1、 STD-ALMA 72bC-ENGL 1777 b87575 b205 953 U AGMA 926- C99 (Replaces AGMA 246.02a) AMERICAN GEAR MANUFACTURERS ASSOCIATION Recommended Practice for Carburized Aerospace Gearing 4 0 AGMA INFORMATION SHEET (This Information Sheet is NOT an AGMA Standard) STD-AGMA 92bC-ENGL L97 198 b87575 000bZb 3T RI Am
2、erican Gear Manufacturers ecommeded Practice for Carburized Aerospace Gearing (Replaces AGMA 246.02a) CAUTION NOTICE: AGMA technical publications are subject to constant improvement, revision or withdrawal as dictated by experience. Any person who refers to any AGMA technical publication should be s
3、ure that the publication is the latest available from the As- sociation on the subject matter. Tables or other self-supporting sections may be quoted or extracted. Credit lines should read: Extracted from AGMA 926-C99, Recommended Practice for Carburized Aero- space Gearing, with the permission of t
4、he publisher, the American Gear Manufacturers Association, 1500 King Street, Suite 201, Alexandria, Virginia 22314.1 AGMA 926-C99 Association Approved May 20, 1999 ABSTRACT This document establishes recommended practices for material case and core properties, microstructure and processing procedures
5、 for carburized AISI 931 O aerospace gears. This document is not intended to be a prac- tice for any gears other than those applied in aerospace. Published by American Gear Manufacturers Association 1500 King Street, Suite 201, Alexandria, Virginia 22314 Copyright O 1999 by American Gear Manufacture
6、rs Association All rights reserved. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without prior written permission of the publisher. Printed in the United States of America ISBN: 1-55589-758-4 II . STDmAGMA 92bC-ENGL 1999 Ob87575 000b207 Z
7、2b U AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 926-C99 Contents Page Foreword . iv I Scope . 1 2 Application . 1 3 Aerospace Grade definitions 1 4 Materials 1 5 Metallurgical properties 2 6 Preliminary treatments . 3 7 Carburizing 5 8 9 Hardening . 6 10 Quality control 6 Subcritical annealing - o
8、ptional procedure 5 Tables I 2 Typical aerospace carburizing steels . 2 Typical heat treat process for AISI 9310 Aerospace Grade 3 carburized gears 5 Fig u res I 2 Minimum effective case depth. he. for carburized gears . 3 Standards of acceptance for AISI 931 O carbide networks (root area) . 4 Bibli
9、ography . 8 iii b87575 000b208 Lb2 I AGMA 926-C99 AMERICAN GEAR MANUFACTURERS ASSOCIATION Foreword The foreword, footnotes and annexes, if any, in this document are provided for informational purposes only and are not to be construed as a part of AGMA Information Sheet 926-C99, Recommended Practice
10、for Carburized Aerospace Gearing. AGMA Standard 246.02A, Practice for Carburized Aerospace Gearing, dated June, 1983, was prepared by the Metallurgy and Materials Committee and was designed to be a guide to manufacturers who make carburized gears to the high quality standards required of gears used
11、in aerospace applications. AGMA 926-C99 has been updated by the Aerospace Gearing Committee and replaces AGMA 246.02A, and includes references to the latest standards of other standard setting bodies including SAE/AMS and AISI. Also, reference is made to modern steel making techniques and carburizin
12、g methods which produce gears to three classes of quality. AGMA Standards and Information Sheets are subject to constant improvement, revision, or withdrawal as dictated by experience. Any person who refers to AGMA technical publications should satisfy himself that he has the latest information avai
13、lable from the Association on the subject matter. AGMA 926-C99 was approved by the AGMA Technical Division Executive Cornmittee on May 20,1999. Suggestions for improvement of this standard will be welcome. They should be sent to the American Gear Manufacturers Association, 1500 King Street, Suite 20
14、1, Alexandria, Virginia 22314. iv b87575 000bZ UT9 M AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 926-C99 PERSONNEL of the AGMA Aerospace Gearing Committee Chairman: A.G. Meyer . AlliedSigna1 Engines Vice Chairman: K. Buyukataman UTC Pratt premium aircraft quality; ultra-premium aircraft quality Aer
15、ospace Grade 1 materials are typically air melted (AM). Aerospace Grade 2 materials are typically single vacuum melted (SVM), while Aerospace Grade 3 materials are typically double vacuum melted (DVM) from the initial stock. 4 Materials 4.1 Materiais selection The following paragraphs describe the s
16、uggested materials for carburized aerospace gearing. The grades of steel recommended are based on the indicated specifications of the American Iron and Steel Institute (AISI) and the Society of Automotive Engineers/Aerospace Material Specifications (SAE/ AMS). Typical carburizing steels are shown in
17、 table 1. NOTE: It is to be understood that the materials listed are suggestions only and that specific material selection should be made by the engineer on the basis of material hardenability, material cleanliness, performance, and economic considerations. Performance criteria include, but are not
18、limited to, the following: toughness, notch sensitivity, bending and contact fatigue, bending strength, wear resistance, high temperature and environmental operational characteristics. 4.2 Aerospace quality grades - carburizing alloy steels For aerospace applications, Aerospace Grade 3 and 2 materia
19、ls require conformance to ANSI/SAE AMS 2300 quality level, while Aerospace Grade 1 material requires ANSI/SAE AMS 2301. Aerospace Grade 3 and 2 materials may also require additional specific mill processing conditions such as tighter ultrasonic inspection requirements. These requirements are more st
20、ringent than those given in ANSI/AGMA 2001-C95, table 9, note 13 or other industry standards. 1 W b87575 000b211 757 Bl AGMA 926-C99 AMERICAN GEAR MANUFACTURERS ASSOCIATION Surface, HRC2) 58-64 58-62 60-64 58-60 59-64 58-62 Table 1 - Typical aerospace carburizing steels Core, HRC 32-42 42-48 36-44 4
21、8-52 36-44 34-42 Material AIS1 9310 33v VASCO X2M3) HP 9-4-30 PYROWEAR 533) CBS600 AMS spec 626516260 64271641 1 (None) 6526 6308 6255 Typical applications Main drive, accessory, actuators Actuators Main drive, high temperature4) Actuators Main drive, high temperature4) High temperature4) NOTES: 1)
22、Drawing specified hardness limits are based on performance considerations and are normally narrower than the full range shown in this table. 2) Rockwell hardness scale (HRC) is shown for direct comparison only. In general, that scale is not specifically recom- mended for measurement where other, mor
23、e appropriate hardness scales are commonly used. 3, Proprietary material designation. 4, High temperature property - capable of operating somewhat below the tempering temperature for indefinite periods. 4.3 Forgings tooth surface at 112 whole depth. Effective case When optimum properties and/or reli
24、ability are desired, double vacuum melted steel forgings should be used. It is recommended that forgings have a minimum forging cross sectional reduction (ratio) of 3:l. A metallurgical analysis should be performed on one pari from the first production run. The analysis should include, but not be li
25、mited to, the inspection of grain flow, banding, cleanliness, dis- tribution of inclusions and grain size. Forgings should conform to the requirements of ANSI/SAE AMS 23758, MIL-F-7190B or equivalent. 5 Metallurgical properties 5.1 Drawing specifications The properties usually specified on engineeri
26、ng drawings for carburized aerospace gearing are (1) case depth range, (2) minimum surface hardness (or range), and (3) core hardness range. Surface and core hardness values should be in accordance with table 1. In addition, carburized aerospace gears require limitations on the case and core microst
27、ruc- ture as outlined in 5.3 and 5.4. 5.2 Case depth The case depth for carburized aerospace gearing is specified as the effective case depth normal to the depth is defined as the perpendicular distance from the surface of the case on a finished part to a point where the hardness is equivalent to 50
28、 HRC, as measured by a microhardness tester. The tester load used should be 500 grams. Variations in the effective case depth at the gear tooth pitch diameter, root fillet, and center of the root should be specified and mutually agreed upon between the gear manufacturer and purchaser. The minimum ef
29、fec- tive case depth for gears with respect to diametral pitch should be in accordance with figure 1 unless otherwise specified. NOTE: When core hardness exceeds 45 HRC, the method for determining effective case depth shall be specified and agreed upon between customer and manufacturer. 5.3 Case and
30、 core microstructure The case and core microstructure requirements for carburized aerospace gearing should be specified and agreed upon between the gear manufacturer and purchaser. The location where the microstruc- tural requirements are to be met should be detailed, e.g., in the root area or on th
31、e flank. The type of test sample to be evaluated should also be specified, .e., a test slug or gear segment of the identical material. Typical requirements are: 2 . AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 926-C99 z 0.001 I I IIIII I1111 III I1111 r the values shown on the case depth curve are t
32、o be used as a guide. - For gearing in which maximum performance is required, detailed studies must be made of the application, loading, and manufacturing procedures to obtain desirable gradients of both hardiness and inter- - na1 stress. Furthermore, the method of measuring the case as well as the
33、allowable tolerance in case depth should be specified and agreed upon between the gear manufacturer and purchaser. I - Case. The case is primarily tempered martensite with a typical maximum of 1 O percent retained austenite as evaluated metallographical- ly using an appropriate etchant at a magnific
34、ation of 500X. The retained austenite percentage may be determined by x-ray diffraction instead of by metallographic technique. Carbide network, .e., undissolved carbides, should be scattered and discontinuous (as shown in figures 2a and 2b). A semi-continuous or very heavy continuous net- work, as
35、shown in figures 2c and 2d (AISI 9310 root area) are not permitted. Carbide network should be evaluated particularly in the root areaof the gear tooth test sample. Decarburization and intergranular oxidation are not permitted on ground surfaces. drawing. Variation of hardness between bands should no
36、t exceed 3 points HRC for Aerospace Grade 3, and 4 points HRC for Aerospace Grade 2, as converted by a microhardness tester with a 500 gram load. 5.4 Carbon content The desired carbon content at the surface of the carburized tooth should be specified and agreed upon between the gear manufacturer and
37、 the purchaser. A method of determining and evaluating this requirement should also be detailed. 6 Preliminary treatments 6.1 Preliminary treatments and considerations - Core. The core is primarilytempered marten- site. Banding, which results from the steel manufacturing should be kept at a minimum.
38、 If banding does exist, all direct core hardness readings must be within the range specified by the StreSS relieving heat treatnIentS may be performed at any time prior to carburizing. All Aerospace Grade 2 and 3 gears are to be quenched and tempered to approximately 30 HRC or normalized and tempere
39、d before machining prior to carburizing. 3 AGMA 926499 AMERICAN GEAR MANUFACTURERS ASSOCIATION . a - Acceptable light discontinuous network b - Acceptable heavy partially continuous network c - Not acceptable semi -continuous network d - Not acceptable very heavy continuous network NOTE: Alkaline so
40、dium pyrate electrolytic etch - all photomicrographs at 400X. Figure 2 - Standards of acceptance for AISI 9310 carbide networks (root area) 6.2 Furnace requirements All furnaces used for carburizing and hardening should be in accordance with requirements of MIL-H-6875H and ANSI/SAE AMS 2750, with re
41、gard to furnace temperature uniformity, tempera- ture control, and accuracy of temperature recording and control instruments. 6.3 Masking Surfaces which are not to be carburized should be masked off with a suitable masking vehicle, or have sufficient excess stock to permit complete removal of the ca
42、se by machining after carburizing. Masking material should be capable of preventing change in carbon content of the surface being protected. Experience has shown copper plating 0.025 mm (0.001 inch) minimum to be an effective method of masking. Care should be taken to ensure that the copper plating
43、does not leak onto areas that are to be carburized. 6.4 Furnace loading Parts to be carburized should be loaded into the furnace in such a manner that the gear teeth are not in contact, and the surfaces to be carburized are not touching other parts. When surfaces to be carburized must touch heat tre
44、atment fixtures, the contacting surfaces should be a non-critical area and the contact area of the fixture should be rounded. 4 AMERICAN GEAR MANUFACTURERS ASSOCIATION AGMA 926-C99 7 Carburizing 7.1 Method Gears may be carburized by gas or vacuum methods. Pack carburizing is not permitted. The combi
45、nation of carburizing and diffusing cycles may be used to produce a gradual case to core carbon gradient. Parts to be carburized shall be cleaned of any surface scale, grease or oil prior to carburizing. Generally, internal carburizing specifications are developed by the gear manufacturer. MIL-S-609
46、0 may also be used as a minimum. 7.2 Carburizing process The carburizing temperature for aerospace gears should permit carburization within an economical time period, yet not permit substantial grain growth. Carburizing temperatures between 845C and 955C (1 550F and 1750F) are recommended for aerosp
47、ace gearing. Carburizing time should start when the entire furnace load has reached carburiz- ing temperature and carburizing atmosphere has been attained. Carburized parts should be cooled in a protective atmosphere to prevent decarburization. Aerospace Grade 3 and Aerospace Grade 2 gears should be
48、 carburized in furnace equipment with continuous carbon potential control. Table 2 shows a typical carburizing process for a Aerospace Grade 3 gear. Note that many of the carburizing materials listed in the table 1 require a surface treatment prior to carburizing. This pre-oxidation procedure must b
49、e accomplished in accordance with the proper specifi- cation requirements. 8 Subcritical annealing - optional proced Ure Gears may be given a subcritical annealing treat- ment immediately after carburizing and before hardening. This should be done as soon as the parts are cool enough to handle. The purpose of this annealing is: (1) to relieve the stresses developed during cooling after carburizing; (2) to refine the case structure by spheroidizing any carbides present after carburizing; (3) to facilitate machining of the surfaces that will not be carburized and hard
