Fe-fe3c phase diagrams PDF

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Fe-fe3c phase diagrams...

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Fe-Fe3C Phase Diagrams: Steel is an alloy composed of iron (Fe) and carbon (C), however the proportions of Fe to C vary, giving each type of steel different mechanical properties. Below is a phase diagram for Fe-Fe3C that shows all the different phases. - L represents the liquid phase - Austenite is the name given to the gamma phase of steel (FCC structure) - Ferrite is the name given to the alpha phase of steel (BCC structure) - Cementite is an intermetallic compound that has the formula Fe 3C and is a phase with an increased hardness - Pearlite is a eutectoid mixture of ferrite and cementite - α is a phase that is a mixture of the element on the left and either the element on the right or the intermetallic compound - β is a phase that is a mixture of the element on the right and either the element on the left or the intermetallic compound - γ is a phase that is commonly a mixture of an intermetallic solid and either another intermetallic solid or an element. It is also used to represent a significantly high temperature solid

Austenite is stable between 727˚C and 1493˚C, whilst ferrite is stable between 400˚C and 912˚C. There are four types of point; eutectic, eutectoid, peritectic and peritectoid… - Eutectic: an invariant point with three phases, whereby a liquid is transformed into two solid phases at the same time upon cooling.

- Eutectoid: a reversible reaction in which a solid phase is converted into two or more mixed solids on cooling. The eutectoid structure formed is called pearlite and is not its own phase but is a mixture of ferrite and cementite. Eutectoid steel contains 0.8% C, whereas hypereutectic steel has more than 0.8% C.

- Peritectoid: the reaction where two solids are transformed into a third solid.

- Peritectic: the reaction where three solids are in equilibrium and a liquid and solid phase is transformed into another solid phase when cooled.

Austenite cools at the eutectoidic point to form the following two phases, with the following compositions.

At the eutectoid point, the composition is 0.8% C and 99.2% Fe (forming pearlite).

Pearlite forms by the slow cooling of austenite, allowing the carbon to diffuse into the nucleation sites in the crystals. Pearlite is therefore a mix between ferrite and cementite and is normally shown by a striped structure.

- The image on the left shows ferrite (white grains) and pearlite (grey striped grains), 0.02% C - The middle image shows pearlite (striped grains), 0.8% C - The image on the right shows pearlite (striped grains) surrounded by cementite (white region), 6.7% C When you can see ‘rabbit ears’ on the phase diagram, it is either a eutectic (one liquid) or eutectoid (all solids) point.

When you can see a ‘moustache’ on the phase diagram, it is either a peritectic (one liquid) or peritectoid (all solids) point....