It determines in the work-piece a tough core with tensile residual stresses and a hard surface layer with compressive stress, which have proved to be very effective in extending the component fatigue life and wear resistance. Table 8.13 gives the various common power sources used for induction-hardening: Motor-generate power source is used for frequencies up to 10000 c/s. It is sometimes the case that workpiece characteristics determine which method must be used. Frequently Asked Questions About The Induction Hardening Process with examples of Induction Heating Applications, The National Metals Centre offering Design, Modeling & Simulation (DMS) technologies relating to Induction Hardening processes - NAMTEC, https://en.wikipedia.org/w/index.php?title=Induction_hardening&oldid=970885728, Creative Commons Attribution-ShareAlike License, fast process, no holding time is required, hence more production rate, This page was last edited on 2 August 2020, at 23:47. The presence of alloy carbides in these steels, which are relatively more difficult to dissolve in austenite, will greatly affect the induction-hardening response of these steels. This magnetic field induces eddy currents (and hysteresis currents) in the metal bar. Heat is applied to the part being hardened, using an oxy- acetylene (or similar gas) flame on the surface of the steel being hardened and heating the surface above the upper critical temperature before quenching the steel in a spray of water. , Faraday concluded that an electric current can be produced by a changing magnetic field. It was already understood that the depth of current penetration in steel was a function of its magnetic permeability, resistivity and the frequency of the applied field. As there was no physical connection between the primary and secondary windings, the emf in the secondary coil was said to be induced and so Faraday's law of induction was born. Closely following the heating coil, a water quench jacket (omitted for clarity) moves along the shaft, quenching the austenite material and providing a hard, martensitic case. However, if the alloying elements are added in a steel to derive some other property, but the steel is to be induction-hardened, then it is advisable to use a relatively higher austenitising temperature in order to obtain a better hardening response. Case and surface-hardening methods such as carburising, nitriding, carbonitriding, cyaniding, induction and flame- hardening, result in a ‘depth of case’ which is substantially harder than the inside section of the component called the ‘core’. The effectiveness of these treatments depends both on surface materials properties modification and on the introduction of residual stress. Gears can be induction hardened by any of the methods described in Fig. Induction hardening, case-depth profile, dynamic response, three-dimensional laser Doppler vibrometer, curvature change factor, response surface methodology Date received: 9 April 2014; accepted: 24 J uly 2014 Introduction Surface/through hardening is most essentialfor improv-ing wear resistance and strength of steel components. For plain carbon steels, with suitable prior structure, temperatures about 30° more than the conventional hardening temperatures are suitable. higher case depth in hardening of shafts . After experimentally optimizing the induction hardening process parameters for the manufacturing of the specimens, the final heat treatment depth reveals an almost identical value of about 3 mm compared to the crankshaft. In double hardening, a variation could be made in which the first austenitising temperature could be at higher temperature to obtain better carbon (and some alloying elements) diffusion and more uniform distribution. The above table is purely illustrative, good results can be obtained outside these ranges by balancing power densities, frequency and other practical considerations including cost which may influence the final selection, heat time and coil width. As the induction heating takes place, the heat is rapidly conducted from the surface to the interior. It can be seen from the above table that the selection of the correct equipment for any application can be extremely complex as more than one combination of power, frequency and speed can be used for a given result. Now, based on this actual result of depth of hardening, and how close this is to the desired depth, the induction-hardening factors are adjusted to obtain the exact depth. All process parameters were the same for each trial. Since induction hardening does not change the chemical composition of steel, the steel grade must have sufficient carbon and alloy content and be capable of achieving a certain surface hardness, case depth, and core strength. , Induction heating is a non contact heating process which uses the principle of electromagnetic induction to produce heat inside the surface layer of a work-piece. al. Optimization of Process Parameters in Induction Hardening of 41Cr4 Steel… 85 problem in manufacturing industry. A large alternating current is driven through a coil, generating a very intense and rapidly changing magnetic field in the space within. As well as the power density and frequency, the time the material is heated for will influence the depth to which the heat will flow by conduction. The heated component can be dropped from the fixture in the quenching liquid, or mechanically lifted to be immersed in the quenching liquid. The power source is then adjusted for the frequency and the time relay for the chosen time. A procedure for reading effective case depth may be established by correlating … For case hardened parts the specification should have a tolerance of at least ±0.005 in (0.13 mm). The workpiece weight is also the same, and the 8-ton load corresponds to 2,667 shafts. Induction hardening covers a series of thermal heat treatment processes where a direct hardening metal, usually steel or cast iron, is heated, usually locally, by Eddy Currents generated by a water cooled copper encircling coil or shaped inductor through which alternating current is passed, followed by rapid cooling/quenching using air blast, polymer mixes or water. To help you develop accurate parts and specify reasonable tolerances for hardness and case depth results, Zion Industries has created the following guidelines for the maximum surface hardness achievable using induction hardening. A carbon content of 0.3–0.6 wt% C is needed for this type of hardening. Copyright 10. Alloy steels used for automotive valves, bearings etc. A transfer function was generated from the calibration data. The quenched metal undergoes a martensitic transformation, increasing the hardness and brittleness of the part. (Fig. Wear resistance behavior of induction hardened parts depends on hardening depth and the magnitude and distribution of residual compressive stress in … Only a limited type of steels could be induction-hardened. Induction hardening is a type of surface hardening in which a metal part is induction-heated and then quenched. , Early last century the principles were explored as a means to melt steel, and the motor generator was developed to provide the power required for the induction furnace. 8.58 (b). UltraGlow® Induction Hardening is a form of heat treatment in which a steel or cast iron part is heated by electromagnetic induction, immediately followed by rapid cooling (quenching). Typically plain carbon steels give case depths of 1-3 mm and alloy steels 3-12 mm depending on the process. According to literature, induction hardening results (depth of the hardened layer, residual stress distribution…) are affected by material, hardening process, also induction machine design-related parameters. The depth of hardened layer to be obtained by induction heating depends on the working conditions of the components. With the aid of Maxwell’s equations it can be shown that the current density decreases exponentially with depth. Fig. i.e. Induction hardened case depth plays a very important part in determining the static and fatigue properties of shafts. Plagiarism Prevention 5. Induction hardening depth at fillet of crankshaft (left) and microstructure in surface-hardened layer (right) Full size image. i. 8.67 a). 8.63 (a) illustrates the effect of initial microstructure during induction-hardening a AISI 1070 steel. In order to select the correct power supply it is first necessary to calculate the surface area of the component to be heated. Finished bores on gears, sprockets and wheels Distortion of the bore is basically determined by the wall thickness. Account Disable 12. Due to space limitation, coverage is necessarily limited in this article. Larger depths of hardening can be achieved by allowing the induction heat developed in the surface layer to be further penetrated into the material by means of conduction in case of a delayed heating. The following expression roughly gives depth of heating dependent on the frequency: In practice, high frequency current is used for shallow hardening depths, whereas lower frequency current is used for deeper depths, with appropriate power density, and the time requirements to be experimentally determined. Modern techniques typically use finite element analysis and Computer-aided manufacturing techniques, however as with all such methods a thorough working knowledge of the induction heating process is still required. Types of Induction Coils for Induction-Hardening of Steels: The coils, also called inductors are made of copper tubes and are cooled during operation by internal water flow as these too get heated up by electric current as well as by radiation from the heated steel. UltraGlow® Induction Hardening is a form of heat treatment in which a steel or cast iron part is heated by electromagnetic induction, immediately followed by rapid cooling (quenching). Spatial Manipulation Again, it’s simply a matter of applying the electrical energy in a directed manner that puts this desirable work feature in the induction hardening win column. Terms of Service 7. With a conventional method (or if we induction hardened the entire length for that matter), there would be significantly more warpage. Fig. Australian Standard AS2028-1977 “Methods for the Measurement of Depth of Hardening in Flame and Induction Hardened Steel Products” provides the following basic but important definitions: Case A surface layer having a higher hardness than the core (such differences arise from micrographic changes which occur as a result of heating, by flame or induction methods, and quenching). To help you develop accurate parts and specify reasonable tolerances for hardness and case depth results, Zion Industries has created the following guidelines for the maximum surface hardness achievable using induction hardening. In alloy steels, the response to induction hardening treatment is further effected by the presence Of carbide forming elements, like Cr, Mo, V, W, Nb, etc. 8.60 could be used. c. Cheaper steels could be used as better properties could be developed. In induction-hardening as well as in conventional hardening, martensitic hardening is aimed and performed, but in induction heating, the austenitising time is inherently very small (few seconds compared to 1/2-2 hours), but because of very rapid heating rates during continuous heating (in induction heating), the Ac1 and Ac3 temperatures are raised and austenite is seen to form in a fraction of second at these raised temperatures. Induction hardening of steel components improves the resistance to wear by changing and microstructure of the surface region. Of the heating inductor can be combined with the spray into one unit, so that the spray ring itself also acts as the inductor (Fig. Steels suitable for case hardening have a carbon content of approximately 0.1-0.3% weight percent. Image Guidelines 4. By quenching this heated layer in water, oil, or a polymer based quench, the surface layer is altered to form a martensitic structure which is harder than the base metal. , A widely used process for the surface hardening of steel. a. Methods 5. Fig. If induction-hardened parts are to be given grinding treatment, then tempering may be done at 150°-160°C to avoid cracks during grinding. Example 2: Induction Hardening of Quenched-and-Tempered Steel (42CrMo4) The case-hardening depth is approximately 2 mm and the hardness is 57-62 HRC by single-shot hardening. Generally, the larger the depth and diameter of the material being heated, the lower the frequency required. Introduction to Induction-Hardening 2. By this method, it is possible to obtain differential hardness in a component. That is why, while designing a coil for an irregularly shaped component, care should be taken that portions closest to the coil will usually be heated at a very fast rate. Induction hardening is a hardening process in which the surface layer can be partially hardened by a local electric heating to austenitizing temperature via electromagnetic fields, by means of inductors and faster cooling down with water, up to a defined depth. Induction hardening however, can easily go … This is normally obtained from medium frequency current. 8.68 (b) illustrates an example where progressive hardening is done but the mass of the component being large compared to volume of the induction hardened part, so that air cooling, or remaining part acts as quenching medium. Prohibited Content 3. The darker periphery of a typical round plate, as shown in Figure 1(a), shows the ECD of a hardened sample. This creates a “case” of martensite on the surface. Hardening of Tooth Tips by Single-Shot Hardening Method: The spin-hardening used is simple but is used up to module 3, using high frequency current, and up to module 5, using intermediate frequency current. The more carbon is inside an area of the workpiece, the more successful the hardening in that area. Figure 2 shows examples of some induction hardening patterns. Before uploading and sharing your knowledge on this site, please read the following pages: 1. For single shot applications the total area to be heated needs to be calculated. ... Conversely, the adjustment of the electromagnetic frequency ensures precise control of hardening depth, so repeatable results are much easier to achieve. In the final heating stage, when the steel becomes nonmagnetic with significantly increased current penetration depth δsteel and becomes substantially more ductile, it is beneficial to use a higher frequency. Quenched and tempered state attains maximum hardened case depth on induction hardening under similar conditions. The additional penetration due to this heat conduction is given by: dx = depth of heating in mm (due to conduction). If the part is to be ground after heat treatment, the case depth is assumed to be after grinding. Various probes were designed and evaluated. Normalised state also shows this but to a lesser extent. Induction heating systems for hardening are available in a variety of different operating frequencies typically from 1 kHz to 400 kHz. The surface is heated using a high-frequency AC current up to the austenitic phase (fcc) and then quenched. With inductive hardening, products up to 76 HRc can be hardened (depending on the type of material). But when high frequency alternating current is passed through this coil, highly concentrated varying magnetic field is setup. Flame or Induction Hardening: 4340 hardened and tempered bar can be further surface hardened by either the flame or induction hardening methods resulting in a case hardness in excess of Rc 50. Traditionally this was done using a series of graphs, complex empirical calculations and experience. Distortion is low. This normally needs valve-generator set for high frequency current. Time is then fixed for an arbitrary period (usually 5-10 seconds) based on previous experience. The parts to be heat treated are placed inside a water cooled … According to literature, induction hardening results (depth of the hardened layer, residual stress distribution…) are affected by material, hardening process, also induction machine design-related parameters. Tooth-Gap Hardening (Progressive Hardening): This method leads to improvement in wear resistance, bending and fatigue strength. During surface layer induction hardening, a copper coil charged with alternating current and adapted to the work piece is responsible for heating up the component. This magnetic field persists even if a metal bar (a conducting material) is inserted in the coil, as illustrated in Fig. In traverse hardening systems the work piece is passed through the induction coil progressively and a following quench spray or ring is used. A copper coil carrying a significant level of alternating current is placed near (not touching) the part. It is many times not feasible to heat treat a component to obtain a desired microstructure before induction-hardening is done. c. Each shape of component requires inductor to be designed for it, and some shapes thus become difficult to be induction-hardened. Depth of hardness is easily controlled. The component is normally held in position in a rotating chuck. The depth of hardening is then determined, say by metallographic method. Induction is a no-contact process that quickly produces intense, localized and controllable heat. Gregory A. Fett * Dana Corp. Maumee, Ohio *Member of ASM International and member, ASM Heat Treating Society his article updates work origi-nally published in February 1985 Metal Progress, which … By placing a conductive material into a strong alternating magnetic field, electric current can be made to flow in the material thereby creating heat due to the I2R losses in the material. Induction heating is a non contact heating process which uses the principle of electromagnetic induction to produce heat inside the surface layer of a work-piece. Content Filtration 6. In magnetic materials, further heat is generated below the curie point due to hysteresis losses. without the rotation of the part as illustrated in Fig. This method thus improves the wear resistance as well as bending strength of the tooth. Automobile and machine tool industries, also commonly require such range of depth for parts. For power output normally required, around 50 kW, copper tubing of internal diameter of around 5 mm is used. There are two alternative methods of induction hardening: conventional “scanning hardening” and the less common “single-shot hardening.” This article looks at the induction hardening process and discusses these options. The Fig. Other parts may be tempered to required hardness values. This creates a moving band of heat which when quenched creates the hardened surface layer. This rotation gives greatest possible degree of uniformity of healing in depth and width. The part has to be car… Also, the normalised state is easily austenitised than the annealed state. Classification of Aluminium Alloys | Metallurgy, 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, Types of Induction Coils for Induction-Hardening, Metallurgical Control in Induction-Hardening, Advantages and Disadvantages of Induction-Hardening. A procedure for reading effective case depth may be established by correlating microstructures with a hardness traverse method. ii. , Induction surface hardened low alloyed medium carbon steels are widely used for critical automotive and machine applications which require high wear resistance. g. Because of finer martensite, higher hardness can be obtained. Due to space limitation, coverage is necessarily limited in this article. The need for rapid easily automated systems led to massive advances in the understanding and use of the induction hardening process and by the late 1950s many systems using motor generators and thermionic emission triode oscillators were in regular use in a vast array of industries. Low-alloy and medium-carbon steels with 0.4 to 0.55% C (e.g., SAE 1040, 15B41, 4140, 4340, 4150, 1552) are commonly used in induction gear hardening. Induction hardening is a form of heat treatment in which a metal part with sufficient carbon content is heated in the induction field and then rapidly cooled. For rolls used in cold- rolling, depths of 10 mm, or more are suitable and is obtainable from low frequency current (2500-150 c/s) with optimum frequency of 500 c/s and power input of 0.1 kW/cm2. In addition the ability to use coils which can create longitudinal current flow in the component rather than diametric flow can be an advantage with certain complex geometry. 8.68. The heating rate in the temperature range of phase transformation A1 to A3 for hypoeutectoid steel is about 30 to 300°C/s. However in practice many selections are immediately obvious based on previous experience and practicality. By varying speed and power it is possible to create a shaft which is hardened along its whole length or just in specific areas and also to harden shafts with steps in diameter or splines. The main consideration in selecting proper operating conditions, i.e., the power, time and frequency for a given required depth of hardening is that the surface should not get overheated by the time the austenite is obtained in the required depth, or that the heating is not too slow such that the material is heated to a depth larger than specified in the time the proper austenitising temperature is reached. This magnetic field in turn induces eddy currents in the surface layer of the metallic component, which result in local heating up. The depth of hardening below the base of the spline should at least be equal to the height of the spline ribs. Types of Induction Coils 4. Deeper case depth: The case for conventional case hardening rarely exceeds 3mm due to the cycle duration (can take days to achieve deeper cases). Induction hardening is a surface hardening technique which uses induction coils to provide a very rapid means of heating the metal, which is then cooled rapidly, generally using water. Fig. This increases both the hardness and brittleness of the part. Special measures are taken to reduce the eddy currents to minimum level in transformers). Higher frequencies are obtained with valve-generators. 3. Induction Hardening Machines & Equipment. Single-Shot Spin Hardening of Complete Tooth: Here also, the gear rotates and all gear teeth are heated and hardened at once. The method is used for gears with modules up to 5. Monitoring case depth in steel components is critical for quality control of both new and remanufactured products. Spur Gear, Helical Gear, Bevel Gear, Rack, Pinion, Worm Gear, Worm Ring Gear,Shaft, Gear Casing, Gear Coupling, Infernal Gear External Gear etc. If the component has rotational symmetry, i.e., is circular like a gear, the component may also rotate during heating and, if possible during cooling in the quenching bath to avoid soft spots. The process is applicable for electrically conductive magnetic materials such as steel. Often the use of ferrite or laminated loading materials is required to influence the magnetic field concentrations in given areas thereby to refine the heat pattern produced. This is used for modules ≥ 2 when high frequency current is used and for modules ≥ 5 when intermediate frequency is used. Induction hardening is performed on just these surfaces, a total of 4” length. It is apparent that higher the Ac3 temperature, lower the case-depth obtained. After general acceptance of the methodology for melting steel, engineers began to explore other possibilities for the use of the process. induction hardened steel rods with case depth varying from 1mm to 6mm. Faraday proved that by winding two coils of wire around a common magnetic core it was possible to create a momentary electromotive force in the second winding by switching the electric current in the first winding on and off. The required depth of the casehardened layer varies depending on the purpose for which the component is needed. Metallurgical Control 6. Flame or Induction Hardened Cases - Since no chemical change occurs in flame or induction hardening, readings must be made in the hardened or hardened and tempered condition only. Experimental investigation shown that for making shafts, axles or automobile components from medium carbon steel, raw material should be first normalized and then induction hardened so that uniform hardness of material can be obtained [1, 2]. The component is fed through a ring type inductor which normally features a single turn. The whole depth can be penetrated by using low frequencies, and the low power input does not permit over heating of the surface layers. 8.61 illustrates some coil designs and the heating patterns obtained. The figure also illustrates the individual hardenabilities of the steels in terms of ideal critical diameter, Dl. Though this steel has high hardenability, but it responds poorly to induction-hardening treatment, because it contains high chromium, which gives it a high Dl value. 8.63 (b) illustrates the temperature gradient during the process, and the Ac3 temperatures for different initial micro- structure. This region, next to the austenitised region, when attains high temperature, the coarsening of carbide occurs which results in slight softening there. This region is called ‘heat affected zone’. The depth of hardening-obtained is increased with increasing Dl, except for SAE 52100 steel. the lower the frequency the deeper the case. Induction hardening uses induced heat and rapid cooling (quenching) to increase the hardness and durability of steel. Many methods are used to provide the progressive movement through the coil and both vertical and horizontal systems are used.
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