An Introduction to Metallurgy

567 Pages·2016·9.45 MB·English

by  Cottrell A.

An Introduction to
Metallurgy
SECOND EDITION
Sir Alan Cottrell

THE INSTITUTE OF MATERIALS
1995
Book 626
Published in 1995 by
The Institute ofMaterials
1Carlton House Terrace
London SW1Y50B
This book isareprint ofthe
second edition published by
Edward Arnold (Publishers) Ltd
in 1975
Reproduced by kind
permission
© Alan Cottrell 1975
Allrights reserved
ISBN 0901716 936

Printed and bound by
Antony Rowe Ltd, Eastbourne
Preface
Because of their great practical value and scientific interest, metals lie at
the cross-roads of many scientific and technological disciplines. Chemists
are interested in the oxidation and reduction of metals, the catalytic proper-
ties of metals and the laws by which metals combine together to form alloys.
Chemical engineers apply their general principles of chemical processing to
the production of pure metals from ores. Solid-state physicists are fasci-
nated by the electronic and atomic structures of metals and by the ways in
which these structures determine the characteristic properties of metals and
alloys. Mechanical engineers are interested in the plastic working of metals,
structural engineers in the mechanical performance of metals in practical
use, and electrical engineers in all the special electrical and magnetic
properties obtainable from metallic materials.
The contributions to the science and technology of metals made by
people in these fields are immensely valuable. Nevertheless, and quite
naturally, each of them sees only his own side of the subject. The essential
task of the metallurgist is to complement and coordinate the work of these
specialists by acting as a general practitioner over the whole field..To take
an example, if we wish to make an intelligent choice of a steel for a nuclear
reactor pressure vessel we must know about the chemistry of steelmaking,
about the rolling and welding ofsteel, about corrosion, about brittle fracture
at low temperature and creep deformation at high temperature, about
effects of damage to the atomic structure of metals by nuclear radiation,
about commercial and economic factors, and about the interrelations of all
these and many other things with one another. An equally wide spectrum
of knowledge is required in other problems; for example, to develop a new
turbine alloy or to diagnose the cause of failure in a broken aircraft under-
carriage. A metallurgist, however much he may specialize in practice, must
be able, when required, to take this wide, all-embracing view.
It was with such thoughts in mind that I considered an invitation to
prepare a new edition of my book Theoretical Structural Metallurgy. When
that book was written, the pure science of metals was still quite new and
there seemed a good case for bringing it to the attention of metallurgists in
an elementary but specialized book. The position is now different. This
science has become well established and triumphant. The need now, itseems
to me, is to re-assert the unity of all metallurgical knowledge and to link
up this new science with the more traditional aspects of the subject. A new
vi PREFACE
edition under the old title could not do this. I was thus led to attempt,
instead, acomplete survey ofthe whole metallurgical field. What I have tried
to do particularly isto show metallurgy as asingle applied science. This has
meant developing the science as a continuous thread running through the
subject, from atomic theory, through thermodynamics, reaction kinetics
and crystal physics, to elasticity and plasticity, but stopping at all suitable
places to show how the characteristic features of metals, alloys, and the
processes of practical metallurgy, such as extraction, refining, casting,
working, and. heat-treatment, grow out of this science. In choosing this
pattern I have also been influenced by the feeling that the most intellec-
tually exciting thing to do in metallurgy today is to apply the newly-
discovered science to the invention and development of new metallurgical
processes and materials.
Naturally, I have not been able to go very far into anyone aspect of the
subject. The book has been aimed, however, at those who are at the begin-
ning of their metallurgical studies and so I hope that it will be forgiven its
admitted lack of depth, for the sake of what I hope is a broad view.
Christ's College, Cambridge ALAN COTTRELL
1966
Acknowledgements
Much of this book has grown out of the more elementary parts of the
courses taught in the Department of Metallurgy, University of Cambridge,
and I am grateful to many friends there for their advice and help. I would
additionally like to thank Mr G. C. Smith, Dr R. B. Nicholson, Dr B.
Ralph, Dr S. Ranganathan and Dr J. R. Griffiths for kindly making avail-
able the photographs used in this book.
Acknowledgement is made for kind permission to reproduce the following
diagrams: Figs. 15.6 and 15.14 from DESCH, c. H. (1944) Metallography

6th ed, Longmans, Green, London; Figs. 17.8 and 17.9 from CHALMERS, B.
(1949) Prog, Metal Phys. 1, 77 (Pergamon Press, Oxford); Figs. 17.10 and
17.12 from CHALMERS, B. (1953) Prog. Metal Phys. 4, 205 (Pergamon Press,
Oxford); Fig. 19.5 from the Clarendon Press, Oxford; Fig. 19.12 from
SMITH, c. s. (1948) Trans. Am. Inst, Min. metall, Engrs., 175, 15; Fig. 19.14
from The Institute of Physics and The Physical Society.
Preface to the Second Edition
Since the first Edition was written the scientific community has largely
yielded to the pressures brought upon it to conform to the 81 system of units.
Ihave therefore accepted the inevitable and converted the text, in this second
Edition, also to these units. For those who nevertheless find other systems,
such as c.g.s., more congenial, Ihave included some conversion factors in a
table at the front ofthe book.
Ihave also taken the opportunity to up-date some ofthe information in the
text.
Jesus College, Cambridge ALAN COTTRELL
1974
Contents
Preface
Chapter Page
1 Prologue 1
The art and science of metals. Chemical metallurgy. Mechanical
metallurgy. Physical metallurgy. Metallurgical science and industry.
2 The Atomic Nucleus 9
Composition of nuclei. Nuclear binding. Radioactive changes.
Uses of radioactivity. Materials in nuclear reactors. Origin and
abundance of the elements.
3 Atomic Structure 18
Electropositive and electronegative elements. The periodic table.
Quantum mechanics. The Schrodinger equation. The hydrogen
atom. Atomic structures of the elements. Sizes of atoms and ions.
4 Chemical Bonding 39
Forces between atoms. Origin of interatomic forces. Covalent
bonding. Transition to ionic bonding. Transition to metallic
bonding. The metallic state.
5 Heat and Energy 54
Thermodynamics. Internal energy and enthalpy. Standard
thermodynamic properties. Combustion. Furnaces.
6 Entropy and Free Energy 67
Direction of chemical change. Entropy. Free energy. Phase
changes; vaporization. The physical nature of entropy. The
exponential energy distribution. Activation energy.
7 Free Energies of Metallic Compounds 81
The Ellingham diagram. Effect of temperature. Dissociation
temperature and pressure. The equilibrium constant. Oxidizing-
reducing gas mixtures. Solutions. Refractories.
x CONTENTS
8 Extraction ofMetals 94
Metallic ores. Concentration of ore. Slags. Tin. Sulphide ores.
Lead. Copper. Nickel.Zinc. The zincblast furnace.
9 Electrochemical Extraction and Refining Processes 107
Electrolysis. Aluminium. Magnesium, calcium and alkali metals.
Electrochemistryofaqueoussolutions.Electrolyticextractionfrom
aqueous solutions.Electrolyticrefiningin aqueoussolutions.
10 Extraction of Reactive and Refractory Metals 117
Introduction. The Pidgeonprocessformagnesium.Useofhalides.
Titanium. Uranium. Refractory metals. Tungsten and Molyb-
denum.
11 Iron and Steel Making 122
Introduction. The iron-making blast furnace. Chemistry of iron-
making. Recent developments in the blast furnace method.
Wrought iron. Early steel-making processes. The Bessemer
process. The open hearth process. Killed and rimming steels.
Electric steel-making.Ferro-alloys. Oxygensteel-making.
12 Kinetics of Metallurgical Reactions 143
Introduction. Theory ofreaction rates. Homogeneousand hetero-
geneous reactions. Diffusion and heat conduction. Effects of
mixing.Nucleation.
13 Solids, Liquids and Solidification 158
Metal crystals. Liquid metals. Nucleation ofcrystalsfrom amelt.
Nucleation of melting. Glasses. Growth of crystals from a melt.
The grain structure of metals. Solidification of solutions and
impure metals. Structures of cast metals. Casting and related
processes.Growth ofsinglecrystals.
14 Alloys 189
Types of alloys. So lid solutions. Primary substitutional solid
solutions.Intermediate phases. Interstitial phases.The freeenergy
ofsolidsolutions.Phasemixtures.The stablestateofanalloy.Equa-
tions of phase equilibrium; the phase rule. The free energy of
intermediate phases. Variation of solubility with temperature.
Long-range order in solid solutions. Short-range order and anti-
phase domains. Ordering ofcarbonatomsinmartensite.
15 The Phase Diagram 224
Introduction. Completemiscibilityinthe solidstate.Partialmisci-
bility in the solid state. Systems containing intermediate phases.
More complicatedphase diagrams.Phase changesin alloys.Zone
refining. The determination of phase diagrams. Gas-metal
systems.The chemicalpotential.
xi
CONTENTS
16 Ternary Phase Diagrams 250
Representation of the phase diagram. Simple eutectic system.
Horizontal sections. Vertical sections. Ternary solid solutions.
More complexdiagrams.
17 Metal Crystals-I Periodicity 261
Introduction.. Periodicity. Translational symmetry and crystal
plasticity. Dislocations. Miller indices. Burgers vectors and glide
systems in metals. Diffraction of x-rays. Electron and neutron
diffraction.Electronmicroscopy.Field-ionmicroscopy.
18 Metal Crystals-II Directionality 296
Rotationalsymmetry.Stereographicprojection.Anisotropy.Strain.
Stress. Hooke's law. Plastic glide of metal crystals. Plasticity of
polycrystals.Coherent and non-coherent crystalboundaries.
19 MetalCrystals-III Energiesand Processes 322
Cohesion.Thermal properties.Energiesofdislocations.Energiesof
surfaces.Grain boundariesandinterfaces.Misfitenergiesofsolute
atoms and inclusions. Energies of point defects. Diffusion.
Vacancycreepand sintering. Radiationdamage.
20 Heat-treatment ofAlloys 365
Introduction. Decomposition of supersaturated solid solutions.
Development ofcommercialage-hardening alloys.Heat-treatment
ofsteels.Formation ofpearlite.Pro-eutectoid reactions.Formation
ofbainite.Formation ofmartensite.Tempering ofquenched steel.
Case-hardeningofsteel.
21 Mechanical Properties 386
The tensile test. The yield stress. Yield points in metals. Effects
of grain size. Alloy hardening. Work hardening. Recovery, re-
crystallization,and hot working. Combined dispersion hardening
andworkhardening. Creep.Theory offracture. Brittlefracture of
steel. Chemical embrittlement. Creep rupture. Metal fatigue.

Fibre strengthening.
22 PlasticWorking 428
Introduction. Simple elongation. Forging. Mechanics of plane
strain deformation, The friction hill. Surfaceindentation. Rolling.
Extrusion. Wire drawing.Deep drawingand sheetmetalworking.
Seamlesstube making.Metalworkingathighspeeds.Superplasti-
city.
23 Oxidationand Corrosion 451
Introduction. Oxidation. Prevention of oxidation. Corrosion in
acids and alkalies. Electrochemical corrosion. Atmospheric cor-
rosion. Intergranular corrosion and dezincification.Prevention or
restraint ofcorrosion. Stress-corrosion. Corrosion-fatigue.
xii CONTENTS
24 Electronic Structure and Properties 470
Electrons in a lattice. Brillouin zones. Metals and insulators. Con-
ductivity of metals. Semi-conductors. Zone theory of alloys.
Magnetic properties. Magnetic domains. Superconductivity.
25 Properties and Uses 509
Strength and cost. Plain carbon steels. Alloy steels. Cast iron.
Strength and weight. Aluminium and its alloys. Chemical inertness.
Copper and its alloys. Fusibility. High-temperature properties.
Electromagnetic and nuclear properties.
Index 537
List of Plates
Plate Page
1 A. Grains in lightly-etched aluminium, x 100 244
B. Etched grains in nickel, x 300 244
2 A. Cored dendritic structure in chill cast 70-30 brass, x 100 245
B. Structure of cadmium-bismuth eutectic, x 100 245
3 A. Ferrite and pearlite in aslowly cooled 0·55 per cent carbon
steel, x 1000 276
B. Electron microscope picture ofdislocations in two sets ofslip
lines near a grain boundary in an Ni-Fe-Cr alloy, x 35 000 276
4 Helium field-ion microscope picture of a tungsten tip, showing
atomic structure 277
5 Helium field-ion microscope picture of a dislocation in iridium,
showing the helicoidal structure of atomic layers round the
dislocation 372
6 A. Slip bands on differently oriented glide systems in polycrys-
talline aluminium, x 500 373
B. Structure of ma rtensite in quenched 1·2 per cent carbon
steel, x 750 373
7 A. Electron microscope picture of dislocation rings in a
quenched AI-Cu alloy, x 56 000 404
B. Electron microscope picture of spherical G.P. zones, about
90 A diameter, in a quenched and aged AI-Ag alloy,
x 190 000 404
8 A. Electron microscope picture ofholes formed byplastic defor-
mation round spherical silica particles in copper, x 80 000 405
B. Small cleavage cracks near a major crack in a silicon-killed
steel broken at IOoe, x 650 405