پاورپوینت بررسی جامع کلیه ساختار های میکروسکوپی فولاد به زبان انگلیسی
پاورپوینت بررسی جامع کلیه ساختار های میکروسکوپی فولاد به زبان انگلیسی
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دانلود پاورپوینت با موضوع بررسی جامع کلیه ساختار های میکروسکوپی فولاد به زبان انگلیسی،در قالب ppt و در 247 اسلاید قابل ویرایش.بخشی از پاورپوینت :در این فایل به صورت جامع ساختار های میکروسکوپی و مایکروسکوبی فولاد ها همراه با تصاویر به نگارش درآمده است انواع مارتنزیتمارتنزیت و آستنیتفاز مارتنزیتساختار مارتنزیتساختار سمنتیتمارتنزیت لایه ای و ….MicrostructuresofAlloysFerrite and PearliteTypes of FerriteIdiomorphic FerriteIdiomorphic Ferrite plus inclusionsCCT DiagramWidmanstatten FerriteFerriteAnother form of ferrite is epitaxial ferrite, formed when a steel is heated into thetwo-phase ferrite + austenite region. An example of epitaxial ferrite can be seen (arrows) in Fig. 4. Duringcooling, new ferrite has grown epitaxially on the existing ferrite grains. Some dual-phase steels show eptiaxialferrite, because they were annealed in the two-phase region.PearliteFerrite & PearliteBlocky Ferrite or Idiomorphic FerriteFerrite & Pearlite in SEMFerrite & PearliteSpheroidizationكروي سازي پرليت ياكروي سازي سمانتيتspheroidizedThis is a spheroidized hypereutectoid steel, shown at 1000X with a Nital etch.Now the cementite is no longer the continuous phase; the hard cementite particles do not impinge upon the cutting tool used to machine such a specimen; and the hardness is as low as possible because of the large size of the cementite particles and the large distances between them.Even high alloy tool steels are cold workable in this condition, for example by bending, cold forging, or wire drawing.Pearlite/Begin to SpheroidizationFerrite & spheroidized PearliteFull SpheroidizedCementite (Carbides)roeutectoid Cementiteas a network structure سمانتيت پروتكتوئيدproeutectoid cementite and proeutectoid ferriteUse this specimen to learn to distinguish between proeutectoid cementite and proeutectoid ferrite.Cementite is smooth etching and usually looks slightly yellowish as well as having a distinct boundary around it, whereas proeutectoid ferrite is a flat (not glossy) off white light grey and is continuous with the ferrite in the adjoining pearlite.proeutectoid cementite and proeutectoid ferriteThis specimen has been gas carburized and then slowly cooled from the all austenite region. The photomicrograph at left was made at 500X with a Nital etch near the core of the specimen, while the second photomicrograph was made of the high carbon case at the same magnification.network of cementiteThe first specimen in this lesson, which has 1.34% carbon, and which was slowly cooled from the all austenite region of the iron-cementite phase diagram, consists of pearlite delineated by a network of cementite. There are also Widmanstaetten cementite platelets crossing the interiors of the larger prior austenite grains.The first photomicrograph at left was taken at 200X; the one below it was made at 500X. A Nital etch was used.This is a hypereutectoid steel. During the (incorrect) slow cool from the all austenite region, cementite precipitated, mainly at the austenite grain boundaries, decorating them during passage through the austenite plus cementite two phase field of the iron – cementite phase diagram. The austenite grains were of nonuniform size because of discontinuous grain growth; small impurity particles stopped normal grain growth by pinning the austenite grain boundaries until excessive heating permited some of the particles to dissolve. Thereafter, a few austenite grain boundaries broke free of the remaining particles, consuming most of the remaining austenite grains. Carbon could not diffuse out of the centers of the larger austenite grains to join the cementite forming at the grain boundaries during the subsequent cooling, so cementite platelets grew inwards from the grain boundaries in order to cnsume the excess carbon in the grain interiors. Proeutectoid cementite like that seen here can be distinguished from proeutectoid ferrite because the cementite at the prior austenite grain boundaries is continuous with the minority phase (also cementite) in the pearlite. Cementite is a different color than ferrite, a faint lemon yellow instead of off white grey in the case of ferrite. For a hypoeutectoid steel, the ferrite at the prior austenite grain boundaries would be continuous with the majority phase in the pearlitenetwork of cementiteNetwork of FerriteThe arrangement of the soft, ductile ferrite in this 1045 steel led to a fatigue failure. The specimen was used in the as-hot-rolled condition. It is shown here at 500X; Nital etch.Even though the ferrite is the minority microconstituent, it forms a continuous envelope around the prior austenite grains. The faitigue crack (not shown here) followed this ferrite network because of the lower shear strength compared to the pearlite. This piece wasn’t any better than a completely ferritic steel.Martensitic and Bainitic Structuresساختارهاي مارتنزيتي و بينايتيBainiteLighter etch of upper bainite as compared to pearlite (dark areas). Acicular structure is upper bainite in a pearlitic matrix. 1045 steel, 50 mm (2 in.) bar stock, austenitized at 843 °C (1550 °F) for 2 h, oil quenched 15 s, air cooled 5 min, and oil quenched to room temperature. 4% picral etch. Original magnification 500×1018 water Quenched Steel,×400,BainiteMartensiteTempered MartensiteMartensite & Retained AusteniteMartensite and Retained AusteniteMixed MicrostructureBanding and Banded StructuresBandingBandingBandingBandingBanded StructureThis is a medium carbon steel, consisting of ferrite and pearlite (a lamellar mixture of ferrite and cementite). It is banded (dark bands = pearlite; light bands = ferrite) an undesirable condition. The photomicrograph was taken at 50X magnification. The etchant was Nital (1% to 3% nitric acid in ethanol).This piece was probably hot rolled, followed by air cooling to room temperature, which permitted the metastable iron – cementite phase diagram to be followed.As the piece cooled below the all-austenite region within which the hot rolling had been performed, ferrite was first precipitated at the austenite grain boundaries, thereby causing carbon to be rejected into the remaining austenite. Once the piece cooled below the eutectoid temperature (727C) the 0.8% carbon austenite transformed discontinuously via coupled growth of ferrite and cementite in a lamellar (layered) morphology called pearlite because of its appearance to the unaided eye after etching. The banding in this piece is the result of microsegregagtion of manganese during solidification of the original ingot, which has not been homogenized during the subsequent thermomechanical processing.Manganese lowers the eutectoid temperature and eutectoid composition in the iron – cementite phase diagram and also lowers the chemical acyivity of carbon in austenite. As this piece cooled from the all-austenite region, alpha ferrite was precipitated – more so, the less the local manganese content. Therefore, the last areas to transform were richer in both manganese and carbon, so those regions are now mostly pearlite.Banding can be eliminated by prolonged heating and/or extensive hot working to homogenize the metal with respect to the manganese, or it can be circumvented by short time, high temperature austenitization, which levels out the local carbon content but not the manganese variations. MacrostructureCast IronsچدنهاWhite IronWhite Cast IronLedeburiteLedeburiteChromium Carbide(a) Sketch and (b) photomicrograph of the flake graphite in gray cast iron (x 100).Grey IronLamellar GraphiteLamellar GraphiteNodular GraphiteNodular GraphiteEye-Cow GraphiteEye-Cow GraphiteCompacted GraphiteDegenerated GraphiteFerritic ductile IronFlake & Nodular GraphiteFerritic Mallable Ironwith Tempered GraphiteFig. 17 Same as in Fig. 16 but after etching with hot alkaline sodium picrate. C, eutectic cementite; L,ledeburite; F, ferrite; and P, pearlite with slightly etched cementite. 650× (microscopic magnification500×)Fig. 45 Same as in Fig. 43 but as-polished and examined in differential interference contrast. Primaryand eutectic carbides are sticking up from the softer austenitic matrix. 400×Grey cast ironAt 500X at left you can see the large graphite flakes plus grey MnS inclusions and a few irregular islands of iron – iron phosphide eutectic microconstituent. These features are seen in most cast irons.Phosphide eutecticHere the magnification is 500X, and there is an exaggeration of the volume fraction of phosphide eutectic in this particular area, because this is the lowest freezing microconstituent in this cast iron, and so it is concentrated in the last portions of the casting that freeze.Malleable cast ironThis microstructure is far more ductile than grey (i.e., flake graphite) cast iron, because these graphite nodules have rounded edges in spite of their lumpy appearance, compared to the very sharp edges of the disk-shaped graphite flakes in grey cast iron.Ductile IronNodular cast iron is made by changing the solidification morphology of graphite in what would otherwise be a grey cast iron. It is a ductile material like malleable iron.Ductile IronThis nodular cast iron has a bullseye microstructure due to an intermediate cooling rate. The magnification is 500X. Can you tell whether the white rings are ferrite or cementite ?The white rings have to be ferrite because iron carbide cannot be stable in direct contact with graphite. Also, the white rings are continuous with the majority (ferrite) phase in the pearlite. White IronIn this 5% carbon cast iron, shown here at 100X magnification, what is the primary phase … the first solid to form during solidification ?this has to be a white iron, and so the primary phase is cementite. It couldn’t be austenite The matrix is ledeburiteConstituents commonly found in cast iron microstructures, and their general effect on physical propertiesGraphite : Free carbon; soft; improves machinability and damping properties; reduces shrinkage and may reduce strength severely, depending on shape (hexagonal crystal structure)Austenite : Face-centered cubic crystal structure. The character of the primary phase, which solidifies from the oversaturated liquid alloy in dendrite form, is maintained until room temperature. Austenite is metastable or stable equilibrium phase (depending upon alloy composition). Usually transforms into other phases. Seen only in certain alloys. Soft and ductile, approximately 200 HBFerrite : Body-centered cubic crystal structure. Iron with elements in solid solution, which is a stable equilibrium, low-temperature phase. Soft, 80–90 HB; contributes ductility but little strengthCementite (Fe3 C) :Complex orthorhombic crystal structure. Hard, intermetallic phase, 800–1400 HV depending upon substitution of elements for Fe; imparts wear resistance; reduces machinabilityPearlite : A metastable lamellar aggregate of ferrite and cementite due to eutectoidal transformation of austenite above the bainite region. Contributes strength without brittleness; has good machinability, approximately 230 HBMartensite : Generic term for microstructures that form by diffusionless transformation, where the parent and product phases have a specific crystallographic relationship. Hard metastable phaseSteadite :A pseudobinary or ternary eutectic of ferrite and iron phosphide or ferrite, iron phosphide, and cementite, respectively. It can form in gray iron or in mottled iron with a phosphorous content >0.06%. Hard and brittle; solidifies from the liquid on cooling at the cell boundaries as a last constituent of the icrostructure)Ledeburite : Massive eutectic phase composed of cementite and austenite; austenite transforms to cementite and pearlite on cooling. Produces high hardness and wear resistance; virtually unmachinableMartensite in IronThis is a nodular cast iron with an unusual microstructure, shown at left at 500X.It is martensitic, as the result of a heat treatment after casting that consisted of austenitization for 8 hours at 940C followed by water quenching.High Speed SteelAlloy CarbideSegregationHigh Alloy SteelHigh Alloy SteelHigh Alloy SteelThis set of pliers, made of SAE8650 steel, was austempered by isothermal transformation from austenite (formed at 840C in 20 minutes) to lower bainite at 300C. This specimen was held for too short a time at the lower temperature – only 20 minutes. The photomicrograph at left was made at 50X with a Nital etch in the center of the specimen.The image below was made at 500X in the same place. The gold colored euhedral particles at the left side of the 500X photomicrograph at left are probably TiN, titanium nitride. This compound is extremely hard; many modern drill bits come with a TiN coating (usually mis-spelled TIN or tin) for wear resistance.This microstructure demonstrates the effect of segregation on hardenability; the outer parts of the piece are bainite,but the inside has (light colored) untempered martensite in addition to the bainite, because the transformation from austenite to bainite wasn’t completed there in the 20 minute hold at 300C. The untransformed austenite became martensite upon subsequent cooling to room temperature and has not been tempered.Here, shown at 1000X with a Nital etch, is the good bainitic microstructure (which consists of ferrite plus cementite in a slightly different morphology than in tempered martensite) in the outer part of the specimen.SAE8650 steel nominally contains 0.5% carbon, 0.8% manganese, 0.3% silicon, 0.5% nickel, 0.5% chromium, and 0.2% molybdenum. The last three elements provide most of the improved hardenability over a plain medium carbon steel.Structure OxidationZinc CoatingPowder MetallurgyCarburized LayerMicrostructure through a carburized layerdecarburized surfaceThe machinability of this low carbon steel rod (shown here at 200X after a Nital etch) was poor because of the saft, decarburized surface. The microstructure consists of ferrite plus spheroidized pearlite (which isn’t resolved here). The specimen was probably cold rolled and then process annealed (i.e., recrystallized by heating just below the eutectoid temperature). Wrought ironThis stock was purchased as low carbon steel.The first two photomicrographs were taken at 100X and with a Nital etch.The first photomicrograph on the preceding page is a longitudinal section (note the aspect ratios of the slag stringers) while the second is a transverse section.Wrought iron was made by forging or “puddling” a spongy ball of mixed slag and pig iron, which squeezes out excess oxide and oxidizes the carbon out of the pig iron at the same time as the iron is being consolidated.Hot working stretches the oxide stringers while the workpiece is being elongated. The properties are therefore quite anisotropic, the fracture of such a piece being as fibrous as a piece of green wood.The slag is a two phase mixture of iron oxide and silica, and it recrystallizes easily at the hot working temperature.Machining steelHere we have a free machining steel, shown as a transverse section at 200X with a Nital etch. The material is AISI B1112 steel. The dark phase is manganese sulfide (MnS) which has the FCC crystal structure of sodium chloride (NaCl) and which is quite ductile at hot working temperatures, in contrast to ferrous sulfide (FeS) which has a hexagonal crystal structure.Coarse pearliteThis is unusually coarse pearlite in a eutectoid (0.8% carbon) steel. The colors in the first picture at left, shown at 100X with a Nital etch, are interference effects.The apparent interlamellar spacings act as diffraction gratings for the reflected light. The opalescence of the specimen when viewed with the naked eye gives pearlite its name. Most of the other names of microconsituents in steel were chosen to honor early researchers in the field of metallurgy.Coarse pearliteAt 500X at left you can now resolve all but the finest of the apparent interlamellar spacings. The finest spacings seen here were sectioned at right angles to the planes of the lamellae, and so they are the actual spacings. The others were mostly sectioned at shallower angles. The angle of sectioning cannot be determined without tedious serial sectioning of the specimen. There can also be a distribution of actual spacings. Coarse pearliteThe transmission electron microscope is of great help here.That aligned most of the pearlite parallel to the wire axis, so we could then study the effect that wire drawing has on the microstructure of the pearlite. Retained austeniteThis is a transverse section of a leather cutting knife shown at 500X with a Nital etch. The edge became bent because of excessive amounts of soft retained austenite.The alloy is 1% carbon, 1% manganese, and 0.4% molybdenum, which is known as a “nondeforming” tool steel. ‘Nondeforming” is usually meant to mean that it won’t change dimensions during heat treatment. The microstructure consists of tempered martensite plus about 40% retained austenite, ten times as much as would ordinarily be tolerated. The retained austenite is not very strong, but when it transforms to martensite during use or during a subsequent heat treatment, the steel can crack or become embrittled.The start and finish temperatures of the athermal transformation of austenite to martensite in plain carbon steels are quite sensitive to the carbon content of the austenite. Austenite with more than about 0.8% carbon will not transform completely to martensite if the austenite is only quenched down to room temperature. The image below was made at 500X in the same place.The gold colored euhedral particles at the left side of the 500X photomicrograph at left are probably TiN, titanium nitride. This compound is extremely hard.This microstructure demonstrates the effect of segregation on hardenability;the outer parts of the piece are bainite,but the inside has (light colored) untempered martensite in addition to the bainite, because the transformation from austenite to bainite wasn’t completed there in the 20 minute hold at 300C. The untransformed austenite became martensite upon subsequent cooling to room temperature and has not been tempered.Here, shown at 1000X with a Nital etch, is the good bainitic microstructure (which consists of ferrite plus cementite in a slightly different morphology than in tempered martensite) in the outer part of the specimen.SAE8650 steel nominally contains 0.5% carbon, 0.8% manganese, 0.3% silicon, 0.5% nickel, 0.5% chromium, and 0.2% molybdenum. The last three elements provide most of the improved hardenability over a plain medium carbon steel.Quench crackHere is a tension member used for prestressing concrete, made from a 4140 steel, heat treated to Rockwell C45 hardness before machining the screw threads.Note the ferrite network near the oxidized surface. This piece broke at low load during tightening and after the concrete had thoroughly set, ruining the structure.Explanation: This is a quench crack. On the actual fracture surface one could see the oxidation which occurred during tempering subsequent to the quenching operation. The fracture surface had a temper color in the portion of the fracture that took place before tempering and before the final fracture. The rest of the fracture surface was a metallic grey. The temper color is due to the formation during tempering of a thin layer of oxide whose thickness is near the wavelength of light, about 0.5 micrometers. Only low temperature oxidation (at 200C to 500C) does this. There is no remedy for the failed piece, but to avoid cracking another one, the quench should be in a warm oil (50C or so) to reduce the severity of the cooling rate during quenching.Tool SteelThis is a tool steel which was abusively cut with an abrasive saw.As can be seen in the second image at right (1000X, same etch) the darker etching hard spot is martensitic. It is darker etching because the fresh martensite was tempered by the heat remaining in the metal from the cutoff sawing.Carburized plain carbon steelThis is another carburized plain carbon steel, originally 0.2% carbon, which has been furnace cooled after carburizing, then reheated to 930C and water quenched.The photomicrograph at left was made at 500X near the high carbon surface. It shows martensite plus retained austenite. The austenitization temperature was high enough to put most of the carbon into solution in the austenite, so the martensite start temperature was above room temperature.The subsurface, shown at left at 500X and also etched with Nital, consists of blue unresolvable fine pearlite which formed first (because of the low hardenability of the plain carbon steel) plus lower carbon martensite than that near the surface in the photomicrograph above.Widmanstaetten morphologyThe core (500X at left) consists of proeutectoid ferrite with a Widmanstaetten morphology due to the rapid rate of phase transformation during cooling plus low carbon martensite.This is a tough microstructure for the core of such a workpieceInductioned hardenedThis inductioned hardened cylinder liner was rejected because of the ferrite network seen here at 100X with a Nital etch.The photomicrograph was taken at the junction between the hardened [brown] case and the spheroidized [blue] pearlitic core.High speed steelThe specimen shown at left at 500X with a Nital etch was austenitized at 1150C and then oil quenched. Its hardness is Rockwell C65.The microstructure consists of undissolved excess carbides in a matrix of martensite. These carbides are probably the types M6C (where M is either molybdenum or tungsten) and vanadium carbide (VC). High speed steelThis is another high speed steel of the 18-4-1 type like the previous specimen, but it has been oil quenched from 1315C. It has a hardness of Rockwell C63.The specimen has been burned. It was hot enough to melt partially, followed by catastrophic oxidation of the liquid at the austenite grain boundaries. The prior austenite grains became very coarseAustenitic stainless steelThe specimen at left is an austenitic stainless steel containing 18% chromium, 8% nickel, and a trace of almost unavoidable carbon as an impurity. The magnification is 500X, and the microstructure has been made visible by etching electrolytically in an oxalic acid solution.This Type 316 stainless steel (18% chromium, 12% nickel, 3% molybdenum, 2% manganese, and less than 0.08% carbon) has greater strength and is more stable mechanically than Type 304 (18% chromium, 8% nickel) stainless steel. This specimen has been properly heat treated and then deeply etched electrolytically in the oxalic acid solution. It is shown at 200X at left.Coring … microsegregation during solidification of the original ingot … which caused differential resistance to etching … followed by hot working, which elongated the cored regions in the direction of rolling. The black areas are etch pits near the oxide stringers, where oxidation depleted the chromium by another mechanism.Hadfield Manganese steelHadfield’s austenitic manganese steel was one of the earliest high alloy steels to be developed. It has 12% manganese and 1.1% carbon; and it is used where extreme resistance to abrasion is necessary.In the 500X photomicrograph at left, the manganese steel has been etched with Nital. It is shown in the cast and heat treated condition. Metastable austenite that is mostly free of carbides (except at the grain boundaries) has been retained by water quenching from 1040C.The grey particles are nonmetallic inclusions, while the dark spots are shrinkage pores. This steel is extremely difficult to machine, so it is almost always cast to shape.Nichrome AlloyNichrome (shown at left at 50X) is an alloy of 70% nickel and 30% chromium, which is a face centered cubic (FCC) solid solution. It is oxidation resistant (because the oxide scale is adherent) and creep resistant (because of solid solution strengthening of the nickel by the chromium). It also has a high electrical resistivity because of the high alloy concentration. These properties make nichrome useful for electric furnace heating elements.specimen is coarse grained, wrought and annealed FCC with annealing twins.Hard chromium coatA metallurgical bond can be achieved without any visible transition zone if the coating is applied correctly to a clean substrate. This is an example of hard chromium plating onto steel.This is a pump component of tempered martensite shown at 500X with a Nital etch. The unetched chromium at the top has a hardness of Rockwell C64 .chromium serves both for corosion protection and also as a wear resistant layer over the tempered martensite, which thereby can be tempered for toughness rather than for wear resistance.Mixed microstructureA mixed microstructure of martensite and bainite. Red needles are bainite in this micrograph, larger brown plates are martensite, the white bits are the untrasformed austenite.The contrast is from viewing the etched surface (nital) using differential interference contrast.Weld ZoneQuench CracksDenderiteDendritic StructureFibrous grain structureWrought StructureTypes of Inclusions in SteelsInclusionsManganese sulfideThe ferrite formed first next to the manganese sulfide (MnS) stringers because the manganese was depleted there in the process of becoming combined with the sulfur. The brown areas are tempered martensite, and the blue areas are pearlite.Manganese sulfideHere we have a free machining steel (B1144) which failed to induction harden properly because of the banded structure. The image at left was made at 100X, and the image below it was made at 500X. Both used a Nital etch.InclusionsIndividual plate-like inclusions are mostly trigonal or hexagonal platelets (fig. 8.9)Aluminum AlloysAluminum AlloysAluminumAl-CuAl-Mg-Fe-SiAl-SiAl-Si-NaCopper AlloysCopper AlloysTwinning StructureBrassSuper Alloy تـوضـیـحــاتِ فـایــل :- این فایل با فرمت power point ( قابل ویرایش ) در اختیار شما قرار خواهد گرفت. تعداد اسلایدها : 247- قابل ارائه و مناسب بعنوان پروژه کلاسی- این پاورپوینت کاملا استاندارد بوده و در تهیه آن کلیه اصول نگارشی رعایت شده است.
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