1、AEROSPACE RECOMMENDEDPRACTICEARP4715Issued 2000-12Reaffirmed 2011-04Induction Hardening of Steel ComponentsRATIONALEThis document has been reaffirmed to comply with the SAE 5-year Review policy.1. SCOPE:This recommended practice provides guidelines for the establishment of an induction hardening pro
2、cess for steel components. It is intended to be used as a guide for designers of induction hardened parts, for process auditors, and for purchase specifications and/or process sheets as applicable.Induction heat treatment is intended for hardening of only selected areas of plain carbon or alloy stee
3、l components. A prior heat treatment may be specified for improved response of the overall component to induction hardening, or for control of properties in the balance of the part. AMS 2759 is recommended for such prior heat treatment.2. APPLICABLE DOCUMENTS:The following documents are often used i
4、n conjunction with induction hardening and should be considered when induction hardening is needed:2.1 SAE Publications:Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001.AMS 2759 Heat Treatment of Steel Parts, General RequirementsAMS 2649 Etch Inspection of High Strength Steel Pa
5、rtsSAE J423 Methods of Measuring Case DepthARP1820 Chord Method of Evaluating Surface Microstructural CharacteristicsSAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely volun
6、tary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your wr
7、itten comments and suggestions. Copyright 2011 SAE International All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written perm
8、ission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.orgSAE values your input. To provide feedbackon this Technical Report, please visit http:/www.sae.org/tec
9、hnical/standards/ARP4715SAE ARP4715 - 2 -2.2 ASTM Documents:Available from ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19248-2959.ASTM E 18 Rockwell Hardness and Rockwell Superficial Hardness of Metallic MaterialsASTM E 92 Vickers Hardness of Metallic MaterialsASTM E 112 Determining the Avera
10、ge Grain SizeASTM E 384 Microhardness of Materials3. TECHNICAL:3.1 Specifying Induction Hardening:The extent of the induction hardening pattern should be fully defined on the engineering drawing. The definition should include:The minimum and maximum lengths or widths of the hardened zone or case (so
11、metimes calledinduction harden pattern or IHP)The minimum and maximum depth of the hardened zone or caseThe minimum (and in some cases, the maximum) hardness of the caseThe hardness of the core or unaffected base metalThe maximum extent of the heat affected, transition, or intermediate zones. These
12、terms are oftenused interchangeably.The minimum hardness permitted in the overtempered zone (In some cases, the width of theintermediate or transition zone may also be limited.)Locations where hardness measurements or traverses should be taken.Examples of ways to specify the extent and requirements
13、of induction hardening are shown in Figure 1.3.1.1 The transition or overtempered zone is located beneath the hardened zone. Having been exposed to temperatures not high enough to harden it, but substantially higher than the core or base metal tempering temperature, this area may be softer than the
14、core or base metal. The designer may limit the extent of softening, either by specifying a minimum hardness, or by specifying the maximum width of the zone, or both. It is recommended that the permissible hardness reduction in the overtempered or transition zone be 4 to 8 points HRC below the origin
15、al core or base metal hardness. A minimum width of 0.03 inch (0.76 mm) is often obtainable for smaller sections, but specifying the maximum width that can be tolerated in the design is recommended. A transition zone equal to the minimum case depth required by the specification or drawing is consider
16、ed reasonable.3.1.2 Hardness at the surface of the induction hardened range is generally measured by direct Rockwell or Superficial Rockwell hardness testing in accordance with ASTM E 18. However, depth of hardening and extent of heat affected zone are normally determined destructively, on a cross-s
17、ection of the part, using microhardness techniques such as those of ASTM E 384, ARP1820 or SAE J423.SAE ARP4715 - 3 -3.1.3 Material:3.1.3.1 Type of Steel: In general, steels with carbon contents of 0.35% or more will respond to induction hardening, although a carbon content approaching 0.5% may be n
18、ecessary to obtain hardnesses exceeding 55 HRC. A fine grained steel (ASTM No. 5 to 8 determined in accordance with ASTM E 112) is desirable. In general, low alloy steels that have been normalized and tempered or quenched and tempered in accordance with AMS 2759 are desirable.3.1.3.2 Tempering After
19、 Induction Hardening: The as-induction hardened microstructure is dependent on material composition, hardenability, prior structure and quench rate, and will generally consist of a martensitic structure. Since the martensitic structure is normally crack sensitive after cooling from the hardening tem
20、perature, the entire part is invariably tempered after induction hardening, at temperatures ranging from 300 to 1000 F (149 to 538 C). The designer may specify a specific tempering temperature or may specify a maximum or minimum case hardness. However, in all instances, the drawing must require temp
21、ering after hardening.3.1.3.3 Microstructure: Unless the designer specifies otherwise, the resultant microstructure should consist of tempered martensite at the surface and throughout the case or induction hardened zone. All areas of the induction hardened case should meet the minimum case hardness,
22、 with a relatively sudden drop to below the base metal hardness at the start of the transition zone (See Figure 2). Typically, grain size, when determined, which is often equated with toughness, should not increase by more than one or two ASTM grain size numbers, but in no instance should the design
23、er expect grain sizes larger than ASTM No. 3 when starting with a grain size of ASTM No. 5 to 8, nor evidence of free ferrite at the surface, both indicative of excessive heating and detrimental to performance or reliability.An insufficient quench may result in a portion of the material remaining un
24、transformed. Standards for such untransformed material, called retained austenite, may be specified by the designer.3.1.4 Recommended Case Depths: The case depth selected by the designer depends on the application and section size. For surface hardening, the depth should be less than one third of th
25、e cross-sectional thickness of the part, and, when calculated, should exceed with reasonable margin the depth of maximum shear stress created by calculating the maximum bearing load or stress.3.2 Equipment:Induction heat treating equipment consists of a power supply with appropriate controls, an ind
26、uctor or coil that transmits the power from the supply to the work, means of matching the power supply to the inductor or coil, and, if necessary, means for quenching the heated sections or complete components as required.SAE ARP4715 - 4 -3.2.1 Inductor or Coil: The inductor is a loop (partial loop
27、or several loops) of current carrying conductor similar to the primary circuit of a transformer, that transmits power from the power supply to the work. The heating current is electrically induced into the work as the secondary of the transformer, forming eddy currents that produce I2R heating, and
28、is not part of the power circuit directly. The inductor, or coil, may be as simple as a single turn of water cooled copper tubing, or may contain iron laminations or iron powder to help direct the magnetic field.Each inductor or coil should be assigned a part or tool number. Since the pattern produc
29、ed is a function of the shape of the coil, each part or component should have a specific inductor or coil assigned to it.The coupling between the component and the inductor is one of the determining factors in the efficiency of the coil. Generally, the closer the work is to the inductor, the greater
30、 the power transmitted, and the more accurate the pattern. Typical gaps between inductor and component range from 0.02 to 0.1 inch (0.5 to 2.5 mm).3.2.2 Power Supplies: Power supplies as described in Table 1 are generally acceptable for use.3.2.2.1 To control the power supply for induction hardening
31、, there should be a means to turn it on and off, select the power level, and control and regulate the power. Since heating is usually accomplished in seconds and fractions of seconds, it is recommended that the controls be provided with a series of on-off push buttons to start timers that automatica
32、lly control on-time, potentiometers for measuring watts, volts, amperes, frequency, and reactive power or power factor, as applicable.3.2.2.2 The depth to which the induced current flows in the workpiece or component is inversely related to the power supply frequency. Table 2 shows a relationship be
33、tween power supply frequency and depth of direct I2R heating. The minimum values are for high power densities (typically 15KW / square inch or 15 KW / 6.5 square cm). Note that the minimum depth is approximately the depth of the zone actually heated by the eddy currents induced by the inductor. Addi
34、tional depth of heating is obtained by increasing the power supply “on-time” to allow the heat to drift or diffuse beyond the directly heated minimum depth. However, the longer the drift, the wider the heat affected or intermediate or transition zone will be. Too deep a zone with too high a frequenc
35、y may result in overheating at the surface. Conversely, a shallow pattern cannot be obtained with a low frequency power supply. The depths given in Table 2 are not absolute; different materials in different heat treated conditions will produce different results.TABLE 1 - Typical Power SuppliesTypeFr
36、equency (KHz)Typical Power Rating (KW)Vacuum Tube Oscillator 200 to 450 5 to 600Motor Generators 1, 3, 10 7.5 to 500Frequency Inverters 0.5, 1, 3, 10 50 to 1500Frequency Multipliers 180, 540 100 to 1000SAE ARP4715 - 5 -3.2.2.3 The inductor or coil should be well matched to the workpiece and power su
37、pply. Ideally, load matching or impedance matching should be within 15% of the full rated power at or near the 100% voltage and frequency rating. Power supplies should be equipped to regulate power factor for maximum efficiency by adjusting the internal inductance or capacitance as required. Power s
38、upplies should be equipped with meters to assist in regulating reactive power or power factor as needed.3.2.3 Fixturing: The part being treated should be held rigidly and in a reproducibly fixed position to ensure repeatable coil positioning, air gap, and heating pattern. For uniformity of heating p
39、attern, it is often desirable for round components such as shafts, bearing races and similar parts, to be rotated during the heating. Component design and processing capabilities will dictate whether such measures are required.3.2.4 Quenching: The quench method and media, when required, are determin
40、ed by the part design and material selection. Some AISI 400 series steels, some highly alloyed tool steels, and steels generally regarded as air hardening, may need no supplementary quenching. However, when supplementary quenchants are required, as in the case of low alloyed or carbon steels, the pr
41、ocedure should specify and control all aspects of the quench, including, as applicable, quenchant agitation, quench delay, quench composition, quench head position, and fluid pressure, spray on-time, and quench immersion time.TABLE 2 - Frequency / Depth of Hardening RelationshipFrequency cycles per
42、secondPractical Hardening Depth Inch (mm), minimumPractical Hardening DepthInch (mm) working500 0.2 (5) 0.4 to 0.6 (10 to 15)1,000 0.1 (2.5) 0.18 to 0.35 (4.5 to 9)3,000 0.06 (1.5) 0.15 to 0.2 (3.7 to 5)10,000 0.04 (1) 0.1 to 0.15 (2.5 to 3.7)120,000 0.3 (0.75) 0.06 to 0.1 (1.5 to 2.5)500,000 0.02 (
43、0.5) 0.04 to 0.08 (1 to 2)1,000,000 0.01 (0.25) 0.01 to 0.04 (0.25 to 1)SAE ARP4715 - 6 -3.3 Procedures:3.3.1 Documentation: Induction heat treatment should be performed in accordance with an established, documented, and reproducible procedure. That procedure should include:Part number and part name
44、 as applicableCoil or inductor part numberHolding fixture part numberDate procedure was established or last revisedPower supply machine identificationSketch of the location of the part to be induction hardenedIntensifiers or heat sinks, if usedPower ramping schedule, if usedPower settingsPower cycle
45、 timeCoil to workpiece distance and method for assuring itQuench typequench head locationquench delay time, as applicablequenchant compositionfluid flow rate and pressuretime in quench, or on-time of spray quenchantTemper cycle (normally in accordance with AMS 2759 but may be done by induction. If d
46、oneinductively, a similar set of instructions would be needed for the induction tempering cycle.)Test methods and sampling plans3.3.2 Induction Heating Cycle: The induction heating cycle is established by heating the selected area of one or more parts using the selected fixtures, coil, and preselect
47、ed procedures. It may be necessary in some cases to reiterate the parameters several times until the desired results are obtained before production parts are made. Initial cycles may be verified by optical pyrometry, temperature indicating lacquers, or other means. After establishment of the cycle,
48、it is usually acceptable to rely on the reproducibility of the procedure and normal quality control methods.4. QUALITY CONTROL:4.1 Destructive Examination:It is recommended that at least one part be destructively examined by sectioning and metallographic examination, since depth of hardening can onl
49、y be determined destructively. For critical parts, the purchaser may require that parts be destructively examined from each lot or each tool setup, on a statistical basis, or at periodic intervals based on some number of parts or calendar time.SAE ARP4715 - 7 -4.1 (Continued):Examination should include a microhardness traverse that includes sufficient points to ensure the extent of the hardened, transition or intermediate zones, and heat affected zones. Where the pattern is non-uniform due to geometry or other factors, sufficient metallographic sectio
