue.

Red carrier lines(very little carbon exists)

Long straw-colored lines(practically free ofbursts or sprigs)

Magnetic Chisel Fracture Flame Spark*

*For best results, use at least 5,000 surface feet per minute on grinding equipment. (Cir. × R.P.M. / 12 S.F. per Min.)

Test

FIGURE 5. Methods of identifying metals.

Summary:

� Because of the widespread use of metals and the necessity for them in agriculture, itis important to have a basic understanding of metals and metallurgy.

The distinct characteristics used to help identify a given metal are referred to as itsproperties. These characteristics include brittleness, color, corrosion resistance,ductility, malleability, and strength.

Metals can be classified into four main groups: ferrous metals, non-ferrous metals,ferrous alloys, and non-ferrous alloys. The Society of Automotive Engineers devel-oped a system to assist in the grading and classifying of steel.


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Wrought Iron

White Cast Iron

Low-Carbon Steel

Gray Cast Iron

High-Carbon Steel

Malleable Iron

Alloy Steel

Nickel

Average streamlength with powergrinder—65 in.

Volume—large

Long shaftsending in forksand arrowlikeappendages

Color—strawyellow

Color—strawyellow

Color—strawyellow

Color—strawyellow

Color—redColor—red

Color—orange

Color—white


Volume—moderately large

Shafts shorterthan wrought ironand in forks andappendages

Forks becomemore numerousand sprigs appearas carbon contentincreases

Color—white

Averagestream lengthwith powergrinder—55 in.

Volume—large

Numeroussmall andrepeatingsprigs

Shafts may endin forks, buds,or arrows,frequently withbreak betweenshafts andarrows. Few ifany, sprigs.

Stream lengthvaries with typeand amount ofalloy content.

Color—white

Color—white

Average stream lengthwith power grinder—20 in.

Volume—very small

Sprigs—finer than grayiron, small and repeating


Volume—small

Many sprigs, small andrepeating

Color—strawyellow


Volume—moderate

Longer shafts thangray iron ending innumerous smallrepeating sprigs


Short shafts with no forksor sprigs

FIGURE 6. Spark test for identifying metals.

Several different types of physical and chemical tests are used to determine types ofmetals.

Checking Your Knowledge:

� 1. What is the result of the annealing process?

2. How are compressive strength and shear strength different?

3. What are the four major steel-making processes?

4. What are the four common ferrous metals?

5. What is bronze composed of?

Expanding Your Knowledge:

� Did you know that 70 percent of all the metal used is used just one time and thenthrown away! The remaining 30 percent is recycled. Think about this: The amountof steel that Americans throw away each year is about the same as the amount ofsteel needed for all the new cars made in the United States! Do you like cannedgreen beans? What about canned baked beans or canned diced tomatoes? In Amer-ica, we use tin/steel cans mainly in the food industry. We use roughly 100 milliontin/steel cans every day. Once these cans are empty, where do they go? A magnet isused to detect these cans in the trash. Approximately 9,000 tin/steel cans are recov-ered every minute! What can you do to improve steel recycling efforts?

Web Links:

� Steel Recycling Institute

http://www.recycle-steel.org/

How Iron and Steel Work

http://www.howstuffworks.com/iron.htm

Classification of Steels

http://info.lu.farmingdale.edu/depts/met/met205/steelclassification.html

Agricultural Career Profiles

http://www.mycaert.com/career-profiles


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