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the lowest temperature at which a material is totally liquid |
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| irregular shaped nodules of graphite that form when white cast iron is exposed to an extended heat treatment (around 900C) causing carbon to be converted to the graphite; clump graphite; popcorn graphite |
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| a hard, wear resistant structure that forms from steel that has been rapidly cooled |
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| an isothermal reversible reaction in which a liquid, upon cooling, decomposes into a second liquid of a different composition and a solid |
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| the transition region comprised of both white and gray irons, when white and gray cast iron occur in the same component |
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| cast iron treated in the molten state with a master alloy containing an element such as magnesium which favors formation of spheroidal graphite |
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| a substance that causes the formation of smooth-surface spheres when added to certain materials |
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| a compound in which some degree of chemical deviation is tolerable in it’s fixed atomic ratio and the vertical line expands into a single phase region in the phase diagram |
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| a mixture of ferrite and cementite forming distinct layers or bands in slowly cooled carbon steels |
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| a phase that occurs at 1495C for alloys with a low weight percentage of carbon |
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| an isothermal reversible reaction in which a solid phase, upon cooling, reacts with another solid phase to form a third solid phase |
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| a form of material possessing a characteristic structure and characteristic properties such as a definable structure, a uniform and identifiable chemistry, and distinct boundaries; ie. solid, liquid, gas |
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| a graphic mapping of the natural tendencies of a material assuming that equilibrium has been obtained for all possible conditions |
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| the only crystalline phase capable of existing in equilibrium with a given liquid |
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| the highest temperature at which a material is completely solid |
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| maximum solute concentration that can be dissolved at a given temperature |
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| a transition in the phase diagram, where the single phase solid solution becomes a two phase mixture |
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| an alloy with less than 2.11% carbon |
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| a compound that cannot tolerate any deviation from it’s fixed atomic ratio and appears as a single vertical line in the phase diagram |
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| a reaction in which a liquid reacts with another liquid to form a solid |
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| a reaction in which 3 phases are present that is characterized by a V or inverted V intersecting the horizontal line. The reaction occurs where the 3 lines intersect |
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| a line, in a phase diagram, drawn through the point of consideration that terminates at the boundaries of the single-phase regions on either side, at a constant temperature |
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| iron carbide, in which favorable conditions of formation include a low carbon equivalent and rapid cooling |
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- From 1394C-912C (2541F-1674F) pure iron assumes a face-centered cubic (FCC) structure known as Austenite in honor of the famed metallurgist Sir Robert Austen of England.
a. Key Features-
i. High formability of characteristic of FCC structure
ii. High Solubility of carbon (Over 2% C can be dissolved in Austenite)
iii. Hot forming of steel takes advantage of the high ductility and chemical uniformity of austenite
iv. Most of the heat treatments of steel begin with the single-phase austenite structure. |
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- Carbon Equivalent= (wt. % carbon C) + 1/3 (wt % Silicon)
a. In most cast irons, Silicon partially substitutes for carbon so that the use of the phase diagram requires replacing the weight percent carbon scale with a carbon equivalent. |
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Iron-Carbon alloys with more than 2.11% carbon experience the eutectic reaction during cooling and are known as CAST IRONS.
a. The term cast iron applies to an entire family of metals with a wide variety of properties.
i. Relatively inexpensive
ii. Good Fluidity
iii. Low Liquidus temperatures
iv. Most contain some silicon. |
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Fe3C, Iron-Carbide- The fourth single phase is the stoichiometric intermetallic compound, Fe3C, which goes by the name of Cementite, or Iron-Carbide.
a. Like most intermetallics, Cementite is quite hard and brittle, and care should be exercised in controlling the structures in which it occurs. Rich in carbon
b. Because cementite dissociates prior to melting, its exact melting point is unknown, and the liquidus line remains undetermined in the high-carbon region of the diagram. |
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| Compacted Graphite Cast Iron ( A.K.A. Vermicular Graphite Iron, Seminodular Iron, or Quasi-flake Iron) |
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Produced by a method similar to that used to make ductile iron (a Mg-Ce-Ti addition is made), compacted graphite iron is characterized by a graphite structure that is intermediate to the flake graphite of gray iron and the nodular graphite of ductile iron, and it tends to possess the desirable properties and characteristics of each.
a. Bridge the gap between gray and ductile.
b. Strength and stiffness are greater than those of gray iron
c. Castability, machinibiltiy, thermal conductivity and damping capacity all exceed those of ductile.
d. Impact and fatigue properties are good.
e. Usually used where mechanical properties of gray iron are insufficient and those of ductile iron are overkill. |
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If two materials are each completely soluble in the other in both the liquid and solid states, a rather simple diagram results.
a. The upper line is a liquidus line.
i. Above the liquidus line, the two materials form a uniform-chemistry liquid solution.
b. The lower line denotes the highest temperature at which the material is completely slid is known as the solidus line.
i. Below the solidus, the materials form a solid-state solution in which the two types of atoms are uniformly distributed throughout a single crystalline lattice.
c. Between the liquidus and solidus is a freezing range, a two-phase region where solid and liquid solutions coexist. |
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| A uniform and identifiable chemistry |
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| Transitions in structure appear as characteristic points in temperature-versus-time plot of the cooling history, known as a cooling curve. a. Example would be following pure water from its liquid state as temperature decreases to the freezing point, where the material changes state and releases heat energy as part of the liquid-to-solid transition. |
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| If the cooling rate is too rapid, the temperature may drop before sufficient diffusion occurs, resulting in a material with a nonuniform chemistry. The initial solid that formed will retain a chemistry that is different from the solid regions that formed later. When these variations occur on a microscopic level, the resultant structure is referred to as being CORED. |
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| Ductile Cast Iron (Nodular Cast iron) |
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| if a high-carbon-equivalent cast iron is sufficiently low in sulfur (either by original chemistry or desulfurization), the addition of certain materials can promote graphite formation and change the morphology (shape) of the graphite product. Inoculation with ferrosilicon will promote the formation of graphite. If magnesium (in the form of MgFeSi or MgNi alloy) is also added just prior to solidification, the graphite will form as smooth-surface spheres. The latter addition is known as a Nodulizer and the product is known as Ductile or Nodular Cast Iron. |
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| Equilibrium (as in Equilibrium Phase diagram) |
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| the natural tendencies of a material or material system. |
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One common type of the three-phase reaction, known as EUTECTIC, is when a liquid mixture transitions into solid 1 + solid 2.
-Liquid Solid 1 + Solid 2
The eutectic structure is an intimate mixture of 2 single-phase solids.
- All alloys containing more than 2.11% carbon will experience the eutectic reaction and are classified by the general term cast irons. |
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At 727C (1341F) Alloys with less than 2.11% carbon miss the eutectic reaction and form a two-phase mixture when they cool through the eutectoid.
- These alloys are known as steels
-The point in an equilibrium diagram for a solid solution at which the solution on cooling is converted to a mixture of solids |
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Body Centered Cubic-
Can contain only .02% carbon in solid solution
Found when iron in steel cools through 727C(1341F), and the iron wants to change from the face-centered cubic austenite to the body-centered-cubic ferrite. |
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| a two-phase region where liquid and solid solutions coexist between the liquidus and solidus.-A range where further lowering the temperature continues to add additional solid to the solution. |
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Graphite formation is promoted by slow cooling, high carbon and silicon contents, heavy section sizes, inoculation practices, and the presence of sulfur, phosphorous, aluminum, magnesium, antimony, tin, copper, nickel, and cobalt.
-Graphite is a polymorph of the element carbon. |
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| the least expensive and most common variety of cast iron, gray cast iron, is characterized by those features that promote the formation of graphite. Typical composition ranges from 2.5%-4.0% carbon, 1.0%-3.0% silicon, and 0.4%-1.0% manganese. The microstructure consists of 3-D graphite flakes. |
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| Hypereutectoid (as in hypereutectoid steels) |
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| contain more than the eutectoid amount, 0.77% of carbon for steel. When a hypereutectoid steels cools, the primary or proeutectoid phase is now cementite. |
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| Hypoeutectoid (as in hypoeutectoid steels) |
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| steels having less than the eutectoid amount of carbon ( less than 0.77%) are called hypoeutectoid steels. At high temperatures, the material is entirely austenite. Upon cooling, however, it enters a region where the stable phases are ferrite and austenite. |
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inoculation practices are used in the formation of graphite
-Inoculation is the placement of something that will grow or reproduce, and is most commonly used in respect of the introduction of a serum, vaccine, or antigenic substance into the body of a human or animal, especially to produce or boost immunity. GUESS IT IS USED TO INTRODUCE SOMETHING TO CARBON TO MAKE GRAPHITE/ |
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alloy systems where the bonding attraction of the component materials is strong enough to form compounds. These compounds are single-phase solids and tend to break the diagram into recognizable subareas.
If components A and b form a compound AxBy, and the compound cannot tolerate any deviation from that fixed atomic ratio, the product is known as a stoichiometric intermetallic compound.
If compound can tolerate some degree of chemical deviation, the compound is known as a nonstoichiometric intermetallic compound.
IN GENERAL, INTERMETALLIC COMPOUNDS tend to be HARD, BRITTLE MATERIALS, SINCE THESE PREPERTIES ARE A CONSEQUENCE OF THEIR IONIC OR COVALENT BONDING. |
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If a point lies in a two-phase region , the relative amounts of the two components can be determined by a LEVER-LAW calculation using the tie-line.
(Point a – S2/L2-S2) * 100%
Refer to Figure 4-8 on pg. 70 for more help on Lever-law calculation. |
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