In the continuation of previous upload. This presentation is Part 2 of Advances in Special Steels. This is a overview of fundamentals of different carbides found in steels.

1. By Shamail Ahmad, Metallurgical Engineering Department,
NED University of Engineering and Technology & Peoples
Steel Mills Ltd.
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3.  Introduction
 Classification of carbides
 Interstitial Carbides
 Covalent Carbides
 Intermediate Carbides
 Salt-Like Carbides
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M + C  MC
These temperature ranges are some what 50-100 ۫۫C lower when carbides are
formed in Steels

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12.  Interstitial Carbides
 Intermediate Carbides
 Covalent Carbides
 Salt-Like Carbides
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15.  Difference between Electronegativities of Metal and
Carbon is quite large (except Cr3C2 which is a border
line case)
 (Atomic Radius of Carbon / Atomic Radius of
Metal)<= 0.59
 Bonding may be partly ionic and covalent, but
primarily Metallic
 High Thermal and Electrical Conductivities
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16.  Their Compositions are often indefinite
 Posses High Hardness, Melting Points and Chemical
Inertness
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The carbides of these elements are also called Refractory Carbides (for Chromium
only Cr3C2 is refractory carbide)

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Group IV
Group V
Group VI

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Group VI-B carbides have variety of compositions and they mostly
exist in Hexagonal and Orthorhombic Structures

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27.  The difference between the electronegativities of
Metal and Carbon is relatively small
 The bonding is primarily covalent
 Silicon and Boron carbides are considered to be
refractory carbides
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32.  Few metals of Group VII and VIII like Mn, Fe, Co, Ni
and Cr (which is from VI) have too small radii to
accommodate carbon atoms in interstitial spaces
without considerable distortion of the lattice, so, they
form intermediate carbides
 Carbon atoms are close enough to form C-C and
Carbon chains
 Usually unstable chemically
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34.  They are also called Salinic Carbides
 Formed Between more Electropositive metals, normally
with Group IA, IIA, IIIA elements
 The difference of electronegativity >=2
 The bond is at least 50% ionic
 They are transparent to optical radiations and electrical
insulators
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35.  C4- ions carbides like Al4C3 and Be2C are called
methanides because they are hydrolyzed to give
methane
 C2- ions carbide like Ca2C is called acetylides because
it is hydrolyzed to give acetylene
 Although covalent carbides posses high melting points
but still they are not categorized as refractory carbides
because they are decomposed at low temperature by
dilute acids
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36. 1. Hugh O. Pierson, Handbook of Refractory Carbides
& Nitrides: Properties, Characteristics, Processing
and Applications, 1st edn, William Andrew, 1997
2. George Krauss, George Roberts and Richard
Kennedy, Tool Steels, 5th edn, ASM, 1998
3. Introduction and Background on Transition Metal
Carbides, Chap. # 8,
http://www.ropine.com/chapter8.html
4. R. Wilson, Metallurgy and Heat Treatment of Tool
Steels, McGraw-Hill, London, 1975
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37. 5. H. Brandis, E. Haberling, and H.H. Weigard,
Metallurgical Aspects of Carbides in HighS peed Steels,
Processing and Properties of High Speed Tool Steels,
M.G.H. Wellsand L.W. Lherbier, Ed., TMS-AIME,
1980,p1-18
6. L.P. Tarasov, The Microhardness of Carbides in Tool
Steels, Met. Prog., Vol 54 (No.6), 1948, p 846
7. L.E. Toth, Transition Metal Carbides and Nitrides,
Academic Press, 1971
8. FD. Richardson, The Thermodynamics of Metallurgical
Carbides and of Carbon in Iron, J. Iron Steel/ntf., Vol 175,
1953, p 3
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38. 9. Wehr, M. R., Richards, J. A., Jr. and Adair, T . W., III,
Physics of the Atom, Addison-Wesley Publishing Co.,
Reading, MA (1978)
10. March, J., Advanced Inorganic Chemistry, John Wiley
& Sons, New York (1985)
11. Storms, E. K., The Refractory Metal Carbides, Academic
Press, New York (1967)
12. Evans, R. C., An Introduction to Crystal Chemistry,
Cambridge Univ. Press, Cambridge (1979)
13. Galasso, F. S., Structure and Properties of Inorganic
Solids, Pergamon Press, New York (1970)
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39. 14. Kosolapova, T. Ya., Carbides, Plenum Press, New York
(1971)
15. Kisly, P. S., The Chemical Bond Strength and the
Hardness of High Melting Point Compounds, in
Science of Hard Materials, Institute of Physics Conf.
Series No. 75, Adam Hilger Ltd., Bristol, UK (1984)
16. Toth, L. E., Transition Metal Carbides and Nitrides,
Academic Press, New York (1971)
17. Aselage, T. L., and Tissot, R. G., Lattice Constants of
Boron Carbide, J. Am. Ceramic Sot., 75(8):2207-2212
(1992)
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