Seetharaman S. Fundamentals of metallurgy
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Chapters 1 and 7
Professor H. Y. Sohn*
Department of Metallurgical
Engineering
University of Utah
135 S 1460 E
Salt Lake City
UT 84112-0114
USA
E-mail: hysohn@mines.utah.edu
Professor S. Sridhar
Department of Materials Science
Carnegie Mellon University
Pittsburgh
PA 15213-3890
USA
E-mail: sridhars@andrew.cmu.edu
Chapter 2
Dr R. E. Aune* and Professor S.
Seetharaman
Division of Materials Process
Science
Department of Materials Science and
Engineering
Royal Institute of Technology
SE-100 44 Stockholm
Sweden
E-mail: aune@mse.kth.se
E-mail: raman@kth.se
Chapter 3
Professor K. Morita*
Department of Metallurgy
The University of Tokyo
Bunkyo-ku
Tokyo 113-8656
Japan
E-mail: morita@wood2.mm.t.u-
tokyo.ac.jp
Professor N. Sano
Executive Advisor
Nippon Steel Corporation
E-mail: sano@re.nsc.co.jp
Chapter 4
Professor K. C. Mills
Department of Materials
Imperial College of Science,
Technology and Medicine
Prince Consort Road
South Kensington
London SW7 2BP
UK
E-mail: kenmills@tesco.net
Contributor contact details
Chapter 5
Professor A. K. Lahiri
Department of Metallurgy
Indian Institute of Science
Bangalore 560012
India
E-mail: metakl@metalrg.iisc.ernet.in
Chapter 6
Professor Emeritus K. Mukai
Department of Materials Science and
Engineering
Kyushu Institute of Technology
Sensui-Cho
Tobata-ku
Kitakyushu 804 8550
Japan
E-mail: hiro_mukai@nifty.com
Chapter 8
Professor O. N. Mohanty
Research and Development Services
The Tata Iron and Steel Company Ltd
11T Kharagpur-721302
India
E-mail: onmohanty@lot.tatasteel.com
onm@metal.iitkgp.ernet.in
Chapter 9
Professor Du Sichen
Department of Materials Science and
Engineering
Royal Institute of Technology
SE-100 44 Stockholm
Sweden
E-mail: du@mse.kth.se
Chapter 10
Professor A. W. Cramb
Department of Materials Science and
Engineering
Carnegie Mellon University
Pittsburgh
PA 15213
USA
E-mail: cramb@andrew.cmu.edu
Chapter 11
Dr G. Engberg*
MIK Research AB (MIKRAB)
Teknikdalen
Forskargatan 3
SE-781 27 Borlange
Sweden
E-mail: goran.engberg@mikrab.se
Dr L. Karlsson
Dalarna University
Chapter 12
Dr F. Lemoisson* and Professor L.
Froyen
Physical Metallurgy and Materials
Engineering Section
Katholieke Universiteit Leuven
Kasteelpark Arenberg 44
BE 3001 Heverlee
Belgium
E-mail: fabienne.lemoisson
@mtm.kuleuven.ac.be
E-mail:
ludo.froyen@mtm.kuleuven.ac.be
Chapter 13
Professor T. Emi
Takasu 5-1
B1905
Urayasu-shi
Chiba 279-0023
Japan
E-mail: t-emi@yb3.so-net.ne.jp
xii Contributor contact details
Metallurgy refers to the science and technology of metals. The subject area can
be considered as a combination of chemistry, physics and mechanics with
special reference to metals. In later years, metallurgy has expanded into
materials science and engineering encompassing metallic, ceramic and
polymeric materials.
Metallurgy is an ancient subject linked to the history of mankind. The
development of civilisations from stone age, bronze age and iron age can be
thought of as the ages of naturally available ceramic materials, followed by the
discovery of copper that can be produced relatively easily and iron that needs
higher temperatures to produce. These follow the patter n of the Ellingham
diagram known to all metallurgists. Faraday introduced the concept of
electrolysis which revolutionised metal production. Today, we are able to
produce highly reactive metals by electrolysis.
The prime objective to produce metals and alloys is to have materials with
optimised properties. These properties are related to structure and thus, physical
as well as mechanical properties form essential parts of metallurgy. Properties of
metals and alloys enable the choi ce of materials in production engineering.
The book, Fundamentals of Metallurgy is a compilation of various aspects of
metallurgy in different chapters, written by the most eminent scientists in the
world today. These participants, despite their other commitments, have devoted
a great deal of time and energy for their contributions to make this book a
success. Their dedication to the subject is admirable. I thank them sincerely for
their efforts.
I also thank Woodhead Publishing Company for this initiative which brings
the subject of metallurgy into lime light.
Seshadri Seetharaman
Stockholm
Preface
Part I
Understanding the effects of processing
on the properties of metals
1.1 Introduction
Metallurgical reactions take place either at high temperat ures or in aqueous
solutions. Reactions take place more rapidly at a higher temperature, and thus
large-scale metal production is mostly done through high-temperature processes.
Most metallurgical reactions occurring at high temperatures involve an
interaction between a gas phase and condensed phases, which may be molten
liquids or solids. In some cases, interactions between immiscible molten phases
are important.
High-temperature metallurgical reactions involving molten phases are often
carried out under the conditions of near equilibria among all the phases; other
such reactions proceed under the control of interphase mass transfer with
equilibria at interphase boundaries. Reactions involving gas±solid contact also
often take place under the rate control of mass transfer with chemical
equilibrium at the interf ace, but the chemical kinetics of the heterogeneous
reactions are more often important in this case than those involving molten
phases. Even in this case, mass transfer becomes increasingly dominant as
temperature increas es. The solid phases undergo undesirable structura l changes,
such as fusion, sintering, and excessive reduction of internal porosity and
surface area, as temperature becomes too high. Thus, gas±solid interactions are
carried out in practice at the highest possible temper atures before these
undesirable changes in the solid structure become damaging. In the case of high
temperature oxidation, the structure of the product oxide determines the mass
transport of gases and ions.
The treatment of metals in their molten state, e.g. refining and alloying,
involves reactions between the melt and a gas phase or a molten slag. Interfacial
reaction kinetics, mass transport in the molten or gaseous phase becomes
important. The production of metals and alloys almost always involves
solidification, the rate of which is often controlled by the rate of heat transfer
through the mold.
1
Descriptions of high-temperature
metallurgical processes
H Y S O H N , University of Utah and
S S R I D H A R , Carnegie Mellon University, USA
1.2 Reactions involving gases and solids
Since metals occur in nature mostly as compounds (minerals), the first step in
the utilization of the naturally occurring sources is their chemical separation into
elemental forms. More often than not, the first reaction in this chemical
separation step involves an interaction between the solid-phase minerals and a
reactant gas.
1.2.1 Reduction of metal oxides by carbon monoxide, carbon,
or hydrogen
Metal oxides are most often reduced by carbon or hydrogen. The reas on why
reduction by carbon is treated in this section on gas±solid reaction is because the
actual reduction is largely effected by carbon monoxide gas generated by the
reaction of carbon dioxide with carbon, when carbon is used to reduce metal
oxides in solid state. These reactions can in general be expressed as follows:
M
x
O (s) CO (g) = xM (s) CO
2
(g) (1.1)
yC (s) yCO
2
(g) = 2yCO (g) (1.2)
Overall, M
x
O (s) yC (s) = xM (1 ÿ y)CO
2
+ (2y ÿ 1)CO (1.3)
The amount y, which is determined by the p
CO
2
=p
CO
ratio in the product gas
mixture, depends on the kinetics and thermodynamics of the two gas±solid
reactions (1.1) and (1.2). In many systems of practical importance, reaction (1.1)
is much faster than reaction (1.2), and thus the p
CO
2
=p
CO
ratio approaches the
equilibrium value for reaction (1.1). Th e overall rate of reaction (1.3) is then
controlled by the rate of reaction (1.2) taking place under this p
CO
2
=p
CO
ratio
(Padilla and Sohn, 1979).
The reduction of iron oxide is the most important reaction in metal
production, because iron is the most widely used metal and it occurs in nature
predominantly as hematite (Fe
2
O
3
). The production of iron occupies more than
90% of the tonnage of all metals produced. The most important reactor for iron
oxide is the blast furnace, in the shaft region of which hematite undergoes
sequential reduction reactions by carbon monoxide (Table 1.1).
Table 1.1
Reaction Equil. CO/CO
2
Heat generation
ratio at 900 ëC (900 ëC)
3Fe
2
O
3
CO 2Fe
3
O
4
CO
2
0 10.3 kcal (1.4)
Fe
3
O
4
CO 3FeO CO
2
0.25 ÿ8.8 kcal (1.5)
FeO CO Fe CO
2
2.3 4.0 kcal (1.6)
4 Fundamentals of metallurgy
In the blast furnace, the solid charge flows downward, and the tuyere gas with
a high CO/CO
2
ratio flows upward. Thus, the tuyere gas first comes into contact
with wustite (FeO), the reduction of which requires a high CO/CO
2
ratio, as seen
above. The resulting gas reduces magnetite (Fe
3
O
4
) and hematite (Fe
2
O
3
) on its
way to the exit at the top of the furnace.
The equilibrium percentage of CO in a mixture with CO
2
is shown in Fig. 1.1
as a function of temperature. Again, it is seen that the equilibrium concentr ation
of CO for the reduction of hematite to magnetite is essentially zero; i.e., CO is
completely utilized for the reduction. The equilibrium content of CO for the
reduction of Fe
3
O
4
to FeO and that of FeO to Fe depend on temperature. It is
also noted that wustite is a non-stoichiometric compound Fe
x
O with an average
value of x equal to 0.95 in the temperature range (approximately 600 ëC±
1400 ëC) of its stability. The actual value of x and thus oxygen cont ent depend
on temperature and CO/CO
2
ratio, as illustrated by the curves drawn within the
wustite region in Fig. 1.1. Furthermore, the CO/CO
2
ratio is limited by the
Boudouard reaction given by eqn (1.2) and shown as a sigmoidal curve in Fig.
1.1 (for 1 atm total pressure without any inert gas). Thus, the reduction reactions
indicated by the dashed lines to the left of this curve are thermodynamically not
feasible. (In practice, however, reduction by CO to the left of the Boudouard
curve is possible because the carbon deposition reaction (the decomposition of
CO) to produce solid carbon is slow.)
1.1 Equilibrium gas compositions for the reduction of iron oxides by carbon
monoxide. (Adapted from Evans and Koo, 1979.)
Descriptions of high-temperature metallurgical processes 5