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  • 3. The Structure of MetalBy Bob CapudeanApril 24, 2003Lets start with the obvious: Molten metals have no particular structure. The atoms that make upthat 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 movingfaster than cold atoms. And those fast-moving atoms are bumping into other atoms, causing themto move quickly.Furthermore, the warmer a metal-or any material, for that matter-is, the faster the atomscomposing that metal are moving. Yes, there are internal attractions that help keep the atoms in apuddle, preventing them from just vaporizing, but the fact is, if they get moving fast enough-thatis, get hot enough-they eventually will evaporate, just like hydrogen and oxygen do when waterboils.As thermal energy is transferred to another part, the atoms give up energy, slowing down andcooling. 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 callednuclei, which take on specific and identifiable crystal structures. Because the nuclei have themetals crystal structure, additional atoms join the nuclei. As these nuclei get bigger, they formgrains. 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, whichmeans eventually these different areas of growing grains have to meet. When they do, thearrangement of the atoms in the grain structure is disrupted at that meeting point. This is called agrain boundary. Grain boundaries form a continuous network throughout the metal, and becauseof the disrupted structure at the boundary, the metal often acts differently at the boundarylocations.Grain boundaries aside, each grain in a pure metal has the same crystalline structure as any othergrain, assuming the temperature is the same. This structure, which is identifiable under themicroscope, has a huge influence on the metals characteristics.
  • 4. Common Crystal StructuresFor our purposes, all metals and alloys are crystalline solids, although some metals have beenformed in the lab without crystalline structure. And most metals assume one of three differentlattice, 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 isshown in Figure 1.A number of metals are shown below with their roomtemperature crystal structure indicated. And for the record, yes,there are substances without crystalline structure at roomtemperature; 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), andAlloys and Atomic Arrangements (c) hexagonal close-packed (HCP).Everything covered so far applies to pure metals, which begs thequestion, What happens when you add an alloy or two? After all, most common metals are alloyscontaining 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 alloys properties.But how those elements dissolve, or in other words how they combine with the existing atoms inthe parent metals crystal lattice, can also greatly influence both the physical and nonphysicalproperties of the end product.Basically, there are two ways the alloying element(s)-called solutes-combine with the base, orparent, metal, which is also called the solvent. The alloys atoms can combine through eitherdirect substitution, creating a substitutional solid solution, or they can combine interstitially,forming an interstitial solid solution.Substitutional Solid Solution. When the alloys atoms are similar to the parent metals atoms,theyll simply replace some of the parent metals atoms in the lattice. The new metal dissolves in
  • 5. the base metal to form a solid solution. Examples include copper dissolved in nickel, golddissolved in silver, and carbon dissolved in iron (ferrite).Interstitial Solid Solution. When the alloys atoms are smaller than the parent metals atoms,theyll fit between the atoms in the parent metals lattice. The alloy atoms dont occupy latticesites and dont replace any of the original atoms. Of course, this causes strain in the crystalstructure because the fit isnt perfect: There are atoms taking up space that was originallyunoccupied.The end result is usually an increase in tensile strength and a decrease in elongation. Examplesinclude small amounts of copper dissolved in aluminum and carbon, and nitrogen dissolved iniron and other metals.Phases, Microstructures, and Phase ChangesOften neither direct nor interstitial solution can completely dissolve all the added atoms. Andwhen this happens, the result is mixed atomic groupings. In other words, different crystallinestructures exist within the same alloy. Each of these different structures is called a phase, and thealloy-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 andetched. 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 alloys 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, grainboundaries contain lower-melting-point atoms compared to the atoms within the grains. Theseforeign atoms cause microstructure distortion and harden the alloy at room temperature. But astemperature goes up, alloy strength goes down because these lower-melting-point atoms begin tomelt sooner, allowing slippage between the grains.Furthermore, foreign or odd-sized atoms tend to congregate at grain boundaries because theatomic structure is irregular. This can lead to phases that reduce ductility and lead to crackingduring welding.Consider this: Cold working a metal distorts its entire microstructure. The end result, in mostcases, is that the metal gets harder. Atoms from an alloying element distort the metalsmicrostructure, and again, the metal gets harder. The same is true for alloy atoms that aredissolved in a base metal and then precipitate out. The atoms leave, but a distortion remains, andthe metal is harder.Grain size is also important. Generally speaking, fine-grained metals have better properties atroom 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 areimportant. Overall, these characteristics in total determine a metals capabilities and usefulness.In short, a metals overall microstructure determines its characteristics. Today just about everymetal we use is an alloy, with one or more elements added to modify, adjust, correct, or changethe base metals 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 thatmicrostructure.This should give you an overview of how metals are structured and what happens when we meltthem to weld them together. Next time well consider phase transformations, carbon content,hardening, the relationship between austenite and martensite, and the influence of welding onmetallurgical structure.
  • 7. Microstructure of Ferrous AlloysGeorge F. Vander Voort, Director, Research & Technology, Buehler Ltd., Lake Bluff, ILJanuary 10, 2001The microstructure of iron-base alloys is very complicated and diverse, being influenced bychemical composition, material homogeneity, processing and section size. This article offers abrief explanation of the terminology describing the constituents in ferrous alloys, and offers abasic review of steel microstructures.Microstructures of castings look different from those of wrought products, even if they have thesame chemical composition and are given the same heat treatment. In general, it is easiest toidentify heat-treated structures after transformation and before tempering. For example, if amixed microstructure of bainite and martensite is formed during quenching, these constituentswill become more difficult to identify reliably as the tempering temperature used for the productincreases toward the lower critical temperature. Further, ferrous metallographers tend to use nitalalmost exclusively for etching, but nital is not always the best reagent to use to properly revealall microstructures. Picral is an excellent etchant for revealing certain micro-structuralconstituents in steel, but the use of picral is prohibited by some companies because picric acidcan be made to explode under certain conditions. However, picral-related accidents are lesscommon than for nital. Vilellas reagent, which also contains picric acid, is exceptionallyvaluable for certain compositions and microstructures.
  • 8. Because of misuse and confusion regarding certain terms, there is a need to discuss theterminology describing the constituents in ferrous alloys. Certain terms, such as sorbite andtroostite, were dropped from the metallographic lexicon in 1937 because they referred tomicrostructural constituents inaccurately. However, such terms still are occasionally used. Theterm phase often is used incorrectly in reference to mixtures of two phases, such as pearlite orbainite. A phase is a homogeneous, physically distinct substance. Martensite is a phase whenformed by quenching but becomes a constituent after tempering as in decomposes from bodycentered 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 variousphases and constituents in ferrous alloys.SPECIMEN PREPARATIONFerrous metals must be properly prepared to observe their microstructures. Many view this taskas a trivial exercise, yet its proper execution is critical to successful interpretation. The first stepin the process is to select the test locations to be sampled. The specimens selected must berepresentative of the lot; this is critical if the interpretation is to be valid for the part or lot beingevaluated. The plane of polish may be oriented in different directions relative to the piece beingsampled. For example, for a casting, the test plane may be perpendicular or parallel to thesolidification 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 varygreatly over the cross section. However, this is not the case for large castings. Also, the use of aseparately cast keel block (a block of metal from which test coupons are taken) for testevaluations may be highly misleading, as its solidification characteristics may be quite differentfrom that of the casting.Wrought alloys are sampled in a similar manner, using either longitudinally or transverselyoriented cutting planes, which may be taken in any location from the surface to the center. Themidradius location is often selected as being representative of the overall condition, which maybe true in many cases. Additional processing alters the microstructure, usually producing greaterhomogeneity and finer structures. But, problems still can arise.Sectioning is almost always required to obtain a test piece of the proper size and orientation formetallographic examination. An abrasive cutoff saw is the most commonly used device forsectioning, producing a good surface having minimal damage when the proper blade is used withadequate 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 truestructure is to be revealed.After obtaining a specimen, it may be mounted in a polymeric material to facilitate handling, tosimplify 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 athermosetting or thermoplastic resin or with castable resins that do not require external heat andpressure for polymerization.The use of automation in specimen preparation has grown enormously over the past twenty-fiveyears. Automated devices produce better results than can be achieved manually. They yield moreconsistent results, better flatness and better edge retention, and offer greater productivity. Manyprocedures for successfully preparing ferrous specimens could be listed; there is no one correctprocedure. Some methods favor certain types of specimens or problems. There also are manydifferent products that give successful results. Tables 1 and 2 list procedures that can be used toprepare most steel specimens. These methods give consistent results with good specimen edgeretention. For the most difficult specimens, a 1-Km diamond step can be added after the 3-Kmdiamond step, using the same materials, speeds and direction, but somewhat less time. Othervariations are possible depending on particular needs and specimens.The first step, often called planar grinding, can be done using several products. Traditionalsilicon-carbide (SiC) paper always is satisfactory, and aluminum-oxide (Al2O3) paper also maybe used. The process should always start using the finest possible abrasive that can remove thedamage 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 efficiencywill generate heat and damage the specimen. The Ultra-Prep disks recommended in Table 1 areexcellent for obtaining flatness and edge retention and yield high stock removal rates. The disksurface is covered with diamond in small pads, and diamond-free regions surrounding the spotsreduce 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; theyproduce a very flat surface and are recommended when edge retention is critical. Two types ofRGD are available: type H and type S. In general, all steels can be prepared with the H disk, butit 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 alternativesthat 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 moreaggressive and heavier and has a longer life, while the latter yields a better surface finish and isrecommended for the most difficult to prepare metals and alloys of any composition.ETCHANTSA steel specimen that is to be examined for inclusions or nitrides should not be etched. To seethe other microstructural constituents, etching is needed. Nital (usually 2%) is most commonlyused. It is excellent for revealing the structure of martensite, and also is very good for revealingferrite 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 structureof ferrite-cementite constituents, pearlite and bainite. Nital and picral both dissolve ferrite butnitalns dissolution rate is a function of crystal orientation, while picralns rate is uniform. Otherreagents have specific uses, especially when dealing with higher alloy grades, such as tool steelsand stainless steels, or when trying to selectively reveal certain constituents or prior-austenitegrain boundaries. Etchants for steels are listed in many standard text books (1) and handbooks,and in ASTM E 407.MICROSTRUCTURESFig. 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 below912C (1674F) while ferrite is a solid solution of one or more elements in bcc iron. Often theseterms are used synonymously, which is incorrect. Ferrite may precipitate from austenite inacicular form under certain cooling conditions. Acicular means the shape is needle-like in threedimensions. However, this is not the actual shape of acicular ferrite in three dimensions. Figure 1shows the appearance of ferrite grains in a carbon steel used for laminations. There are alsoferritic stainless steels, which contain high chromium contents and very little carbon. Ferrite is avery 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 ironthat is stable between 912 and 1394C (1674 and 2541F) while austenite is a solid solution of oneor more elements in fcc iron. Again, these terms are often used interchangeably, which isincorrect. For heat-treatable steels, austenite is the parent phase for all transformation productsthat make ferrous alloys so versatile and useful commercially. Austenite is not stable at roomtemperature in ordinary steels. In chrome-nickel (Cr-Ni) steels, know as stainless steels, there isa family of very important grades where austenite is stable at room temperature.Fig. 2. Austenite grains, with annealing twins, in AISItype 316 austenitic stainless steel; Kalling?s number 2etch.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 inthe fully austenitic Hadfield manganese steels.In high-carbon, high-alloy steels, such as tool steels, use of an excessively high austenitizingtemperature will depress the temperatures where martensite begins and completes its
  • 12. transformation. These martensite start and end temperatures are depressed to such an extent thatthe 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 thecarburized case of AISI type 8620 alloy steel; 2% nitaletch.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). Excessiveretained austenite in tool steels usually is detrimental to die life, because it may transform tofresh martensite and cause cracking in the die, or reduce die wear resistance. In the case of acarburized gear tooth, retained austenite usually is not detrimental because the gear teethtypically are not shock loaded, so the retained austenite would transform to martensite and thetoughness of the austenite, when stabilized, could be beneficial. There are grades of stainlesssteel where the composition is balanced to produce approximately equal amounts of ferrite andaustenite (dual phase) at room temperature.
  • 13. Fig. 4. Ferrite (dark) and austenite (white) in 2205dual-phase stainless steel; etch: 20% NaOH in water, 3V 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 moreelements in bcc iron. Delta ferrite may be observed in as-cast austenitic stainless steels (it is putinto solution after hot working and solution annealing), in some precipitation hardened stainlesssteels (for example, 17-4 PH) when the composition is not balanced to avoid it, in somemartensitic stainless steels and in some tool steels. Delta ferrite usually is considered detrimentalto 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 hardenablestainless steel.Carbon in iron exists either as graphite or as cementite. Graphite is the stable form of carbon iniron (mainly observed in cast iron), while cementite is metastable and can transform to graphiteunder long-term, high-temperature exposure. Cementite is a compound of iron and carbon withthe approximate formula Fe3C and has an orthorhombic crystal structure. Some substitution ofother carbide forming elements, such as manganese and chromium, is possible. Therefore, it ismore general to refer to the formula as M3C, where M stands for metal. Only small amounts ofthe various carbide forming elements can be substituted before alloy carbides of other crystalstructures and formulae are formed.Fig. 6. Cementite (white) and pearlite (dark) in whitecast iron; 4% picral etch.Figure 6 shows cementite in white cast iron. The carbon content of cementite is 6.67 wt%, whichusually 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 alloyedM3C).Carbon are alloy steels are in the austenitic condition when they are hot worked. Subsequentcooling results in the transformation of austenite to other phases or constituents. If a carbon orlow-alloy steel is air cooled after hot rolling, a diffusion-controlled transformation occurs whereferrite 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 andtemperature, the cementite in the pearlite will become spheroidized; that is, it changes from alamellar to a spheroidal shape. This reduces the strength and hardness of the material, whileincreasing 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, reversiblereaction 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 precipitatesbefore the eutectoidal transformation and is called proeutectoid ferrite.Fig. 7. Proeutectoid ferrite and pearlite structure ofplate from the ship RMS Nomadic; 2% nital etch.Figure 7 shows proeutectoid ferrite and lamellar pearlite in a piece of plate steel from the shipRMS Nomadic, a tender for the RMS Titanic. The ferrite is white and the pearlite is dark becasuethe 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 fullyannealed AISI type 4140 alloy steel; 4% picral etch.Figure 8 shows coarse pearlite in a fully annealed specimen of AISI type 4140 alloy steel wherethe 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 inthe grain boundaries before the eutectoid reaction occurs and is called proeutectoid cementite.Pearlite increases the strength of carbon steels. Refining the interlamellar spacing also increasesthe strength, and toughness, as well. In a slowly cooled specimen, the amount of pearliteincreases to 100% as the carbon content increases to the eutectoidal carbon content. Thehardness of a fully pearlitic eutectoidal steel varies with the interlamellar spacing from about 250to 400 HV for the finest spacings. Pearlite can be cold drawn (cold worked) to exceptionally hightensile 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 tothe steel to increase hardenability, a different two-phase constituent may be observed, calledbainite. Bainite is a metastable aggregate of ferrite and cementite, which forms from austenite attemperatures below where pearlite forms and above the temperature where martensite starts toform. 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 iscommon in grades having high carbon contents. The term acicular is not a perfect description ofthe shape of "lower" bainite.
  • 17. Fig. 9. Upper bainite (dark) and martensite (light) in apartially transformed (1525?F - 30 min, 1000?F - 1min, water quench) specimen of AISI type 5160 alloysteel. The austenite which had not transformed toupper bainite after 1 minute formed martensite in thequench; 2% nital etch.Figures 9 and 10 show the appearance of upper and lower bainite, respectively, in partiallytransformed AISI type 5160 alloy steel specimens.Fig. 10. Lower bainite (dark) and martensite (light) ina partially transformed (1525?F - 30 min, 650?F - 5min, water quench) specimen of AISI type 5160 alloysteel. The austenite which had not transformed to
  • 18. lower bainite after 5 minute formed martensite in thequench; 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 thebody-centered tetragonal phase that forms by diffusionless transformation, and the parent andproduct phases have the same composition and a specific crystallographic relationship.Martensite can be formed in alloys where the solute atoms occupy interstitial sites, such ascarbon 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 theaustenite.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, properlyaustenitized AISI type 52100 bearing steel specimen(fine white, spheroidal particles are undissolvedcementite) is virtually featureless at 1000?; 2% nitaletch. (Compare with coarse plate martensite in Figure3.)
  • 20. When quenched from the proper temperature, so that the correct amount of cementite isdissolved (see discussion following) and the grain size is quite fine, martensite will appearvirtually featureless by light microscopy, as shown in Figure 12 for AISI type 52100 bearingsteel.Fig. 13. Soft, carbon-free martensite in low-residual18Ni250 maraging steel; 500?, modified Fry?s reagentetch.Figure 13, for comparison, shows the structure of martensite in nearly carbon-free 18Ni250maraging steel.The strength and hardness of martensite varies linearly with percent carbon in austenite up toabout 0.5% C. As the carbon in the austenite increases beyond 0.5%, the curve starts to flattenand then goes downward due to the inability to convert the austenite fully to martensite (theamount of retained austenite increases). Therefore, when high-carbon steels are heat treated, theaustenitizing 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 areof two types: those that arise from the restricted solubility of oxygen and sulfur in the solid phasecompared with the liquid; and those that come from outside sources, such as refractories incontact with the melt. The former are called indigenous and the later are called exogenous. Manypoor terms are used in reference to inclusions. Nitrides and carbonitrides result when certainnitride forming elements are present in adequate quantities, aluminum, titanium, niobium, andzirconium, for example. A certain amount of nitrogen always is present in the melt and thisvaries 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 lightmicroscope, 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 temperatureexposure.SUMMARYThe microstructure of ferrous alloys is very complicated and this review has only touched thesurface of knowledge about steel microstructures. It is a basic tenet of physical metallurgy thatcomposition and processing establishes the microstructure, and that microstructure influencesmost properties and service behavior. To maintain control of the quality of steel products and todiagnose problems in processing, testing, or service, the microstructure must be identified and, insome cases, quantified. This can only be accomplished when the metallographer can properlydistinguish the phases or constituents present, which depends on proper specimen preparationand etching.References1. G.F. Vander Voort, Metallography: Principles and Practice, ASM International, MaterialsPark, OH, 1999.
  • 22. Daftar Pustaka :Bienias.J, Walczak.M, Surowska.B, Sobczak.J. ( 2003 ). Microstructure And CorrosionBehaviour Of Aluminum Fly Ash Composites. Journal of Optoelectronics and AdvancedMaterials Vol. 5, No. 2, June 2003, p. 493 – 502.Masyrukan. ( 2006 ). Penelitian Sifat Fisis dan Mekanis Baja Karbon Rendah AkibatPengaruh Proses Pengarbonan dari Arang Kayu Jati. MEDIA MESIN, Vol. 7, No. 1, Januari2006, 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 : 2001 ). Microstructure of Ferrous Alloys. [ cited 2011 Oct 18 ]. Available from :URL :