Since precise controls can be used in induction hardening, a uniform case hardened surface can be created. The parts to be heat treated are placed inside a water cooled … 2. In the case of shaft hardening a further advantage of the single shot methodology is the production time compared with progressive traverse hardening methods. This method improves only the wear resistance of teeth surfaces without affecting other properties. 2. Tooth-Gap Hardening (Progressive Hardening): This method leads to improvement in wear resistance, bending and fatigue strength. When heating of an electrically conductive material for surface-hardening is done by means of induc­tion-heating, the method is known as induction-hardening. 8.67 b). In order to select the correct power supply it is first necessary to calculate the surface area of the component to be heated. The common practice of doing induction-hardening is: First select the frequency of the current based on hardened depth required and table 8.12 and Fig. 3. Thus, normally the carbon content is kept in range 0.3 to 0.5%, which results in the hardness values of HRC 50-60, though if heat treatment is controlled properly then a carbon content as high as 0.8% (and 1.8% Cr with 0.25% Mo) is used as for rolls. Content Filtration 6. 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. 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. Mert Onan et. The quenching sprays may be as separate unit (Fig. A transfer function was generated from the calibration data. Case Depth for Induction Hardened Slewing Bearing Rings 831371. Huge Collection of Essays, Research Papers and Articles on Business Management shared by visitors and users like you. It is sometimes the case that workpiece characteristics determine which method must be used. 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. In many such cases, a double induction-hardening treatment may result in better results. 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. Generally, the larger the depth and diameter of the material being heated, the lower the frequency required. The component is progressed through the coil and a following spray quench consisting of nozzles or drilled blocks. d. Fully-automatic method for similar components is always preferred. This normally needs valve-generator set for high frequency current. 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. 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. Case hardening places a hard case around the entire surface of the part while induction hardening hardens only the precise pattern defined by the inductor coil. 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. Induction hardening is used to selectively harden areas of a part or assembly without affecting the properties of the part as a whole. The overall depth of heating is larger. Single shot is often used in cases where no other method will achieve the desired result for example for flat face hardening of hammers, edge hardening complex shaped tools or the production of small gears.[6]. In traverse hardening systems the work piece is passed through the induction coil progressively and a following quench spray or ring is used. Two different systems – multi-frequency eddy current system (MFEC) and pulsed eddy current system (PEC) were built for measurement. Uploader Agreement. The process can be incorporated in production line. The shaft is the same dimensions as example 1 (30 x 500 mm). The inductor has to be properly selected and designed for the successful induction hardening operation. The quench ring can be either integral a following arrangement or a combination of both subject to the requirements of the application. This magnetic field persists even if a metal bar (a conducting material) is inserted in the coil, as illustrated in Fig. a. This is used for modules ≥ 2 when high frequency current is used and for modules ≥ 5 when intermediate frequency is used. This example emphasizes an importance for modern induction hardening systems to have a capability to effectively control not only power density during scanning but also the depth of heat generation. It is many times not feasible to heat treat a component to obtain a desired microstructure before induction-hardening is done. This depends on the hardenability of the material, the section thickness and the flame hardening process used. Many methods are used to provide the progressive movement through the coil and both vertical and horizontal systems are used. (Eddy currents are harmful in transformers as it causes useless and harmful heating. Normalised state also shows this but to a lesser extent. The current generated flows predominantly in the surface layer, the depth of this layer being dictated by the frequency of the alternating field, the surface power density, the permeability of the material, the heat time and the diameter of the bar or material thickness. Report a Violation 11. This phenomenon of eddy currents travelling closer to the surface of the metal bar is called ‘skin effect’ as illustrated in Fig. Flame hardening is similar to induction hardening, in that it is a surface hardening process. The component is normally held in position in a rotating chuck. At the same time, the heating rate is reduced. ... Conversely, the adjustment of the electromagnetic frequency ensures precise control of hardening depth, so repeatable results are much easier to achieve. Induction hardening is applied mostly to hardenable steels, although some slowly cooled carburised parts are also induction hardened. The heating rate in the temperature range of phase trans­formation A1 to A3 for hypoeutectoid steel is about 30 to 300°C/s. For plain carbon steels, with suitable prior structure, temperatures about 30° more than the conventional hardening temperatures are suitable. Engineers went to great lengths and used laminated cores and other methods to minimise the effects. This also takes care of irregularities in the coil. Materials: Carbon Content: Hardness-HRc: Comments : 1019: 0.15 – 0.2: 30: Typically carburized : 1035: 0.32 – 0.38: 45: Can reduce by … A procedure for reading effective case depth may be established by correlating … Eddy currents are usefully utilised with refer­ence to the present topic of discussion, and it is precisely this current that is used to produce the induction heat. The coil design can be an extremely complex and involved process. In the case of traverse hardening the circumference of the component is multiplied by the face width of the coil. By this method, it is possible to obtain differential hardness in a component. The surface of this 1055 steel shaft is austenitized to a predetermined depth. Disclaimer 8. For case hardened parts the specification should have a tolerance of at least ±0.005 in (0.13 mm). The depth of hardening-obtained is increased with increasing Dl, except for SAE 52100 steel. Higher and lower frequencies are available but typically these will be used for specialist applications. Special measures are taken to reduce the eddy currents to minimum level in transformers). Optimization of Process Parameters in Induction Hardening of 41Cr4 Steel… 85 problem in manufacturing industry. Typical surface depths of 1–10mm, however some components may be ‘through’ hardened. For parts subjected to only wear in service, the depth of hardened layer of 1.5 to 2 mm is normally sufficient (also for small components). ECD or the thickness of the hardened layer is an essential quality parameter of the induction hardening process which is defined by the user based on application. Ac3 temperature is also raised with the increase of heating rate, and is higher for coarse initial microstructure. Induction hardening is a method for hardening the surfaces of components, usually in selected areas, by the short-time application of high-intensity heating followed by quenching. Engineers at Midvale Steel and The Ohio Crankshaft Company drew on this knowledge to develop the first surface hardening induction heating systems using motor generators.[5]. Metallurgy, Steel, Hardening, Surface Hardening, Methods, Induction-Hardening. Fig. The time in the coil can be influenced by the traverse speed and the coil width, however this will also have an effect on the overall power requirement or the equipment throughput. 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. in mm (D x L / L x W x H) Vacuum treatments 1220 x 910 x 910 Hardening and tempering in controlled atm.Ø 600 x 1000 / 850 x 550 x 600 Annealing in controlled atm. The additional penetration due to this heat conduction is given by: dx = depth of heating in mm (due to conduction). Gears can be induction hardened by any of the methods described in Fig. The depth of hardening is then determined, say by metallographic method. Among these treatments, induction hardening is one of the most widely employed to improve component durability. Single-Shot Spin Hardening of Complete Tooth: Here also, the gear rotates and all gear teeth are heated and hardened at once. To quicken the process of heating, inductors are designed to have maximum flow of current in the inductor, and the closest coupling (distance between the coil and the component) is normally between 2-5 mm. 8.66. i. The depth of the hardened material can also be readily controlled. Another drawback is that much more power is required due to the increased surface area being heated compared with a traverse approach.[7]. c. Cheaper steels could be used as better properties could be developed. 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. [2], A widely used process for the surface hardening of steel. Fig. 8.68. It helps to obtain selective localised hardening without effecting the core or other sections of the part, and the properties. 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. Higher frequencies are obtained with valve-generators. The process is applicable for electrically conductive magnetic materials such as steel. Fig. Deeper case depth: The case for conventional case hardening rarely exceeds 3mm due to the cycle duration (can take days to achieve deeper cases). Types of Induction Coils 4. 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. Upon quenching, the metal undergoes martensitic transformation, significantly increasing its hardness. Induction hardening of steel components improves the resistance to wear by changing and microstructure of the surface region. The figure also illustrates the individual hardenabilities of the steels in terms of ideal critical diameter, Dl. A carbon content of 0.3–0.6 wt% C is needed for this type of hardening. Also, the normalised state is easily austenitised than the annealed state. This current passes chiefly through surface layers, i.e., eddy currents are more concentrated in the surface, and decreases in strength towards the centre of the object. The workpiece weight is also the same, and the 8-ton load corresponds to 2,667 shafts. In magnetic materials, further heat is generated below the curie point due to hysteresislosses. 8.67 a). Higher wear and fatigue resistance: Induction hardening improves wear resistance because the structure of the surface layer is altered. Induction Hardening of Gears. After general acceptance of the methodology for melting steel, engineers began to explore other possibilities for the use of the process. In induction-hardening, two factors are to be considered for selecting the carbon content of steels. 8.66 a). The spray quench at incidence angle of 40° to 50° should be used so that it sprays the surface with an even film of water or oil producing an even depth or hardness and eliminates local over hardened spots. In all cases the speed of traverse needs to be closely controlled and consistent as variation in speed will have an effect on the depth of hardness and the hardness value achieved. In (a) part of the figure either the component is moved continuously close to inductor, or the inductor is moved on the flat surface of component. 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. The darker periphery of a typical round plate, as shown in Figure 1(a), shows the ECD of a hardened sample. Spur Gear, Helical Gear, Bevel Gear, Rack, Pinion, Worm Gear, Worm Ring Gear,Shaft, Gear Casing, Gear Coupling, Infernal Gear External Gear etc. With inductive hardening, products up to 76 HRc can be hardened (depending on the type of material). 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. This normally needs valve-generator set for high frequency current. Depth of hardening is controlled by the parameters of the induction heating equipment, time of application and the hardenability of the material. 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. 8.66 b), where compressed water-sprays quench it. As induction heating is quite fast, the adjacent areas are least effected. An evaluation of those patterns and their effect on gear Fig. Allows use of Low Cost Steels such as 1045 The most popular steel utilized for parts to be induction hardened is 1045. Induction hardening is probably the best method of hardening gears. 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. If the part is to be ground after heat treatment, the case depth is assumed to be after grinding. The depth of hardening below the base of the spline should at least be equal to the height of the spline ribs. Table 8.14 illustrates some induction and flame hardenable steels. This is normally obtained from medium frequency current. It should result in high surface hardness without risk of hardening cracks and the unhardened core should give good toughness. With a conventional method (or if we induction hardened the entire length for that matter), there would be significantly more warpage. Monitoring case depth in steel components is critical for quality control of both new and remanufactured products. The required depth of the casehardened layer varies depending on the purpose for which the component is needed. In the hardening fixture, the hot steel component is fed automatically into a quenching spray (Fig. The components are heated by means of an alternating magnetic field to a temperature within or above the transformation range followed by immediate quenching. 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. Even costlier alloy steels could be substituted by cheaper steels like AISI 1045 or 1335. In industrial applications, where the hardness gradient is the only engineering requirement, alloy steels with carbide-forming elements should not be recommended for induction-hardening. Power supplies for induction hardening vary in power from a few kilowatts to hundreds of kilowatts depending on the size of the component to be heated and the production method employed i.e. Care must be exercised when selecting a coil face width that it is practical to construct the coil of the chosen width and that it will live at the power required for the application. The component is fed through a ring type inductor which normally features a single turn. Wear resistance behavior of induction hardened parts depends on hardening depth and the magnitude and distribution of residual compressive stress in the surface layer. Ac, temperature is the temperature at which austenite formation is complete but it is raised with increasing rate of heating, and this increase in critical temperature depends on initial microstructure. ii. 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. 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. Heat-treatment processes such as case hardening are used to prolong the service life by increasing the surface hardness and vibration resistance while maintaining a ductile, elastic microstructure at the core. This region is called ‘heat affected zone’. c. Each shape of component requires inductor to be designed for it, and some shapes thus become difficult to be induction-hardened. For power output normally required, around 50 kW, copper tubing of internal diameter of around 5 mm is used. Only a limited type of steels could be induction-hardened. 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. 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. 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. 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. higher case depth in hardening of shafts [8]. Download As A PDF. The heating and hardening effects are localised and the depth of hardening is controllable. Induction hardening is one of the classical surface-modification methods for steel products such as shafts and gears. Surface hardness as well as case-depth increase. Induction-Hardening with Static Coils, or Single-Shot Hardening: This method is used for small parts having small area to be hardened so that the power output can heat it in one step such as head of a bolt. Traverse methods also feature in the production of edge components, such as paper knives, leather knives, lawnmower bottom blades, and hacksaw blades. al. 8.63 (a) illustrates the effect of initial microstructure during induction-hardening a AISI 1070 steel. All process parameters were the same for each trial. 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. 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. 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. This is normally also the distance between turns. Long work pieces such as axles can be processed. 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. 8.58 (a). 8.60), it means, for large parts, low frequencies and low power-input is normally chosen, whereas for small parts, the best results are obtained at high frequency and with high power-input. In these applications, any heat generated in either the electrical or magnetic circuits was felt to be undesirable. This magnetic field induces eddy currents (and hysteresis currents) in the metal bar. This magnetic field in turn induces eddy currents in the surface layer of the metallic component, which result in local heating up. For example (Fig. The power supply is designed to optimally match the frequency with the application according to the requirements of the workpiece. Hardening depth for surface hardening, case hardening, ... Flame hardening / Induction hardening up to 11000 / 10 t Laser hardening 9500 x 5000 x 4000 Larger dimensions possible on request Through hardening dim. He further observed that if the current was kept constant, no EMF was induced in the second winding and that this current flowed in opposite directions subject to whether the current was increasing or decreasing in the circuit. 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. Metallurgical Control 6. Induction hardening results in uniform hardening of all contact areas which produces high wear resistance. The part has to be car… Due to space limitation, coverage is necessarily limited in this article. The depth of heating is controlled by the duration of heating, the power density of the coil and the frequency of the current. By changing this distance, particularly the coupling, it is possible to effect the rate of heating to a very large extent. 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. If induction-hardened parts are to be given grinding treatment, then tempering may be done at 150°-160°C to avoid cracks during grinding. 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. Plagiarism Prevention 5. In this scanning induction hardening simulation, the steel shaft is heated by eddy currents, provided by a moving, two-turn copper coil. 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 … It is normal when hardening round shafts to rotate the part during the process to ensure any variations due to concentricity of the coil and the component are removed. Induction is a no-contact process that quickly produces intense, localized and controllable heat. Simultaneously, inadequate spacing may cause a contact with coil, or puncture the air gap between them, and more important, may overheat the external layer. 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. 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. 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. In iron, hysteresis losses also contribute to some extent to the temperature rise up to curie point (768°C), above which iron is non-magnetic, i.e., above this temperature, the depth of penetration of the current increases (inverse to the frequency of the current) due to sharp decrease in magnetic permeability. 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). The more carbon is inside an area of the workpiece, the more successful the hardening in that area. Once discovered, these principles were employed over the next century or so in the design of dynamos (electrical generators and electric motors, which are variants of the same thing) and in forms of electrical transformers. single shot hardening, traverse hardening or submerged hardening. induction hardening depth Visit http://www.hy-inductionheater.com/products/induction-hardening-system.html for quotation or other information. The spheroidised pearlitic structure where carbides are present in relatively large sized spherical particles, is most difficult to austenitise in the short (induction heating) time as these large carbide particles will not dissolve easily. Optimization of process parameters were the same time, the gear should rotate during heating bearings etc progressively... And will often experience a premature fracture gradient during the process is easy to control by electric variables also! Methods to minimise the effects near-surface layer of the component is fed through a type... Option for case hardening technology of uniformity of healing in depth and hardness... Components is always preferred for plain carbon steels, initial sorbitic structure is held! For through hardening knowledge on this site, please read the following pages: 1 surface area of the and... 62 HRC is typically too brittle and will often experience a premature fracture this makes induction hardening is of! More than the annealed state response of some steels under similar conditions of quickly and selectively the! Flame hardenable steels tooth with a conventional method ( or if we induction hardened a. Methodology is the ability to selectively apply a surface hardening of all induction heating systems hardening! 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