1. TUGAS 1 – PENCARIAN ARTIKEL
STRUKTUR KRISTAL
KULIAH MATERIAL TEKNIK
ZUL FAUZI FACHRI ABIDIN
(07525008)
JURUSAN TEKNIK MESIN
FAKULTAS TEKNOLOGI INDUSTRI
UNIVERSITAS ISLAM INDONESIA
YOGYAKARTA
2011

2. TUGAS 1 – PENCARIAN ARTIKEL
STRUKTUR KRISTAL
ZUL FAUZI FACHRI ABIDIN
( 07525008 )
JURUSAN TEKNIK MESIN
FAKULTAS TEKNOLOGI INDUSTRI
UNIVERSITAS ISLAM INDONESIA
YOGYAKARTA
2011

3. The Structure of Metal
By Bob Capudean
April 24, 2003
Let's start with the obvious: Molten metals have no particular structure. The atoms that make up
that metal are just whipping around helter-skelter—at a high rate of speed—with no real orderly,
defined pattern.
As you think about molten metal, keep a couple of points in mind. First, heat flows to cold-
always. And that becomes more understandable when you consider that warm atoms are moving
faster than cold atoms. And those fast-moving atoms are bumping into other atoms, causing them
to move quickly.
Furthermore, the warmer a metal-or any material, for that matter-is, the faster the atoms
composing that metal are moving. Yes, there are internal attractions that help keep the atoms in a
puddle, preventing them from just vaporizing, but the fact is, if they get moving fast enough-that
is, get hot enough-they eventually will evaporate, just like hydrogen and oxygen do when water
boils.
As thermal energy is transferred to another part, the atoms give up energy, slowing down and
cooling. What evaporates is still water, in the form of steam.
As a molten metal cools, atomic forces begin to pull or force the atoms into solid particles called
nuclei, which take on specific and identifiable crystal structures. Because the nuclei have the
metal's crystal structure, additional atoms join the nuclei. As these nuclei get bigger, they form
grains. This orderly arrangement of the atoms is called a lattice.
But as the metal solidifies and the grains grow, they grow independently of each other, which
means eventually these different areas of growing grains have to meet. When they do, the
arrangement of the atoms in the grain structure is disrupted at that meeting point. This is called a
grain boundary. Grain boundaries form a continuous network throughout the metal, and because
of the disrupted structure at the boundary, the metal often acts differently at the boundary
locations.
Grain boundaries aside, each grain in a pure metal has the same crystalline structure as any other
grain, assuming the temperature is the same. This structure, which is identifiable under the
microscope, has a huge influence on the metal's characteristics.

4. Common Crystal Structures
For our purposes, all metals and alloys are crystalline solids, although some metals have been
formed in the lab without crystalline structure. And most metals assume one of three different
lattice, or crystalline, structures as they form: body-centered cubic (BCC), face-centered cubic
(FCC), or hexagonal close-packed (HCP). The atomic arrangement for each of these structures is
shown in Figure 1.
A number of metals are shown below with their room
temperature crystal structure indicated. And for the record, yes,
there are substances without crystalline structure at room
temperature; for example, glass and silicone.
Aluminum — FCC
Chromium — BCC
Copper — FCC
Iron (alpha) — FCC
Iron (gamma) — BCC
Iron (delta) — BCC
Lead — FCC
Nickel — FCC
Silver — FCC
Titanium — HCP Figure 1
Tungsten — BCC Three crystal structures
Zinc — HCP favored by metals are (a) body-
centered cubic (BCC), (b)
face-centered cubic (FCC), and
Alloys and Atomic Arrangements (c) hexagonal close-packed
(HCP).
Everything covered so far applies to pure metals, which begs the
question, What happens when you add an alloy or two? After all, most common metals are alloys
containing residual and added metallic and nonmetallic elements dissolved in a base metal.
Of course, those added elements can have a dramatic effect on the resulting alloy's properties.
But how those elements dissolve, or in other words how they combine with the existing atoms in
the parent metal's crystal lattice, can also greatly influence both the physical and nonphysical
properties of the end product.
Basically, there are two ways the alloying element(s)-called solutes-combine with the base, or
parent, metal, which is also called the solvent. The alloy's atoms can combine through either
direct substitution, creating a substitutional solid solution, or they can combine interstitially,
forming an interstitial solid solution.
Substitutional Solid Solution. When the alloy's atoms are similar to the parent metal's atoms,
they'll simply replace some of the parent metal's atoms in the lattice. The new metal dissolves in

5. the base metal to form a solid solution. Examples include copper dissolved in nickel, gold
dissolved in silver, and carbon dissolved in iron (ferrite).
Interstitial Solid Solution. When the alloy's atoms are smaller than the parent metal's atoms,
they'll fit between the atoms in the parent metal's lattice. The alloy atoms don't occupy lattice
sites and don't replace any of the original atoms. Of course, this causes strain in the crystal
structure because the fit isn't perfect: There are atoms taking up space that was originally
unoccupied.
The end result is usually an increase in tensile strength and a decrease in elongation. Examples
include small amounts of copper dissolved in aluminum and carbon, and nitrogen dissolved in
iron and other metals.
Phases, Microstructures, and Phase Changes
Often neither direct nor interstitial solution can completely dissolve all the added atoms. And
when this happens, the result is mixed atomic groupings. In other words, different crystalline
structures exist within the same alloy. Each of these different structures is called a phase, and the
alloy-which is a mixture of these different crystalline structures-is called a multiphase alloy.
These different phases can be distinguished under a microscope when the alloy is polished and
etched. Pearlite is a good example of a multiphase alloy within the carbon-iron family.
The phases present in an alloy, along with the overall grain arrangements and grain boundaries,
combine to make up an alloy's microstructure. And the microstructure of an alloy is critical,
being largely responsible for both the physical and mechanical properties of that alloy.
For example, because the boundary areas are the last to freeze when an alloy cools, grain
boundaries contain lower-melting-point atoms compared to the atoms within the grains. These
foreign atoms cause microstructure distortion and harden the alloy at room temperature. But as
temperature goes up, alloy strength goes down because these lower-melting-point atoms begin to
melt sooner, allowing slippage between the grains.
Furthermore, foreign or odd-sized atoms tend to congregate at grain boundaries because the
atomic structure is irregular. This can lead to phases that reduce ductility and lead to cracking
during welding.
Consider this: Cold working a metal distorts its entire microstructure. The end result, in most
cases, is that the metal gets harder. Atoms from an alloying element distort the metal's
microstructure, and again, the metal gets harder. The same is true for alloy atoms that are
dissolved in a base metal and then precipitate out. The atoms leave, but a distortion remains, and
the metal is harder.
Grain size is also important. Generally speaking, fine-grained metals have better properties at
room temperature. And size is determined by cooling rate. Fast cooling leads to smaller grains,

6. and vice versa. But the fact is, grain size, grain boundary structure, and phases present all are
important. Overall, these characteristics in total determine a metal's capabilities and usefulness.
In short, a metal's overall microstructure determines its characteristics. Today just about every
metal we use is an alloy, with one or more elements added to modify, adjust, correct, or change
the base metal's microstructure, creating a multiphase system that can better serve our needs.
And every time we put torch to metal, we cause a phase change and influence that
microstructure.
This should give you an overview of how metals are structured and what happens when we melt
them to weld them together. Next time we'll consider phase transformations, carbon content,
hardening, the relationship between austenite and martensite, and the influence of welding on
metallurgical structure.

7. Microstructure of Ferrous Alloys
George F. Vander Voort, Director, Research & Technology, Buehler Ltd., Lake Bluff, IL
January 10, 2001
The microstructure of iron-base alloys is very complicated and diverse, being influenced by
chemical composition, material homogeneity, processing and section size. This article offers a
brief explanation of the terminology describing the constituents in ferrous alloys, and offers a
basic review of steel microstructures.
Microstructures of castings look different from those of wrought products, even if they have the
same chemical composition and are given the same heat treatment. In general, it is easiest to
identify heat-treated structures after transformation and before tempering. For example, if a
mixed microstructure of bainite and martensite is formed during quenching, these constituents
will become more difficult to identify reliably as the tempering temperature used for the product
increases toward the lower critical temperature. Further, ferrous metallographers tend to use nital
almost exclusively for etching, but nital is not always the best reagent to use to properly reveal
all microstructures. Picral is an excellent etchant for revealing certain micro-structural
constituents in steel, but the use of picral is prohibited by some companies because picric acid
can be made to explode under certain conditions. However, picral-related accidents are less
common than for nital. Vilella's reagent, which also contains picric acid, is exceptionally
valuable for certain compositions and microstructures.

8. Because of misuse and confusion regarding certain terms, there is a need to discuss the
terminology describing the constituents in ferrous alloys. Certain terms, such as sorbite and
troostite, were dropped from the metallographic lexicon in 1937 because they referred to
microstructural constituents inaccurately. However, such terms still are occasionally used. The
term phase often is used incorrectly in reference to mixtures of two phases, such as pearlite or
bainite. A phase is a homogeneous, physically distinct substance. Martensite is a phase when
formed by quenching but becomes a constituent after tempering as in decomposes from body
centered tetragonal (bct) martensite to body centered cubic (bcc) ferrite and cementite.
Definitions will be given in this article in the process of describing and illustrating various
phases and constituents in ferrous alloys.
SPECIMEN PREPARATION
Ferrous metals must be properly prepared to observe their microstructures. Many view this task
as a trivial exercise, yet its proper execution is critical to successful interpretation. The first step
in the process is to select the test locations to be sampled. The specimens selected must be
representative of the lot; this is critical if the interpretation is to be valid for the part or lot being
evaluated. The plane of polish may be oriented in different directions relative to the piece being
sampled. For example, for a casting, the test plane may be perpendicular or parallel to the
solidification axis and may be located anywhere between the surface (where solidification

9. begins) and the center (where solidification ends). In a small casting, the structure will not vary
greatly over the cross section. However, this is not the case for large castings. Also, the use of a
separately cast keel block (a block of metal from which test coupons are taken) for test
evaluations may be highly misleading, as its solidification characteristics may be quite different
from that of the casting.
Wrought alloys are sampled in a similar manner, using either longitudinally or transversely
oriented cutting planes, which may be taken in any location from the surface to the center. The
midradius location is often selected as being representative of the overall condition, which may
be true in many cases. Additional processing alters the microstructure, usually producing greater
homogeneity and finer structures. But, problems still can arise.
Sectioning is almost always required to obtain a test piece of the proper size and orientation for
metallographic examination. An abrasive cutoff saw is the most commonly used device for
sectioning, producing a good surface having minimal damage when the proper blade is used with
adequate coolant. More aggressive sectioning methods often are used in production operations.
These produce greater damage to the structure that must subsequently be removed if the true
structure is to be revealed.
After obtaining a specimen, it may be mounted in a polymeric material to facilitate handling, to
simplify preparation, to enhance edge retention, and for ease of identification of the specimen
(by scribing identification information on the material). Mounting may be done in a press using a
thermosetting or thermoplastic resin or with castable resins that do not require external heat and
pressure for polymerization.
The use of automation in specimen preparation has grown enormously over the past twenty-five
years. Automated devices produce better results than can be achieved manually. They yield more
consistent results, better flatness and better edge retention, and offer greater productivity. Many
procedures for successfully preparing ferrous specimens could be listed; there is no one correct
procedure. Some methods favor certain types of specimens or problems. There also are many
different products that give successful results. Tables 1 and 2 list procedures that can be used to
prepare most steel specimens. These methods give consistent results with good specimen edge
retention. For the most difficult specimens, a 1-Km diamond step can be added after the 3-Km
diamond step, using the same materials, speeds and direction, but somewhat less time. Other
variations are possible depending on particular needs and specimens.
The first step, often called planar grinding, can be done using several products. Traditional
silicon-carbide (SiC) paper always is satisfactory, and aluminum-oxide (Al2O3) paper also may
be used. The process should always start using the finest possible abrasive that can remove the
damage from cutting and get all of the specimens in the holder co-planar in a reasonable time.
SiC paper does have a short life. Continuing to grind after the paper has lost its cutting efficiency
will generate heat and damage the specimen. The Ultra-Prep disks recommended in Table 1 are
excellent for obtaining flatness and edge retention and yield high stock removal rates. The disk
surface is covered with diamond in small pads, and diamond-free regions surrounding the spots
reduce surface tension and increase cutting efficiency. These disks have a long life. The metal-
bonded disks used for the harder ferrous alloys and the resin-bonded disks for the softest.

10. BuehlerHerculesT rigid grinding disks (RGD) offer an alternative grinding possibility; they
produce a very flat surface and are recommended when edge retention is critical. Two types of
RGD are available: type H and type S. In general, all steels can be prepared with the H disk, but
it is best to use the S disk for the softest steels. These disks do not contain embedded abrasive;
diamond is periodically added to the surface, usually as a suspension. There are cloth alternatives
that work well for the second step, but they have a shorter life than a rigid grinding disk. Ultra-
PadT and Ultra-PolT are two excellent cloths for the 9-Km diamond step. The former is more
aggressive and heavier and has a longer life, while the latter yields a better surface finish and is
recommended for the most difficult to prepare metals and alloys of any composition.
ETCHANTS
A steel specimen that is to be examined for inclusions or nitrides should not be etched. To see
the other microstructural constituents, etching is needed. Nital (usually 2%) is most commonly
used. It is excellent for revealing the structure of martensite, and also is very good for revealing
ferrite in a martensite matrix and to bring out ferrite grain boundaries in low-carbon steels.
Picral, on the other hand, is better for revealing the cementite in ferritic alloys and the structure
of ferrite-cementite constituents, pearlite and bainite. Nital and picral both dissolve ferrite but
nitalns dissolution rate is a function of crystal orientation, while picralns rate is uniform. Other
reagents have specific uses, especially when dealing with higher alloy grades, such as tool steels
and stainless steels, or when trying to selectively reveal certain constituents or prior-austenite
grain boundaries. Etchants for steels are listed in many standard text books (1) and handbooks,
and in ASTM E 407.
MICROSTRUCTURES
Fig. 1. Ferrite grain structure of a lamination steel; 2%

11. nital etch.
Alpha iron, strictly speaking, refers only to the bcc form of pure iron, which is stable below
912C (1674F) while ferrite is a solid solution of one or more elements in bcc iron. Often these
terms are used synonymously, which is incorrect. Ferrite may precipitate from austenite in
acicular form under certain cooling conditions. Acicular means the shape is needle-like in three
dimensions. However, this is not the actual shape of acicular ferrite in three dimensions. Figure 1
shows the appearance of ferrite grains in a carbon steel used for laminations. There are also
ferritic stainless steels, which contain high chromium contents and very little carbon. Ferrite is a
very soft, ductile phase, although it looses its toughness below some critical temperature.
Gamma iron, as with alpha iron, pertains to only the face-centered cubic (fcc) form of pure iron
that is stable between 912 and 1394C (1674 and 2541F) while austenite is a solid solution of one
or more elements in fcc iron. Again, these terms are often used interchangeably, which is
incorrect. For heat-treatable steels, austenite is the parent phase for all transformation products
that make ferrous alloys so versatile and useful commercially. Austenite is not stable at room
temperature in ordinary steels. In chrome-nickel (Cr-Ni) steels, know as stainless steels, there is
a family of very important grades where austenite is stable at room temperature.
Fig. 2. Austenite grains, with annealing twins, in AISI
type 316 austenitic stainless steel; Kalling?s number 2
etch.
Figure 2 shows an example of the microstructure of AISI type 316 austenitic stainless steel.
Austenite is a soft, ductile phase that can be work hardened to high strength levels, particularly in
the fully austenitic Hadfield manganese steels.
In high-carbon, high-alloy steels, such as tool steels, use of an excessively high austenitizing
temperature will depress the temperatures where martensite begins and completes its

12. transformation. These martensite start and end temperatures are depressed to such an extent that
the austenite is not fully converted to martensite during quenching and the remaining austenite,
called retained austenite, is present (but not necessarily stable) at room temperature.
Fig. 3. Coarse plate martensite (black ?needles?),
retained austenite (white areas between martensite
?needles?), and some cementite (arrows) in the
carburized case of AISI type 8620 alloy steel; 2% nital
etch.
Figure 3 shows an example of retained austenite in the carburized case of AISI type 8620 low-
alloy alloy steel. The retained austenite is white and lies between the plate martensite "needles."
However, there are also a few white particles of cementite in the micrograph (arrows). Excessive
retained austenite in tool steels usually is detrimental to die life, because it may transform to
fresh martensite and cause cracking in the die, or reduce die wear resistance. In the case of a
carburized gear tooth, retained austenite usually is not detrimental because the gear teeth
typically are not shock loaded, so the retained austenite would transform to martensite and the
toughness of the austenite, when stabilized, could be beneficial. There are grades of stainless
steel where the composition is balanced to produce approximately equal amounts of ferrite and
austenite (dual phase) at room temperature.

13. Fig. 4. Ferrite (dark) and austenite (white) in 2205
dual-phase stainless steel; etch: 20% NaOH in water, 3
V dc, 12 sec.
Figure 4 shows the microstructure of such a stainless steel.
Delta iron is the bcc form of pure iron that is stable above 1394C (2541F) to the melting point,
1538C (2800F), while delta ferrite is the stable high-temperature solid solution of one or more
elements in bcc iron. Delta ferrite may be observed in as-cast austenitic stainless steels (it is put
into solution after hot working and solution annealing), in some precipitation hardened stainless
steels (for example, 17-4 PH) when the composition is not balanced to avoid it, in some
martensitic stainless steels and in some tool steels. Delta ferrite usually is considered detrimental
to transverse toughness when it is present in a hardened structure.

14. Fig. 5. Delta ferrite (dark) stringers in AM 350 PH
(precipitation hardenable) stainless steel; etch: 20%
NaOH in water, 3 V dc, 5 sec.
Figure 5 illustrates delta-ferrite stringers (longitudinal plane) in AM350 precipitation hardenable
stainless steel.
Carbon in iron exists either as graphite or as cementite. Graphite is the stable form of carbon in
iron (mainly observed in cast iron), while cementite is metastable and can transform to graphite
under long-term, high-temperature exposure. Cementite is a compound of iron and carbon with
the approximate formula Fe3C and has an orthorhombic crystal structure. Some substitution of
other carbide forming elements, such as manganese and chromium, is possible. Therefore, it is
more general to refer to the formula as M3C, where M stands for metal. Only small amounts of
the various carbide forming elements can be substituted before alloy carbides of other crystal
structures and formulae are formed.
Fig. 6. Cementite (white) and pearlite (dark) in white
cast iron; 4% picral etch.
Figure 6 shows cementite in white cast iron. The carbon content of cementite is 6.67 wt%, which
usually is the terminus for the iron-carbon (Fe-C) phase diagram. Cementite is hard but brittle
(about 800 HV, or Vickers hardness, for pure Fe3C, and up to about 1400 HV for highly alloyed
M3C).
Carbon are alloy steels are in the austenitic condition when they are hot worked. Subsequent
cooling results in the transformation of austenite to other phases or constituents. If a carbon or
low-alloy steel is air cooled after hot rolling, a diffusion-controlled transformation occurs where
ferrite first precipitates, followed by pearlite. Pearlite is a metastable lamellar (plate-like)

15. aggregate of ferrite and cementite that forms at temperatures below the lower critical temperature
(the temperature where austenite starts forming from ferrite upon heating). With time and
temperature, the cementite in the pearlite will become spheroidized; that is, it changes from a
lamellar to a spheroidal shape. This reduces the strength and hardness of the material, while
increasing its ductility. The degree of change is a function of the carbon content of the alloy.
Pearlite forms by a eutectoidal reaction. A eutectoid transformation is an isothermal, reversible
reaction in which a solid solution (austenite) is converted into two intimately mixed solid phases,
ferrite and cementite. All eutectoidal products are lamellar, even in nonferrous systems.
For steels having carbon contents below the eutectoidal value (0.77% carbon), ferrite precipitates
before the eutectoidal transformation and is called proeutectoid ferrite.
Fig. 7. Proeutectoid ferrite and pearlite structure of
plate from the ship RMS Nomadic; 2% nital etch.
Figure 7 shows proeutectoid ferrite and lamellar pearlite in a piece of plate steel from the ship
RMS Nomadic, a tender for the RMS Titanic. The ferrite is white and the pearlite is dark becasue
the lamellae are much too finely spaced to be resolved at the 200X magnification in Figure 7.

16. Fig. 8. Coarse pearlite and proeutectoid ferrite in fully
annealed AISI type 4140 alloy steel; 4% picral etch.
Figure 8 shows coarse pearlite in a fully annealed specimen of AISI type 4140 alloy steel where
the lamellae can be resolved. The cementite lamellae appear dark while the ferrite remains white.
In steels having carbon contents above the eutectoidal composition, cementite will precipitate in
the grain boundaries before the eutectoid reaction occurs and is called proeutectoid cementite.
Pearlite increases the strength of carbon steels. Refining the interlamellar spacing also increases
the strength, and toughness, as well. In a slowly cooled specimen, the amount of pearlite
increases to 100% as the carbon content increases to the eutectoidal carbon content. The
hardness of a fully pearlitic eutectoidal steel varies with the interlamellar spacing from about 250
to 400 HV for the finest spacings. Pearlite can be cold drawn (cold worked) to exceptionally high
tensile strengths, as in piano wire, which also has considerable ductility.
If the cooling rate is faster than that achieved by air cooling, or if alloying elements are added to
the steel to increase hardenability, a different two-phase constituent may be observed, called
bainite. Bainite is a metastable aggregate of ferrite and cementite, which forms from austenite at
temperatures below where pearlite forms and above the temperature where martensite starts to
form. The appearance of bainite changes with the transformation temperature, being called
"feathery" in appearance at high temperatures and "acicular" at low transformation temperatures.
The feathery appearance of "upper" bainite also is also influenced by carbon content and is
common in grades having high carbon contents. The term acicular is not a perfect description of
the shape of "lower" bainite.

17. Fig. 9. Upper bainite (dark) and martensite (light) in a
partially transformed (1525?F - 30 min, 1000?F - 1
min, water quench) specimen of AISI type 5160 alloy
steel. The austenite which had not transformed to
upper bainite after 1 minute formed martensite in the
quench; 2% nital etch.
Figures 9 and 10 show the appearance of upper and lower bainite, respectively, in partially
transformed AISI type 5160 alloy steel specimens.
Fig. 10. Lower bainite (dark) and martensite (light) in
a partially transformed (1525?F - 30 min, 650?F - 5
min, water quench) specimen of AISI type 5160 alloy
steel. The austenite which had not transformed to

18. lower bainite after 5 minute formed martensite in the
quench; 2% nital etch.
If the cooling rate from the austenitizing temperature is rapid enough (a function of section size,
hardenability and quench medium), martensite will form. Martensite is a generic term for the
body-centered tetragonal phase that forms by diffusionless transformation, and the parent and
product phases have the same composition and a specific crystallographic relationship.
Martensite can be formed in alloys where the solute atoms occupy interstitial sites, such as
carbon in iron, producing substantial hardening and a highly strained, brittle condition. However,
in carbon-free alloys having high nickel contents, such as maraging steels, the solute atoms (Ni)
can occupy substitutional sites, producing martensites that are soft and ductile. In carbon-
containing steels, the appearance of the martensite changes with carbon in the interstitial sites.
Low-carbon steels produce lath martensites, while high-carbon steels produce plate martensite
(often incorrectly called "acicular" martensite) when all of the carbon is dissolved into the
austenite.
Fig. 11. Lath martensite in AISI type 8620 alloy steel;
2% nital etch.
Lath martensite is shown in Figure 11 (see Figure 3 for plate martensite).

19. Fig. 12. Plate martensite in a fine-grained, properly
austenitized AISI type 52100 bearing steel specimen
(fine white, spheroidal particles are undissolved
cementite) is virtually featureless at 1000?; 2% nital
etch. (Compare with coarse plate martensite in Figure
3.)

20. When quenched from the proper temperature, so that the correct amount of cementite is
dissolved (see discussion following) and the grain size is quite fine, martensite will appear
virtually featureless by light microscopy, as shown in Figure 12 for AISI type 52100 bearing
steel.
Fig. 13. Soft, carbon-free martensite in low-residual
18Ni250 maraging steel; 500?, modified Fry?s reagent
etch.
Figure 13, for comparison, shows the structure of martensite in nearly carbon-free 18Ni250
maraging steel.
The strength and hardness of martensite varies linearly with percent carbon in austenite up to
about 0.5% C. As the carbon in the austenite increases beyond 0.5%, the curve starts to flatten
and then goes downward due to the inability to convert the austenite fully to martensite (the
amount of retained austenite increases). Therefore, when high-carbon steels are heat treated, the
austenitizing temperature is selected to dissolve no more than about 0.6% C into the austenite.
There are other minor constituents in steels, such as nonmetallic inclusions, nitrides,
carbonitrides, and intermetallic phases, such as sigma and chi phases. Nonmetallic inclusions are
of two types: those that arise from the restricted solubility of oxygen and sulfur in the solid phase
compared with the liquid; and those that come from outside sources, such as refractories in
contact with the melt. The former are called indigenous and the later are called exogenous. Many
poor terms are used in reference to inclusions. Nitrides and carbonitrides result when certain
nitride forming elements are present in adequate quantities, aluminum, titanium, niobium, and
zirconium, for example. A certain amount of nitrogen always is present in the melt and this
varies with the melting procedure used. Electric-furnace steels usually have around 100 ppm
(parts per million) nitrogen while basic oxygen-furnace steels have about 60 ppm nitrogen.
Aluminum nitride is extremely fine and can be seen only after careful extraction replica work

21. using transmission electron microscopy (TEM). The other nitrides often are visible in the light
microscope, although submicroscopic size nitrides can also be present. Sigma and chi phases
(not shown in this article) can be produced in certain stainless steels after high temperature
exposure.
SUMMARY
The microstructure of ferrous alloys is very complicated and this review has only touched the
surface of knowledge about steel microstructures. It is a basic tenet of physical metallurgy that
composition and processing establishes the microstructure, and that microstructure influences
most properties and service behavior. To maintain control of the quality of steel products and to
diagnose problems in processing, testing, or service, the microstructure must be identified and, in
some cases, quantified. This can only be accomplished when the metallographer can properly
distinguish the phases or constituents present, which depends on proper specimen preparation
and etching.
References
1. G.F. Vander Voort, Metallography: Principles and Practice, ASM International, Materials
Park, OH, 1999.

22. Daftar Pustaka :
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Behaviour Of Aluminum Fly Ash Composites. Journal of Optoelectronics and Advanced
Materials Vol. 5, No. 2, June 2003, p. 493 – 502.
Masyrukan. ( 2006 ). Penelitian Sifat Fisis dan Mekanis Baja Karbon Rendah Akibat
Pengaruh Proses Pengarbonan dari Arang Kayu Jati. MEDIA MESIN, Vol. 7, No. 1, Januari
2006, 40-46.
Saptono.R. ( 2008 ). Pengerahuan Bahan 2008 : Bab 3 Logam dan Paduan Berbasis Besi.
Departemen Metalurgi dan Material FTUI 2008.
Capudean.B. ( 2003 ). The Structure Of Metal. [ cited 2011 Oct 18 ]. Available from : URL :
http://www.thefabricator.com/article/metalsmaterials/the-structure-of-metal
George.F.( 2001 ). Microstructure of Ferrous Alloys. [ cited 2011 Oct 18 ]. Available from :
URL :
http://www.industrialheating.com/Articles/Cover_Story/93096f835cbb7010VgnVCM100000f93
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