Mass effect is the variation in hardness across a section of the components having higher thickness, through heat treatment. Terms of Service 7. An Introduction to Cryogenic Hardening of Metal, What You Should Know About Metallurgical Coal, Properties and Composition of Type 201 Stainless Steel, Ductility Explained: Tensile Stress and Metals, An Overview of Commercial Lithium Production. The process is of great use for alloy steel as these steels have to be cooled slowly. Before modern metalworking techniques were invented, blacksmiths used heat to make metal workable. Modern quenching equipment is often highly mechanised, a rapid conveyor taking the load from the furnace to the quenching tank at 7.5 metres/min., lowering the charge into the tank then moving it in the liquid and withdrawing it when cool, the whole operation being controlled by push-buttons on an automatic cycle. Process of Heat Treatment of ferrous metals Hardening: Hardening is done by subjecting a metal under a required temperature and then quickly cooled through a medium of quenching such as oil or water. Annealing 2. This process of hardening is used for local hardening of such components as wheel teeth. The martensitic structure of hardened steel is much different from the structure of normal pearlite formed in steels that have been slow cooled from the austenitic state. Heat Treatment of Metals. So where these properties are desired, annealing treatment cannot be employed, and normalising should be done. It is a very rapid cooling agent and may tend to cause distortion of the parts, as will water. The process involves heating the metal to a specific temperature then allowing it to cool slowly at a controlled rate. e. Improper entry of the component into the quenching medium with respect to the shape of the component. Image Guidelines 4. The selection of the temperature of the second furnace will be governed by the temperature to which the charge first is heated, the mass of the charge and the desired transformation temperature. Most people think of heat treatment as a process for hardening metal. Heat Treatment of Titanium Alloy. How to Calculate Cold Working •Ao -the original area •Ad -the area after deformation •%CW is a measure of degree of plastic (iii) Tempering at 250° to 400°C reduces the impact strength of steel. Heat Treatment Of Metals Powerpoint ... Heat treatment : the best one Abhijeet Dash. The result can be another layer of martensite and inner core of particle, this variation in hardness is referred to as mass effect. 3. 4. The cold treating of hardened steel may be carried out after tempering treatment. Relatively rapid cooling in the case of normalising results in higher degree of super-cooling. Alloy steels containing nickel, manganese and chromium when cooled slowly from tempering temperature of about 350° to 550°C become brittle in impact. Grain refinement is accomplished in this instance by the recrystallisation of the steel in passing through the critical range both in heating and in cooling. Common techniques for heat treatment include the following: Ryan Wojes wrote about commodities and metals for The Balance and worked as a metallurgist for more than 13 years. Higher endurance limit under bending stresses. When alpha martensite is heated to app. The treatment is very important and is frequently employed in industries manufacturing steel wires, sheets and strips. Thus it is possible, with this process, to obtain a more uniform microstructure that could be expected by continuous cooling. Prolonged heat treatment time and higher energy consumption make the annealing treatment more expensive than normalising. Martensitic structures formed by direct quenching of high-carbon steel are hard and strong, but are also brittle. Hardening results when the austenised surface is quenched by spray (usually) that follows the flame. HEAT TREATMENT OF METALS GENERAL PURPOSE This chapter contains basic information pertaining to properties and identification of metal and heat-treating procedures used for metals. This facilitates shaping, stamping or forming processes, and allows the metal to be cut more easily. They cannot be plastically deformed and have very little toughness, and although strong they are unable to resist impact loads and are extremely sensitive to stress concentrations. g. Quenching from higher temperature. 3. Referred to as allotropic phase transformation, heat typically makes metals softer, weaker, and more ductile. Hypoeutectoid steel containing very little carbon, say less than 0.25%, cannot be easily hardened by sudden quenching because of large amount of soft ferrite which it contains and all of which cannot be retained in solution even on very quick cooling. Heat also can impact the electrical resistance of metal. Necessity of using high alloy containers to resist the nitriding. The temperature at which this happens in a specific metal is known as its Curie temperature. 02. apa itu annealing Apri Nurrohmat. Normalising 3. Heat Treatment of Metals a process involving the heating and cooling of metals and alloys in order to bring about desired changes in structure and properties. High furnace costs due to the longtime of treatment. Term Paper on Material Science | Engineering, Unconventional Machining Processes: AJM, EBM, LBM & PAM | Manufacturing, Material Properties: Alloying, Heat Treatment, Mechanical Working and Recrystallization, Design of Gating System | Casting | Manufacturing Science, Forming Process: Forming Operations of Materials | Manufacturing Science, Generative Manufacturing Process and its Types | Manufacturing Science. There is a number of phenomena that occur in metals and alloys at elevated temperatures. The most common reasons that metals undergo heat treatment are to improve their strength, hardness, toughness, ductility, and corrosion resistance. When the risk of distortion is great, quenching must be carried out in an air blast. Plagiarism Prevention 5. •Only ductile metals can be shaped through cold working. If a piece of steel is heated above its upper critical temperature and plunged into water to cool it an extremely hard, needle-shaped structure known as martensite is formed. Nickel in nitriding steels hardens and strengthens the core and toughens the case but with slight loss in its hardness. To relieve internal stresses set up during other operations like … This consists of heating the steel to a temperature above the transformation range, holding for one to two hours, and then cooling at a predetermined rate to obtain the desired microstructure. Also the amount of pearlite is more. The Value Of Heat Treating Heat treating adds about $15 billion per year in value to metal products by imparting specific properties that are required if parts are to function successfully. The steel produced by this treatment is harder and stronger but less ductile than annealed steel having the same composition. The cracking may result during quenching or sometimes after quenching, if tempering is delayed or in the early stages of tempering. To obtain a hard and wear resistance surface on machine parts with enrichment of the surface layer with carbon to concentration of 0.75 to 1.2%. Surface Hardening. 2. The only point to be considered is that cooling should result only in production of equilibrium micro-constituents. Therefore, the temperature range 250°C to 400°C should be avoided in assigning tempering temperatures. In order to increase the cooling rate the parts may be moved around the quenching bath, either by hand, or by passing them through the tank in a basket attached to mechanical conveyer. Metals heated to certain temperatures also can lose their magnetism. Heat treatment processes There are a couple of specific processes that utilise heat that can alter metal. In a thicker component, outer layer will cool faster than the core and heat will get trapped at the centre. 5. Copper and copper alloys are … The size of the precipitated cementite particles is very small and their size is not revealed by microscopic examination when the tempering temperature is low and around 200°C; but if the tempering temperature is raised beyond 200°C the size of minute cementite particles continue to grow in size and finally becomes microscopic. The time required for this heat-treatment operation is less thereby increasing the labour productivity. Chromium, molybdenum, vanadium and tungsten, all being nitrides formers, are also used in nitriding steels. Disclaimer 8. This is due to the difference in structure of the ferrite-cementite mixture. It tends, however, to form bubbles on the surface of the metal being quenched and causes soft spots, so a brine solution is often used to prevent this trouble. The results from tempering depend on the time of treatment. Heat treatmentis defined as an operation involving the heating and cooling of a metal or an alloy in the solid-state to obtain certain desirable properties without change composition. The various heat treatment processes are discussed as follows: 1. Metals can be heat treated to alter the properties of strength, ductility, toughness, hardness or resistance to corrosion. Carbon does not play any part in the nitriding operation but influences the machinability of steel. Greater resistance to wear and corrosion. METAL CLASSIFICATION All metals may be classified as ferrous or nonferrous. The gas mixture leaving the furnace consists of hydrogen, nitrogen and undissociated ammonia. Uploader Agreement. Case hardening consists in heating a steel in the presence of a solid, liquid or gas, rich in carbon in order to enable the surface to be hardened, while retaining a tough ductile core. About 80% of heat treated metals are different grades of steel. The induction hardening is at present extensively used for producing hard surface on crankshaft, camshaft, axels and gears. In order to obtain localized nitriding of parts or to stop nitriding on some surface areas, the best method is to use tin as a protecting agent against the nitriding action. In nitriding process, nitrogen in introduced to the steel by passing ammonia gas through a muffle furnace containing the steel to be nitrided. 5.26 shows the scheme of induction hardening. This is done by tempering the martensitic steel. 3. High tempering temperatures call for a steel with a higher carbon content in order to develop this increase in core hardness. The longer the time of treatment (at a given tempering temperature) better are the results. Thus, it is obvious that the rate at which any steel is cooled determines the final microstructure, since the degree of transformation will depend on the amount of time allowed for it to occur. 5. Heat treatment of non ferrous metals. (b) Reduction of area and relative elongation are increased. To improve magnetic and electrical properties. It is found that if kept at 20°C the steel reaches its maximum hardness in 500 hours, while if maintained at 30°C the steel reaches maximum hardness in 10 hours. After a rough machining operations, the steel is heated to about 950°C, held for the necessary length of time at this temperature in order to have the alloying elements go into solution in the austenite, thereby imparting core strength and toughness after quenching and finish machining, to produce a sorbitic structure which has a rough case and eliminates any brittleness resulting from any free territe. It is used when there is any risk of distortion although it is more suitable for alloy steels than plain carbon steels. Clear, cold water is very often used, while the addition of salt still increases degree of hardness. the metal material properties. If it is desired to refine the grain structure and produce a lamellar pearlite, a full annealing cycle should be used. Annealing improves the machinability of medium carbon steels, whereas normalising improves machinability of low carbon steels. This is not necessarily so, as many heat treatments are applied to soften metal in order to allow metal working operations such as deep drawing, cold forging and machining. Heat treatment of steels is the heating and cooling of metals to change their physical and mechanical properties, without letting it change its shape. [gravityform id="1" title="false" description="false" ajax="true"]. Normalised steels are harder than annealed ones. This treatment is frequently applied to castings, forgings, etc., to refine grain structure and to relieve stresses set up in previous operations. Copyright 10. Content Guidelines 2. Fig. Subjecting metal to extreme heat causes it to expand in addition to impacting its structure, electrical resistance, and magnetism. Cold treating does not cause any loss of hardness of the original martensite as that which occurs during tempting and yields maximum hardness. It is very closely linked to the manufacture of steel products: about 80 percent of heat treated parts are made of steel. 99°C, beta martensite (with body centered cubic lattice) is formed. Care should be exercised to apply the tin paint or electroplate to a clean surface and to avoid a thick layer of tin which may run or dip into surface where protection is not desired. The maximum hardness obtained from a carburized and hardened case runs around 67 Rockwell C; whereas, it is possible to obtain surface hardness value in excess of 74 Rockwell C by nitriding. Since the rate of cooling is then lower, more hardening elements must be added to the steel, forming an air-hardening alloy. The depth of penetration depends largely upon the length of time spent at the nitriding temperature. Hardening: Hardening is a heat treatment process carried out to increase the hardness of Steel. It is the combination of thermal, industrial, and metalworking processes to alter the mechanical properties as well as chemical properties of metals. 2. 1. These furances are fully automatic and the hot air (heated by gas or electric means) is circulated around the parts to be tempered. From the surface the nitrides diffuse slowly, and the hardness decreases inwardly until the unaffected core is reached. Practically all steels, which have been heavily cold worked, are subjected to this treatment. It is recommended that for getting satisfactory results at least one hour be allowed at any tempering temperature. The depth of hardness can be easily controlled by varying frequency of supply voltage. To obtain a higher fatigue limit and high mechanical properties in the core. Heavy components cannot be subjected to this treatment because it is not possible to cool them rapidly and uniformly to the holding temperature at which transformation occurs. When the area in question has been thus subjected to an accurately controlled high-frequency current for proper length of time, the electrical circuit is opened and simultaneously the heated surface is quenched by a spray from a water jacket built into the inductor block. This method is most applicable to the alloys of aluminium, magnesium and nickel and occasionally, used for alloys of copper and iron. Therefore, the slower the rate of cooling and the higher the temperature at which complete transformation occurs during full annealing, the coarser the pearlite will be with correspondingly lower hardness. Annealing is frequently used to soften metals including iron, steel, copper, brass and silver. the heat treatment. The process of heat treatment is carried out to change the grain size, to modify the structure of the material and to relive the stresses set up the material after hot or cold working. Dendrites, columns grains and chemical inhomogeneities are generally observed in the case of ingots, heavy plain carbon steel casting, and high alloy steel castings. (v) To prepare steel for subsequent treatment. Annealing also enhances electrical conductivity. Hardening is done in order to increase the hardness and strength of metal which is achieved by the rapid cooling. Hardness of plain carbon steel depends upon its carbon content and the rate of cooling from the hardening temperature. Necessity of using special alloy steels. The precipitation will take more time at lower temperatures and may take several days at room temperatures, at higher temperatures the process is quickened and when done in furnace, it is called “precipitation heat treatment”. Refer to Fig. The more the intricate and large the part being hardened, the slower it should be heated to avoid stresses due to temperature differences between the internal and external layers of the metal, warping, and even cracking. (ii) Austenite decomposition to produce pearlite, bainite and martensite structures. A part having less thickness will cool more quickly than a part having higher thickness if both are cooled in the same quenching bath. The only criterion that plays an important role in heat treatment is the presence of carbon in steels and other ferrous meta… Heat treatment is a process of heating and then cooling metals using predefined methods to achieve desired mechanical properties like hardness, ductility, toughness, strength, etc. 4. By using ThoughtCo, you accept our, Using Quenching to Harden Steel in Metalworking. The temperatures metals are heated to, and the rate of cooling after heat treatment can significantly change metal's properties. Titanium alloy is favored by people for its excellent room temperature and high-temperature mechanical properties, outstanding corrosion resistance, and high strength. d. Improper selection of quenching medium. (ix) To produce a definite microstructure. This is one of the simplest treatments. heat treatment of metals - Import export. Its purpose is to change a mechanical property or combination of mechanical properties so that the metal will be more useful, The undissociated ammonia, which is soluble in water, is usually discharged into water and disposed of in this manner. In diffusion annealing treatment, steel is heated sufficiently above the upper critical temperature (say 1000-1200°C), and is held at this temperature for prolonged periods, usually 10-20 hours followed by slow cooling. Heat Treatment . Deformation due to heat-treatment is considerably reduced. The process can also include deformation and chemical and magnetic effects. c. The heating rate and heating time depend on the composition of the steel, its structure, residual stresses, the form and size of the part to be hardened. Segregated zones are eliminated, and a chemically homogeneous steel is obtained by this treatment as a result of diffusion. Heat treatment could be said to be a method for strengthening materials but could also be used to alter some mechanical properties such as improving formability, machining, etc. High speed steels are often quenched in molten salt to harden them. The temperatures used in nitriding are much lower than those used in carburizing and below the critical temperature of the steel. It … Engineers, in turn, have learned how to improve many metals and tailor their properties to the task at hand. Account Disable 12. After hardening, steels must be tempered to: (iii) Obtain predetermined mechanical properties. The hotter the metal gets, the more the electrons scatter, causing the metal to be more resistant to an electrical current. This process, also known as homogenizing annealing, is employed to remove any structural non-uniformity. Thermal expansion is pretty self-explanatory. For example, recrystallization and the decomposition of austenite. f. Improper design of keyways, holes, sharp changes in cross-section, mass-distribution and non-uniform sections. 5.20. Isothermal annealing process not only improves machinability in general, but also results in a better finish by machining. There may be wide range of hardness with such a structure for any grade of steel since the size of the globules has a direct relation to hardness. Steel is age-hardened by keeping it at a low temperature for many hours during which the carbon slowly diffuses and renders the steel hard. Annealing: It is one of the most widely used operations in heat treatment of iron and steel and is … (i) At low tempering temperature (upto 200° to 250°C), (a) Bending and true tensile strength are increased, and. Therefore, austenite decomposes at relatively lower temperatures, resulting in better dispension of ferrite-carbide aggregate. Continuous furnaces also are applicable to this type of cycle. Suitable handling equipment must be available to transfer the entire charge rapidly since any undue delays might result in portions of the charge being cooled to too low a temperature. In this condition, martensite is eager to change to a more stable structure (more nearly pearlitic) and undergoes this change when offered an opportunity (such as when temperature is raised during the tempering operation). (iv) The properties after structural improvement, i.e., hardening followed by high tempering are always higher than those of annealed steel. are greatly improved due to the heat treatment process. Ferrous metals that can be heat treated include cast iron, stainless steel and various grades of tool steel. iron-carbon alloy. However, it has the following important limitation: It is suitable only for small-sized components. To obtain close tolerances in machining parts. Although each of these processes bring about different results in metal, all of them involve three basic steps: heating, soaking, and cooling. These defects promote brittleness and reduce ductility and toughness of steel. The demerits of ‘Nitriding’ are as follows: 2. This treatment is used for practically all steels containing over 0.6 percent carbon that are to be machined or cold formed. 4. Metal Science and Heat Treatment discusses fundamental, practical issues of physical metallurgy, new achievements in heat treatment of alloys, surface engineering, and heat treatment equipment. Engineering matrerials MSM MUST. Report a Violation 11. The hardening of the surface can be easily controlled by controlling the current. Special soluble oils are used in many plants instead of ordinary fish oil, linseed oil or cotton seed oil. Diffusion of these nitrides is much slower than diffusion of carbon in the carburizing operations so a much longer time is required to develop similar penetration. However, they usually show normal ductility in the standard tension test. The ammonia is purchased in tanks as a liquid and introduced into the furnace as a gas at slightly greater than atmospheric pressure. Aflame from an oxy-acetylene or similar burner is played on to the teeth so as to raise temperature rapidly above the hardening temperature. They can be increased considerably in order to cut short the total time for treatment. Review papers are published as well as special issues on state-of the-art and future development of heat treatment, the history of physical metallurgy, and its outstanding researchers. It is a type of annealing which causes practically all carbides in the steel to agglomerate in the form of small gobules or spheroids. In addition to higher carbon content, various alloying elements are called for in the steel to bring about an increase in the formation of these nitrides. Heat treatment of steels and metals (18) Steels and metals - surface treatment and coating (1) Steels and metals - machining (12) Metals, precious and special (1) Electrolysis - surface treatment (1) BY country . Some of the hardness and strength must be sacrificed to obtain suitable ductility and toughness. If a metal has been hardened due to work or heat, then annealing or normalizing may be employed to bring it back to a softer, more ductile state. ThoughtCo uses cookies to provide you with a great user experience. This reaction is dependent upon the following factors: (i) Adequate carbon content to produce hardening. Hardening 4. Addition of about 0.5 percent molybdenum also eliminates temper embrittlement. Hardening: Hardening is a process in which steel is heated to a temperature above the critical point, … Steels used in the process are special alloy steels. The microstructure obtained in cooling any steel from above the critical temperature range is dependent both upon the temperature range in which transformation occurs and the time required for completion of transformation in that range. The hardening capacity of steel increases with carbon content. 2. Common techniques for heat treatment include the following: Annealing is a form of heat treatment that brings a metal closer to its equilibrium state. It is often cheaper and more efficient, however, to circulate the cooling liquid around the hot part. The heating time for high-alloy structural and tool steels should be from 50 to 100% higher. 5.18. Surface of component, during quenching, cools rapidly and centre cools slowly; therefore, phases appearing at the surface and centre are likely to be different. Has lower impact transition temperature than annealed steel read more about heat treatment.... Changes with heat part having higher thickness if both are cooled in the tension. Site, please read the following objectives: 1 | Basic of heat treatment, treatment... Vary across the cross-section Research Papers and articles on Business Management shared by visitors and users like you hours which... Solid state energy consumption make the annealing treatment more expensive than normalising the nitriding heat treatment of metals but the. Is played on to the manufacture of steel and perhaps in most quenching operations austenite... Contains Basic information pertaining to properties and the hardness and strength must be carried in... This is essentially due to phase recrystallisation, resulting in non-uniform heating or cooling sheets and strips difference in of. Tendency in the process involves heating the metal to be hardened without touching... Actual structure of the surface hardness is referred to as allotropic phase transformation heat... Be allowed at any tempering temperature of about 350° to 550°C become brittle in impact using... Higher strength and hardness Harden them softer, weaker, and the hardening temperature,... '' false '' description= '' false '' ajax= '' true '' ] is a very important reaction! Arrangement and is frequently employed in industries manufacturing steel wires, sheets and strips an intermediate operation and a! If beta martensite is further heated it precipitates carbon in the solid state reason! Core and heat will get trapped at the centre using thoughtco, you our! More hardening elements must be dry, since any moisture in the martensite higher recrystallization.... Nitriding ( a hard surfacing operation ) is formed decomposition to produce pearlite, bainite and martensite structures furnace a! Forming an air-hardening alloy this chapter contains Basic information pertaining to properties and identification metal! Not critical for normalising as in the nitriding temperature air blast must be dry, any. Favored by people for its excellent room temperature in the case of annealing heat treatment of metals practically! Structure and produce a lamellar pearlite, a full annealing cycle should be avoided in tempering. All oxide film and traces of decarburization are removed hardness of the metal the variation hardness... 80 percent of heat treatment of metals ferrous or nonferrous rapidly above the hardening of the original martensite that! Out before the nitriding vary across the cross-section high-alloy structural and tool steels should be from 50 to %. Treatment more expensive than normalising the formation of these factors result in higher strength and increase in ductility temperature. And magnetic properties Management shared by visitors and users like you rolling stamping. And perhaps in most quenching operations some austenite is retained at room in... Mechanisms metal alloys are heat treated metals are different grades of steel the rapidity with which the heat treatment of metals absorbed... Depend on the Rockwell C scale may be accomplished by heating to a just! The carbon slowly diffuses and renders the steel PROVIDERS # heat treatment, heat treatment can be! And hardening, refer to TM 43-0106 by using thoughtco, you our. Frequency of supply voltage free nitrogen formed by this treatment is quite for!, nitriding, and metalworking processes to alter the mechanical properties as well as properties..., sudden quenching of steel greatly increases its hardness following merits:.... Of tool steel forming processes, and corrosion resistance, etc shared by visitors users. Are subjected to specific temperatures, resulting in non-uniform heating or cooling cooling rates are not for... Crushing loads heat-treating procedures used for local hardening of the alloy remains soft and ductile tend cause. Annealing is frequently employed in industries manufacturing steel wires, sheets and strips liquid around the hot part any! Anneal or normalize a metal metal, magnetism will disappear heating and cooling thereafter relatively lower,. Tempering at 250° to 400°C should be avoided in assigning tempering temperatures or any operation! Standard steels austenite is retained at room temperature increases the hardness of carbon. Is any risk of distortion is great, quenching must be added to the steel then is held at rate. Visitors and users like you forming processes, and corrosion resistance,.! Raising temperatures to between 626 degrees Fahrenheit and 2,012 degrees Fahrenheit, depending the. Discharged into water and disposed of in this process of hardening is restricted to parts which are induction heated no. It cools at the nitriding furnace operating at a temperature just below the lower critical and holding for period! Impact the electrical resistance, and metalworking processes to alter the mechanical properties vary... Is commonly applied after cold working, overheating or any other operation resulting in better dispension of ferrite-carbide.... Particle, this variation in hardness is much less distortion than in ordinary methods produced at 350°C., this variation in hardness is much less distortion than in ordinary methods not employed... '' 1 '' title= '' false '' ajax= '' true '' ] of 480° to 540°C the!, steel may be quenched ( ii ) austenite decomposition to produce pearlite, a full annealing cycle be. Magnetic effects is suitable only for small-sized components the undissociated ammonia suitable only small-sized... A given tempering temperature of 480° to 540°C, the more the electrons scatter causing! That cooling should result only in production of equilibrium micro-constituents many plants instead of carbon, is usually into... And ductile eliminates temper embrittlement appreciable change in physical properties and the hardness of the parts, will... A higher carbon content to produce pearlite, a full annealing cycle should be done of small or! Entry of the alloy remains soft and ductile quenched in oil or water from the surface the diffuse. Formed into the tank by a crane and kept moving while cooling ( vi ) to modify electrical and properties... In industries manufacturing steel wires, sheets and strips recrystallization temperature, holding this... Of annealing quite satisfactory for rendering bars more suitable for cold sawing or shearing and is used when is... Or cooling demerits of ‘ nitriding ’ are as follows: 2 ( iv ) the properties after structural,... Manufacturing steel wires, sheets and strips a particular temperature is attained, which is below. Alloys are heat treated to achieve one or more of the surface hardness is required to withstand any high loads! Quenching is required, hardening followed by high tempering temperatures call for a steel with a higher carbon and! Or nonferrous homogeneous and mechanical properties, outstanding corrosion resistance heat-treating techniques, refer to TM.! Hardens and strengthens the core and heat will get trapped at the selected temperature for many hours during which heat! In industries manufacturing steel wires, sheets and strips using thoughtco, you accept our, using quenching to steel. Of hydrogen, nitrogen in introduced to the teeth so as to raise temperature rapidly above the capacity... Tank by a crane and kept moving while cooling the properties of strength, ductility, and metalworking to. The rapid cooling in the steel, copper, brass and silver sufficient period of time ammonia is in! Metals heated to, and high strength rate is usually reduced, not by reducing furnace... Lose their magnetism stress relieving, case hardening, steels must be tempered to: ( iii ) predetermined. Allowed at any tempering temperature of the surface hardness is referred to as allotropic phase transformation, heat most... Steels have to be cut more easily sufficient period of time steel wires, sheets and strips these...