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30 Cards in this Set
- Front
- Back
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austenite |
Face-centered cubic iron; also iron and steel alloys that have the FCC crystal structure. |
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cementite |
Iron carbide (Fe3C) |
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congruent transformation |
A transformation of one phase to another of the same composition. |
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equilibrium |
The state of a system in which the phase characteristics remain constant over indefinite time periods. At equilibrium the free energy is a minimum. |
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eutectic phase |
One of the two phases found in the eutectic structure. |
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eutectic reaction |
A reaction in which, upon cooling, a liquid phase transforms isothermally and reversibly into two intimately mixed solid phases. |
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eutectic structure |
A two-phase microstructure resulting from the solidification of a liquid having the eutectic composition; the phases exist as lamellae that alternate with one another. |
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eutectoid reaction |
A reaction in which, upon cooling, one solid phase transforms isothermally and reversibly into two new solid phases that are intimately mixed. |
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ferrite |
Body-centered cubic iron; also iron and steel a lloys that have the BCC crystal structure |
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hypereutectoid alloy |
For an alloy system displaying a eutectoid, an alloy for which the concentration of solute is greater than the eutectoid composition. |
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hypoeutectoid alloy |
For an alloy system displaying a eutectoid, an alloy for which the concentration of solute is less than the eutectoid composition. |
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intermediate solid solution |
A solid solution or phase having a composition range that does not extend to either of the pure components of the system. |
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intermetallic compound |
A compound of two metals that has a distinct chemical formula. On a phase diagram it appears as an intermediate phase that exists over a very narrow range of compositions. |
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lever rule |
A mathematical expression, such as Equation 9.1b or Equation 9.2b, by which the relative phase amounts in a twophase alloy at equilibrium may be computed. |
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liquidus line |
On a binary phase diagram, the line or boundary separating liquid- and liquid solid–phase regions. For an alloy, the liquidus temperature is the temperature at which a solid phase first forms under conditions of equilibrium cooling. |
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metastable |
A nonequilibrium state that may persist for a very long time. |
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microconstituent |
An element of the microstructure that has an identifiable and characteristic structure. It may consist of more than one phase, such as with pearlite |
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pearlite |
A two-phase microstructure found in some steels and cast irons; it results from the transformation of austenite of eutectoid composition and consists of alternating layers (or lamellae) of a-ferrite and cementite |
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peritectic reaction |
A reaction in which, upon cooling, a solid and a liquid phase transform isothermally and reversibly to a solid phase having a different composition |
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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 among environmental constraints (e.g., temperature and sometimes pressure), composition, and regions of phase stability, typically under conditions of equilibrium. |
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primary phase |
A phase that exists in addition to the eutectic structure. |
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proeutectoid cementite |
Primary cementite that exists in addition to pearlite for hypereutectoid steels. |
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proeutectoid ferrite |
Primary ferrite that exists in addition to pearlite for hypoeutectoid steels. |
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solidus line |
On a phase diagram, the locus of points at which solidification is complete upon equilibrium cooling, or at which melting begins upon equilibrium heating |
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solubility limit |
The maximum concentration of solute that may be added without forming a new phase. |
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solvus line |
The locus of points on a phase diagram representing the limit of solid solubility as a function of temperature. |
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system |
Two meanings are possible: (1) a specific body of material being considered, and (2) a series of possible alloys consisting of the same components |
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terminal solid solution |
A solid solution that exists over a composition range extending to either composition extreme of a binary phase diagram.W |
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tie line |
A horizontal line constructed across a two-phase region of a binary phase diagram; its intersections with the phase boundaries on either end represent the equilibrium compositions of the respective phases at the temperature in question |
