metallurgy answer key

7/27/2019 Metallurgy Answer Key

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kirgyFifth Edition

Answer Key

2012 by American Technical Publishers, Inc.All rights reserved

5 6 7 8 9 - 1 2 - 9 8 7 6 5 4 3 2 1Printed in the United States of America

ISBN 978-0-8269-3524-3

AMERICAN TECHNICAL PUBLISHERSORLAND PARK, ILLINOIS 60467-5756


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I.The materials sciences consist of sixbranches, five of which are devoted to aparticular class of engineering materials.These five branches are metallurgicalengineering, ceramic engineering, polymer engineering, composite engineer

ing, and surface engineering. Materialsengineering is the final branch, and itcompares the properties of the variousclasses of engineering materials.

2. The three groups of metallurgy areextractive, mechanical, and physicalmetallurgy. Extractive metallurgy is thestudy of the extraction and purificationof metals from their ores. Mechanicalmetallurgy is the study of the techniquesand mechanical forces that shape ormake finished forms of metal. Physicalmetallurgy is the study of the effect ofstructure on the properties of metals.

3. The two structures studied in physical

metallurgy are the crystal structure andmicrostructure. The crystal structure isthe arrangement of atoms in the metal.The microstructure is the microscopicarrangement of the components, orphases, within a metal.

4. A cermet is a class of materials that liesbetween ceramics and metals. Cermetsconsist of a hard constituent (usually tungsten carbide) that is embedded in a smallamount of a soft material, such as nickelor cobalt, which provides toughness.

5. Composites are typically designed to bestronger than metals, ceramics, or polymers in order to improve their structuralusefulness.

6. The purpose of material substitutions isto improve the performance or lower thecost of the components.

7. There is one dominant property that mostoften makes metals preferred over mostnonmetals for structural applications.This dominant property is the greaterability of metals to yield in the presenceof stress rather than break in a brittlemanner. Metals tend to yield in the presence of excessive stress and thus givesome warning of impending failure.

8. Metal identification is performed by

studying certain characteristics that met

als exhibit. A metal is described as a pure

metal or as an alloy. Metals may further

identified as ferrous or nonferrous, and

of a certain alloy.

9. A metal is a pure metal, composed of a

single chemical element. An alloy is a

material that has metallic properties and

is composed of two or more chemical

elements.

10 Metals and alloys are described as ferrous and nonferrous. Ferrous metals are

alloys with iron as the major alloying ele

ment. Nonferrous metals are pure metals

and alloy systems that do not include iron

as the major alloying element.

11. Chemical analysis is the key to theidentification of alloys and is used todetermine the weight percentages of allthe elements that make up alloys. Thepercentages are used to describe alloysand the sum must equal 100%.

12. A property is a measurable or observableattribute of a material that is of a physical, mechanical, or chemical nature.

A physical property is a characteristicresponse of a material to forms of energy such as heat, light, electricity, andmagnetism. A mechanical property is acharacteristic dimensional change of amaterial in response to applied externalor internal mechanical forces. A chemicalproperty is a characteristic response ofa material in low and high temperaturechemical environments.

13. Designers rely on measured propertiesin order to select the size and shapeof components. From these designs,metallurgists write specifications to indicate the alloy, product form, and qualitylevel. Suppliers and purchasers then use

specifications as a basis for orderingmaterials.

14. Cast metals are produced from moltenmetal solidifying in a mold cavity. Castmetals are metal objects produced bypouring molten metal into a mold cavity,which is the desired shape of the casting.Wrought metals are worked into finishedforms. They are worked using processessuch as drawing, extruding, rolling, andpressing.

15. Metal powders are used when stringent

composition controls are required. For

example, metal powders are used in the

production of superalloys.

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1. Density is the mass per unit volume ofa material. It is measured in grams per

cubic centimeter (g/cm3) or pounds percubic inch (lb/in3).

2. The mel ting point depends on thestrength of the atomic bonds. When a

metal melts, its atoms are no longer

packed in the solid state, but move about

freely with respect to one another. The

higher the atomic bond strength, the less

freely the atoms move. More thermal

energy is required to break strong atomic

bonds between the atoms. This results

in a higher melting point

3. Heat capacity is the amount of thermal

energy required to raise the temperature

of a body by one degree. Specific heat

capacity is the amount of thermal energy

required to raise the temperature of one

unit of mass by one degree.4. Thermal expansion is the change in a

material's size due to changes in tem

perature. The length axis change, or

linear dimensional change, is usually

the greatest and is expressed as the

coefficient of linear expansion. The coef

ficient of linear expansion is the change

in length per unit length per degree of

temperature change.

5. The three types of magnetic suscepti

bility are ferromagnetic, paramagnetic,

and diamagnetic. A ferromagnetic metalis a metal that has high and variable

magnetic susceptibility and is strongly

attracted to a magnetic field. A paramagnetic metal is a metal that has low values

of magnetic susceptibility. A diamagnetic

metal is a metal that has low negative

values of magnetic susceptibility.

6. To convert Celsius to Fahrenheit, multiply

1.8by the Celsius reading and then add32. To convert Celsius to Fahrenheit,

apply the following formula: F = (1.8 xC) + 32.

7. To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit reading andthen divide by the 1.8 ratio. To convertFahrenheit to Celsius, apply the followingformula: C = (F - 32) ^ 1.8.


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2 Metallurgy Answer Key

8. The Kelvin (K) and Rankine (R) scalesuse absolute zero as a common base.

The Kelvin scale is the absolute tem

perature scale related to the Celsiusscale. The Rankine scale is the absolute

temperature scale related to the Fahren

heit scale.

9. A pyrometer is an instrument used for

measuring temperatures (beyond the

range of mercury thermometers) by

the increase of electrical resistance in a

metal, generation of electrical current of

a thermocouple, or increase in intensity

of light radiated by an incandescent

body.

10. Pyrometer types include the bimetal

lic coil, liquid expansion, gas or vapor

pressure, resistance, thermoelectric,

radiation, and optical.

11 . A liquid expansion pyrometer is a pyrometer with a bulb containing a liquid, such

as mercury or alcohol, that is exposed to

the metal to be measured. Temperature

change causes the liquid in the bulb

to expand or contract. The expansion

or contraction causes a Bourdon tube,

which is connected to the bulb, to expand

or contract.This expansion or contraction

of the Bourdon tube moves a tempera

ture indicator.

12. A thermocouple is a device consistingof two electrically connected dissimilar

metal wires that produces a small volt

age in proportion to temperature.

13 . A thermowell is a protective sheath usedto protect a thermocouple from a harshenvironment and mechanical abuse. A

thermowell significantly extends the

life of the enclosed thermocouple. The

chief disadvantage of thermowells isthe time lag introduced into the tem

perature measurement, which can

be significant when temperatures are

fluctuating. The time lag is caused by

the time required for heat to be con

ducted through the wall thickness of

the thermowell.

14. Radiation and optical pyrometers can

focus and accurately measure tem

peratures of small areas or movingparts and can measure extremely high

temperatures , ranging from 538C

to 5538C (1000F to 10,000F). Radiation and optical pyrometers are not

exposed directly to high temperature.

This lack of exposure prolongs the life

of the instrument.

15. A temperature-indicating crayon is a

marker made from a material that meltsat a certain temperature. These cray

ons are used for monitoring the tem

perature of a surface that must meet

some specified minimum or maximum

value.

1. Mechanical force is applied using fivemethods: tension, compression, shear,torsion, and flexure.Tension is the forceof a load applied axially on an object in

a stretching manner. Compression is

the force of a load applied axially on an

object in a squeezing manner Shear is

the application of two equal and paral

lel forces on an object from opposite

directions. Torsion is the application of

twisting force on an object. Flexure is

the application of a force that causes the

bending of an object.

2. With dynamic tests, the load is applied

very rapidly and may also be applied

continuously or repeatedly. The inertia

of the test specimen and the rate of application of the load have a significant

effect on test results. In static tests, the

load is applied slowly enough so that

the speed of testing has a negligible ef

fect on the results. Static tests last from

several minutes to several hours.

3. Damping capacity is the rate at which a

material dissipates energy of vibration.

4. Fatigue strength is the stress at which a

material fails by fatigue after a specific

number of cycles.

5. Toughness is the ability to absorb energy

and deform plastically before fractur

ing. Tests used to measure toughness

include notched bar impact tests, nilductility transition temperature tests, and

fracture toughness tests.

6. A tensile test is a static test that mea

sures the effects of a tensile force on amaterial. The data from this test includestensile strength, yield point and yield

strength, percent elongation and reduc

tion in area, and modulus of elasticity.

7. The tensile test procedure is conducted

by fixing the test specimen firmly in the

grips of the testing machine. An exten-

someter, a device for measuring theextension or elongation of the test speci

men, is fitted to the specimen across its

gauge length. An axial load is applied

and the test specimen is stretched. Asthe test specimen is stretched, a load-

extension (stress-strain) curve is plotted.The extensometer is removed before thetest specimen breaks.

8. The guided bend test consists of bend

ing a rectangular piece of metal around

a U-shaped die. This test is most com

monly used to check the quality of welds.

Formability tests measure the ductility

of sheet metal used for deep drawing

or stretching. In cupping tests, a metal

sheet test specimen is stretched over an

advancing punch with a rounded head

to determine the fracture point.

9. The compression test, the opposite of

the tensile test, is not often used for

metals because of limitations in the

test technique. The compression testis limited because it is difficult to apply

a true axial load to the test specimen

without introducing other stresses, such

as bending.

10. A torsion test is a static test that mea

sures a material's resistance to shear.The test is performed by applying torque

(twisting force) to a cylindrical bar or

tube-shaped test specimen in a specially

designed torsion testing machine. The

amount of torque on the specimen is

measured and recorded by a tropometer.11 . Scratching hardness tests include the

Mohs scale and the file hardness test.

The Mohs scale is a collection of 10 minerals, listed in order of increasing hard

ness, that is used in scratching hardness

tests. A file hardness test is a hardness

test that uses a file to rub against the

surface of a material to note the degree

of bite, which indicates hardness.

12. The tests must be performed on a firmly

supported surface because vibration of

the test specimen affects the height of

rebound. To detect any chipping of the

hammer or flattening of the ball bearing,

instruments must be calibrated prior to

each test using a standard block of knownhardness. The surface of the test speci

men must be free of oil, scale, and other

contaminants and must not be rough.13 . The Rockwell hardness test is the mostused and versatile hardness test. A Vis"diameter steel ball and a 120diamondcone are the two types of indenters.

The Rockwell hardness test uses two

loads that are applied sequentially. A

minor load of 10 kg is applied that helpsseat the indenter and remove the effect

of surface irregularities. A major load,

which varies from 60 kg to 150 kg, is

then applied. The difference in depth of

indentation between the major and minor

loads provides the Rockwell hardness

number.

14. The microhardness of the test specimenis always higher than the bulk surface

hardness measured by any of the other

indentation techniques. The surface

hardening effect of the polishing opera

tion and the extremely light load result

in a relatively shallow impression and a

higher apparent hardness.

15. The approximate relationship between

hardness and tensile strength is calcu

lated by applying the following formula:

S,= HB-r2where

Sr = tensile strengthHB= Brinell hardness number


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Textbook Answers3

4 Sfcrumjf'B at Mates1. Atoms contain three types of particles:

protons, neutrons, and electrons. Aproton is a subatomic particle with apositive electrical charge. A neutron is asubatomic particle with a neutral electrical charge. An electron is a subatomicparticle with a negative electrical charge.

2. A valence electron is an electron in an

incompletely filled outermost shell.

3. Atomic weight is the relative mass of theprotons and neutrons in the nucleus of anatom. An atomic number is the numberof protons in the nucleus of an atom.

4. An isotope is a form of a chemical element with a different number of neutrons.

5. Atoms exhibit four types of atomic bonding: metallic bonding, covalent bonding,ionic bonding, and Van der Waals bonding. Metallic bonding is a type of atomicbonding that occurs in a solid metal whenvalence electrons leave individual atomsand are shared between all atoms in afree electron cloud. Covalent bondingis a type of atomic bonding that occurswhen valence electrons are sharedbetween like atoms. Ionic bonding isa type of atomic bonding that occurswhen valence electrons are exchangedbetween unlike atoms. Van der Waalsbonding is a type of atomic bondingthat involves no exchanging or sharingof electrons but occurs when the atoms

or molecules behave like dipoles.6. A crystal structure is a configuration of

atoms as they add to one another in anorderly and repeating three-dimensionalpattern.

7. A space lattice and unit cell are used toillustrate crystal structures. The repetition of atoms in three dimensions in acrystal structure may be shown by athree-dimensional array of points. Thepoints represent the center of each atomor arrangement of atoms.

8. Although 14 types of unit cell types arepossible, most metals exhibit one ofthree types. The three common typesare body-centered cubic (BCC), face-

centered cubic (FCC), and close-packedhexagonal (CPH).

9. The crystal structure of alloys is determined by the proportions of alloyingchemical elements present. Atomic mixing between chemical elements leadsto the formation of a solid solution or anintermediate phase.

10. A crystallographic plane is a plane alongwhich the atoms are arranged withincrystal structures.

11 . A corner of a unit cell is taken as the ori gin of three axes in space.The crystallographic plane is defined by the reciprocalof the intercepts (intersections) it makes

with the three axes. The lowest commondenominator is found for the reciprocalsand is used as a multiplier to produce

fractions, which can be reduced. Thereduced fractions are the Miller indicesand are expressed in parenthesis.

12. The wavelength of the X ray is similarto the atomic spacing in crystals. X-raydiffraction causes a beam of incidentX rays to be diffracted when passedthrough a crystal. The diffracted X raysare analyzed and used to identify thecrystal structure of the metal.

13. In the first stage, tiny clusters of atoms(nuclei) form into crystal structures. Inthe second stage, atoms add to thenuclei, producing more unit cells. In thethird stage, dendritic growth begins.Eventually, the spikes of the dendrites

begin to meet and interfere with eachother's growth. The spaces between thedendrites fill with more branches untilsolidification is complete.

14. The atoms adjacent to the grain boundaries are at a higher energy level thanthose in the bulk of the grain.

15. Grain size is directly related to the number of nuclei that originally formed in themolten metal. The greater the numberof nuclei, the smaller the grain size andvice versa. Chemical compounds aresometimes added to molten metals justbefore casting to increase the number ofnuclei and promote small grain size.

5 ifediogrffirf1. The purpose of metallographic examina

tion is to look for clues as to how a metalwas made and/or how it performed. Itmay also give clues as to how a metalwill perform in the future.

2. An artifact is a false microstructural indication that does not correspond to thetrue microstructure and is caused whena metallographic mount is prepared.

3. The most common specimen orientations are longitudinal (parallel to theaxis) and transverse (perpendicular tothe axis).

4. Rough grinding prepares specimens formounting by removing subsurface deformation, unnecessary roughness, flash,and scale caused by cutting operations.

5. Mounting is usually performed in amounting press, which encapsulates thespecimen in a thermosetting resin underpressure and at an elevated temperature. The specimen is placed face downin a vertical cylindrical mold in the mounting press. A predetermined quantity of

thermosetting resin is poured into the

mold and it is closed. The temperature

is raised and pressure is maintained

while the resin cures, making the resinhard and strong. After the mold cools,

the mount is demolded.6. Cold mounting is performed when the

specimen is too large for the mounting

press or when the heat involved might

alter the microstructure.

7. Rough polishing is a polishing process

that is performed on a series of rotating

wheels covered with a low-nap cloth (cloth

containing a small amount of fiber). Suc

cessively finer grades of diamond rouge

(polishing powders) are applied to each

wheel, usually starting at 45 micron size.

The mount is moved in an elliptical path

against each wheel, using firm hand pres

sure that is decreased as the diamond

rouge becomes finer.

8. Electrolytic polishing is a polishing pro

cess in which the mount is the anode

(connected to the positive terminal) in

an electrolytic solution and current is

passed through it from a metal cathode

(negative terminal). Chemical polishing

is a polishing process that uses chemical

reactions to remove the rough peaks on

a specimen surface.

9. Etching of the mount is the last stage

of metallographic preparation. Etching

is the selective attack by a chemical

reagent on a surface in order to reveal

its microstructural detail,

10. Higher magn ifications up to 2500x

cannot be achieved with an air space

between the lens and the specimen.

Higher magnifications require the use of

water or oil immersion. A small amount

of water or oil is daubed on the objective

lens, which is raised to make contact

with the specimen surface. If water or

oil immersion is to be followed by lower

magnification work, the water or oil is re

moved from the specimen and the mount

may require repolishing and reetching.

11 . Microstructural characteristics areenhanced by various forms of illumi

nation. The four illumination forms formicrographs are brightfield, darkfield,polarized, and Nomarski.

12. Quantitative metallography is the useof metallography to measure specific

aspects of microstructures such as grainsize and density of nonmetallic inclusions for quality control purposes.

13. The intercept procedure is based on

counting the number of grains intercepted

by one or more straight lines of sufficient

total length to yield at least 50 interceptsThe intercept procedure is often used to

resolve disputes because it is the most

accurate procedure.


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14. Inclusion counting methods are used toestimate the internal cleanliness of metals. The density and shape of inclusions

are the primary factors that determinethe internal cleanliness of steels andother alloy systems.

15. Macroscopic examination is performedwith the naked eye or at magnificationsup to 10x using a binocular microscope.

Lhi^i:'1. A phase diagram is a graphic represen

tation of the phases present in an alloy

system at various temperatures andpercentages of the alloying chemicalelements.

2. Alloying modifies the crystal structure ofa pure metal by forming a solid solutionor a compound.The grain structure of apure metal is also modified by alloying.

3. A substitutional solid solution is a solidsolution formed when solute metal atomsare substituted for solvent metal atomsin the crystal structure. An interstitialsolid solution is a solid solution formedwhen interstitial (solute) atoms fit into theinterstices (spaces) of a solvent metalcrystal structure.

4. Impurities are inclusions and/or porosity

in the microstructure and are not shownon phase diagrams. An inclusion is aparticle of foreign material in a metal.Porosity is the presence of pockets ofgas inside a metal, either macroscopicor microscopic.

5. The two basic types of phase diagramsare equilibrium and constitutional. Equilibrium diagrams indicate the composition and temperature limits for phasesunder conditions of thermal equilibrium.Constitutional diagrams indicate thecomposition and temperature limits forphases under specific rates of heatingand cooling.

6. Dilatometry is the monitoring and analysis of the length of a specimen duringcooling or heating.

7. Coring is the condition of variable alloycomposition between the center and thesurface of a microstructure such as adendrite, grain, or inclusion. Coring results from nonequilibrium growth, whichoccurs over a range of temperatures andcompositions.

8. A eutectic reaction is an isothermaltransformation in which a liquid transforms into two solid phases.

9. The three types of intermediate phasesare interstitial compounds, intermetalliccompounds, and electron compounds.

An interstitial compound is a type ofintermediate phase where one elementof the compound fits in interstices of the

crystal lattice of the other compound. Anintermetallic compound is a type of intermediate phase formed from chemicalelements having a fixed compositionalrange, which results in a fixed meltingpoint. An electron compound is a typeof intermediate phase that has a widerrange of solid solubility than interstitialand intermetallic compounds, but exhibits similar properties.

10. A peritectic reaction is an isothermal reaction in which a solid phase reacts with theliquid from which it is solidifying to yield asecond solid phase. A m onotectjc reactionis one of several phase change reactionsthat exhibit nonmixing liquid phases overpart of an alloy composition range.11 . The various solid-state phase transformations are allotropy, order-disordertransformations, second-phase precipitation, eutectoid reaction, and peritectoidreaction.

12. Precipitation (age) hardening is a delayedprecipitation reaction consisting of theprecipitation of finely dispersed particlesof a second phase in a supersaturatedsolid solution, or one containing a secondphase in excess of its solubility limits.Precipitation hardening is achieved byrapidly cooling the alloy from a single-phase region into a two-phase region.The second phase is then released slowlyfrom the supersaturated original phase.

13. A ternary phase diagram is an equilibrium or constitutional diagram thatindicates the phases present in alloysystems consisting of three elements.

14. An isotherm is a section through aphase diagram that depicts all phasesin equilibrium for an alloy compositionat one temperature. An isopleth is avertical section through a space diagram that simplifies ternary and morecomplex diagrams by holding constantthe percentage of one or more alloyingcomponents.

15. A plan diagram is a phase diagram thatindicates the boundaries separatingprimary phase fields in ternary or morecomplex alloy systems.

'iii^Jir1. Plastic deformation is a stress-induced

alteration of shape that remains permanent after removal of the applied load.Plastic deformations may be in the formof slip or mechanical twinning.

2. Slip is a process of plastic deformationin which one part of a metal grain undergoes a shear displacement relative

to another.3. A slip band is a group of closely spaced,parallel slip displacements that appearas a single line when observed under anoptical microscope.

4. Shear force is calculated by applying thefollowing formula:

?*-,= F* cos Iwhere

Fhfgr = shear forceF- applied force

X = angle between applied force and slipplanes

5. Mechanical twinning is the movement ofplanes of atoms in a lattice so that the

two parts are mirror images of each otheracross the twin plane.

6. The amount of atomic movement involved and the difference in microscopicappearance are the two major differences between slip and mechanical twinning.

7. A point defect is a defect associatedwith a discrete point in a crystal latticethat includes vacancies or interstitialatoms. A line defect is a defect associated with planes of atoms in a crystallattice that include dislocations andstacking faults,

8. Edge dislocation and screw dislocationare the two main types of dislocations.An edge dislocation is a dislocation of a

crystal lattice in the form of extra partialplanes of atoms. A screw dislocation is adislocation of a crystal lattice in the formof a spiral around an axis.

9. A stacking fault is a two-dimensionaldeviation from the normal stacking sequence of atoms in a crystal, They maybe formed during the growth of a crystalor may also result from partial dislocations. Stacking faults are most commonin close-packed planes of atoms.

10. Cold working is plastic deformation performed below the recrystallization temperature, which leads to work hardening.

11 . The metal parallel to the direction ofthe cold working exhibits an increase intensile strength, yield strength, and hardness. The percent elongation, percentreduction in area, and notch toughnessare reduced.

12. Annealing is a heat treatment processused to relieve residual stresses andchange the mechanical properties ofa metal. Annealing consists of heatinga component to a certain temperature,holding at temperature, and then coolingat a certain rate.

13. As the annealing temperature is raised,the metal reverts to a softer conditionand three major changes occur inthe crystal and grain structure. These


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Textbook Answers5

changes are recovery, recrystallization,and grain growth. Recovery is the reduction of residual stresses by holding acomponent at an elevated temperature.Recrystallization is the formation, whilecooling from an elevated temperature, ofa new strain-free grains structure froman existing grain structure. Grain growthis an undesirable increase in grain sizecaused by heating a metal above a certain temperature.

14. Annealing twins are mirror-image twinbands formed in the grain structureduring recrystallization of certain cold-worked FCC metals.

15. Advantages include the reduction inthe power required for plastic deformation, break down and elimination of theundesirable cast structure of an ingot or

billet, and redistribution of brittle filmsand constituents. Hot working welds upporosity in ingots or billets and improvesthe mechanical properties, especiallystrength.

Q Fradnpoptyand1. Tension, compression, and torsion are

the three most common types of force.

2. Ductile metals loaded under compres

sion become shorter and wider as shearoccurs along shear planes at a 45angleto the direction of the tensile stress.Brittle metals loaded under compression exhibit a tensile stress in a directionperpendicular to the compressive force.

3. A microvoid is a tiny cavity formed as ametal separates in weak areas prone toshear.

4. Brittle fractures occur when the tensilestress from the force applied to a metalexceeds the cohesive strength of themetal.

5. Fatigue is the most common form offracture in engineering components.Fatigue fractures occur under repeatedor fluctuating stresses, which have amaximum value less than the tensilestrength of the metal. A fatigue fracturepropagates along a narrow crack front,which grows in stages under the actionof the stresses.

6. The three most common markings usedto locate the origin of a fracture are radiallines, chevron patterns, and arrest lines.A radial line is a fracture surface markingthat looks like continuous rough peaksand points back toward the origin of thefracture. A chevron pattern is a V-shapedfracture surface marking with an apexthat points toward the origin of a fracture.

Arrest lines are markings that indicaterest periods of fracture propagation in aprogressive fracture.

7. The initiat ion zone, propagation zone,and final failure zone are the three characteristic zones on a fracture surface.

8. Damage may occur during the failureitself and also during a failure analysisinvestigation. Damage during a failureoccurs when the two halves of the fracture surface rub against one anotherduring the propagation of the fracture,separate into pieces during final failure,corrode because the broken pieces areexposed to the environment, or sufferabuse because the broken pieces areexposed to operations after the failure.

9 Three tasks performed during fieldevidence collection include developing

a history of the operating conditionsleading to the failure, documentingmaterials of construction, and selectingand preserving specimens for laboratoryexamination.

10. Ultrasonic cleaning is a cleaning methodthat uses an organic solvent and ultrasonic vibration to loosen lightly adheringsurface contamination from a fracturesurface. Replication cleaning is a cleaning method that used replication tape tostrip adherent deposits from a fracturesurface. Cathodic cleaning is a cleaningmethod that uses the flow of electricalcurrent to strip adherent deposits from afracture surface. Acid cleaning is a clean

ing method that uses special corrosivechemicals to strip extremely stubborndeposits from the fracture surface.

11 . The four types of lighting methods include main lighting, fill lighting, backlighting, and build-up lighting. Main lightingis a primary lighting method that has alight source at a 40to 60angle to thesubject. Fill lighting is a lighting methodthat uses a small region of brighter lightto highlight detail in a dark area of a subject. Backlighting is a lighting method thatuses a diffused light source to eliminateor soften shadow detail. Build-up lightingis a lighting method that combines various types of light sources to achieve the

desired lighting effect.

12. A backscattered electron is an electronfrom an electron beam that is reflectedback after interaction with a specimensurface. A secondary electron is an electron emitted from the specimen surfaceas a result of electron beam interaction.

13. Energy-dispersive X-ray analysis (EDXA)is a quantitative chemical analysis of thesurface of a specimen using the characteristic energies of X-ray fluorescence.Wavelength-dispersive X-ray analysis(WDXA) is a chemical analysis of the surface of a specimen using the characteristic wavelengths of X-ray fluorescence.

14. Destructive examination is an examination of a specimen that requires thespecimen to be cut, machined, broken,melted, dissolved, or otherwise alteredfrom its original state. Destructive examination techniques include mechanicalproperty testing, metallography, and bulkchemical analysis.

15. The three sections of a failure analysisreport are the conclusions, discussion,and supporting evidence. The conclusions section consists of a brief historyof the failure, description of the proposedcause(s), and recommendations toprevent the recurrence of the failure.The discussion section documents thereasons for the failure (revealed by theevidence obtained). The supportingevidence section consists of a descriptionof the evidence obtained from the field,fractography, and destructive examination.

9 Wteltertltoteto1. The two types are the certificate of

heat analysis and certificate of productanalysis. A certificate of heat analysisis a statement of the chemical analysisin weight percent of an ingot or billet.A certificate of product analysis is astatement of the chemical analysis in

weight percent of an end product that ismanufactured from an ingot or a billet.

2. A mill test report (MTR) is a certifiedstatement issued by a primary metalmanufacturer that indicates the chemicalanalysis and mechanical properties of ametal product.

3. The types of information typically includedare ASTM grade number, foundry nameor logo, heat number, and foundry shorthand description for the alloy. Additionalinformation, such as pressure and temperature ratings, is included for productsintended for certain applications.

4. Chemical elements in some paints andmarking materials used for color codes or

stencil marks may cause cracking in susceptible alloy systems, such as stainlesssteels and high-nickel alloys. Crackingis most likely to occur when the paint ormarking material on the metal is exposedto heat (such as through welding) orcertain corrosive environments. Markingmaterials that are used on susceptible alloys must contain less than 50 ppm (partsper million) of the harmful chemical elements, which include chlorine (CI), sulfur(S), and zinc, to lessen the potential forcatastrophic cracking. Even if approvedmarking materials are used, it is goodpractice to remove them from areas thatare to be welded, brazed, or soldered.


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5. Positive materials identification (PMI) isthe classification, sorting, and/or analy

sis of metal alloys, principally through

nondestructive methods.6. With intuitive ident ification methods,

metals are classified according to their

physical properties.

7. Qualitative PMI techniques include sparktesting, chemical spot testing, tribo-electric sorting, thermoelectric potentialsorting, electromagnetic sorting, andmetallographic identification.

8. Characteristic features include carrierlines, forks, bursts, and arrowheads. Carrier lines are glowing streaks that tracethe path of each spark. Forks are simplebranchings of the carrier lines. Bursts arecomplex branchings of the carrier lines.Arrowheads are terminations of the car

rier lines in the shape of arrowheads.

9. Electrographic chemical spot testing isthe application of a chemical reagent toa solution containing small amounts ofmetal. It is the most common method ofchemical spot testing.

10 . In triboelectric sorting, the unknown metal and a probe with a roughened surfacelike a file are electrically connected to theterminals of a millivoltmeter.The rubbingaction of the probe against the surfaceproduces a voltage that is measured bythe millivoltmeter.Thisvoltage is used toidentify the unknown metal by comparingit to voltages produced by known metals.

11 . Metallographic identification is a qualitative method of identifying metals byexamining their microstructures. Themicrostructure is revealed by grindingand polishing an area about the size ofa postage stamp on the unknown metal'ssurface to a mirrored finish. The areais then etched with a suitable etchantto reveal the microstructure. Using aportable metallurgical microscope, themicrostructure is examined at magnifications of 10Ox to 500x to identify theunknown metal.

12. X-ray fluorescence (XRF) analysis is aquantitative method of identifying metalsby the fluorescent X rays emitted by theirconstituent chemicals.

13. Energy-dispersive X-ray analysis (EDXA)instruments use a probe that contains ashutter that opens for a specific lengthof time to emit the gamma rays or the Xrays. The energy levels of the resultingfluorescent X rays are measured by theEDXA detector to identify various chemical elements and their concentrations.

Wavelength-dispersive X-ray analysis (WDXA) instruments use a lithiumcrystal to disperse the fluorescent X raysby wavelength into the detector system.The wavelengths identify the chemicalelements present in the unknown metal,

and the relative intensities of each wavelength are measured to determine theelement proportions.

14. Optical emission spectroscopy (OES)is a quantitative method of identifying

metals by analyzing the light of an arc

(spark) caused by an electric current and

emitted from an unknown metal surface.

15. Mass spectroscopy is a quantitativemethod of identifying metals by analyzing the radiated energy of the metalswhen vaporized. With this method, asolution of the sample is dissolved in asuitable reagent. This solution is introduced, as an aerosol of droplets, intoargon plasma, where it vaporizes. Aspectrometer then detects and analyzesthe emissions.

10 hhftatai1. A standard is a document developed by

consensus that serves as a model in the

establishment of a procedure.

2. The first step of developing a standard isthe production of a draft document that isreviewed by a committee, which refinesand improves it. Each subsequent draftis reviewed in a similar manner and thechanges are balloted (voted on), Thedevelopment process may take severalyears, but the final document representsa consensus of committee opinion andindicates current industrial practices.

3. A standard must be reviewed regularly

(minimum of once every five years) to

determine whether it will be reaffirmed

or revised.

4. The three classes of standards arespecifications, test methods, and recommended practices. A specification is astatement of technical and commercialrequirements that a product must meet.A test method is a set of instructionsfor the identification, measurement, or

evaluation of the properties of a material. A recommended practice is a set ofinstructions for performing one or moreoperations or functions other than theidentification, measurement, or evaluation of a material.

5. A code is a standard or set of applicable

regulations that a jurisdictional (law

enforcing) body has adopted as law.

6. A trade association is an organizationthat represents the producers of a specific type of product.

7. A technical society is an organizationcomposed of engineers and scientistsunited by a common professional interest.

8. The American Welding Society (AWS) isan organization that publishes standardson welding, brazing, and soldering of

metals. AWS also administers AWSD1.1 Structural Welding Code, whichprovides rules for the constructionof bridges, buildings, structures, andpractically any other welded structureto which the Boiler and Pressure VesselCodeor other codes do not apply. AWSalso maintains naming conventions forwelding filler metals, such as prefixes todesignate the type of filler metal.

9. ASTM International is the world's largest source of voluntary consensusstandards. ASTM develops standardson the characteristics and performanceof materials, products, systems (suchas magnetic particle examination), and

services (such as assessment of testlaboratories).

10. ASTM Book of Standards is publishedyearly and consists of over 70 volumes,containing over 12,000 standards. Thevolumes are divided by subject matter,so the users can purchase the volumesappropriate for and related to their business interests.

11. There are 17 series of UNS designations. Each series consists of a capitalletter followed by five numbers. The letter identifies the alloy family, and wherepossible, the five numbers are related tothe pre-UNS designation of the alloy.

12. The American National Standards Institute is the coordinator of the AmericanNational Standards system. ANSI is astandard-developing organization thatadopts standards that are written and approved by member organizations. ANSIbranches out and connects its memberorganizations by unifying their adoptedstandards. ANSI also manages UnitedStates participation in internationalstandards activities.

13. Foreign national standards are identified by their prefix letters. For example,the JIS prefix identifies the Japanesenational standards and the B.S. prefixidentifies the Great Britain standards.

14. Among the departments of the UnitedStates government that develop materials-related standards, the work of the Department of Defense (DOD) is the mostsignificant. DOD standards are known asthe United States Government MilitaryStandards (MIL Standards). MIL Standards cover the specifications of manymaterials used by the armed forces, butare not to be restricted to them.

15. Most welding codes rely on ASME Section IX, Welding and Brazing Qualifications, and AWS D1.1, Structural WeldingCode, Steel, for requirements pertainingto qualified welding procedures andwelders.


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Textbook Answers7

i .1. Iron is made by reducing iron ore by the

process of converting iron oxides to iron.This reduction is performed by blast furnace reduction or direct reduction. Blastfurnace reduction is the reduction of ironore to pig iron in a blast furnace. Directreduction is a series of several reductionprocesses that produce metallic ironfrom ores by removing most of the oxygen at temperatures below the meltingpoints of the materials in the process.

2. Pig iron is an impure form of iron. Pigiron is very impure and unsuitable forany practical purpose. It contains excessive amounts of carbon, phosphorous,and sulfur. These elements, and alsomanganese and silicon, must be refined

to allowable amounts so the iron can beused in steelmaking.

3. The principal commercial iron productsare wrought iron, ingot iron, and enameling iron.

4. An integrated steelworks is a large andcomplex steelmaking operation consisting of all the necessary productionunits to manufacture a wide range ofsemifinished forms from both iron oreand scrap steel. A merchant mill is arelatively small steelmaking operationthat produces a limited range of finishedforms from scrap steel.

5. There are three types of steelmakingfurnaces, which are the basic oxygen

furnace, the open hearth furnace, andthe electric furnace. The basic oxygenfurnace takes about an hour to producea heat of steel. Open hearth furnaces arelarge and take 6 to 10 hours to make aheat of steel. It takes from 3 to 7 hours tomake a heat of steel in an electric furnace.

6. The first stage is oxidation, the second stage is deoxidation, and the finalstage is ladle refining. Oxidation is ahigh-temperature reaction in which themetal forms an oxide. Deoxidation is theremoval of oxygen from molten metal.Ladle refining is a process that involvesvarious secondary techniques of purifying molten steel prior to solidification.

7. Semikilled steel is steel in which a de-oxidizer such as aluminum or silicon isadded to the molten metal. Killed steelis steel that is completely deoxidized bya deoxidizing agent.

8. A semifinished form is one of four basicshapes from which all finished steelproducts are produced, and includeblooms, billets, slabs, and rounds. Abloom is a square-shaped, semifinishedform that is greater than 20 cm x 20 cm(8" x 8"). A billet is a square-shaped,semifinished form that is less than20 cm x 20 cm (8" x 8"). A slab is arectangular-shaped, semifinished form

that has a width-to-thickness ratio of 2:1or greater. A round is a semifinished formthat is a circular section of any diameter.

9. Compared with ingot casting, soaking,and primary rolling, continuous castingleads to a better yield of product perheat of steel. Energy savings, less pollution, reduction of capital and operatingcosts, and greater freedom from specificdiscontinuities characteristic of ingotcast products are also characteristic ofcontinuous casting.

10. A hot top is a refractory-lined containerthat is placed on top of an ingot mold. Itabsorbs heat less rapidly than the ingotmold and therefore maintains a reservoirof molten steel. The reservoir feeds thesolidifying metal below it. The hot topmaterial is cropped off and discardedafter primary rolling.

11 . Hot working is plastic deformationperformed above the recrystallizationtemperature. The principal methods ofhot working are hot rolling, heavy pressforging, and piercing and hot extrusion.

12. Cold wo rking is plastic deformationperformed below the recrystallizationtemperature, which leads to work hardening. The principal methods of coldworking are cold rolling, cold drawing,and cold extrusion.

13. A discontinuity is an interruption in thenormal physical structure of a component.

14. Steels are broadly classified as carbonsteels or alloy steels. A carbon steel is analloy of iron with carbon, manganese, andsilicon, specifically containing up to 1.6%Mn and 0.6% Si, plus smaller amountsof sulfur and phosphorus. Alloy steel is asteel that contains specified quantities ofalloying elements other than carbon andthe common amounts of manganese,copper, silicon, sulfur, and phosphorous.

15. ASTM specif icatio ns a re th e most widelyused for the procurement of steels.ASTM specifications have the prefixletter A followed by a number. Specifications for steel are written at two levels.The first level consists of generic requirements for a family of products, and thesecond level consists of individual specifications for particular product forms.

1 2o*tinHife1. The eutectoid reaction is the most im

portant phase change reaction on theiron-carbon diagram because it indicatesthe transformation of austenite (a carbon solid solution) to fertile (a carbonsolid solution), cementite (iron carbideor Fe 3C), and pearlite (an aggregate offerrite and cementite).

2. Curie temperature is the temperature ofmagnetic transformation above which ametal is nonmagnetic, and below whichit is magnetic.

3. The five solid phases in iron-carbondiagrams are ferrite (alpha, a), austenite(gamma, y), cementite, delta ferrite (delta, 5), and pearlite (ferrite and cementite).

4. Austenite is a gamma solid solution ofone or more elements in FCC iron. Ferrite is an alpha solid solution of one ormore elements in BCC iron. Cementite isa compound of iron and carbon referredto as iron carbide. Pearlite is a lamellar aggregate of ferrite and cementiteformed from the eutectoid decompositionof austenite during slow cooling.

5. Carbon steels are classified as hypoeu-tectoid if ferrite-pearlite is formed whencooled, eutectoid if pearlite is formed,or hypereutectoid if pearlite-cementiteis formed.

6. Hypoeutectoid steels encompass thelargest group of carbon steel compositions and provide product designerswith a range of strength and fabricationcharacteristics to work with.

7. Eutectoid steel is selected for its combination of strength and wear resistanceand is typically used for railroad rails.

8. A hypereutectoid steel is a carbon steelwith a carbon content that lies to theright of the eutectoid point on the iron-carbon diagram and contains more thanapproximately 0.8% C.

9. A critical temperature is a temperaturefor any specific steel composition atwhich the austenite phase change begins or is completed (for a specific rateof heating or cooling).

10. Critical temperatures are designatedby the uppercase letter A (for arrest)followed by a subscript. A, is the boundary between the pearlite phase field andthe austenite phase field, which is theeutectic transformation line. A3 is theboundary between the ferrite-austenitephase field and the austenite phasefield. A ^ is the boundary between thecementite-austenite phase field and theaustenite phase field.

11 . The mechanical properties of carbonsteels are determined by the carbon andmanganese contents, pearlite interla-mellar spacing, and grain size.

12. Carbon and manganese increase hard-enability, which is a property in steel thatdetermines the depth to which ft hardenswhen quenched.

13. Normalizing is a heat treatment thatdecreases pearlite intertamellar spacingand refines grain size. Normalized steelis heated in a furnace into the austeniteregion (above the Ac,), held for a specified period of time, removed from thefurnace, and allowed to cool in still air.


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14. Fine-grain size is generally beneficial

in carbon steels because it increases

ductility and toughness.

15. Grain refinement is a method used toinduce finer-than-normal grain size.Grain refinement is achieved by ther

mally cycling a steel through the critical

temperature range.

G e a f if t| | R a t e a r e iI.Carbon diffusion is the spontaneous

movement of carbon atoms within amaterial.

2. Products produced when steel is slowlycooled from the austenitizing temperatureinclude ferrite, pearlite, or cementite, depending on the carbon content of the steel.

3. Upper bainite forms closer to the temperature range for pearlitic productsand has a feathery structure. Lowerbainite forms closer to the martensitetemperature range and has a needle-shaped structure.

4. The three main diagrams used to depictthe transformation products of austeniteare the iron-carbon diagram, l-T diagrams, and C-T diagrams.

5. The iron-carbon diagram is used to predictthe structure of carbon steels from heat

treatments such as annealing. It also canbe used to estimate critical temperature,stress-relieving temperature, or other keyheat treatment temperatures.

6. An isothermal transformation diagramis a plot of temperature against log timethat indicates the austenite transformation products for specific steels underisothermal conditions.

7. Despite the general similarity of shapebetween C-T diagrams and l-T diagrams for identical steels, the data ispresented differently On C-T diagrams,phase changes are recorded within thestart and finish boundaries, whereas onl-T diagrams, this region indicates thetransforming phases. On C-T diagramsthe products of transformation appear atthe bottom of the diagram, whereas onl-T diagrams, they are indicated on theright-hand side of the finish boundary.

8. Hardenability is a measure of the depthof hardening obtained on quenching,whereas hardness is a measure of thehardness obtained at the surface of thesteel. Hardness is a function of the carbon content of a steel and hardenabilityis a function of several factors.

9. Critical cooling rate is the slowest continuous cooling rate that produces 100%martensite in a steel.

10. The Jominy end-quench test is a laboratory procedure for determining the hardenability of steels.

11 . A hardenability band is a band thatdefines the boundaries for the minimumand maximum end-quench hardenabilitycurves for standard steels. The boundaries indicate the range of hardenabilityexpected from such alloys.

12. End-quench hardenability curves areused to predict the hardness obtainedat various depths in oil-quenched andwater-quenched bars. End-quench hardenability curves are used to select steelto meet specific toughness requirementsand indicate the largest bar diameterthat will harden completely through itssection when quenched.

13. Severity of quench is calculated using

the following formula:H=HD+Dwhere

H mseverity of quench

HD = value obtained by matching thecurves

Dm bar diameter14. Retained austenite is austenite that has

survived a heat treatment cycle in whichit would have been expected to transformto other products. Retained austenite isundesirable because it reduces hardenability, and it must be removed as muchas possible by modification of the heattreatment procedures.

15. Several methods are empl oyed toeliminate or reduce retained austeniteto acceptable levels. These includesubzero quenching and double or tripletempering (repeated tempering operations). Subzero quenching, performedat temperatures as low as -100C(-148F), cools steel near or below itsMp, resulting in complete austenite transformation. Double or triple temperinghelps transform the retained austeniteto martensite, which is then temperedin the next tempering cycle.

14 TirMtSTiMl af 3lii1. The sequence of austenitizing, quench

ing, and tempering is the most commonheat treatment process for steels.

2. Staged heating is the process of heatingat a controlled rate to a set temperature,holding the component until the temperature equalizes throughout the section, andthen continuing the heating at a higherrate to the austenitizing temperature.

3. Two types of gaseous atmospherescommonly used for protecting steel at

high temperatures are exothermic gasand endothermic gas. Exothermic gas isa gaseous atmosphere made by pass

ing a partially burned gas-air mixtureover a catalyst, which is heated by thepartial combustion. Endothermic gas is agaseous atmosphere made by passing amixture of fuel gas (usually propane) andair over an externally heated catalyst.

4. Decarburization leads to reduced surface hardening compared with the bulkof the section when the component isquenched. To reduce decarburization,the component is wrapped with paper.The paper burns off, which leaves behinda surface richer in carbon. This helpscounteract the tendency for carbon tobe lost from the surface.

5. Quenching consists of three steps, which

are vapor blanket, vapor transport, andliquid cooling. Vapor blanket coolingoccurs when the component is first immersed in the quenching medium. Anunbroken vapor blanket develops, surrounding and insulating the component.Vapor transport cooling occurs when thecontinuous vapor blanket collapses withthe falling surface temperature of thecomponent. This leads to violent boilingof the quenching medium and rapid heatremoval, mostly as heat from vaporizationof the quenching medium. Liquid coolingoccurs when the surface temperature isreduced below the boiling range of thequenching medium. Cooling in this stage

is by conduction and convection.

6. Quench cracking is the fracture of steelduring quenching. It is associated withthe volume expansion that occurs whena steel transforms from austenite to martensite when quenched. The surface ofthe component is the first to transform,and its expansion is not restricted. Whenmartensite begins to form inside the component, its expansion is restricted by theouter layers of martensite. This resultsin internal stresses that place the innerlayers of the component in compressionand the outer layers in tension.

7. The primary purpose of tempering is

to improve the mechanical propertiesof the steel, which means increasingductility and toughness while reducinghardness. Tempering relieves stressesand improves dimensional stability. Also,significant microstructural changes occur during tempering

8. Problems that occur during tempering

of steel are retained austenite, blue

brittleness, temper embrittlement, andtempered martensite embrittlement.

9. Interrupted quenching is a stepwisequenching process that develops specific microstructures in steels and minimizes distortion and cracking.


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Textbook Answers9

10. The principal annealing processes arefull annealing, normalizing, spheroidiz-ing, process annealing, and stressrelieving. Full annealing is a heat treat

ment in which a component is held inthe austenitizing temperature range andthen cooled inside the furnace Normalizing is a heat treatment that decreasespearlite interlamellar spacing and refinesgrain size. Spheroidizing is a heat treatment that produces a globular form ofcarbide in a steel product. It is primarilyperformed to produce maximum softnessin a steel product.

Process annealing is a heat treatmentperformed below the lower critical temperature that is designed to restore ductility to cold-worked steel products. Stressrelieving is a heat treatment in which asteel is heated to a suitable temperature

below the lower critical temperature,held for long enough to reduce residualstresses induced by cold deformation orthermal treatments, and cooled slowlyenough to minimize the development ofnew residual stresses.

11 . Case hardening is a group of heat treatment processes that develop a thin, hardsurface layer on a component but leavethe core relatively soft, strong, and tough.

12. Gas carburizing is a case-harden ingtechnique in which the componentis placed in a furnace containing agaseous carburizing environment.Pack carburizing is a case-hardeningtechnique in which carbon monoxide

derived from a solid carbon-containingcompound decomposes at the metalsurface into nascent (newborn) carbonand carbon dioxide. Liquid carburizingis a case-hardening technique in whichthe component is held in a molten saltbath to introduce carbon and sometimesnitrogen into the surface.

13. Most nitrid ing operations produce asurface layer consisting of two zones.The white layer is the zone at the surface and consists of a thin layer of aniron-nitrogen compound. This layer isbrittle and undesirable, so the nitridingconditions are adjusted to minimize it.Below the white layer is the nitrogen-

enriched diffusion zone, which may bea solid solution or contain precipitatesof the alloying elements in the steel. Thediffusion zone is in extreme compressionand has enhanced fatigue resistance.

14. The pattern of heating obtained byinduction is determined by the shape ofthe coil, the number of turns in the coil,the frequency of the alternating current,the power input, and the shape of thecomponent.

15. Fabrication processes that can lead toheat treatment difficulties include cold-forming operations, cutting operations,identification markings, welding, andmachining and grinding.

1 5TooJ1. A tool steel is a type of steel with generally

high carbon and nigh alloy contents that ischaracterized by high hardness and wearresistance, which are sometimes accompanied by toughness and resistance toelevated temperature softening.

2. Most tool steels contain between 0.6% Cand 1.3% C, and the most commonlyused tool steels contain between 0.8% Cand 1.1% C.

3. Three common methods of identifyingtool steels are the Unified NumberingSystem for metals and alloys, manufacturers'trade names, and the AISI system.

4. Tool steels are divided into seven divisions, which are water-hardening, cold-work, shock-resisting, special-pur pose,mold steel, hot-work, and high-speed.5. A water-hardening tool steel is a hypereutectoid steel made according torelatively stringent melting practices.Water-hardening tool steels are the leastcostly and have the most applications.They contain small amounts of alloyingelements.

6. Group W steels are used for items suchas cold header dies, cutlery, embossingtools, forging dies, hammers, reamers,twist drills, and woodworking tools.

7. Cold-work tool steels are the most commonly used tool steels. A cold-work toolsteel is a steel that has an alloy composition designed to provide moderate-to-high hardenability and good dimensionalstability during heat treatment.

8. Group A steels consist of two subgroups.The subgroups are steels with highchromium content (approximately 5% Cr)and those with high manganese content(approximately 2% Mn to 3% Mn). High-chromium steels develop moderate resistance to softening at elevated temperatures due to chromium carbide particlesin the microstructure. High-manganesesteels have improved hardenability.

9. A shock-resisting tool steel is a steel thathas a relatively low carbon content (0.4%C to 0.6% C) and contains manganese,silicon, tungsten, and molybdenum.Shock-resisting tool steels offer a combination of high strength, high toughness, high ductility, and low-to-mediumwear resistance. Shock-resisting toolsteels are designed for applicationsinvolving impact loading because oftheir combination of high strength andtoughness under repeated shock andlow-to-medium wear resistance.

10. Group L steels are used for machinecomponents, such as arbors, cams,chucks, and collets. Some specialapplications may require the goodstrength and toughness characteristicsof group L steels.

11 . A mold steel is a steel that containschromium and nickel as the principalalloying elements. Mold steels have alow-to-medium carbon content and atotal alloy content of 1.5% to 5%. Moldsteels consist of group P steels.

12. A hot-work tool steel is a steel thatwithstands combinations of heat, pressure, and abrasion associated withmanufacturing operations performed athigh temperatures, from 480C to 760C(900F to 1400F). Hot-work steels arethe group H steels and consist of threesubgroups: chromium, tungsten, andmolybdenum hot-work tool steels.

13. High-speed tool steels resist softeningand maintain sharp cutting edges athigh service temperature because oftheir excellent red hardness, which is theresistance to soften at red heat (540C,or 1000F). This property is attributed tothe presence of complex alloy carbidesin the microstructure of the steel. Thetoughness of high-speed tool steels isnormally not high.

14. The benefits of P/M processes includereduction of segregation, fine grain size,and more uniform microstructure anddistribution of carbides and inclusions.These attributes result in improved transverse mechanical properties, machin-ability, grindability, dimensional control,toughness, ductility, and thermal-fatigueresistance.

15 . Cemented carbides are hard materialsused for wear-resistant componentsin cutting and forming metals, suchas plastic extrusion dies, knives, wearguides, seal rings, and slitters. Cemented carbides consist of grains oftungsten carbide (WC) embedded in abinder metal. Cemented carbides usedifferent binder metals and proportionsand different grain sizes.

I D CmiHins1. Carbon equivalent (CE) is the equiva

lent percentage of carbon of an alloycomposition that can be used to predictcertain properties of iron and steel. CEis calculated using the following formula:CE= %C+W%>Si+%P)where

CE -carbon equivalent%C - percent carbon

%Si =percent silicon

%P =percent phosphorus

2. The six divisions of cast irons are grayiron, white iron, malleable iron, ductileiron, compacted graphite iron, and alloyiron.


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3. Gray iron is the most widely used castiron. Gray iron is a cast iron that consistsof a matrix of pearlite (iron carbide), ferrite, or martensite containing a distribution of graphite flakes. Gray iron can behardened and tempered like steel. Thegraphite flakes in the microstructuremake gray iron extremely brittle.

4. White iron is an extremely hard cast ironformed when the cartoon does not precipitate as graphite during solidificationbut combines with the iron and any ofthe alloying elements to form carbides.This formation occurs during extremelyfast cooling from the molten state and isachieved by the use of metal or graphitechills embedded in the mold. Chills rapidly extract heat from the molten metal,unlike the regular sand molds normallyused for cast iron.

5. Chilled iron is an area of a casting thatsolidifies more slowly and has a readilymachinable gray iron microstructure thatcontains graphite. Chilled iron is usedin applications such as railway wheels,stamp shoes, and heavy-duty machinerycomponents.

6. Malleable iron is a ductile form of castiron that is produced by heat-treatingwhite iron.

7. The principal difference between malleable and gray iron is ductility. Malleableiron is significantly more ductile becausethe temper carbon nodules do not present a continuous fracture path like that

presented by the graphite in gray iron.Malleable iron is also characterized bymoderate strength, good toughness,castability, and machinability.

8. Ductile iron is a cast iron that containssimilar amounts of carbon and silicon togray iron, but differs in the shape of thegraphite constituent. In ductile iron, thegraphite is spheroidal.

9. Compacted graphite iron is produced byinoculating the molten metal to preventthe formation of flake graphite. This issimilar to the manner in which ductileiron is produced. However, the graphite isin the form of interconnected flakes withblunted edges and a relatively short span.

10. Alloying has a great effect on the properties and the end use of the alloy iron.This effect is used to separate the alloyirons into the three groups of abrasion-resistant iron, corrosion-resistant iron,and heat-resistant iron.

11 . Alloying elements are either graphitizersor carbide stabilizers. A graphitizer is analloying element that promotes graphiteformation. A carbide stabilizer is an alloying element that promotes cementiteor alloy carbide formation.

12. Growth is a permanent increase in volume as a result of prolonged exposureto elevated temperatures or repeated

cycles of heating and cooling. It hasan appearance of fine cracks on thesurface.

13. Cast irons are difficult to weld, chieflybecause of their high carbon content andlow ductility. These factors, accompaniedby the high-shrinkage stresses that occur in welding, promote cracking.

14. The factors that influence the selection ofa welding filler metal include the type ofcast iron, mechanical properties desiredin the joint, need for welding filler metalto deform plastically and relieve weldingstresses, machinability of the joint, colormatching between base and weldingfiller metal, allowable dilution (chemicalcomposition change caused by meltingand mixing of the welding filler metal andthe base metal), and cost.

15 . Normally, post-weld heat treatment isperformed immediately after welding byincreasing the temperature to 590C to620C (HOOT to 1150F), and holdingthe casting at temperature for about 1 hr/in. of thickness. The cooling rate shouldbe 30C/hr (50F/hr) until the casting hascooled to 370C (700F).

1 TlifteSiaite1. There are five families of wrought stain

less steels, which include martensitic, fer-ritic, austenitic, precipitation-hardening,and duplex stainless steels. Cast stainless steels exhibit various types of metallurgical structures and are classified asa sixth family.

2. When 12 % Cr or more is added to ironor steel, it becomes stainless (immune torusting). Chromium has a form of corrosion resistance known as passivity and isthe key ingredient in the development ofa passive surface film. A passive surfacefilm is film on the outer surface layerof a metal that has superior corrosionresistance.

3. A Schaeffler diagram is a graphica lrepresentation of stainless steel phasesformed by plotting nickel equivalentsagainst chromium equivalents.

4. The martensit ic stainless steels havestrong resistance to softening duringtempering.They are tempered at highertemperatures than low-alloy steels torestore their ductility and toughness.Temperatures range from 595C to760C (1100F to 1400F). Martensiticstainless steels must not be tempered orslow cooled through the range 440C to540C (825F to 1000F) due to temperembrittlement.

5. Ferritic stainless steels have lower carbon contents than the martensitic stainless steels and generally have higherchromium contents. They are weak, onlyslightly stronger than carbon steel, buthave better corrosion resistance and better high-temperature scaling resistancethan the martensitic stainless steels.

6. Austenitic stainless steels are the largestand most widely used family of stainlesssteels. They have excellent corrosionresistance, weldability, high-temperaturestrength, and low-temperature toughness. Austenitic stainless steels are generally nonmagnetic. They are hardenedonly by cold work.

7. Sensitization is the precipitation of chro

mium carbide in austenitic stainless steels.

8. The precipitation-hardening stainless

steels consist of the martensitic, semi-austenitic, and austenitic groups.9. Duplex stainless steels possess certain

desirable qualities that austenitic and ferritic stainless steels do not. For example,duplex stainless steels have betterstrength and chloride stress-corrosioncracking resistance than austenitic stainless steels. They also have a better abilityto be fabricated and better toughnessthan ferritic stainless steels.

10. Cast stainless steels are martensitic,ferritic, austenitic, or duplex in structure.Certain duplex types are precipitationhardening.

11 . Pickling is the removal of surface oxidesfrom metals by chemical or electrochemical reaction.

12. Quench welding is sometimes used toreduce sensitization. Quench welding isa joining technique where a small lengthof metal is welded and then quenchedwith a wet rag. This causes rapid coolingand avoids sensitization. The techniqueis repeated until the entire component iswelded.

13. Stainless steels are usually cut by shearing or blanking. They require greaterpower in shearing than used for carbonsteels. Stainless steels are hot cut usingplasma-arc cutting, which is a fast andaccurate method of cutting. Air-carbon arc

gouging is another cutting process used.14. Stainless steels generally fail because

of localized forms of corrosion.The mostcommon of these are pitting and crevicecorrosion, intergranular corrosion, andstress-corrosion cracking. Pitting andcrevice corrosion occur when the passive surface film is broken in discretelocations, leading to deep attack ofsmall areas of the surface. Intergranularcorrosion is microstructural corrosionof a metal along its grain boundaries.Stress-corrosion cracking is crack formation in an alloy exposed to a specificcorrosive, often intensified by the presence of tensile stresses.


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Textbook Answers11

15. Although stainless steels are resistant tonatural waters, pitting can occur understagnant conditions, especially wherethe chloride concentration is high orwhere microbe-containing organismscan settle out. Continuous flow is required to prevent this problem. In order toprevent pitting, stainless steel equipmentthat is hydrotested, or tested by filling itwith water, should be completely drainedand dried after testing.

18I.The extraction and production steps

used for copper depend on the type ofore. Sulfide ore is concentrated, melted,and refined. Nonsulfide ore is leachedand refined.

2. Cast copper alloys are classified as high-shrinkage alloys or low-shrinkage alloys.High-shrinkage alloys are extremely fluidin the molten state and, with carefuldesign, produce high-grade castingsby sand, permanent mold, plaster, die,and centrifugal casting. High-shrinkagealloys include the manganese bronzes,aluminum bronzes, silicon bronzes, andsome nickel silvers. Low-shrinkage (lessfluid) alloys are usually limited to sand,permanent mold, plaster, and centrifugalcasting. Low-shrinkage alloys include theyellow brasses.

3. The most common hardening heattreatments for copper alloys consist ofprecipitation hardening, transformationhardening, and spinodal decomposition.

4. Commercially pure coppers contain atleast 99.9% Cu, plus extremely smallamounts of other elements. Commercially pure coppers are used primarilyfor their high electrical conductivity, and,to a lesser extent, thermal conductivity.Commercially pure coppers are soft,weak, and very ductile. Commerciallypure coppers are used in all productforms for architectural applications,

electrical components, electrical wire,and gaskets.They consist of tough pitch,deoxidized, and oxygen-free coppers.5. Modified coppers consist of free -

machining coppers, anneal-resistantcoppers, and high-strength coppers.Free-machining coppers are modifiedcoppers containing tellurium (C14500),lead (C14700), or sulfur (C18700). Anneal-resistant coppers are modified copperscontaining cadmium or silver, whichincrease resistance to elevated temperature. High-strength coppers are modifiedcoppers containing zirconium, chromium,or nickel and phosphorus, which developstrength by precipitation hardening.

6. Heat treatment of beryllium coppersis performed in two stages, which aresolution annealing and precipitationhardening.

7. Brasses are the most popular and leastexpensive of the copper alloys. A brassis a wrought alloy of copper and zinc.The zinc content may vary from 5%Zn to 50% Zn. Some wrought brassesmay contain additions of tin and otherelements. They display a wide range ofmechanical properties, are easy to work,have pleasing color, and exhibit goodcorrosion resistance.

8. Casting brasses are alpha or betabrasses containing specific alloying additions to improve their castability andstrength beyond that of regular copper-zinc binary alloys. The alloying additionsconsist of combinations of tin, lead, iron,manganese, aluminum, and nickel. Casting brasses can be poured into complexshapes having very low levels of porosityand good mechanical properties.

9. Tin bronzes have high strength, goodtoughness, high corrosion resistance,and low coefficients of friction. Thismakes tin bronzes suitable for bearingsoperating under high loads.

10. Aluminum bronzes are wrought andcast alloys of copper containing 7.0% Alto 13.5% Al, plus small amounts ofmanganese, nickel, and iron. Aluminumbronzes are not leaded.

11 . Spinodal decomposition is the growth ofcompositionally different waves withinthe crystal structure without any basicchange in the crystal structure.

12. Copper alloys are formed or shaped bya wide variety of processes that includeblanking and piercing, bending, drawingand stretch forming, coining, spinning,and forging.

13. Hot shortness occurs with coring or segregation during solidification and leadsto grain boundary separation. Methodsof combatting hot shortness includereducing joint restraint, decreasing thesize of the root opening, and increasingthe size of the root pass.

14. Copper alloys are used for bearings

because they offer a combination ofstrength, corrosion resistance, and eitherwear resistance or self-lubricity.

15. Copper alloys in waters and other fluidenvironments are subject to erosion-corrosion from fast moving streams.The erosive action of the flowing streamremoves protective films on the metalsurface, which rapidly increases therate of corrosion. Erosion-corrosionis characterized by undercut grooves,waves, ruts, gullies, rounded holes, andhorseshoe patterns on the metal surface.Erosion-corrosion can be prevented byreducing fluid velocity or alloy upgradingto copper-nickels.

1 9Nteiir->dEMil1. Extraction and refining is performed

on two types of nickel-containing ores,sulfide and laterite (silicate) ores, which

are found in many parts of the world. The

sulfide ores (sometimes associated with

iron, copper, and minerals that contain

precious metals) are present in hard rock

deposits. The laterite ores, by contrast,

are clay-like materials that contain no

other useful extractable elements.

2. Electric melting is the preferred method

of melting nickel. It reduces contamina

tion and provides operational flexibility.

3. Nickel alloys are strengthened by work

(strain) hardening, precipitation harden

ing, and dispersion hardening (mechani

cal alloying).4. Annealing processes for nickel include full

annealing, stress relieving, stress equal

izing, solution annealing, and stabilizing.

Full annealing is a heat treatment in which

a component is held in the austenitiz

ing temperature range and then cooled

inside the furnace. Stress relieving is an

annealing process that is performed to

remove stresses in work-hardened, non-

precipitation-hardenable alloys and does

not recrystallize the grain structure.

Stress equalizing is a low-temperatureheat treatment that is performed to balance stresses in cold-worked materialwithout the appreciable decrease in the

mechanical strength produced by coldworking. Solution annealing is a high-temperature heat treatment that dissolves precipitates such as carbides andage-hardening compounds. Stabilizingis an annealing process performed oncorrosion-resistant nickel-iron-chromium-molybdenum alloys that contain additionsof titanium, niobium, or tantalum.

5. The microstructure of commercially pure

nickel is single phase and consists of

grains of gamma solid solution. Twin

ning may be present in cold-worked or

annealed material. Carbon is present as

finely distributed spheroidal graphite in

cast commercially pure nickel.6. Nickel-copper alloys consist of solution-

hardening, precipitation-hardening, andfree-machining alloys.

7. Managing steels are ultra-high-strength

steels that are strengthened by precipita

tion hardening. Maraging steels contain

approximately 18 % Ni with additions ofcobalt or chromium and of molybdenum,

titanium, and aluminum. The matrices

of maraging steels consist of very

low-carbon martensite, which makes

them extremely strong and tough when

precipitation hardened. Maraging steels

are also highly weldable


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8. The addition of chromium and molybdenum to nickel yields alloys withresistance to oxidizing and reducing

corrosives. Resistance to oxidizing corrosives is due to the addition of chromium,and resistance to reducing corrosives isdue to the addition of molybdenum.

9. Superalloys are speci fically made forcreep resistance in the range 650C to1095C (1200Fto2000F). Superalloysare used in aircraft, marine gas turbines,nuclear reactors, spacecraft structures,and petrochemical production.

10. The principal methods of forming nickelproducts are forging and cold forming.

11 . Swarf is a mixture of grinding chips andfine particles of abrasive.

12. Except for oxyfuel welding, virtually allwelding processes may be used to join

nickel alloys. Oxyfuel welding has limitedapplicability and should be used onlywhen other equipment is not available.

13. Except for pure nickel, the thermalconductivity of nickel-base alloys israther low. With the exception of the low-expansion nickel-iron alloys, the thermalexpansion coefficients of nickel-basealloys are approximately the same asthose for carbon and low-alloy steels.

14. The pure metal is used as a targetin X-ray tubes and for other specialcomponents. However, cobalt is usedchiefly as an alloying element. Cobaltalloys are used for wear resistance, heatresistance, and corrosion resistanceSome cobalt alloys have specific usesin permanent magnets and as matrixmaterial in cutting tools.

15. The chief families of wear-resistantcobalt-base alloys are Stellites and

Tribaloys. Stellites are wrought powder metallurgy or cast cobalt alloys containing from 25% Cr to 35% Cr, 1% Cto 3% C, 4% W to 25% W, plus minoramounts of other alloying elements.Tribaloys are intermetallic materialsmade by powder metallurgy.

20lfemtrmm1. Aluminum is extracted electrolytically

from bauxite ore.

2. Aluminum and aluminum alloys are castby all common casting processes, whichinclude die casting, permanent moldcasting, sand casting, shell molding,plaster casting, investment casting, andcontinuous casting.

3. Die casting is the most popular castingprocess for aluminum and is suited tohigh-volume production. Die casting is a

process that consists of using substantialpressure to inject molten metal into thecavity of a metal die.

4. Aluminum and aluminum alloys arestrengthened by solid solution or dispersion hardening, cold working, andprecipitation hardening.

5. Annealing is performed on heat-treatableand non-heat-treatable alloys to removethe effects of cold work. It is accomplished by heating within 300C to 450C(570F to 840F). The rate of softeningdepends on the time at temperature andcan vary from several hours at low temperature to seconds at high temperature.

6. A temper designation is a letter that indicates the final condition of cold-worked(H) or heat-treated (T) material.

7. The Unified Numbering System for

metals and alloys identifies wroughtand cast aluminum alloys with the uppercase letter A followed by five numbersthat identify a composition range for aspecific alloy. For wrought aluminumalloys, the first number is 9 followed bythe Aluminum Association number forthe alloy. For cast aluminum alloys, thefirst number varies from 0 to 6.

8. An aldad is a composite wrought productcomprised of an aluminum alloy corehaving, on one or both surfaces, a metal-lurgically bonded aluminum or aluminumalloy coating that is resistant to corrosion.

9. The principal alloying elements in aluminum are copper, magnesium, silicon,

manganese, zinc, and tin.10. Aluminum alloys are joined by welding,brazing, soldering, mechanical fastening, and adhesive bonding.

11 . The density of aluminum is approximately one-third of that of copper andsteel.

12. The thin aluminum oxide film that formsinstantaneously on aluminum in airserves as protection against corrosion inmany environments. Contact with someacidic solutions or with moist corrosivematerials prevent access of oxygen tothe film and result in a breakdown of thefilm, which leads to severe corrosion.

Some alkaline solutions dissolve the filmand lead to significant corrosion.13. Exfoliation is a form of corrosion thatoccurs in certain cold-worked tempersand proceeds along selective subsurfacepaths parallel to the surface.

14. Galvanic corrosion is the selective attack of one metal when it is electricallycoupled to another metal in a conductive environment. Deposition corrosionis a variation of the galvanic corrosionthat occurs when metals plate out fromsolutions on the surface of aluminum.

15. The two most common surface treatments used to prevent the corrosion ofaluminum are anodizing and cladding.

Anodizing is an electrolytic oxidationprocess in which the protective oxide filmis artificially thickened to improve corro

sion resistance. Cladding is the bondingtogether of two and/or three layers ofmetals to form a composite metal.

pl -V ;JM!ir-1. Magnesium is extracted from magne

sium chloride in seawater, which contains 0.13% Mg.

2. Wrought magnesium alloys are produced by extrusion, forging, and rolling.

3. Cast magnesium alloys are usuallyproduced by sand casting, permanentmold casting, or die casting.

4. For precipitation hardening to be applicable, the magnesium end of the phasediagram must display a solvus (solidsolubility boundary line), which exhibitsrapidly decreasing solubility for magnesium with decreasing temperature.

5. The various types of coatings that areused are divided into dip coatings andanodic coatings. A dip coating is a thincoating used primarily for protectionduring shipment and storage and as aprimer for subsequent painting. Dip coatings should not be heated above 260C

(500F). Anodic coatings are thicker andharder than dip coatings. Anodic coatings can be heated to 345C (650F)with no reduction in corrosion resistance.

6. The ASTM system for magnesiumalloys consists of four parts. The firstpart indicates the two principal alloyingelements. The second part indicatesthe approximate amounts of the twoprincipal alloying elements. The thirdpart distinguishes between magnesiumalloys having the same amounts of thetwo principal alloying elements. Thefourth part indicates the temper conditionof the alloy and is similar to the codesused for aluminum alloys.

7. Aluminum addi tions to magnesiumprovide the greatest strengthening andhardening effects. Alloys with more than6% Al are precipitation hardenable.

8. M1A has moderate mechanical properties and excellent weldability, corrosionresistance, and hot formability. M1A isnot strengthened by heat treatment.

9. Zinc is added to improve the room temperature strength of magnesium alloys.Zinc is usually added in combinationwith rare earth elements (ZE), thorium(ZH), or zirconium (ZK) to produceprecipitation-hardenable alloys.

10. Magnesium exhibits a CPH structure.


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Textbook Answers 13

11 . Magnesium is easier to machine thanother structural metals. The powerrequired to remove a given amount ofmagnesium is lower than that requiredfor any other commonly machined metal.

12. Magnesium is readily joined by resistancespot welding, gas metal arc welding, andgas tungsten arc welding. Adhesive joining and riveting are also used.

13. Restraint is a measure of the rigidity ofa joint.

14. The most important characteristics ofmagnesium and magnesium alloys arethe low density and the correspondinghigh strength-to-weight ratio.15. Magnesium can suffer galvanic corrosionwhen electrically coupled with certainmetals. Preventive measures to avoidgalvanic corrosion include the selection

or electroplating of the contact metal sothat it does not form an unfavorable galvanic couple with magnesium, the use ofa suitable surface treatment or insulatinggasket to protect the magnesium fromelectrical contact with the incompatiblemetal, and the prevention of water accumulation at the dissimilar metal assembly.

tSm C M J tBWJP^1. First, titanium ore is reduced to titanium

metal (sponge). Second, the sponge(plus reclaimed scrap) is melted intoingots. Third, the ingots are converted togeneral mill products, or primary products. Fourth, certain primary productsare converted into specific shapes orsecondary products.

2. Die forging is the mechanical reductionof billets under specific temperatureconditions to obtain properties that arenot achieved in the billets themselves.

3. UNS designations consist of the uppercase letter R (for reactive and refractorymetals) followed by five numbers. Titanium alloys occupy the series R50000to R59999.

4. Based on their crystal structures at roomtemperature, titanium alloys are dividedinto alpha, alpha-beta, and beta alloys.

5. The crystal structure of pure titanium isCPH (alpha).

6. Aluminum additions stabilize the alphaphase and raise the a

metallurgy answer key

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