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(Effect of Quench Hardening)
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Involves water and stuff
[[Image:ArthurSiegelcoke1.jpg|thumb|250px|[[Coke (fuel)|Coke]] being pushed into a quenching car, Hanna furnaces of the Great Lakes Steel Corporation, [[Detroit, Michigan]], November 1942.]]
In [[materials science]], '''quenching''' is the rapid [[Conduction (heat)|cooling]] of a workpiece to obtain certain [[material properties]]. It prevents low-temperature processes, such as [[phase (matter)|phase]] transformations, from occurring by only providing a narrow window of time in which the reaction is both thermodynamically favorable and kinetically accessible. For instance, it can reduce [[crystallinity]] and thereby increase toughness of both [[alloy]]s and [[plastic]]s (produced through [[polymerization]]).
In [[metallurgy]], it is most commonly used to harden [[steel]] by introducing [[martensite]], in which case the steel must be rapidly cooled through its [[eutectoid]] point, the temperature at which [[austenite]] becomes unstable. In steel alloyed with metals such as [[nickel]] and [[manganese]], the eutectoid temperature becomes much lower, but the kinetic barriers to phase transformation remain the same. This allows quenching to start at a lower temperature, making the process much easier. [[High speed steel]] also has added [[tungsten]], which serves to raise kinetic barriers and give the illusion that the material has been cooled more rapidly than it really has. Even cooling such alloys slowly in air has most of the desired effects of quenching.
Extremely rapid cooling can prevent the formation of all crystal structure, resulting in [[amorphous metal]] or "metallic glass".
==Quench hardening==
Quench hardening is a mechanical process in which steel and cast iron alloys are strengthened and hardened. These metals consist of ferrous metals and alloys. This is done by heating the material to a certain temperature, depematerial. This produces a harder material by either surface hardening or through-hardening varying on the rate at which the material is cooled. The material is then often [[Tempering|tempered]] to reduce the brittleness that may increase from the quench hardening process. Items that may be quenched include gears, shafts, and wear blocks.
Quenching metals is a progression; the first step is soaking the metal, i.e. heating it to the required temperature. Soaking can be done by air ([ air furnace]), or a bath. The soaking time in air furnaces should be 1 to 2 minutes for each millimeter of cross-section. For a bath the time can range a little higher. The recommended time allotment in salt or lead baths is 0 to 6 minutes. Uneven heating or overheating should be avoided at all cost. Most materials are heated from anywhere to {{convert|815|to|900|C|F|-1|abbr=on}}.
The next item on the progression list is the cooling of the part. Water is one of the most efficient quenching media where maximum hardness is acquired, but there is a small chance that it may cause distortion and tiny cracking. When hardness can be sacrificed, whale, cottonseed and mineral oils are used. These often tend to oxidize and form a sludge, which consequently lowers the efficiency. The quenching velocity (cooling rate) of oil is much less than water. Intermediate rates between water and oil can be obtained with water containing 10-30% UCON from [[Dow Chemical Company|DOW]], a substance with an inverse solubility which therefore deposits on the object to slow the rate of cooling.
To minimize distortion, long cylindrical workpieces are quenched vertically; flat workpieces are quenched on edge; and thick sections should enter the bath first. To prevent steam bubbles the bath is agitated.
===Effect of Quench Hardening===
Before the material is hardened, the microstructure of the material is a pearlite grain structure that is uniform and lamellar. [[Pearlite]] is a mixture of [[Ferrite (iron)|ferrite]] and [[cementite]] formed when steel or cast iron are manufactured and cooled at a slow rate. After quench hardening, the microstructure of the material form into martensite as a fine, needle-like grain structure.<ref>[ Ira A. Fulton College of Engineering and Technology<!-- Bot generated title -->]</ref>
Before using this technique it is essential to look up the rate constants for the quenching of the excited states of metal ions.{{cn|date=April 2012}}
There are three types of furnaces that are commonly used in quench hardening: salt bath furnace,<ref>[ Salt Bath Furnaces<!-- Bot generated title -->]</ref> continuous furnace,<ref></ref> and box furnace. Each is used depending on what other processes or types of quench hardening are being done on the different materials.
===Quenching media===
When quenching, there are numerous types of media. Some of the more common include: air, brine (salt water), oil and water. These media are used to increase the severity of the quench.<ref>Todd, Robert H., Dell K. Allen, and Leo Alting. Manufacturing Processes Reference Guide. 1st. Ed. New York: Industrial Press Inc., bharani 1994</ref>
==Quenching Distance==
Quenching distance is an important property in the study of combustion. It is defined as the smallest hole a flame can travel through. For example hydrogen has a quenching distance of 0.64 mm.{{cn|date=April 2012}}
==See also==
*[[Quench press]]
[[Category:Metal heat treatments]]
[[ar:رواية (تكنولوجيا)]]
[[ca:Tremp de l'acer]]
[[de:Abschrecken (Metallurgie)]]
[[el:Βαφή (μεταλλουργία)]]
[[pt:Têmpera (metalurgia)]]
[[ru:Закалка металлов]]
[[ar:تسقية المعادن]]
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