Iron-carbon phase diagram.pdf

7/21/2019 Iron-carbon phase diagram.pdf

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Iron-carbon phase

diagram & basicdefinitions


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Alloy:A metallic substance that is

composed of two or more elements

Austenite: Face-centered cubic iron or aniron alloy based on this structure.

Bainite: The product of the final

transformation of austenite decomposition

Binary Eutectic: In this context, it means

a phase diagram that consists of two

elemwnts that are not completely solublein the solid state


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Binary Isomorphous: In this context, it

means a phase diagram that consists of

two elements that are completely soluble

in both the liquid and solid states.

Body-centered:A structure in which

every atom is surrounded by eight

adjacent atoms, whether the atom is

located at a corner or at the center of a

unit cell.


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Cementite: The second phase formed

when carbon is in excess of the solubilitylimit.

Component: Either a pure metal or a

compound of which an alloy is composed. Compositions: The concentrations of all

components or elements that are found in

an alloy.


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Constituents: Severing to form, compose,

or make up a unit or whole: component

Critical point: Point where the densitiesof liquid and vapor become equal and the

interface between the two vanishes.

Above this point, only one phase can exist Delta iron: The body-centered cubic

phase which results when austenite is no

longer the most stable form of iron. Existsbetween 2802 and 2552 degrees F, has

BCC lattice structure and is magnetic


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Dilatometer:An instrument used to

measure thermal expansion in solids,liquids, and gases.

Eutectic:A eutectic system occurs when

a liquid phase tramsforms directly to a

two-phase solid.

Eutectoid:A eutectoid system occurs

when a single-phase solid transforms

directly to a two-phase solid


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Face-centered:A structure in which there

is an atom at the corner of each unit cell

and one in the center of each face, but noatom in the center of the cube.

Ferrite: Body-centered cubic iron or an

iron alloy based on this structure

Fine pearlite:Results from thin lamellae

when cooling rates are accelerated anddiffusion is limited to shorter distances


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Free Energy:A function of the internal

energy of a system - a measure of entropy

of a system

Heterogeneous system: When a system

is composed of multiple phases

Homogeneous system: When only onephase is present in the system


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Hypereutectoid: Hypereutectoid systemsexist below the eutectoid temperature.

Hypoeutectoid: Hypoeutectoid systemsexist above the eutectoid temperature

Isomorphus: Having the same structure.In the phase diagram sense, isomorphicitymeans having the same crystal structureor complete solid solubility for allcompositions.


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Incongruent phase transformation: This

is a phase transformation where at least

one of the phases involved undergoes achange in composition

Lamellae:A thin scale, plate, or layer ofphases

Ledeburite: Eutectic of cast iron. It exists

when the carbon content is greater than 2percent. It contains 4.3 percent carbon in

combination with iron.


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Lever rule:A mathematical expression

whereby the relative phase amounts in a

two-phase alloy at equilibrium may becomputed

Liquidus Line: On a binary phase

diagram, that line or boundary separatingliquid and liquid + solid phase regions. For

an alloy, the liquidus temperature is that

temperature at which a solid phase firstforms under conditions of equilibrium

cooling


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Martensite:An unstable polymorphic phase

of iron which forms at temperatures below

the eutectoid because the face-centeredcubic structure of austenite becomes

unstable. It changes spontaneously to a

body-centered structure by shearing action,not diffusion.

Mass spectrometer:An instrument used to

separate charged particles from a prepared

beam by means of an electromagnetic field

and to photograph the resulting distribution

or spectrum of masses


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Microstructure: Structure of the phases

in a material. Can only be seen with an

optical or electron mircoscope.

Pearlite:A lamellar mixture of ferrite and

carbide formed by decomposing austenite

of eutectoid composition.

Phase:A homogeneous portion of a

system that has uniform physical and

chemical characteristics


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Phase diagram:A graphical

representation of the relationships

between environmental constraints,composition, and regions of phase

stability, ordinarily under conditions of

equilibrium. Polymorphic: The ability of a solid

material to exist in more than one form or

crystal structure. Quench: To rapidly cool


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Reference State: Usually an elements

most stable state at a given temperature

Solidus Line: On a phase diagram, thelocus of points at which solidification is

complete upon equilibrium cooling, or at

which melting begins upon equilibriumheating.

Solubility: The amount of substance that

will dissolve in a given amount of anothersubstance.


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Tie line:A horizontal line constructed

across a two phase region of a binary

phase diagram; its intersections with thephase boundaries on either end represent

the equilibrium conditions of the respective

phases at the temperature in question. Xray diffraction: The scattering of x-rays

by atoms in a crystal, producing a

diffraction pattern that yields informationabout the structure of the crystal


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Xray flourescence:A method of

determining the amount of an element

present in a substance by bombarding itwith electrons and measuring the intensity

of the charicteristic x-rays that are given

off by the sample.

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Iron-carbon phase diagram.pdf