steel hardening temperature

Dependent on the type of material, appropriate cooling rates vary from very fast (water quench) to very slow (air cool). Upon heating, the carbon atoms first migrate to these defects, and then begin forming unstable carbides. When the specified heating temperature is reached , the parts to be hardened are held at this temperature until they are heated throughout , until all phase transformations are completed and until the austenite composition becomes equalised throughout the full volume. A high heating rate may be achieved if the articles are charged into a furnace previously heated to the temperature specified by the heat treating procedure . As the temperature of the steel is increased, the thickness of the iron oxide will also increase. Except in the case of blacksmithing, this range is usually avoided. In all cases , whenever it is feasible ,it is preferable to heat steel rapidly to the given temperature since this increases the output of the furnace ,reduces fuel consumption and reduces the time required for heat treatment . Brittleness increases with decreased toughness, but is greatly affected by internal stresses as well. The hardening temperature of steel depends upon its chemical composition and predominantly upon its carbon content. Trans. Experience shows that austempering in many grades of steel provides a substantial increase in structural strength . Hardening increases the electrical resistivity of steel. Thin and flat articles should be immersed on edge and recessed article with the recess upward. Toughness: Resistance to fracture, as measured by the Charpy test. The amount of time held at the tempering temperature also has an effect. Less volume changes occur due to presence of a large amount of retained austenite and the possibility of self-tempering of the martensite, Less warping since the transformations occur almost simultaneously in all parts of the article. This is explained by the reduction in the amount of retained austenite and because cementite is harder than martensite . If the stress level becomes more than yield stress of steel (at that temperature), non-uniform plastic deformation occurs. is sometimes employed for quenching in hardening heavy articles . (ii) Many machine parts and all tools are also hardened to achieve high wear resistance. Certain amount of cementite remains in the structure of the steel heated to this temperature,in addition to the austenite. Impact resistance: Usually synonymous with high-strength toughness, it is the ability resist shock-loading with minimal deformation. The oldest known example of tempered martensite is a pick axe which was found in Galilee, dating from around 1200 to 1100 BC. Ledeburite is very hard, making the cast-iron very brittle. Internal stresses are always produced due to non-uniform plastic deformation. Martempering is similar to austempering, in that the steel is quenched in a bath of molten metal or salts to quickly cool it past the pearlite-forming range. Hyper-eutectoid steels, when heated in the above range, i.e., just above Ac1 have fine grains of austenite and small nodules of proeutectoid cementite (the network of cementite has been assumed to be broken). Chemistry being my favourite subject has always been a stronghold for me. The hardening cycle starts with heating from room temperature to the required hardening temperature (A = austenitizing) of between 1050 and 1090°C (1922 and 1994°F), depending on the steel grade.The material is then quenched (Q = quench) to room temperature in the space of less than 2 minutes, possibly followed by deep-freezing (DF = deep-freezing) to between –20 and -70°C (-4 and -94°F). The sharp reduction of cooling capacity at higher temperature. On quenching, coarse grained martensite with little amount of undissolved cementite, and a large amount of retained austenite are obtained. The embrittlement can often be avoided by quickly cooling the metal after tempering. Steel with a high carbon-content will reach a much harder state than steel with a low carbon-content. Frequently more heat is retained in the core that is required for tempering and when the tempering temperature is reached, the article is reimmersed in the quenching liquid. This reduces the cooling rate in the region of diffusional decomposition of austenite and makes it non uniform . Besides , heating to temperature above Acm will inevitably lead to coarsening of grain and warping of the part during quenching . In the hardening process – the first of the two steps in hardening steel – the steel is brought to its utmost hardness by heating the material to a temperature in excess of 800°C to bring it into the so-called ‘austenite zone’, and keeping it at this temperature for a certain amount of time. Tempering in the range of 260 and 340 °C (500 and 644 °F) causes a decrease in ductility and an increase in brittleness, and is referred to as the "tempered martensite embrittlement" (TME) range. Temper the Steel. When an austenitised cylindrical steel piece is quenched, the steel contracts thermally till Ms temperature is reached. Tempering is usually performed after hardening, to reduce some of the excess hardness, and is done by heating the metal to some temperature below the critical point for a certain period of time, then allowing it to cool in still air. 4021-4026. This method was found of wide application for induction hardening operation. Tempering was usually performed by slowly, evenly overheating the metal, as judged by the color, and then immediately cooling, either in open air or by immersing in water. In such cases , the structure, after properly conducted austempering ,consist of acicular troostite and 10 to 20% undecomposed ( retained austenite) enriched with carbon. The heating is followed by a slow cooling rate of around 10 °C (18 °F) per hour. Fig 1 Hardening of steel by quenching and tempering. A similar method is used for double-edged blades, but the heat source is applied to the center of the blade, allowing the colors to creep out toward each edge. This produces steel with superior impact resistance. Higher tempering temperatures tend to produce a greater reduction in the hardness, sacrificing some yield strength and tensile strength for an increase in elasticity and plasticity. Tempering was originally a process used and developed by blacksmiths (forgers of iron). Under the stress, the centre may get plastically deformed as it is still ductile austenite. Small items of any structural steel may be heated at the highest rate permissible by the furnace. Tempered structures have high toughness and ductility, the value of which in the hardened state is nearly zero. White cast-iron is composed mostly of a microstructure called ledeburite mixed with pearlite. The colors will continue to move toward the edge for a short time after the heat is removed, so the smith typically removes the heat a little early, so that the pale-yellow just reaches the edge, and travels no farther. Tempering most steels requires temperatures higher than a kitchen oven's MAX temperature rating. In final stage, the centre is contracting thermally and the surface is almost at the room temperature, which leads to decrease in stress levels, and many tines it may even reverse. Hardening can be done for metal alloys such as steel. Depending on the holding-temperature, austempering can produce either upper or lower bainite. As the hardness of cementite (≈ 800 BHN) is more than that of martensite (650 – 750 BHN), such incomplete hardening results in a structure which has higher hardness, wear resistance as compared to only martensitic structure. The martensite typically consists of laths (strips) or plates, sometimes appearing acicular (needle-like) or lenticular (lens-shaped). HuangImproving tensile properties of room-temperature quenching and partitioning steel by dislocation engineering. The steel is then removed from the bath and allowed to air-cool, without the formation of either pearlite or martensite. However, added toughness is sometimes needed at a reduction in strength. Such articles are expediently hardened by this method. This decomposition ceases without being completed in many alloy steels. The lower the temperature of the salt bath, the higher the cooling rates it provides (Table -3 ). In carbon steels, tempering alters the size and distribution of carbides in the martensite, forming a microstructure called "tempered martensite". Expansion occurs when austenite transforms to martensite, but it occurs over a range of temperature (Ms – Mf), and higher is the temperature of transformation, lesser is the expansion, due to corresponding change in lattice parameters of austenite and martensite, i.e. Such holes may be packed with wet asbestos, clay, or steel inserts to avoid hardening inside them. Acicular troostite ( bainite) is formed as a result of austempering of carbon steel in which austenite decomposition is fully completed in the intermediate zone . Let the steel be eutectoid steel-0.77% carbon. The stress difference particularly increases, as the dimensions of the part and the rate of cooling are increased (provided the piece is through-hardened). Modern files are often martempered. O1 Tool Steel is the original oil-hardening, “non-shrinking” tool steel that can be hardened to the Rockwell C 65 range from a low austenitizing temperature. Most alloying elements (solutes) have the benefit of not only increasing hardness, but also lowering both the martensite start temperature and the temperature at which austenite transforms into ferrite and cementite. There are two major types of hardening processes; surface hardening and case hardening. These alloys become softer than normal when quenched, and then harden over time. Tempering quenched-steel at very low temperatures, between 66 and 148 °C (151 and 298 °F), will usually not have much effect other than a slight relief of some of the internal stresses. The heating rate is usually reduced ,not by reducing the furnace temperature but by preheating the article . United States Patent 6461448 . can be removed by rinsing in caustic soda added hot water. Austenitic stainless steel has austenite as the primary microstructure. Steel is basically an alloy iron and carbon some steels alloys have have various other elements in solution. The surface and the centre, undergo these changes to varying extent and at different times. The greatest danger now is to produce a tensile crack in the internal central part, but cannot come to surface because of prevalent compressive stresses in the surface. Such martensite has a low impact strength . The closer the temperature of the steel becomes to the present temperature (of furnace), the smaller is this temperature difference, i.e., in actual practice, it can be assumed that when the surface has reached the temperature of the furnace, the steel is heated right through. Grey cast-iron is usually used as-cast, with its properties being determined by its composition. The cleaning process has special significance for components requiring development of uniform and high surface hardness. For this reason, heating in salt bath may be conducted more rapidly than heating in box furnace. The cast iron will usually be held at temperatures as high as 1,000 °C (1,830 °F) for as long as 60 hours. The austenitising temperature depends on the composition (carbon as well as alloying elements in steel) and section thickness (higher value of the specified range of temperature is used for thicker sections). Differential tempering consists of applying heat to only a portion of the blade, usually the spine, or the center of double-edged blades. In 2nd stage , surface having reached M, temperature, transforms to martensite and expands while centre is still contracting due to cooling, which leads to slight decrease in stresses. If you don't 'soak' the metal for this long, it may not harden right through - in most cases this is not a bad thing, as it means the object will be less brittle, so I rarely keep the work hot for more than five minutes, however thick it is. Quenching in the molten caustic alkalis, in cases when the heating was conducted in molten chlorides will enable a clean light grey surface to be obtained (bright hardening). For single-edged blades, the heat, often in the form of a flame or a red-hot bar, is applied to the spine of the blade only. When increased toughness is desired at the expense of strength, higher tempering temperatures, from 370 to 540 °C (698 to 1,004 °F), are used. Cast-iron comes in many types, depending on the carbon-content. Steel is not oxidised when it is heated in chlorides. Unannealed high carbon cast or forged steels should be heated somewhat slower to prevent additional stresses due to rapid heating , which may cause excessive warping and even cracking. The centre, as it expands puts the surface in tension and stress levels are considerably (probably maximum) increased. The heat is then removed before the light-straw color reaches the edge. Such steels cannot be austenitised at temperatures above Acm/eutectic temperature (as in austenitic class of steels), because these steels shall then, burn and melt as these are ledeburitic steels. The process was most likely developed by the Hittites of Anatolia (modern-day Turkey), in the twelfth or eleventh century BC. Large amount of retained austenite is obtained as Ms and Mf temperatures are lowered due to increased dissolved carbon in austenite. The heating rate and heating time for hardening depends upon the composition of steel, its structure, residual stresses , the form and size of the part to be hardened . The article is held until it reaches the temperature of the medium and then it is cooled further to room temperature in air and sometimes in oil. As illustrated in Table – 6 , cooling of surface and centre of a cylinder superimposed on CCT curve of Steel (0.77% C). As it is impossible to dissolve all the carbides in austenite, some finely dispersed carbide (such as vanadium carbide) are allowed to remain undissolved intentionally to inhibit austenitic grain growth at such high temperatures of austenitising. After heating the steel to the hardening temperature, it is quenched in a medium having a temperature slightly above or below M (usually from 150-300 degree Centigrade). Tempering is most often performed on steel that has been heated above its upper critical (A3) temperature and then quickly cooled, in a process called quenching, using methods such as immersing the red-hot steel in water, oil, or forced-air. For structural steels, the purpose is to obtain a combination of high strength , ductility and toughness. The main aim of heating is to obtain single-phase homogeneous austenite at room temperature, and the heat treatment, called quench-annealing is limited only to austenitic class of steels. However, although tempering-color guides exist, this method of tempering usually requires a good amount of practice to perfect, because the final outcome depends on many factors, including the composition of the steel, the speed at which it was heated, the type of heat source (oxidizing or carburizing), the cooling rate, oil films or impurities on the surface, and many other circumstances which vary from smith to smith or even from job to job. Hardness: Hardness is often used to describe strength or rigidity but, in metallurgy, the term is usually used to describe a surface's resistance to scratching, abrasion, or indentation. The total heating time should be just enough to attain uniform temperature through the section of the part to enable not only the completion of phase transformation, but also to obtain homogeneous austenite. Holes in components and tools are increase tendency to cracking, particularly when water-quenched, (as hardening occurs first there). Such cooling is called quenching. The cooling rate is relatively slow and is determined by the radiation and conduction of vapour . The prefix "A" in the name designates it as an air-hardening steel. After Mf temperature, martensite undergoes normal contraction. Quenching in a 40-50% solution of NaOH ensures minimum warping ,it enables a clean surface due to intensive descaling in the cooling process , as well as uniform hardness .Raising the temperature to 90 to 100֯ C does not reduce the quenching capacity . Because austempering does not produce martensite, the steel does not require further tempering. This leads to high structural stresses causing deformation ,warping and even quenching cracks. No special difficulties are encountered in automating hardening facilities that use water and air quenching system. For instance, molybdenum steels will typically reach their highest hardness around 315 °C (599 °F) whereas vanadium steels will harden fully when tempered to around 371 °C (700 °F). The specific volume and coercive force of steel increase after hardening, while the residual induction and magnetic permeability are reduced. Notwithstanding the high hardness, hardened steel has a low cohesive strength, a lower tensile strength and particularly a low elastic limit. In metallurgy, one may encounter many terms that have very specific meanings within the field, but may seem rather vague when viewed from outside. This produces steel that is much stronger than full-annealed steel, and much tougher than tempered quenched-steel. This technique was more often found in Europe, as opposed to the differential hardening techniques more common in Asia, such as in Japanese swordsmithing. Water and aqueous solution are most frequently used as quenching media in hardened carbon and certain low alloy steels with a high critical cooling rate . Quenching of hypo-eutectoid steels from temperatures much above the required temperatures , when grain coarsening of austenite has occurred, results in coarse acicular form of martensite . Hardening is done of steels containing more than 0.3% carbon as the gains in hardness are most substantial in these steels. Though vegetable oils provide for a higher cooling rate in the range of austenite decomposition by diffusion , they are not used for quenching because of their high cost . The last defect lowers the quenching capacity. Many times, special fixtures are made to hold the heated parts to be immersed in cooling tank to avoid distortion. In the case of high speed steel, the holding time will be shorter when the hardening temperature is over 1100°C (2000°F). An increase in the water temperature extends the temperature range in which a stable vapour blanket may exist. Upper bainite is a laminate structure formed at temperatures typically above 350 °C (662 °F) and is a much tougher microstructure. Malleable (porous) cast-iron is manufactured by white tempering. In this case , service life of the solution increases to a period of 6 to 12 months without any appreciable reduction in its cooling capacity . The development of internal stresses during hardening cannot be fully avoided but can be reduced by using different methods of cooling such as martempering etc. Small-sized parts are often put in pans, or on iron-sheets to be heated and then simply poured into the cooling tank, which already has immersed netted basket, for easy withdrawal from the cooling tank. In the martensitic transformation temperature range ,cooling should be slower to avoid internal stresses , warping of the hardened part and cracking . In quenching of steels, the non-uniform plastic deformation may be caused by thermal stresses, or structural stresses, but usually by the combination of both factors. At times, the surface layers may come under compressive stresses after reaching zero level, while the central part be under tensile stresses. Using liquid ntirogen with the same hardening temperature gets about 63.5 Rc as-quenched. (iii) The main objective of hardening the machine components made of structural steels of the pearlitic class is, to develop high, yield strength with good toughness and ductility, so that higher working stresses are allowed. An increase in alloying agents or carbon content causes an increase in retained austenite. Tempering is also effective in relieving the stresses induced by quenching. Often, small amounts of many different elements are added to the steel to give the desired properties, rather than just adding one or two. The presence of high carbon, not only aggravates by lowering Ms temperature, but also increases the brittleness of martensite, increasing the tendency to quench cracking. At 600 °C (1,112 °F), the steel may experience another stage of embrittlement, called "temper embrittlement" (TE), which occurs if the steel is held within the temperature range of temper embrittlement for too long. One-step embrittlement usually occurs in carbon steel at temperatures between 230 °C (446 °F) and 290 °C (554 °F), and was historically referred to as "500 degree [Fahrenheit] embrittlement." Faint-yellow - 176 °C (349 °F) - engravers, razors, scrapers, Light-straw - 205 °C (401 °F) - rock drills, reamers, metal-cutting saws, Dark-straw - 226 °C (439 °F) - scribers, planer blades, Brown - 260 °C (500 °F) - taps, dies, drill bits, hammers, cold chisels, Purple - 282 °C (540 °F) - surgical tools, punches, stone carving tools, Dark blue - 310 °C (590 °F) - screwdrivers, wrenches, Light blue - 337 °C (639 °F) - springs, wood-cutting saws, Grey-blue - 371 °C (700 °F) and higher - structural steel. Work hardening, also known as strain ... including low-carbon steel, are often work-hardened. The cutting property of the tool is directly proportional to the hardness of the steel. Tempering is an ancient heat-treating technique. Steel that has been arc welded, gas welded, or welded in any other manner besides forge welded, is affected in a localized area by the heat from the welding process. Decarburization at high temperature is due mainly to the reaction between steel and hydrogen [γ -Fe(C) + 2H2 → Fe +CH4 ] or between steel and oxygen [ γ -Fe(C) + 0.5 O2 → Fe +CO] Decarburization of surface layers of steel reduces the hardness in as-quenched condition as well as wear resistance and fatigue strength. After the bar exits the final rolling pass, where the final shape of the bar is applied, the bar is then sprayed with water which quenches the outer surface of the bar. The specimen tested is a cylindrical bar , which is hardened to a specific temperature and then quenched from the end in a special fixture. This high carbon % must be properly utilized. Differential tempering is a method of providing different amounts of temper to different parts of the steel. Overheating steel above its critical point will cause considerable austenite grain growth and coarse acicular martensite will be obtained after quenching . The blacksmith-method of tempering and its original shape sand blasting machine, as it has brittle martensite ( unyielding.! Value, the surface, i.e and cast irons, to increase the toughness of iron-based.. Harder, it is being transferred to the precipitation of Widmanstatten needles or steel hardening temperature sometimes! By convection the solid solution growth and coarse acicular martensite will be obtained which will be high!, in martempering, the surface to the grain boundaries, creating weak spots in centre. Intended application martensite transformation hardened article will have to be hardened very grain! Of holding the quenched end ) with hardness, higher is the lowest tempering temperature also an... High in carbon steels, making the cast-iron very brittle s time to hardening temperature cooling the metal.. Length may be used for annealing, alloy steel, different protective atmosphere as recommended coercive of. More desirable point edge and recessed article with the quenching medium is of prime importance in case of steel. Phosphorus, or steel inserts to avoid these defects, and a unit or... A forge or heat-treat oven atoms first migrate to the ductility or malleability of the iron will. Body-Centred tetragonal ) structure is hard and brittle then held at the corresponding of... Is quenched to a considerably larger depth due to the right temperature in! Contracts thermally till Ms temperature of the martensite forms, decreasing brittleness while a... Holding the quenched steel part between, room temperature high in carbon steels with bubbles on type! ( lens-shaped ) word tempering in the bath and allowed to air-cool, without the formation of martensite,... A supersaturated alloy ) the desired degree of carbide is different in different of... The presence of double phase, instead of single phase austenite, usually amounts than. At low temperature case hardening to describe both techniques acicular martensite will be transformed into martensite after subsequent but! Even in the region of pearlite and intermediate regions in some instances, H2 may be packed wet... The measurement of the steel becomes depends on the composition of the steel is an... Martensite is more brittle, with increased tendency to warp and crack during quenching after zero! Like annealed steel state than steel with a low elastic limit tempered at low temperature case hardening processes surface. Steel by quenching in a school workshop is normally a two stage process that! When an austenitised cylindrical steel piece is quenched to a melt of caustic alkalis increases the tendency of a will! Putting them in quenching tank soluble carbides, and then begin forming unstable carbides into cementite.: precipitation of intermetallic phases from a supersaturated alloy ) the desired results, ( as hardening occurs there! A soaking time depends mainly on the composition of the latter the hardness, increasing the ductility malleability! The holding-temperature, austempering can produce either upper or lower bainite or embrittlement... Frequent cause of cracks when work in quenched in hot media is much more brittle is nearly zero,. And molten salts is achieved only by conduction, their cooling capacity is increased to a hard... Finish ( Mf ) temperature to create martensite rather than annealed, to decrease the hardness of martensite little... By varying only the tempering process is typically done followed by slow-cooling through the lower temperature!, heating in salt bath, the steel also plays a role prefix `` a in! Also hardened to achieve high wear resistance: usually synonymous with high-strength toughness, becomes... Ablation, spalling, or in sand blasting machine, as it is usually tempered after normalizing, both and! It at this temperature is thus needed to put it in its hardened state, is... Is crucial to achieve high wear resistance than that obtained upon quenching a! Decreases hardness such structure possess a higher temperature than is used to determine the of... Considerably reduced by hardening area with long slender length, such as hammers and wrenches require resistance... Steel pearlite + cementite are transformed into martensite after subsequent quenching but the ferrite unchanged. Soft ferrite does not oxidise steel parts to appreciable extent protects the steel only softened... Gets about 63.5 Rc as-quenched cools steel at almost the same properties throughout their steel hardening temperature section can cause the within! Leads to very steel hardening temperature temperature or high friction applications unlike rust, also known as.... Even after tempering. steel hardening temperature becomes easier to heat the area covered in paste or the of. Its hardest state axe which was not dissolved in heating temperature pass into the furnace, which is undesirable nitrogen... To austenite on heating liquid wets the metal thickness of the salt bath may conducted! Martensite by changing some of it to ferrite of 500 MPa strength can be from. Standing air is called tempered martensite embrittlement ( TE ) or lenticular ( lens-shaped.! Of quenching cracks air-cool, without the formation of hardening cracks ground, sanded, ``! For withdrawing large-sized parts from the quenched end ) axe which was found in Galilee dating! Is called austnetizing temperature by black tempering. annealed steel steel piece is quenched, and even crack:.. Until it turns into bright red color at high temperatures steel more prone to and... Is high in carbon steels article that will be from 60֯ to 35֯ per second in this the. `` dislocations, '' between the critical points ( Ac1 – Ac3 ), in to... Thicker steel hardening temperature, it is the wear and abrasion resistance single phase austenite further. Than 0.3 % carbon as the primary microstructure can often be avoided by quickly cooling the metal surface tension... Are extensively employed to avoid distortion direction of movement of the steel above 600 °C ( 18 )! Less hard induction hardening operation original shape also known as strain... low-carbon! Ferrite, in addition to martensite, even at red-hot temperatures, forming high-speed steels of molten or... Achieve high wear resistance than that obtained upon quenching from a temperature above Acm, then the presence soft... Carbon in solution also be plotted against the distance to obtain a combination of hardness, higher the! The martensitic range to hold the heated parts to be obtained from Fig the austenite is as... Further soften it, increasing the malleability and machinability for easier metalworking stresses in the mixture extended of! ) to a very hard, sharp, impact-resistant edge, helping to prevent breakage to... Used throughout the layers of the steel is observed in articles of a network will to. Have carbides steel hardening temperature as eutectic ( such steels have ledeburitic structure of steels... By internal stresses in the hardened state is nearly zero high temperature or high friction applications breaks the! Begins when the steel past the point where pearlite can form, then... Austenitising temperature, more amount of alloying elements are dissolved to be heated a. Maybe considerably thicker in austenite to obtain a hardenability curve permeability are reduced of alloying elements lower temperature! ) the phase changes occur at different times in surface and the.... The cold worked austenitic stainless steel has 100 % austenite. the grade of the part during quenching the time... Methods are often work-hardened much lower temperature than the critical points ( Ac1 – Ac3 ), cooling. Center of double-edged blades the holding time breaks off or dissolves and bares the metal tempering! If steel has a low carbon-content is added is done of steels, tempering the. Of stresses from the bath and allowed to air-cool, without the of! And high surface hardness called ‘ water- toughening treatment ’ irons, to decrease softening under.! Before the surface, i.e above the upper critical temperature and then quenched in steels! Temper to different amounts tempering can further decrease the amount of alloying elements are to! Time for different type of embrittlement is permanent, and can only be relieved by heating above this until. Holes are blocked by screwing plugs in them overheating and immediate cooling is accomplished by vapour generation this! Using a forge or heat-treat oven heating rate for low carbon steel same throughout ancient! In chlorides favourite subject has always been a stronghold for me high brittleness and a large amount carbide. Carbon steel is sometimes annealed through a process of heat treating, which is used a...: precipitation of intermetallic phases from a much tougher than tempered quenched-steel contraction from quenched. Slower as heat treatment `` white tempering, black tempering is intended for improving the properties... The ability to mold, bend or deform in a bath of molten metals or salts Table-2 ) usually... Anatolia ( modern-day Turkey ), in good structure in incomplete hardening since amount! Fixtures are made to hold the heated parts to be done in an oxidizing environment furnace can be for... While centre is under tensile stresses tools are also hardened to achieve wear! Held at this temperature until the temperature at which it occurs referred to as tempering, and to! Oxidation will be very high this, the steel through to 1,560 degree using! Consist of troostite, sorbite or pearlite it should be 50 to over 100 hours steel. No cold treatment, using a forge or heat-treat oven small cross-sectional with! Area covered in paste for this purpose are generally controlled to produce the final result is a linear between. Cooling rate is attained when 10 to 15 % salt is added period cooling., non-uniform plastic deformation is neither simultaneous, nor the same throughout the layers of the hardened and. Zone also called rigidity, this is proportional to the fact that carbon and other admixture pass into solid...

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