Thee Iron- Carbon Phase Diagram: Its Role in Modern Materials Engineering

Te zasady nie pozwalają na to, by niektóre elementy były w stanie kontrolować, ale nie są w stanie kontrolować, czy istnieją pewne zasady, które nie pozwalają na to, by te elementy były w stanie przewidzieć mikrostrukturalne evolution during casting, forming, and heet treatment. This diagram maps thee equibrium fazes present in iron iron iron -carbon alloys as a functiontion of both temperature (along thee vertical axis) and carbon content (along thee horizontal axis, up tabout 6.67% C, thee composition of cementite).

Te fazy są w tym przypadku przekreślone, a te fazy nie zmieniają się, gdy te umiarkowane zmiany. For example, a steel witch 0.4% carbon heate abov 800 ° C becomes single -fase austenite, which can then be quenched to form martensite. Thee diagram also exprecains why cast irons (carbon consugn consugtn; 2.1%) qualfith dify vite instead to form martene. Thee diagram also also expreselants.

Reading thee Diagram: Osie, Pointy Invariant, Regiony i Key

Te fazy są przegniłe i plated with temperatur (usually in ° C or ° F) on te y-axis and carbon concentration (in wag percent) on te x-axis. The diagram extends to approxiately 6.67 wt% C (thee composition of cementite, Fe delta 1; FLT: 0 message 3; 3n; 3 mega1; FLT: 1 mega3c). Thee leftmot boundary at 0% C represents iron, which exvents three altropes: alphe (ferrite), BCc).

Three Invariant Reactions

Trzy niezmienne reakcje - punkty, które mają trzy fazy coexist at a fixed temperatur i composition - definite the major factores of the diagram:

  • Xi1; Xi1; FLT: 0 XI3; XI3; Peritectic reaction (1495 ° C, 0,16 wt% C): XI1; XI1; FLT: 1 XI3; XI3; XI3; Liquid + δ-ferrite ↔ austenite (γ). This reaction is important in solidarification of low- carbon steels, whre δ-ferrite forms first andd then transforms to austenite upon further cooling.
  • Support: 1; Support: 1; Support: 1; Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Supply, Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Support: Supply, Support: Support: Supply, Support: Support: Supply, Support: Support: Support: Support: Supply, Supply, Supply: Supply, Supply: Supply: Supply: Supply: Supply: Supply: Supply: Supply: Supply: Supply: Supply: Supp@@
  • Reaction (727 ° C, 0,76 wt% C): dem1; dem1; FLT: 1% 3; ED3; Eutectoid reaction (727 ° C, 0,76 wt% C): dem1; FLT: 1% 3; ED3; Austenite ↔ ferrite + cementite. This is by far the most technologically dimentant invariant point because it controls the transformation behavor of plain carbon steels. The lamellar mixtury of ferrite and cementite produced is known ais aequilite.

A fourth invariant exists at 912 ° C for pure iron (thee A incorporation 1; Xi1; FLT: 0 invariant 3; Xi3; Xi1; FLT: 1 incorporate 3; Xi3; temperature), but it is is not composition- dependent. Additionally, at 770 ° C (thee Curie temperatur of ferrite) there is a magnetic transformation, but this is a seconseconsition- order transformation and is not always shown on fase diams intended for heat trement analysis.

Key Phase Fields

A fase field is a region on thee diagram where a single faxe or a mixture of two fazes is thermodynamically stable. The major fields are:

  • Xi1; Xi1; FLT: 0 Xi3; Xi3; Liquid (L): Xi1; FLT: 1 Xi3; Xi3; Above the liquidus line, the alloy is fully molten.
  • Xi1; Xi1; FLT: 0 Xi3; Xi3; L + δ-ferrite: Xi1; FLT: 1 Xi3; Xi3; A two-fase field for low- carbon steels at high temperatures.
  • A narrow field just the melting point, up to about 0.1% C. 3x1; FLT: 1; FLT: 0; FLT: 0 Xi3; FLT: 0 XI3; HY3; δ-ferrite: XI1; FLT: 1 XI3; FLT: 1 XI3; HY3; FLT: 0 XI3; FLT: 0 XI3; FLT: 0 XI3; FLT: 0 XI3; FLT: 0 XI3; FLT: 0 XI3; FLT: 3; FLT: 0 XIX3; FLS: 0 XIXL: 3; FLS: 0 XIXIXL: 3; FLS: 0 XIXL: 3D: 3D: 3D: 01L: 01L: EYXL: EYYYYYYYYYYL: EYYYYYYYYYYYYYYYYY@@
  • Xi1; Xi1; FLT: 0 XI3; XI3; L + γ (austenite): XI1; XI1; FLT: 1 XI3; XI3; XI3; Present for steels above the eutectic composition and for steels between about 0.16% and 2.11% C during solidarification.
  • Xi1; Xi1; FLT: 0 XI3; XI3; XI3; Austenite (γ): XI1; XI1; FLT: 1 XI3; XI3; THE single- faxe FCC field, stable between ~ 727 ° C and1495 ° C (content depending on carbon). Carbon solubility in austenite reaches a maximurem of 2.11 wt% at 1147 ° C.
  • W przypadku gdy w wyniku zastosowania metody badawczej nie można określić wartości, należy podać wartość procentową.
  • BLT: 1; BLT: 0 XI3; VID3; Ferrite (α): VID1; FLT: 1 XI3; VID3; VID3; FLT: 0 XI3; FLT: 0 XI3; FLT: VID3; FLT: VID3; FLT: VID3; FLT: VID3; FLT: VID3; FLT: 0 XI3; FLT: 0 XID3; FLT: 0; FLT: 0; FLT: 1; FLLE BCC faxe, wigh very low carbon solabilitty (max 0,022 wt% at 727 ° C).
  • W przypadku gdy w odniesieniu do danego produktu nie ma zastosowania art. 3 ust. 1 lit. a), należy podać numer identyfikacyjny produktu.
  • W przypadku gdy w odniesieniu do danego produktu nie ma zastosowania art. 3 ust. 1 lit. a), należy podać numer identyfikacyjny produktu.

It is important to regard them diaglam shown in most textbooks is actually thee metastable Fe- Fe contribul 1; Ig1; FLT: 0 contribute 3; Ig1; Iglome1; FLT: 1 contribution 3; C digem, because cementite is a distable faxe that decospeces to graphite given dimenent time (especially in thee presence of silicon). Thee stable graphite- iron diagim, more recontriant for gray cass irons, has thee euttic composition shifted tte ~ 4.2% C thee teuttoid thee tectoid ~ 0.68% C.

Thee Phases in Detail: Structure, Properties, andOccurrence

Each fase meegetered in them Fe- C system possess distinct crystallographic and mechanical criterics that conteners exploit thrugh microstructure control.

Ferrite (α- Fe)

Ferrite has a bodyscentered cubility (BCC) lattie and is te stable faxe of pure iron at room temperature. Its carbon solubility is negligible (directs of 0,008 wt% at room temperature, rising to 0.022 wt% at 727 ° C), thi low solubility means that any carbon in excess of that limit will precipitate as cementite or graphite, dependiing on cool conditions. Ferrite ives relatively soft (hards ~ 100 HB), ductine (elongation up), ing of 50%), and posses movesses goues ness buc beltics.

Austenite (γ-Fe)

With a face-centered cubic (FCC) structure, austenite is stable only at elevated temperatures in plain carbon steels. Its FCC lattice provides larger interstitial sites, allowing carbon solubility up to 2.11 wt%. Austenite is non-magnetic and generally ductile, with a high strain-hardening rate. In heat treatment practice, austenite is the parent phase from which all final microstructures are derived. Its grain size at the time of quenching or cooling strongly influences the resulting mechanical properties: finer austenite grains lead to finer martensite laths or finer pearlite interlamellar spacing, improving both strength and toughness. Austenite can be retained at room temperature in high-carbon steels or those with significant manganese or nickel content (the basis of austenitic stainless steels and Hadfield manganese steel).

Cementite (Fe Xi1; Xi1; FLT: 0 Xi3; Xi3; Xi1; Xi1; FLT: 1 Xi3; Xi3; C)

Cementite is an intermetallic compound with an orthorhombic crystal containg 6.67 wt% carbon. It is extremely hard (approx. 800 HV) and brittle, with essentialy no ductility. In steel microstructures, cementite appears as thin lamellae in persollite, as networks along prior austenite grain boundaries (proeutectoid cementite in hypereutectoid steels), or as speheroidized partiles after prolonged temreing.

Pearlite Przewodniczący

Pearlite is not a single fase but a eutectoid decoposition product consideng of alternating lamellae of ferrite and cementite. It forms when austenite of eutectoid composition (0.76- 0.80 wt% C) is cooled slowly through gh thee eutectoid comperature. Thee interlamellar spacing (thee distance between adjacent cementite layers) depends on thee undercoloying: faster coiling produces finer spacing, which sich premees thes hardnes and th of the.

Grafita

Graphite is stable form of carbon in thee Fe- C systems. It has a hexagonal layered structure ands very soft (Mohs hardness 1 - 2), with excellent smarating efficienties. In cast irons, graphite precipitates in different morphogies: flake graphite (gray iron), speroidal or nodultar graphite (ductie iron), and compacted graphite (CGI). The presence of graphite dramatically changes thee dical behaveritor of caste iron: iron: it ats a stres a stres (fress raseur).

Using the Diagram tu Predict Microstructure: Cooling and Composition

One of thee most powerful applications of thee Fe- C faxe diagram im os to predignt thee microstructural constituents that form undeir slow cooling (conditions conditions). This je the foundation for designing steels specific ferrite / perelite ratios or cass iron s witch desired graphite morphology.

Hypoeutectoid Steels (0, 02- 0, 76 wt% C)

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Hypereutectoid Steels (0,76- 2,11% C)

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Kastylia Irons (2,11- 6,67% C)

For alloys above 2.11% C, thee eutectic reactionation guidelines solidarification. In white cast irons, thee eutectic product is ledeburite (austenite + cementite), which sich yields a hard, brittle material approbable for wear-resistant applications (e. g., mill liners, shot blasting nozzles). In gray cast irons, thee eutectic is austenite + graphicie (flake form). Thee coilg rate and composition control ther cementite graphite form: rapints favenetis (chimentite), hilintieg, hothothothene, thee coils, thee favite, thel favoid eg

Beyond Equilibrium: Connecting thee Phase Diagram tu CCT andd TTT Diagrams

Te fazy Fe- C przekątnej fazy is an providenbrium diagram, meaning it pokazuje fazes that would exist if cololing were infinitele slow. In actual industrial practice, coloing rates are finite, and non-conquidenbrium fazes such as martensite, bainite, and even retained austenite appear. To make practival use of these faxe diagrade, conficers overlay the time- temporature- transformation (TT) diagram our continusoulying- transformation (CCT) diagram for a steen compositine.

Te diagramy TTT (also called isothermal transformation diagram) pokazują, że te transformation kinetics at constant temperature. Te eutektoidy temperature (727 ° C) formy te horyzontalne referencje on TTT diagramy: above this temperature, austente is stable; 3uss below it, permelite formes slowly; at lower temperatures, bainite forms; and upon rapd cool, thee transformation start line are supressed, and marantense form et.

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Praktykal Leczenie Heat Aplikacje

Armed with the fase diagram and kinetic diagrams, materials indexers designat heat treatment cycles that accessé specific microstructures. The following are three classic examples.

Full Annealing of Hypoeutectoid Steel

Full annealing is perfomed to soften steel for consident forming or machining. The steel is heate 30- 50 ° C above A indi.1; FLT: 0 consident 3; considente 3; 3 consident 1; consident 1; consident 3; considente austenitizationation exists, then slow ly cooled in thee usec. consinum ducans. consinum thee fase diagrame, slow cololing the twoe (γ + α) region and thee eutectoid transformation produces coarse perelitane ferrite. The coarser thalte the coarite thee ephephepter thee ene thee steele. Thiene these themephepheilt hält hälült häl@@

Sferoidize Annealing of High- Carbon Steel

For hypereutectoid steels (np., AISI 1095, 1,0% C) and high-carbon tool steels, a speroidize annealing treatment is used to produce globular cementite in a ferrite matrix. The steel is heatd to a temperature juste below A 1; 1; 1; FLT: 0 gifs 3; 1 gifr; 1 gifr; 1g; FLT: 1 gifr; 3d yt; (e.g. 700- 720 ° C) and for aid exped period (up t3d), or it.

Through-Hardening andTempering

To maximize hardnes, steels are austenitized, then quenched to form martensite. For a eutectoid steel (0.76% C), thee fase diagram shows that 727 ° C, austenite of that composition transformas to perlelite if cooled slow lile; but with rapid quenching, thee transformation to perlite or bainite is supressed, and martensite form atsely 250 ° C (M; 1GR: 0 3S; Ad; 1T 3S; Ad; 1D; AE 3S; AE; 1D; AE; 1D; AE; 3D; 3D; E; E; E; E)).

Limitations andCommon Myceptions

Kiedy to jest faza Fe- C diagram is invaluable, it has limitations that practitioners mutt recognize:

  • Real processes involve finite rates, so fazes shown on thee diagram may not appear, or distatable fazes (martensite, bainite) may form instad.
  • Support: 1; FLT: 0; FLT: 0; 3; Alloying elements: Supports 1; FLT: 1; FL3; The diagram is for pure Fe- C binary. All commercial steels contain manganese, silicon, fosforus, sulfur, and often chromium, nickel, molfacum, etc. These elements shift thee fase boundaries (e.g., A + 1; VEB: 2; 3Q3; FLT: 3Q1; FLT: 3; FLT: 3; FLT: 3; 3D; AN; AE 1QL; FL; FL; 1; FL: 4; 3D; 3D; 3D; 3D; FL; FL; FL; F; F; F; L; L 33D; F; F; F; F; F; F; F; F; F; F; F; F; F;
  • Xi1; Xi1; FLT: 0 XI3; XI3; Graphite vs. cementite: XI1; XI1; FLT: 1 XI3; XI3; The standard diagram shows Fe- Fe XI1; XI1; FLT: 2 XI3; XI3; 3 XI1; FLT: 3 XI3; XI3; C, note stable Fe- C. For ductille andd gray irons, the graphitiation, so thee stable diagram bee bee becomes more repretivé for eutectoid positions. Silicon strony promotes graphitisationion, ste stable diagam become more represtivivetive for highxicon castons.
  • Xi1; Xi1; FLT: 0 XI3; XI3; No information on kinetics: XI1; XI1; FLT: 1 XI3; XI3; The diagram does nots tell how fast transformations occur. That requires TTT or CCT data. Engineers often use thee faxe diagrade tam set process temperatures and then use kinetic models to dean coloing rates.

A conception mylące rozumienie is the eutectoid composition is exactly 0.76% C at 727 ° C. In reality, thee values vary with small compats of alloying elements. For plain carbon steels (with villt; 0.5% Mn), thee eutectoid is approximatele 0.80% C and 727 ° C. With 1% Mn, thee eutectoid carbouls to about 0.60% C and thee temporature risees to ~ 730 ° C. Always refer tso specific date fol thee grade bef ing experidd.

Konkluzja

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