1、_ SAE 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 voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there
2、from, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions. Copyright 2014 SAE International All rights reserved. No part of this p
3、ublication 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 permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-497
4、0 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/AMS2759/6B AEROSPACE MATERIAL SPECIFICATION AMS2759/6 REV. B Issued 1987-04 Revis
5、ed 2005-11 Reaffirmed 2014-04 Superseding AMS2759/6A Gas Nitriding and Heat Treatment of Low-Alloy Steel Parts RATIONALE AMS2759/6B has been reaffirmed to comply with the SAE five-year review policy. 1. SCOPE:This document specifies the procedure and requirements for heat treating low-alloy and tool
6、 steels and for their subsequent gas nitriding by the use of raw or dissociated ammonia. Specific process parameters are given for Nitralloy 135M, Nitralloy EZ, Nitralloy N, 4140, 4340, D6AC and H11 steels. Additional alloys and steel families (e.g., stainless steels) can also be nitrided using para
7、meters acceptable to the cognizant engineering organization. 1.1 Application: The nitriding process described herein has been used typically for producing a wear resistant and fatigue resistant surface on steel parts but usage is not limited to such applications. This process only applies to gas nit
8、riding. Other processes, such as salt bath nitriding, or ion nitriding, are not included.1.2 Classification: Processes covered by this specification are classified as follows:1.2.1 Class 1: Two-stage nitriding with first stage at 940 to 1050 F (504 to 566 C) and second stage at 975 to 1050 F (524 to
9、 566 C).Class 2: One-stage nitriding at 940 to 1050 F (504 to 566 C).1.2.2 If no class is specified, either Class 1 or Class 2 may be used.SAE INTERNATIONAL AMS2759/6B Page 2 of 10 2. APPLICABLE DOCUMENTS: The issue of the following documents in effect on the date of the purchase order forms a part
10、of this specification to the extent specified herein. The supplier may work to a subsequent revision of a document unless a specific document issue is specified. When the referenced document has been canceled and no superseding document has been specified, the last published issue of that document s
11、hall apply.2.1 SAE Publications: Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001 or www.sae.org.AMS 2418 Plating, CopperAMS 2429 Masking, Bronze Plate, Nitriding Stop-OffAMS 2759 Heat Treatment of Steel Parts, General RequirementsAMS 2759/1 Heat Treatment of Carbon and Low-Allo
12、y Steel Parts, Minimum Tensile Strength Below 220 ksi (1517 MPa)AMS 2759/2 Heat Treatment of Low-Alloy Steel Parts, Minimum Tensile Strength 220 ksi (1517 MPa) and HigherAMS 2759/9 Hydrogen Embrittlement Relief (Baking) of Steel PartsARP1820 Chord Method of Evaluating Surface Microstructural Charact
13、eristics2.2 ASTM Publications: Available from ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959 or www.astm.org.ASTM E 18 Rockwell Hardness and Rockwell Superficial Hardness of Metallic MaterialsASTM E 92 Vickers Hardness of Metallic MaterialsASTM E 384 Microindentation Hardness of Mater
14、ials2.3 ANSI Publications: Available from ANSI, 25 West 43rd Street, New York, NY 10036.ANSI B46.1 Surface Texture2.4 ASM Publications: Available from ASM International, Materials Park, OH 44073-0002.ASM Metals Handbook, Volume 7, Eighth EditionASM Metals Handbook, Volume 9, Ninth EditionSAE INTERNA
15、TIONAL AMS2759/6B Page 3 of 10 3. TECHNICAL REQUIREMENTS: 3.1 Heat Treatment: Shall be conducted in accordance with AMS 2759 and to AMS 2759/1 or AMS 2759/2, as applicable, and the requirements specified herein. In case of conflict, the requirements of this publication shall apply.3.2 Equipment: Sha
16、ll conform to AMS 2759. Furnace temperature uniformity requirements for normalizing, hardening, straightening, stress relieving, and baking shall be 25 F (15 C) degrees, for tempering, 15 F (8 C) degrees, and for nitriding 15 F (8 C) degrees. 3.2.1 Nitriding Atmosphere: Equipment shall be available
17、for introducing ammonia gas into the furnace at a controlled rate. A separate system for ammonia dissociation is recommended.3.2.2 Atmosphere Control: Equipment shall be available to measure and maintain the dissociation of the process atmosphere in the retort within 5 percent of the selected percen
18、t dissociation throughout the nitriding cycle.3.3 Pre-Nitriding Requirements: 3.3.1 Decarburization: Surfaces to be nitrided shall be free from decarburization.3.3.2 Hardening: Unless otherwise specified, all parts shall be hardened and tempered in accordance with Table 1 for applicable alloys prior
19、 to nitriding.3.3.3 Subcritical Annealing and Normalizing: When these thermal treatments are required, they shall be carried out in accordance with Table 1.3.3.4 Stress Relieving: Unless otherwise specified, parts which have been ground, straightened, or otherwise mechanically worked after hardening
20、, shall be stress relieved prior to nitriding. The stress relieving temperature shall not be higher than 50 F (28 C) below the tempering temperature.3.3.5 Contamination: Parts to be nitrided shall be free from grease, oil, scale, and other contaminants. Care shall be exercised after cleaning to prev
21、ent recontamination.3.3.6 Selective Nitriding: Selective nitriding shall be accomplished by masking surfaces not required to be nitrided. Alternatively, parts may be nitrided on all surfaces and the case ground off those surfaces not required to be nitrided.3.3.6.1 Nitriding is prohibited on surface
22、s not designated to be nitrided except where optional nitriding is permitted.SAE INTERNATIONAL AMS2759/6B Page 4 of 10 3.3.6.2 Maskant: Shall be fine grained copper plate, not less than 0.001 inch (25 m) in thickness, applied in accordance with AMS 2418, or shall be bronze plate, not less than 0.000
23、5 inch (12.7 m) in thickness, applied in accordance with AMS 2429. Other maskants may be used if acceptable to the cognizant engineering organization (See 8.10.1).3.3.6.3 Loading: Parts shall be placed and supported to prevent distortion and to ensure free circulation of the nitriding gas to all sur
24、faces. Test specimens, or parts to be destructively evaluated, shall be placed in the working zone in the same location or locations as the parts they represent.3.4 Nitriding: 3.4.1 Temperature Range: Shall be 940 to 1050 F (504 to 566 C).TABLE 1 - Pre-Nitriding Heat Treating Requirements for Nitral
25、loy 135 Mod, Nitralloy EZ,Nitralloy N, 4140, 4340, D6AC and H11(1)SteelTemperaturesF (C)SubcriticalAnneal BeforeHardeningTemperaturesF (C)NormalizeTemperaturesF (C)AustenitizeApproximateTemperingTemperature(2)F (C)RequiredMinimum(4)HRCStrengthRangesksiStrengthRangesMpaQuenchMethodNitralloy135 Mod127
26、5 (690) 1800 (982) 1725 (941) 1000 (538)1100 (593)1200 (649)1225 (663)40363028180-200160-180135-155130-1501241-13791103-1241931-1069896-1034Oil, PolymerNitralloyEZ1275 (690) 1800 (982) 1725 (941) 1100 (593)1200 (649)3123140-160125-145965-1103862-1000Oil, PolymerNitralloyN1275 (690) 1750 (954) 1650 (
27、899) 1200 (649) 28130-150(5)896-1034 Oil, Polymer4140 1250 (677) 1650 (899) 1575 (857) 1025 (552)1100 (593)1200 (649)343127150-170140-160125-1451034-1172965-1103862-1000Oil, Polymer4340 1250 (677) 1650 (899) 1500 (816) 1000 (538)1050 (566)1100 (593)363431160-180150-170140-1601103-12411034-1172965-11
28、03Oil, PolymerD6AC 1250 (677) 1725 (941)1625 (885) (3)1025 (552) 46 220-240 1517-1655 Oil, PolymerH11 1250 (677) 1850 (1010) 1025 (552)1100 (593)1150 (621)464340220-240200-220180-2001517-16551379-15171241-1379Oil, Polymeror Air(1) Preheat parts 36 HRC 160 ksi (1105 MPa) or higher and parts which inc
29、lude complicated shapes, sharp reentrant angles, and drastictransitions in thickness by soaking at 1100 to 1250 F (593 to 677 C).(2) The temperature will vary from the listed typical temperatures depending on the specified core hardness or strength, the hardenabilityof each heat of steel, and the se
30、verity of the quench, thus the as-quench hardness.(3) 1700 F (927 C) is permitted for D6AC parts when approved by the cognizant engineering organization.(4) These values apply to the “as hardened” condition.(5) Strength level will increase after nitriding due to precipitation hardening at the nitrid
31、ing temperature. Final strength level is dependentupon choice of nitriding temperature. A typical strength level of 190 ksi (1310 MPa) is developed after nitriding at 975 F.SAE INTERNATIONAL AMS2759/6B Page 5 of 10 3.4.1.1 Nitriding Temperature: Should be not higher than 50 F (28 C) below the temper
32、ing temperature and shall not exceed the tempering temperature.3.4.2 Ammonia Dissociation: The ammonia gas dissociation shall be 15 to 35 percent for Class 2 and for the first stage of Class 1 (approximately 20 percent of total nitriding time). Ammonia dissociation for the second stage of Class 1 sh
33、all be 65 to 88 percent. Raw ammonia may be used when permitted by the purchaser (See 8.10.2).3.4.2.1 Measurement: Equipment used for measuring shall be checked periodically for accuracy. Water absorption techniques (burette) are acceptable, but infrared analysis or in-situ probes are preferred.3.4.
34、3 Nitriding Procedure: The load shall be held at nitriding temperature(s) in partially dissociated ammonia atmosphere for sufficient time to produce the specified depth of case. Subsequently, the load shall be cooled from the nitriding temperature in a suitable atmosphere to 300 F (149 C) or below.
35、The furnace or retort should be flushed with inert gas before opening.3.5 Postnitriding Operations: 3.5.1 Maskant Stripping: Shall be accomplished by use of a non-embrittling stripper and shall not pit or etch the part.3.5.2 Removal of White Layer: Unless otherwise specified, white layer shall be re
36、moved to meet the requirements of paragraph 3.7 by lapping, honing, grinding, or etching with maximum stock removal of 0.002 inch (0.05 mm). If grinding is used, the parts shall be stress relieved after grinding in accordance with 3.5.2.1. If etching is used, parts shall be embrittlement relieved af
37、ter etching in accordance with 3.5.3.3.5.2.1 Stress Relieving of Ground Parts: Parts shall be stress relieved at 800 F 15 (427 C 8) for not less than 1 hour, plus one additional hour for each inch (25 mm) of thickness, or fraction thereof greater than 1 inch (25 mm), followed by cooling in air. Ligh
38、tly ground parts, subject to approval of the cognizant engineering organization, are not required to be stress relieved.3.5.2.2 Limitation on Metal Removal: When any metal removal is performed, it shall not reduce the effective case depth or surface hardness to below specification requirements.3.5.3
39、 Embrittlement Relief: Pickled, plated, etched (to remove white layer), or electrolytically cleaned parts shall be baked to remove hydrogen as specified in AMS 2759/9. Where pickling or electrolytic cleaning is performed as an integral part of a plating operation, baking is not required after each p
40、rocess but only the final one provided not more than 4 hours elapse between such operations.3.6 Core Hardness and Strength Properties: Shall conform to the requirements of the drawing.SAE INTERNATIONAL AMS2759/6B Page 6 of 10 3.7 Microstructure: The finished case of low alloy steels shall exhibit a
41、uniform distribution of nitrides diminishing gradually from the surface to the core. Corrosion resistant steels and highly alloyed steels (e.g. tool steels) may exhibit one or two metallographically distinct zones which may end abruptly. There shall be no evidence of a continuous nitride network in
42、grain boundaries. Unless otherwise specified, when white layer is permitted, its maximum thickness shall be 0.0005 inch (12.7 m) for Class 1 and 0.001 inch (25 m) for Class 2. Core microstructures shall be uniform tempered martensite. (See 8.11.)3.8 Total Case Depth: Shall conform to drawing require
43、ments. The total case depth shall be the depth of the continuous etching subsurface zone, determined metallographically on the as-nitrided part or specimen prior to machining. On those alloys which do not respond by darker etching, the case depth shall be the depth below the surface at which microha
44、rdness is 10% higher than that of the core, as determined by a Knoop or a Vickers hardness traverse, conducted in accordance with ASTM E 384.3.8.1 Effective Case Depth: Where specified, it shall be in accordance with drawing requirements. It shall be the depth, after finish machining, at which the v
45、alues specified in Table 2, converted from microhardness, are obtained in accordance with ASTM E 384 (See 8.9).3.8.1.1 For gear and splines, case depth applies at the pitch line of the gear or spline. For internal bores, case depth applies in all areas.3.9 Surface Hardness: Shall meet the requiremen
46、ts of Table 3 or equivalent, as determined in accordance with ASTM E 18, ASTM E 92 or ASTM E 384. In case of dispute, Rockwell superficial hardness or microhardness tests, as appropriate, shall govern.TABLE 2 - Hardness at Effective Case DepthSpecification AlloyHardnessHRC or Equivalent(See 8.9)AMS
47、6470, AMS 6471, AMS 6472 Nitralloy 135 Mod 50Nitralloy EZ 50AMS 6475 Nitralloy N 50AMS 6382, AMS 6414, AMS 6415 4140, 4340 40AMS 6431, AMS 6438 D6AC 50AMS 6485, AMS 6487, AMS 6488 H11 60Other alloys As specifiedSAE INTERNATIONAL AMS2759/6B Page 7 of 10 4. QUALITY ASSURANCE PROVISIONS: 4.1 Responsibi
48、lity for Inspection: Shall be in accordance with AMS 2759. Where parts are required for destructive test, these shall be provided by the purchaser.4.2 Classification of Tests: 4.2.1 Acceptance Tests: In addition to the tests specified in AMS 2759, core hardness (3.6), microstructure (3.7), case dept
49、h (3.8) and surface hardness (3.9) are acceptance tests and shall be performed on each lot.4.2.2 Periodic Tests: Shall be as specified in the applicable requirements of AMS 2759.4.2.3 Preproduction Test: In addition to the tests specified in AMS 2759, all tests are preproduction tests and shall be performed prior to initial production nitriding in each furnace.4.3 Sampling and Testing: A lot shall b
