IRON CARBON PHASE DIAGRAM

1 CARBON PHASE DIAGRAMD efinition of structures: VariousphasesthatappearontheIron-Carbone quilibriumphasediagramareasunder: Austenite Ferrite Pearlite Cementite Martensite LedeburiteDefinition of structures: Austeniteisaninterstitialsolidsolutionof Carbondissolvedin ( )iron. C. Highformability,mostofheattreatmentsbegi nwiththissinglephase. , Average properties are: Tensile strength = 150,000 psi; Elongation= 10 percent in 2 in.; Hardness= Rockwell C 40, approx; and toughness= highDefinition of structures: Ferriteisknownas solidsolution. Itisaninterstitialsolidsolutionofasmalla mountofcarbondissolvedin (BCC)iron. : Tensilestrength=40,000psi; Elongation=40%in2in; Hardness>RockwellC0or>RockwellB90 Definition of structures: Converyslowcooling.

2 Itisaveryfineplatelikeorlamellarmixtureo fferriteandcementite. Thewhiteferriticbackgroundormatrixcontai nsthinplatesofcementite(dark).PearliteAv eragepropertiesare:Tensilestrength=120,0 00psi;Elongation=20%in2in.;Hardness=Rock wellC20,BHN-300 Definition of structures: Cementiteorironcarbide,isveryhard,brittl eintermetalliccompoundofiron& CARBON ,asFe 3C, Itisthehardeststructurethatappearsonthed iagram,exactmeltingpointunknown. Itscrystalstructureisorthorhombic. Itishas lowtensilestrength( ,000psi),but of structures: Martensite-asuper-saturatedsolidsolution ofcarboninferrite. Itisformedwhensteeliscooledsorapidlythat thechangefromaustenitetopearliteissuppre ssed.

3 TheinterstitialcarbonatomsdistorttheBCCf erriteintoaBC-tetragonalstructure(BCT).; responsibleforthehardnessofquenchedsteel Definition of structures: Ledeburiteistheeutecticmixtureofaustenit eandcementite. Iron- CARBON DIAGRAM : Amapofthetemperatureatwhichdifferentphas echangesoccuronveryslowheatingandcooling inrelationtoCarbon,iscalledIron-CarbonDi agram. Iron-Carbondiagramshows- thetypeofalloysformedunderveryslowcoolin g, properheat-treatmenttemperatureand curve for pure ironVarious Features of Fe-C diagramMax. solubility of C in ferrite= solubility of C in %austenite=2%IRON CARBON DIAGRAMT hree PHASE Reactions Peritectic, at 1490 , with low wt% C alloys (almost no engineering importance).

4 Eutectic, at 1130 , with C, alloys called cast irons. Eutectoid, at 723 eutectoid composition of C, two- PHASE mixture (ferrite & cementite). They are Eutectic,Eutectoid,&Peritectic: Peritectic-liquid and one solid PHASE transform to a 2nd solid PHASE Solid1 + Liquid Solid2 + L Eutectic-liquid transforms to two solid phasesL + Eutectoid one solid PHASE transforms to two other solid phasesSolid1 Solid2 + Solid3 + Fe3C Simplified Iron- CARBON PHASE DIAGRAM austenite pearlite(mixture of ferrite & cementite)Eutectoid reactionRedistribution of CARBON by diffusionAustenite wt% CFerrite wt% wt% CPearlitey +Fe3 CTheAustenitetoferrite/cementitetransfor mationinrelationtoFe-CdiagramThe Austenite to ferrite / cementitetransformation in relation to Fe-C diagramInordertounderstandthetransformat ionprocesses, ,beingslowcooledalonglinex-x.

5 Attheuppertemperatures,onlyausteniteispr esent, C,severalchangesoccursimultaneously. Theironwantstochangecrystalstructurefrom theFCCaustenitetotheBCCferrite, & growth of pearliteAustenite Microstructure for SteelSchematic picture of the formation and growth of pearliteCementiteStructureMartensiteStru cture:NEEDLE LIKE STRUCTUREP rincipal phases of steel and their CharacteristicsCast , , ).Phasediagramsareusefultoolstodetermine :-thenumberandtypesofphases,thewt% ).Binaryeutecticsandbinaryeutectoidsallo wforarangeofmicrostructureswithdifferent propertiesTHANK YOU