a ...... ...... ....... ..... ...... .... ... ..... ...... .... ... ..... ...... ....... ..... ...... ....,...... ..... ...... .... ... ..... ...... ....... ..... ...... ....... ..... ...... .... ... ....I ...... ....... ..... ...... ....... ..... ...... ....... ..... ...... ....... ..... ...... .... ... ..... ...... .... ... ...... .... ... ...... .... ... ...... ....... ...... .... ... ...... ,....... ... ...... .... ... .....I .... .... ..... ... ... .....(... ....... ... ..... ... ........ ... ... ..... ...... i iG -i Publishedby the EPRl Center for MaterialsFabrication Vol. 2, No. 2, 1985Reprinted March, 1990 Using Induction Heat speed and selective heating capabil- Vol. 2, No. 1. Advantages specific to Treatment to Obtain ity, to produce quality parts cost induction heat treating are: Special Properties effectively. It will answer such ques- Speed - In heat treatment, the Cost Effectively tions as: What are the advantages higher heating rates play a central of induction heat treatment? What role in designing rapid, high- Heat treatment is often one of the heat treatments can I conduct with temperature heat treating most important stages of metal induction? What are some typical processes. Induction heat treating of processing because it determines parts and materials that are induc- steel may take as little as the final properties that enable tion heat treated? What properties 10 percent or less of the time cqmponents to perform under such can I obtain with induction heat required for furnace treatment. demanding service conditions as treatment? Short heating times also lead to less hiah load, hioh temperature, and The differences between induction scaling for materials such as steels aiverse environment. This Tech- and conventional furnace-based that oxidize readily at high heat Commentary illustrates how you heat treating processes and some treating temperatures. can use the special features of advantages of induction heating are Selective Heating-Controlling the nduction heat treatment, such as its discussed in TechCommentary heating pattern by selecting the right induction equipment allows surface and selectwe heat treatments that \ yield an attractive blend of proper- &. HEAT TREATING - PROCESS OVERVIEW ties (e.g., high strength and tough- Heat treatment is the controlled heating and coolingof a solid ness). Such treatments are not metal or alloy to obtain desired properties. Depending on the material feasible with furnace processes, and its intended use, heat treatment can improve such characteris- which are slow and heat the entire tics as formability, machinability, and service performance. Typical workpiece. heat treating operations include: Energy Savings - In addition to Annealing-used to soften metals to improve formability and eliminating dwell periods, induction machinability. heat treating techniques put energy only where needed, improving m Hardening-used to increase the strength and deformation resis- energy efficiency. tance of metals (such as steels). increased ProductionRates m Tempering-used to increase the toughness of hardened metals - and thereby improve their resistance to brittle, catastrophic failure Rapid heating often increases in high-stress. high-integrity applications. production and reduces labor. A glossary at the end of this TechCommentary precisely defines Types Of Induction these and other important heat treating terms. There are two broad categories of heat treating processes-those Heat Treatments involving indirect heating and those using direct heating. With You can utilize the speed and indirect methods, heat is produced in a furnace by burning a fuel or selective heating characteristics of by converting electrical energy into heat by passing a current induction processes for: through resistance heating elements. This energy is then transferred , Hardening of Steels-Steels are to the workpiece by radiation, convection, or conduction.By contrast, hardened by heating to austenitizing direct heating methods, including induction, direct resistance, and temperatures and then quenching. flame heating, supply heat directly to the workpiece. An indepth The speed of induction heating and discussion of how induction heating worksis included in TechCom- minimal soak time mandate higher mentary Vol. 2, No. 1. austenitizing temperatures than those used with furnace processes (Table 1). Depth of austenitization is Furnace Heating, Induction Heating, alloys are induction heat treaied F (C) F (C).. less often than steels. Pending the development of an information base 1650 to 1700 (900 to 925) 1550 to 1600 (845 to 870) on process economics, heat treat- 1525 to 1575 (830 to 855) 1650 (900) ments for titanlum and nickel-base 1525 to 1575 (830 to 855) 1600 to 1650 (870 to 900) alloys, whch are readily heated by 1475 io 1550 (800 to 845) 1600 to 1650 (870 to 900) induction, could become a reality in 1475 to 1550 (800to 845) 1600 (870) the future. Technical And Economic Considerations Determining whether induction heat treatment is suited to your needs requlres evaluation of such easily controlled so that parts can ment for a wide range of parts. The technical factors as: be surface or through hardened. brief list of common applications Workpiece Size and Shape- Tempering of Steels-Tempering that follows is only representative of These influence the shape of the of hardened steels is a function of its potential use. induction coil to be used. It is easiest to design coils for symmetrlc both time and temperature. Induc- Surface Hardening and Tempering parts. However, induction heat treat- tion tempering uses shorter heating of Steels: times (usually only seconds) and ing is readily applied to irregularly higher temperature to produce Transportation-crankshafts, shaped components by using results equivalent to furnace temper- camshafts, axle shafts, transmis- special coil designs. sion shafts, spllned shafts, univer- ing treatments that often require Subsequent Processing- Should .hours. sal joints, gears, valce seats, wheel spindles, bearings. permit easy integration of induction Normalizing -Since normalizing Machine tools-lathe beds, heat treating. This includes, for requires heating to a high tempera- transmission gears, shafts. example, the design of quench ture followed by air cooling, it is an stations following steel hardening ideal application of induction Metalworking, hand tools- rolling operations. The high speed of induc- heating. Induction normalizing mill rolls, pliers, hammers. tion heating may accommodate treatments are often used for Through-Hardening and machining operations on the same products that can be processed on Tempering of Steels: processing line. a continuous basis, such as pipe. m Oil-country tubular products, struc- Metallurgical Condition- Must the Weld Seam Annealing-The speed tural members, spring steel, chain part meet special service require- and selectivity of induction heating links. ments that induction heating can can be called on for local stress Annealing: provide, such as a blend of high relief annealing of welds in sheet Longitudinally welded steel tubes, strength and toughness? Some of metal, tubular, and other kinds of nonferrous sheet metals, ferrous the properties and characteristics of products. and nonferrous wire, steel pipes, induction heat treated parts are Recrystallization Annealing- tanks. discussed below. Annealing treatments for sheet Induction heat treating is also useful In addition to evaluating technical metal have been carried out for a wide range of materials, but feasibility, you must also determine successfully using a new process steel parts comprise the largest if induction heating is cost effective called “transverse flux” (TFX) induc- portion of induction heat-treated ,Nhen compared to other techniques. tion heating, in which sheet is fed components. Some typical induction Important economic factors in your continuously through a specially heat-treated steels are decision should include production lot size, equipment and energy designed coil. Total heating time is Medium-carbon steels, such as only a few seconds, compared to costs, labor requirements, scale and 1030 and 1045, used for welded scrap losses, and floor space many hours for conventional furnace tubing, automotive shafts, and or batch annealing of coils of sheet requirements. The way each of gears metal. Moreover, the fine tempera- these elements figure in an overall ture control with induction heating High-carbon steels, such as 1070, cost analysis is discussed in detail permits partial as well as full used for hand tools in TechCommentary, Vol. 2, No. 1. recrystallization annealing, depend- Alloy and stainless steels used for ing on the annealing temperature bearings, automotive valves, and Properties Of Induction chosen. Thus, a range of properties, machine tool components Heat Treated Parts not obtainable with batch annealing, Tool steels, such as M2 and D2, m The largest amount of property used for cutting tools and metal- is possible. information on induction heating is working dies. Induction Heat Treating for hardened and tempered steel The induction annealing of parts. Such data indicate that induc- Applications And Materials aluminum and its alloys is certainly tion through heat-treated parts have You can use induction heat treat- feasible, but, at present, nonferrous mechanical properties similar to 70 process economics are often suffi- cient to establish whether you $ 60 should use induction or conventional 0) C furnace-based methods for through E 50