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 theref
2、rom, 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 written comments and suggestions. Copyright 2007 SAE International All rights reserved. No part of this publication ma
3、y 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: 724-776-4970 (outside USA)
4、Fax: 724-776-0790 Email: custsvcsae.org SAE WEB ADDRESS: http:/www.sae.org AMS 2759/8A AEROSPACE MATERIAL SPECIFICATION Issued JAN 1992 Revised JUN 2007 Superseding AMS 2759/8 Ion Nitriding RATIONALE AMS 2759/8A changes thermal management, testing, and process requirements. 1. SCOPE 1.1 Purpose This
5、 specification establishes the requirements and procedures for producing a hard, wear resistant ion nitrided surface on steel parts. 1.2 Application The ion nitriding process is typically applied to increase surface hardness, increase wear resistance, and reduce coefficient of friction of alloy stee
6、ls, tool steels, nitriding steels, corrosion resistant steels (CRES), carbon steels, ferrous powder metal products, and other ferrous alloys but usage is not limited to such applications. See 8.2.6 for other materials that can be ion nitrided. 2. APPLICABLE DOCUMENTS The issue of the following docum
7、ents in effect on the date of the purchase order forms a part 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 cancelled and no superseding document
8、has been specified, the last published issue of that document shall apply. 2.1 SAE Publications Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), www.sae.org. AMS 2429 Bronze Plating AMS 2418
9、Copper Plating AMS 2759 Heat Treatment of Steel Parts, General Requirements ARP1820 Chord Method of Evaluating Surface Microstructural Characteristics ARP 1962 Training and Approval of Heat Treating Personnel (R) Copyright SAE International Provided by IHS under license with SAENot for ResaleNo repr
10、oduction or networking permitted without license from IHS-,-,-SAE AMS 2759/8A - 2 - 2.2 ASTM Publications Available from ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959, Tel: 610-832-9585, www.astm.org. ASTM A 370 Standard Test Methods and Definitions for M
11、echanical Testing of Steel Products ASTM E 3 Preparation of Metallographic Specimens ASTM E 18 Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials ASTM E 92 Vickers Hardness of Metallic Materials ASTM E 140 Standard Hardness Conversion Tables for Metals ASTM E 384 Microindentat
12、ion Hardness of Materials 2.3 ASM Publications Available from ASM International, 9639 Kinsman Road, Materials Park, OH 44073-0002, Tel: 800-336-5152 (inside U.S. and Canada), 440-338-5151 (outside USA), www.asm-intl.org. ASM Metals Handbook, Metallography and Microstructure, Volume 9, 9th Edition. 3
13、. TECHNICAL REQUIREMENTS 3.1 Heat Treatment Prior to Nitriding Prior heat treatment shall conform to AMS 2759 or document approved by cognizant engineering organization and to the requirements specified herein for the particular grade of material treated. For steels not covered by AMS 2759, heat tre
14、atment shall be in accordance with steel supplier recommendations and process controls shall be in accordance with AMS 2759. 3.2 Pyrometry 3.2.1 Pyrometric equipment shall conform to AMS 2759 except that temperature uniformity survey (TUS) and system accuracy test (SAT) requirements do not apply. Th
15、e temperature range shall be 50 F (28C) or less at nitriding temperatures determined by four thermocouples during processing of each production load. The maximum temperature shall not exceed the limits of 3.4.2 and 3.4.3 or as otherwise established during preproduction testing. 3.2.1.1 Thermocouples
16、 shall be placed in parts or representative specimens distributed in the load and near test samples in accordance with 4.2 and 4.3 and represent the extreme and mid-range temperatures of the load. A control thermocouple and/or over-temp thermocouple may be used as one of the four thermocouples requi
17、red by 3.2.1. 3.2.1.2 Alternatively, infrared pyrometry may be used when acceptable to the cognizant engineering organization. Unless specified otherwise, the calibration shall be quarterly and shall be in accordance with the vessel system manufacturer instructions. 3.2.1.3 If a thermocouple fails o
18、r has a suspect reading during processing, suppliers engineering and quality departments shall review the run to determine if product conforms to specified requirements. Results of the analysis and any additional evaluation shall be documented, including assessment of corrective actions or improveme
19、nt to prevent recurrence. 3.3 Equipment Vessels, associated equipment, and controls shall be maintained in accordance with the manufacturers recommendations or the processors internal procedures. 3.3.1 Vessels may additionally be equipped with radiation shields and/or auxiliary resistance heating. C
20、opyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AMS 2759/8A - 3 - 3.3.2 Vacuum (Low Pressure) Controls Equipment shall have calibrated recording instruments for sensing, measuring, controlling, an
21、d recording pressure during the entire cycle. The control equipment shall be capable of maintaining the operating pressure level at any setpoint within the equipment operating range with sufficient accuracy to meet the processing requirements of the parts being treated. 3.3.3 Nitriding Atmosphere Th
22、e nitriding gas composition shall be selected to produce a compound layer or a pure diffusion zone as specified by the cognizant engineering organization. Guidelines on gas composition effects on compound layer formation are found in 8.2.5. 3.3.4 Atmosphere Control Equipment for mixing gases shall b
23、e calibrated and capable of providing a measured ratio of the components of the mixed gas within 3% by volume of the selected value or as approved by the cognizant engineering organization. For example, if the gas contains 25% nitrogen, the concentration can range from 22 to 28%. Alternatively, a pr
24、emixed gas of certified composition may be used. 3.3.5 Leak Rate (Rise in Pressure) The vessel leak rate, expressed as microns per hour shall be measured before each treatment cycle. The leak rate shall not exceed 90 microns per hour or other leak rate acceptable to the cognizant engineering organiz
25、ation. Leak rate shall be determined, before starting the heat cycle, after loading and closing the vessel, evacuating to 75 microns (10 Pa) or lower, and closing all valves to the vessel chamber to isolate the pumps. The initial pressure is recorded and a second reading taken at least 15 minutes af
26、ter the first reading. Leak rate shall be calculated by subtracting the first reading from the second, dividing the result by the time interval, and multiplying the resultant number by 60. Alternatively, another method approved by the cognizant engineering organization may be used. 3.3.6 Initial Eva
27、cuation of Vessel At the start of each cycle, before admitting nitriding gas and before turning on power for heating, the vessel shall be evacuated to a pressure of 75 microns (10 Pa) or lower. 3.4 Nitriding Requirements 3.4.1 Surfaces to be nitrided shall be free from decarburization. 3.4.2 Heat tr
28、eatable steels shall be hardened and tempered prior to nitriding. The nitriding temperatures shall be no higher than 50 F (28 C) below the tempering or aging temperature. When approved by the cognizant engineering organization, higher temperatures may be used if core hardness is maintained and all m
29、etallurgical and dimensional requirements are met as demonstrated by testing and sectioning of specimens. 3.4.3 Parts that have been ground or straightened before ion nitriding may be stress relieved prior to nitriding. Based on material, tolerance, and processing, parts that have been straightened,
30、 rough machined, rough ground or otherwise mechanically worked after heat treatment may be stress relieved in accordance with AMS 2759 or customer requirement prior to machining or grinding and ion nitriding. 3.4.3.1 When stress relieving has been performed, the nitriding temperature shall be 50 F (
31、28 C) or more below the stress relieving temperature. When approved by the cognizant engineering organization, higher temperatures may be used if core hardness is maintained and all metallurgical and dimensional requirements are met as demonstrated by testing and sectioning of specimens. Surfaces to
32、 be nitrided shall be mechanically or chemically cleaned subsequent to stress relieving and prior to nitriding. 3.4.4 Parts to be nitrided shall be free of grease, oil, and other contaminants. Copyright SAE International Provided by IHS under license with SAENot for ResaleNo reproduction or networki
33、ng permitted without license from IHS-,-,-SAE AMS 2759/8A - 4 - 3.4.5 When selective nitriding is required, mechanical masking shall be used to prevent nitriding of selected surfaces. When acceptable to the cognizant engineering organization, pastes, paints, or plating may be used. When used, copper
34、 plating shall be in accordance with AMS 2418, or bronze plating in accordance with AMS 2429. Tin-bearing masking material shall not be used. Alternatively, when acceptable to the cognizant engineering organization, parts may be nitrided all over and the case machined off surfaces not to be nitrided
35、. See 8.11. 3.5 Procedure 3.5.1 Establishment of Processing Procedure For each part number, the following shall be established and documented: the minimum and maximum number of parts allowed per load, the loading layout (a sketch, diagram, or photograph of part locations and thermocouple locations),
36、 masking/fixturing, processing parameters, specimen type and locations, and testing practice. 3.5.1.1 Previously Approved Procedure It is permissible, for specific parts, to use equipment, practices and test methods which conformed to the original publication of AMS 2759/8 and were previously accept
37、able to the purchaser. 3.5.2 For parts expected to be nonrecurring (8.12.1) the processing procedure may be limited to vessel log/recorder entries (4.5) and records (4.6). 3.5.3 Test specimens as in 4.3 shall be placed in each load at locations representing the extremes and mid-range of work tempera
38、ture established in 3.2.1 or by other analysis or test data. 3.5.4 Processing parameters shall be documented and shall result in the meeting of all specified requirements. 3.5.5 Nitrided parts shall not be removed from the vessel at temperatures above 300 F (140 C). 3.5.6 Unless otherwise required b
39、y the cognizant engineering organization, nonrecurring loads (8.12.1) of different parts that require the same process parameters may be combined and processed together in the same load, if testing in accordance with 4.3.1 verifies that the requirements of 3.7 are attained. 3.6 Post Nitriding Operat
40、ions 3.6.1 Compound Layer Removal When removal of compound layer generated by nitriding is required, it should be accomplished by lapping or honing with maximum stock removal of 0.001 inch (0.025 mm). If grinding is used, the parts shall be stress relieved as in 3.6.2 after grinding. Alternatively,
41、compound layer may be removed by chemical means if approved by the cognizant engineering organization. When remaining compound layer is permitted, the depth of the compound layer shall be minimized and shall be no greater than 0.0005 inch (0.0127 mm), unless otherwise required by the cognizant engin
42、eering organization. 3.6.2 Stress Relief Parts ground after nitriding shall be stress relieved by heating to a temperature within the range 325 to 650 F (163 to 343 C) holding at the selected temperature within 15 F (8 C) for not less than two hours and cooling in air. 3.6.3 Copper plating when used
43、 for masking shall be chemically stripped. The stripping process shall not roughen, pit, or embrittle the base metal or adversely affect part dimensions. 3.6.4 Paint or paste masking materials shall be removed without affecting the surface roughness. Copyright SAE International Provided by IHS under
44、 license with SAENot for ResaleNo reproduction or networking permitted without license from IHS-,-,-SAE AMS 2759/8A - 5 - 3.7 Properties Nitrided surfaces shall conform to the following requirements. 3.7.1 Type of Compound Layer When the phase composition of the compound layer is specified, verifica
45、tion shall be performed by using metallurgical evaluation. If required by the cognizant engineering organization, X-ray diffraction shall be used. See 8.8 and 8.9. 3.7.1.1 Compound zone layer depth (thickness), when specified, shall be measured metallographically at 400X magnification or greater. 3.
46、7.1.2 Uniformity of Nitride Case There shall be no continuous nitride network or grains fully encircled by nitrides along boundaries when examined at 400X magnification or greater. 3.7.2 Case depth shall be as specified by the cognizant engineering organization. The effective and total case depths s
47、hall be determined by microhardness traverse in accordance with ASTM E 384, on metallographically prepared specimens or parts, or in accordance with ARP1820. Unless specified otherwise case depth shall be defined as in 3.7.2.1 and 3.7.2.2. 3.7.2.1 Total Case Depth Unless otherwise specified, total c
48、ase depth is the depth below the surface at which microhardness is 50 HV or 50 HK units, higher than that of core, as determined by microhardness traverse in accordance with ASTM E 384. 3.7.2.2 Effective Case Depth Unless otherwise specified, is the maximum depth below the surface at which a specifi
49、ed hardness is achieved as measured by microhardness traverse in accordance with ASTM E 384. 3.7.2.2.1 Low Alloy Steels such as 4140 and 4130 Unless otherwise specified, effective case depth is the maximum depth below the surface at which a hardness of 40 HRC equivalent is achieved. 3.7.2.2.2 Tool Steels such as A, D, H, M, and CPM Unless otherwise specified, effective case depth is the maximum depth below the surface at which a hardness of
