The Kansas Building Science Institute is a vocational school located in Manhattan, Kansas . The Institute conducts week-long Home Energy Rater Trainings (HERS) as well as Building Performance Index (BPI) and Weatherization (WX) Trainings, among others.
70-548: The Institute conducts trainings in a 3,000-square-foot (280 m) multi-purpose classroom and training center in Manhattan. The campus also includes a furnace lab, a mobile home for Weatherization Trainings, and an attached house to perform test ratings and inspections on. Other houses around Manhattan are also used for this purpose. 39°10′28″N 96°32′34″W / 39.17444°N 96.54278°W / 39.17444; -96.54278 This article about
140-503: A polymer dissolved in water, or a brine . Upon being rapidly cooled, a portion of austenite (dependent on alloy composition) will transform to martensite , a hard, brittle crystalline structure. The quenched hardness of a metal depends on its chemical composition and quenching method. Cooling speeds, from fastest to slowest, go from brine, polymer (i.e. mixtures of water + glycol polymers), freshwater, oil, and forced air. However, quenching certain steel too fast can result in cracking, which
210-464: A building or structure in Kansas is a stub . You can help Misplaced Pages by expanding it . Metallurgical furnace A metallurgical furnace , often simply referred to as a furnace when the context is known, is an industrial furnace used to heat , melt, or otherwise process metals . Furnaces have been a central piece of equipment throughout the history of metallurgy ; processing metals with heat
280-411: A certain transformation, or arrest (A), temperature. This temperature is referred to as an "arrest" because at the A temperature the metal experiences a period of hysteresis . At this point, all of the heat energy is used to cause the crystal change, so the temperature stops rising for a short time (arrests) and then continues climbing once the change is complete. Therefore, the alloy must be heated above
350-538: A furnace is seen as an unfortunate event. Conversely, starting up a new furnace, or one that had been temporarily shut down, is often a special occasion. In traditional bloomeries, several rounds of fuel would need to be burnt away before the furnace was ready to accept a charge of ore. In English, this process became known as "blowing in" the furnace, while a furnace that had to be shut down and went cold had been "blown out", terms that are still applied to contemporary blast furnaces. A reverberatory furnace still exposes
420-447: A hypereutectoid alloy from the upper transformation temperature, it will usually be the excess solutes that crystallize-out first, forming the pro-eutectoid. This continues until the concentration in the remaining alloy becomes eutectoid, which then crystallizes into a separate microstructure. A hypereutectoid steel contains more than 0.77% carbon. When slowly cooling hypereutectoid steel, the cementite will begin to crystallize first. When
490-436: A localized area and then quenching, by thermochemical diffusion, or by tempering different areas of an object at different temperatures, such as in differential tempering . Some techniques allow different areas of a single object to receive different heat treatments. This is called differential hardening . It is common in high quality knives and swords . The Chinese jian is one of the earliest known examples of this, and
560-615: A martensite transformation. In ferrous alloys, this will often produce a harder metal, while non-ferrous alloys will usually become softer than normal. To harden by quenching, a metal (usually steel or cast iron) must be heated above the upper critical temperature (Steel: above 815~900 Degress Celsius ) and then quickly cooled. Depending on the alloy and other considerations (such as concern for maximum hardness vs. cracking and distortion), cooling may be done with forced air or other gases , (such as nitrogen ). Liquids may be used, due to their better thermal conductivity , such as oil , water,
630-442: A microstructure of pearlite. Since ferrite is softer than pearlite, the two microstructures combine to increase the ductility of the alloy. Consequently, the hardenability of the alloy is lowered. A hypereutectic alloy also has different melting points. However, between these points, it is the constituent with the higher melting point that will be solid. Similarly, a hypereutectoid alloy has two critical temperatures. When cooling
700-417: A particular metal. In alloys, this rearrangement may cause an element that will not normally dissolve into the base metal to suddenly become soluble , while a reversal of the allotropy will make the elements either partially or completely insoluble. When in the soluble state, the process of diffusion causes the atoms of the dissolved element to spread out, attempting to form a homogenous distribution within
770-450: A portion of the stresses created during the welding process. Some metals are classified as precipitation hardening metals . When a precipitation hardening alloy is quenched, its alloying elements will be trapped in solution, resulting in a soft metal. Aging a "solutionized" metal will allow the alloying elements to diffuse through the microstructure and form intermetallic particles. These intermetallic particles will nucleate and fall out of
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#1732773382213840-451: A rate that will produce a refined microstructure , either fully or partially separating the constituents. The rate of cooling is generally slow. Annealing is most often used to soften a metal for cold working, to improve machinability, or to enhance properties like electrical conductivity . In ferrous alloys, annealing is usually accomplished by heating the metal beyond the upper critical temperature and then cooling very slowly, resulting in
910-419: A separate crystallizing phase, called the "pro eutectoid phase". These two temperatures are called the upper (A 3 ) and lower (A 1 ) transformation temperatures. As the solution cools from the upper transformation temperature toward an insoluble state, the excess base metal will often be forced to "crystallize-out", becoming the pro eutectoid. This will occur until the remaining concentration of solutes reaches
980-559: A single chamber. Mechanisms, such as bellows or motorized fans, then drive pressurized blasts of air into the chamber. These blasts make the fuel burn hotter and drive chemical reactions. Furnaces of this type include: Even smaller, pre-industrial bloomeries possess significant thermal mass . Raising a cold furnace to the necessary temperature for smelting iron requires a significant amount of energy, regardless of modern technology. For this reason, metallurgists will try their best to keep blast furnaces running continuously, and shutting down
1050-409: A softer part. Examples of precipitation hardening alloys include 2000 series, 6000 series, and 7000 series aluminium alloy , as well as some superalloys and some stainless steels . Steels that harden by aging are typically referred to as maraging steels , from a combination of the term "martensite aging". Quenching is a process of cooling a metal at a rapid rate. This is most often done to produce
1120-399: A solution. Most often, these are then cooled very quickly to produce a martensite transformation, putting the solution into a supersaturated state. The alloy, being in a much softer state, may then be cold worked . This causes work hardening that increases the strength and hardness of the alloy. Moreover, the defects caused by plastic deformation tend to speed up precipitation, increasing
1190-491: A temperature that is just above the upper critical temperature, in order to prevent the grains of solution from growing too large. For instance, when steel is heated above the upper critical-temperature, small grains of austenite form. These grow larger as the temperature is increased. When cooled very quickly, during a martensite transformation, the austenite grain-size directly affects the martensitic grain-size. Larger grains have large grain-boundaries, which serve as weak spots in
1260-450: A very long time may turn brown or purple, even though the temperature never exceeded that needed to produce a light straw color. Other factors affecting the final outcome are oil films on the surface and the type of heat source used. Many heat treating methods have been developed to alter the properties of only a portion of an object. These tend to consist of either cooling different areas of an alloy at different rates, by quickly heating in
1330-434: A very specific temperature, the iron oxide will form a layer with a very specific thickness, causing thin-film interference . This causes colors to appear on the surface of the steel. As the temperature is increased, the iron oxide layer grows in thickness, changing the color. These colors, called tempering colors, have been used for centuries to gauge the temperature of the metal. The tempering colors can be used to judge
1400-407: Is a technique to remove or reduce the internal stresses created in metal. These stresses may be caused in a number of ways, ranging from cold working to non-uniform cooling. Stress-relieving is usually accomplished by heating a metal below the lower critical temperature and then cooling uniformly. Stress relieving is commonly used on items like air tanks, boilers and other pressure vessels , to remove
1470-403: Is a thermochemical diffusion process in which an alloying element, most commonly carbon or nitrogen, diffuses into the surface of a monolithic metal. The resulting interstitial solid solution is harder than the base material, which improves wear resistance without sacrificing toughness. Laser surface engineering is a surface treatment with high versatility, selectivity and novel properties. Since
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#17327733822131540-521: Is added, becoming steel, the A 2 temperature splits into the A 3 temperature, also called the austenizing temperature (all phases become austenite, a solution of gamma iron and carbon) and its A 1 temperature (austenite changes into pearlite upon cooling). Between these upper and lower temperatures the pro eutectoid phase forms upon cooling. Because a smaller grain size usually enhances mechanical properties, such as toughness , shear strength and tensile strength , these metals are often heated to
1610-573: Is even its own engineering specialty known as pyrometallurgy . One important furnace application, especially in iron and steel production, is smelting , where metal ores are reduced under high heat to separate the metal content from mineral gangue . The heat energy to fuel a furnace may be supplied directly by fuel combustion or by electricity . Different processes and the unique properties of specific metals and ores have led to many different furnace types. Many furnace designs for smelting combine ore, fuel, and other reagents like flux in
1680-400: Is harder than iron, the degree of softness achievable is typically limited to that produced by the pearlite. Similarly, the hardenability is limited by the continuous martensitic microstructure formed when cooled very fast. A hypoeutectic alloy has two separate melting points. Both are above the eutectic melting point for the system but are below the melting points of any constituent forming
1750-399: Is lower than that of any of the constituents, and no change in the mixture will lower the melting point any further. When a molten eutectic alloy is cooled, all of the constituents will crystallize into their respective phases at the same temperature. A eutectoid alloy is similar, but the phase change occurs, not from a liquid, but from a solid solution . Upon cooling a eutectoid alloy from
1820-483: Is often used for cast steel, where a high carbon-content is needed for casting, but a lower carbon-content is desired in the finished product. It is often used on cast-irons to produce malleable cast iron , in a process called "white tempering". This tendency to decarburize is often a problem in other operations, such as blacksmithing, where it becomes more desirable to austenize the steel for the shortest amount of time possible to prevent too much decarburization. Usually
1890-494: Is often used for ferrous alloys that have been austenitized and then cooled in the open air. Normalizing not only produces pearlite but also martensite and sometimes bainite , which gives harder and stronger steel but with less ductility for the same composition than full annealing. In the normalizing process the steel is heated to about 40 degrees Celsius above its upper critical temperature limit, held at this temperature for some time, and then cooled in air. Stress-relieving
1960-510: Is particularly useful for recycling (still relatively pure) scrap metal, or remelting ingots for casting in foundries . The absence of any fuel or exhaust gases also makes these designs versatile for heating all kinds of metals. Such designs include: Other metallurgical furnaces have special design features or uses. One function is heating material short of melting, in order to perform heat treatment or hot working . Basic furnaces used this way include: Another class of furnaces isolate
2030-469: Is referred to as "sphereoidite". If cooled a little faster, then coarse pearlite will form. Even faster, and fine pearlite will form. If cooled even faster, bainite will form, with more complete bainite transformation occurring depending on the time held above martensite start Ms. Similarly, these microstructures will also form, if cooled to a specific temperature and then held there for a certain time. Most non-ferrous alloys are also heated in order to form
2100-489: Is retained after quenching. The heating of steel is sometimes used as a method to alter the carbon content. When steel is heated in an oxidizing environment, the oxygen combines with the iron to form an iron-oxide layer, which protects the steel from decarburization. When the steel turns to austenite, however, the oxygen combines with iron to form a slag, which provides no protection from decarburization. The formation of slag and scale actually increases decarburization, because
2170-440: Is to produce a uniform microstructure. Non-ferrous alloys are often subjected to a variety of annealing techniques, including "recrystallization annealing", "partial annealing", "full annealing", and "final annealing". Not all annealing techniques involve recrystallization, such as stress relieving. Normalizing is a technique used to provide uniformity in grain size and composition ( equiaxed crystals ) throughout an alloy. The term
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2240-426: Is too brittle to be useful for most applications. A method for alleviating this problem is called tempering. Most applications require that quenched parts be tempered. Tempering consists of heating steel below the lower critical temperature, (often from 400˚F to 1105˚F or 205˚C to 595˚C, depending on the desired results), to impart some toughness . Higher tempering temperatures (maybe up to 1,300˚F or 700˚C, depending on
2310-764: Is why high-tensile steels such as AISI 4140 should be quenched in oil, tool steels such as ISO 1.2767 or H13 hot work tool steel should be quenched in forced air, and low alloy or medium-tensile steels such as XK1320 or AISI 1040 should be quenched in brine. Some Beta titanium based alloys have also shown similar trends of increased strength through rapid cooling. However, most non-ferrous metals, like alloys of copper , aluminum , or nickel , and some high alloy steels such as austenitic stainless steel (304, 316), produce an opposite effect when these are quenched: they soften. Austenitic stainless steels must be quenched to become fully corrosion resistant, as they work-harden significantly. Untempered martensitic steel, while very hard,
2380-403: The aerospace industry, a superalloy may undergo five or more different heat treating operations to develop the desired properties. This can lead to quality problems depending on the accuracy of the furnace's temperature controls and timer. These operations can usually be divided into several basic techniques. Annealing consists of heating a metal to a specific temperature and then cooling at
2450-401: The austenizing temperature (red to orange-hot, or around 1,500 °F (820 °C) to 1,600 °F (870 °C) depending on carbon content), and then cooled slowly, forms a laminated structure composed of alternating layers of ferrite and cementite , becoming soft pearlite . After heating the steel to the austenite phase and then quenching it in water, the microstructure will be in
2520-475: The Japanese katana may be the most widely known. The Nepalese Khukuri is another example. This technique uses an insulating layer, like layers of clay, to cover the areas that are to remain soft. The areas to be hardened are left exposed, allowing only certain parts of the steel to fully harden when quenched. Flame hardening is used to harden only a portion of the metal. Unlike differential hardening, where
2590-526: The alloy and application) are sometimes used to impart further ductility, although some yield strength is lost. Tempering may also be performed on normalized steels. Other methods of tempering consist of quenching to a specific temperature, which is above the martensite start temperature, and then holding it there until pure bainite can form or internal stresses can be relieved. These include austempering and martempering . Steel that has been freshly ground or polished will form oxide layers when heated. At
2660-445: The cooling rate is very high in laser treatment, metastable even metallic glass can be obtained by this method. Although quenching steel causes the austenite to transform into martensite, all of the austenite usually does not transform. Some austenite crystals will remain unchanged even after quenching below the martensite finish (M f ) temperature. Further transformation of the austenite into martensite can be induced by slowly cooling
2730-479: The critical temperature for a transformation to occur. The alloy will usually be held at this temperature long enough for the heat to completely penetrate the alloy, thereby bringing it into a complete solid solution. Iron, for example, has four critical-temperatures, depending on carbon content. Pure iron in its alpha (room temperature) state changes to nonmagnetic gamma-iron at its A 2 temperature, and weldable delta-iron at its A 4 temperature. However, as carbon
2800-429: The crystals of the base metal. If the alloy is cooled to an insoluble state, the atoms of the dissolved constituents (solutes) may migrate out of the solution. This type of diffusion, called precipitation , leads to nucleation , where the migrating atoms group together at the grain-boundaries. This forms a microstructure generally consisting of two or more distinct phases . For instance, steel that has been heated above
2870-416: The end condition is specified instead of the process used in heat treatment. Case hardening is specified by "hardness" and "case depth". The case depth can be specified in two ways: total case depth or effective case depth. The total case depth is the true depth of the case. For most alloys, the effective case depth is the depth of the case that has a hardness equivalent of HRC50; however, some alloys specify
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2940-424: The entire piece is heated and then cooled at different rates, in flame hardening, only a portion of the metal is heated before quenching. This is usually easier than differential hardening, but often produces an extremely brittle zone between the heated metal and the unheated metal, as cooling at the edge of this heat-affected zone is extremely rapid. Induction hardening is a surface hardening technique in which
3010-453: The eutectoid level, which will then crystallize as a separate microstructure. For example, a hypoeutectoid steel contains less than 0.77% carbon. Upon cooling a hypoeutectoid steel from the austenite transformation temperature, small islands of proeutectoid-ferrite will form. These will continue to grow and the carbon will recede until the eutectoid concentration in the rest of the steel is reached. This eutectoid mixture will then crystallize as
3080-527: The final properties of the tempered steel. Very hard tools are often tempered in the light to the dark straw range, whereas springs are often tempered to the blue. However, the final hardness of the tempered steel will vary, depending on the composition of the steel. Higher-carbon tool steel will remain much harder after tempering than spring steel (of slightly less carbon) when tempered at the same temperature. The oxide film will also increase in thickness over time. Therefore, steel that has been held at 400˚F for
3150-486: The formation of martensite causes the crystals to deform intrinsically, and the diffusion mechanism causes changes in the homogeneity of the alloy. The crystal structure consists of atoms that are grouped in a very specific arrangement, called a lattice. In most elements, this order will rearrange itself, depending on conditions like temperature and pressure. This rearrangement called allotropy or polymorphism , may occur several times, at many different temperatures for
3220-440: The formation of pearlite . In both pure metals and many alloys that cannot be heat treated, annealing is used to remove the hardness caused by cold working. The metal is heated to a temperature where recrystallization can occur, thereby repairing the defects caused by plastic deformation. In these metals, the rate of cooling will usually have little effect. Most non-ferrous alloys that are heat-treatable are also annealed to relieve
3290-414: The gamma iron. When austenitized steel is exposed to air for long periods of time, the carbon content in the steel can be lowered. This is the opposite from what happens when steel is heated in a reducing environment , in which carbon slowly diffuses further into the metal. In an oxidizing environment, the carbon can readily diffuse outwardly, so austenitized steel is very susceptible to decarburization. This
3360-489: The hardness beyond what is normal for the alloy. Even if not cold worked, the solutes in these alloys will usually precipitate, although the process may take much longer. Sometimes these metals are then heated to a temperature that is below the lower critical (A 1 ) temperature, preventing recrystallization, in order to speed-up the precipitation. Complex heat treating schedules, or "cycles", are often devised by metallurgists to optimize an alloy's mechanical properties. In
3430-423: The hardness of cold working. These may be slowly cooled to allow full precipitation of the constituents and produce a refined microstructure. Ferrous alloys are usually either "full annealed" or "process annealed". Full annealing requires very slow cooling rates, in order to form coarse pearlite. In process annealing, the cooling rate may be faster; up to, and including normalizing. The main goal of process annealing
3500-407: The hardness, wear resistance, and reduce the internal stresses in the metal but, because it is really an extension of the quenching process, it may increase the chances of cracking during the procedure. The process is often used for tools, bearings, or other items that require good wear resistance. However, it is usually only effective in high-carbon or high-alloy steels in which more than 10% austenite
3570-430: The heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding. Metallic materials consist of a microstructure of small crystals called "grains" or crystallites . The nature of the grains (i.e. grain size and composition) is one of the most effective factors that can determine
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#17327733822133640-411: The iron oxide keeps oxygen in contact with the decarburization zone even after the steel is moved into an oxygen-free environment, such as the coals of a forge. Thus, the carbon atoms begin combining with the surrounding scale and slag to form both carbon monoxide and carbon dioxide , which is released into the air. Steel contains a relatively small percentage of carbon, which can migrate freely within
3710-482: The lower critical temperature. Such austenite is highly unstable and, if given enough time, will precipitate into various microstructures of ferrite and cementite. The cooling rate can be used to control the rate of grain growth or can even be used to produce partially martensitic microstructures. However, the martensite transformation is time-independent. If the alloy is cooled to the martensite transformation (M s ) temperature before other microstructures can fully form,
3780-445: The manufacture of many other materials, such as glass . Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve the desired result such as hardening or softening of a material. Heat treatment techniques include annealing , case hardening , precipitation strengthening , tempering , carburizing , normalizing and quenching . Although the term heat treatment applies only to processes where
3850-415: The martensite transformation hardens the metal, while in others, like aluminum, the alloy becomes softer. The specific composition of an alloy system will usually have a great effect on the results of heat treating. If the percentage of each constituent is just right, the alloy will form a single, continuous microstructure upon cooling. Such a mixture is said to be eutectoid . However, If the percentage of
3920-406: The martensitic phase. This is due to the fact that the steel will change from the austenite phase to the martensite phase after quenching. Some pearlite or ferrite may be present if the quench did not rapidly cool off all the steel. Unlike iron-based alloys, most heat-treatable alloys do not experience a ferrite transformation. In these alloys, the nucleation at the grain-boundaries often reinforces
3990-410: The material from the surrounding atmosphere and contaminants, enabling advanced heat treatments and other techniques: Heat treatment Heat treating (or heat treatment ) is a group of industrial , thermal and metalworking processes used to alter the physical , and sometimes chemical , properties of a material. The most common application is metallurgical . Heat treatments are also used in
4060-451: The metal to extremely low temperatures. Cold treating generally consists of cooling the steel to around -115˚F (-81˚C), but does not eliminate all of the austenite. Cryogenic treating usually consists of cooling to much lower temperatures, often in the range of -315˚F (-192˚C), to transform most of the austenite into martensite. Cold and cryogenic treatments are typically done immediately after quenching, before any tempering, and will increase
4130-497: The overall mechanical behavior of the metal. Heat treatment provides an efficient way to manipulate the properties of the metal by controlling the rate of diffusion and the rate of cooling within the microstructure. Heat treating is often used to alter the mechanical properties of a metallic alloy , manipulating properties such as the hardness , strength , toughness , ductility , and elasticity . There are two mechanisms that may change an alloy's properties during heat treatment:
4200-749: The reaction chamber, where metal or ore is combined with reagents, to a stream of exhaust gases. However, no fuel is directly added to the chamber, and combustion occurs in a separate chamber. Furnaces of this type include: In metallurgy, furnaces used to refine metals further, particularly iron into steel, are also often called converters : Just as other industries have trended towards electrification , electric furnaces have become prevalent in metallurgy. However, while any furnace can theoretically use an electrical heating element , process specifics mostly limit this approach to furnaces with lower power demands. Instead, electric metallurgical furnaces often apply an electric current directly to batches of metal. This
4270-434: The remaining steel becomes eutectoid in composition, it will crystallize into pearlite. Since cementite is much harder than pearlite, the alloy has greater hardenability at a cost in ductility. Proper heat treating requires precise control over temperature, time held at a certain temperature and cooling rate. With the exception of stress-relieving, tempering, and aging, most heat treatments begin by heating an alloy beyond
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#17327733822134340-425: The solutes varies from the eutectoid mixture, two or more different microstructures will usually form simultaneously. A hypo eutectoid solution contains less of the solute than the eutectoid mix, while a hypereutectoid solution contains more. A eutectoid ( eutectic -like) alloy is similar in behavior to a eutectic alloy . A eutectic alloy is characterized by having a single melting point . This melting point
4410-436: The solution and act as a reinforcing phase, thereby increasing the strength of the alloy. Alloys may age " naturally" meaning that the precipitates form at room temperature, or they may age "artificially" when precipitates only form at elevated temperatures. In some applications, naturally aging alloys may be stored in a freezer to prevent hardening until after further operations - assembly of rivets, for example, maybe easier with
4480-404: The solution in time. This is called a " diffusionless transformation ." When the crystal matrix changes to its low-temperature arrangement, the atoms of the solute become trapped within the lattice. The trapped atoms prevent the crystal matrix from completely changing into its low-temperature allotrope, creating shearing stresses within the lattice. When some alloys are cooled quickly, such as steel,
4550-416: The solution temperature, the constituents will separate into different crystal phases , forming a single microstructure . A eutectoid steel, for example, contains 0.77% carbon . Upon cooling slowly, the solution of iron and carbon (a single phase called austenite ) will separate into platelets of the phases ferrite and cementite . This forms a layered microstructure called pearlite . Since pearlite
4620-403: The structure of the crystal matrix. These metals harden by precipitation. Typically a slow process, depending on temperature, this is often referred to as "age hardening". Many metals and non-metals exhibit a martensite transformation when cooled quickly (with external media like oil, polymer, water, etc.). When a metal is cooled very quickly, the insoluble atoms may not be able to migrate out of
4690-432: The structure. The grain size is usually controlled to reduce the probability of breakage. The diffusion transformation is very time-dependent. Cooling a metal will usually suppress the precipitation to a much lower temperature. Austenite, for example, usually only exists above the upper critical temperature. However, if the austenite is cooled quickly enough, the transformation may be suppressed for hundreds of degrees below
4760-437: The surface of the metal is heated very quickly, using a no-contact method of induction heating . The alloy is then quenched, producing a martensite transformation at the surface while leaving the underlying metal unchanged. This creates a very hard, wear-resistant surface while maintaining the proper toughness in the majority of the object. Crankshaft journals are a good example of an induction hardened surface. Case hardening
4830-424: The system. Between these two melting points, the alloy will exist as part solid and part liquid. The constituent with the higher melting point will solidify first. When completely solidified, a hypoeutectic alloy will often be in a solid solution. Similarly, a hypoeutectoid alloy has two critical temperatures, called "arrests". Between these two temperatures, the alloy will exist partly as the solution and partly as
4900-525: The transformation will usually occur at just under the speed of sound. When austenite is cooled but kept above the martensite start temperature Ms so that a martensite transformation does not occur, the austenite grain size will have an effect on the rate of nucleation, but it is generally temperature and the rate of cooling that controls the grain size and microstructure. When austenite is cooled extremely slowly, it will form large ferrite crystals filled with spherical inclusions of cementite. This microstructure
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