Agma-923-b05 681o6b

AGMA 923- B05

AMERICAN GEAR MANUFACTURERS ASSOCIATION

AGMA 923- B05

Metallurgical Specifications for Steel Gearing

AGMA INFORMATION SHEET (This Information Sheet is NOT an AGMA Standard)

American Gear Metallurgical Specifications for Steel Gearing Manufacturers AGMA 923--B05 CAUTION NOTICE: AGMA technical publications are subject to constant improvement, Association revision, or withdrawal as dictated by experience. Any person who refers to any AGMA technical publication should be sure that the publication is the latest available from the Association on the subject matter. [Tables or other self--ing sections may be quoted or extracted. Citations should read: See AGMA 923--B05, Metallurgical Specifications for Steel Gearing, published by the American Gear Manufacturers Association, 500 Montgomery Street, Suite 350, Alexandria, Virginia 22314, http://www.agma.org.] Approved May 3, 2005

ABSTRACT This document identifies metallurgical quality characteristics which are important to the performance of steel gearing. The AGMA gear rating standards identify performance levels of gearing by heat treatment method and grade number. For each heat treatment method and AGMA grade number, acceptance criteria are given for various metallurgical characteristics identified in this document. Published by

American Gear Manufacturers Association 500 Montgomery Street, Suite 350, Alexandria, Virginia 22314 Copyright © 2005 by American Gear Manufacturers 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--848--3

ii


AGMA 923--B05

Contents Page

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv 1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4 Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5 Metallurgical requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Tables 1 2 3 4

Metallurgical characteristics for through hardened gearing . . . . . . . . . . . . . . . Metallurgical characteristics for carburize and hardened gearing . . . . . . . . . Metallurgical characteristics for induction or flame hardened gearing . . . . . . Metallurgical characteristics for nitrided gearing . . . . . . . . . . . . . . . . . . . . . . . .

15 17 22 27

Figures 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Continuous carbide network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Semi--continuous carbide network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Discontinuous carbides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Dispersed carbides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Solid on shaft pinion blank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Bore style gearing blank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Disc style gearing blank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Web style gear blank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Intergranular oxidation in carburized gearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Non--martensitic transformation products in carburized gearing . . . . . . . . . . . 8 Tempered martensite and 5% retained austenite in carburized gearing . . . . 10 Tempered martensite and 20% retained austenite in carburized gearing . . . 10 Tempered martensite and 30% retained austenite in carburized gearing . . . 10 Variations in hardening pattern obtainable on gear teeth with flame or induction hardening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

© AGMA 2005 ---- All rights reserved

iii

AGMA 923--B05


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 923--B05, Metallurgical Specifications for Steel Gearing.] In November, 1984, an ad hoc Metallurgy and Gear Rating Committee met to define the factors required to qualify the various metallurgical quality grades that were to be introduced into the gear rating standard that eventually became ANSI/AGMA 2001-- B88, Fundamental Rating Factors and Calculation Methods for Involute Spur and Helical Gear Teeth. In May, 1988, ANSI/AGMA 6033--A88, Standard for Marine Propulsion Gear Units -- Part 1, Materials, was published using a short list of metallurgical factors in table form. In September, 1988, ANSI/AGMA 2001--B88 was published using metallurgical factors in table form. Starting in July, 1992, AGMA representatives participated in writing ISO 6336--5, Calculation of Load Capacity of Spur and Helical Gears -- Part 5: Strength and Quality of Materials, which was a modification of the tables in ANSI/AGMA and DIN Standards. In February, 1993, AGMA 6002--B93, Design Guide for Vehicle Spur and Helical Gears, was published using a modified version of the tables used in ANSI/AGMA 2001--B88. In September, 1993, the AGMA Metallurgy and Materials Committee accepted the task of consolidating the various tables to avoid redundancies and conflicting requirements, and started work on AGMA 923--A00, Metallurgical Specifications for Steel Gearing. In January, 1995, a revised ANSI/AGMA 2001--C95 was published using a version of the ANSI/AGMA 2001--B88 tables as revised by the AGMA Helical Gear Rating Committee. In November, 1997, a revised ANSI/AGMA 2003--B97, Rating the Pitting Resistance and Bending Strength of Generated Straight Bevel, Zerol Bevel and Spiral Bevel Gear Teeth, was published using a version of the ANSI/AGMA 2001--B88 tables as revised by the AGMA Bevel Gearing Committee. The committee reviewed all metallurgical tables of the gear rating standards ANSI/AGMA 2001--B88, ANSI/AGMA 2003--A86, and ISO 6336--5:1996 and their proposed revisions to develop consolidated tables describing the metallurgical characteristics associated with each specific type of heat treatment and metallurgical quality grade. Effort was made to reference ISO specifications where possible. The consolidated tables were submitted to the gear rating committees for their agreement and are published here for reference by other standards. AGMA’s goal is to develop a consistent metallurgical specification which reflects the quality requirements for steel gearing. AGMA 923--A00 was such a document, and was intended to be consistent with the applicable portions of ISO 6336--5:1996, to the extent possible while the two standards were in parallel development. The AGMA Technical Division Executive Committee approved the publication of AGMA 923--A00 in August, 2000. This edition of the information sheet, AGMA 923--B05, incorporates changes to item 8, microstructure, of table 1, Metallurgical characteristics for through hardened gearing. The balance of the document remains unchanged. The AGMA Technical Division Executive Committee approved the publication of AGMA 923--B05 in May, 2005. Suggestions for improvement of this information sheet will be welcome. They should be sent to the American Gear Manufacturers Association, 500 Montgomery Street, Suite 350, Alexandria, Virginia 22314.

iv



AGMA 923--B05

PERSONNEL of the AGMA Metallurgy and Materials Committee Chairman: Phil Terry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lufkin Industries, Inc. Vice Chairman: Dale J. Weires . . . . . . . . . . . . . . . . . . . . . . . Boeing Defense & Space Group

ACTIVE C. Berndt . . . . . . . . . . . . . . . . . . . . . . . . . . I. Botto . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Breuer . . . . . . . . . . . . . . . . . . . . . . . . . R.J. Cunningham . . . . . . . . . . . . . . . . . . . G. Diehl . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Herring . . . . . . . . . . . . . . . . . . . . . . . . . D.R. McVittie . . . . . . . . . . . . . . . . . . . . . . J. Mertz . . . . . . . . . . . . . . . . . . . . . . . . . . . R.L. Schwettman . . . . . . . . . . . . . . . . . . . M. Stein . . . . . . . . . . . . . . . . . . . . . . . . . . . J.B. Walenta . . . . . . . . . . . . . . . . . . . . . . . L.L. Witte . . . . . . . . . . . . . . . . . . . . . . . . . .


Caterpillar, Inc. FFE Minerals Metal Improvement Company Consultant Philadelphia Gear Corporation The Herring Group, Inc. Gear Engineers, Inc. Falk Corporation Xtek, Inc. Applied Process Southridge, Inc. Caterpillar, Inc. General Motors Corporation/Allison Transmission Division

v

AGMA 923--B05


(This page is intentionally blank)

vi



American Gear Manufacturers Association --

Metallurgical Specifications for Steel Gearing

AGMA 923--B05

ANSI/AGMA 2001--C95, Fundamental Rating Factors and Calculation Methods for Involute Spur and Helical Gear Teeth ANSI/AGMA 2003--B97, Rating the Pitting Resistance and Bending Strength of Generated Straight Bevel, Zerol Bevel and Spiral Bevel Gear Teeth ANSI/AGMA 2004--B89, Gear Materials and Heat Treatment Manual ANSI/AGMA 2007--B92, Surface Temper Etch Inspection After Grinding ANSI/AGMA 6002--B93, Design Guide for Vehicle Spur and Helical Gears

1 Scope This information sheet recommends steel material and metallurgical quality characteristics for use in conjunction with AGMA gear rating standards. This information sheet identifies specifications and requirements for various metallurgical quality grades for through hardened, carburize and hardened, induction and flame hardened, and nitrided gearing. Characteristics covered include raw material, heat treatment and post heat treat processing, and their associated inspections. Topics related to gear design and rating, such as case depth, stress numbers, and quality control sampling plans are not included in this document.

2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this document. At the time of initial development, the editions shown were valid. All standards are subject to revision, and parties to agreements based on this document are encouraged to investigate the possibility of applying the most recent editions of the standards shown below. AGMA 904--C96, Metric Usage ANSI/AGMA 1010--E95, Appearance of Gear Teeth -- Terminology of Wear and Failure ANSI/AGMA 1012--F90, Gear Nomenclature, Definitions of with Symbols


ANSI/AGMA 6032--A94, Standard for Marine Gear Units: Rating ASTM A29--99, Specification for Steel Bars, Carbon and Alloy, Hot--Wrought and Cold--Finished, General Requirements for ASTM A148--93b(1998), Specification for Steel Castings, High Strength, for Structural Purposes ASTM A255--99, Test Method for Determining Hardenability of Steel ASTM A275--98, Test Method for Magnetic Particle Examination of Steel Forgings ASTM A290--95(1999), Specification for Carbon and Alloy Steel Forgings for Rings for Reduction Gears ASTM A291--95(1999), Specification for Steel Forgings, Carbon and Alloy, for Pinions, Gears and Shafts for Reduction Gears ASTM A304--96, Specification for Carbon and Alloy Steel Bars Subject to End--Quench Hardenability Requirements ASTM A322--91(1996), Specification for Steel Bars, Alloy, Standard Grades ASTM A370--97a, Test Methods and Definitions for Mechanical Testing of Steel Products ASTM A388--95, Practice for Examination of Heavy Steel Forgings

Ultrasonic

ASTM A519--96, Specification for Seamless Carbon and Alloy Steel Mechanical Tubing ASTM A534--94, Specification for Carburizing Steels for Anti--Friction Bearings ASTM A609--91(1997), Practice for Castings, Carbon, Low--Alloy, and Martensitic Stainless Steel, Ultrasonic Examination Thereof

1

AGMA 923--B05


ASTM A751--96, Test Methods, Practices, and Terminology for Chemical Analysis of Steel Products ASTM A837--91(1996)1, Specification for Steel Forgings, Alloy, for Carburizing Applications ASTM A866--94, Specification for Medium Carbon Anti--Friction Bearing Steel ASTM A919--84 (1993)1, Terminology Relating to Heat Treatment of Metals ASTM A941--99a, Terminology Relating to Steel, Stainless Steel, Related Alloys, and Ferroalloys ASTM A956--97, Test Method for Equotip Hardness Testing of Steel Products ASTM E3--95, Practice Metallographic Specimens

for

Preparation

of

ASTM E8--99, Test Methods for Tension Testing of Metallic Materials ASTM E10--98, Test Method for Brinell Hardness of Metallic Materials ASTM E18--98, Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials ASTM E23--98, Test Methods for Notched Bar Impact Testing of Metallic Materials ASTM E45--972, Test Methods for Determining the Inclusion Content of Steel ASTM E92--82(1997)2, Test Method for Vickers Hardness of Metallic Materials ASTM E110--82(1997)2, Test Method for Indentation Hardness of Metallic Materials by Portable Hardness Testers ASTM E112--96, Test Methods for Determining Average Grain Size ASTM E125--63(1997), Reference Photographs for Magnetic Particle Indications on Ferrous Castings ASTM E140--971, Hardness Conversion Tables for Metals (Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Rockwell Superficial Hardness, Knoop Hardness, and Scleroscope Hardness) ASTM E350--95(1997)1, Test Methods for Chemical Analysis of Carbon Steel, Low--Alloy Steel, Silicon Electrical Steel, Ingot Iron, and Wrought Iron ASTM E384--89(1997)2, Microhardness of Materials

2

Test

Method

for

ASTM E407--99, Practice for Microetching Metals and Alloys ASTM E415--99, Test Method for Optical Emission Vacuum Spectrometric Analysis of Carbon and Low--Alloy Steel ASTM E428--92, Practice for Fabrication and Control of Steel Reference Blocks Used in Ultrasonic Inspection ASTM E709--95, Guide for Magnetic Particle Examination ASTM E1077--91, Test Methods for Estimating the Depth of Decarburization of Steel Specimens ASTM E1444--94a, Practice for Magnetic Particle Examination ISO 642:1979, Steel -- Hardenability test by end quenching (Jominy test) ISO 643:1983, Steels -- Micrographic determination of the ferritic or austenitic grain size ISO 683--1:1987, Heat--treatable steels, alloy steels and free--cutting steels -- Part 1: Direct--hardening unalloyed and low--alloyed wrought steel in form of different black products ISO 683--11:1987, Heat--treatable steels, alloy steels and free--cutting steels -- Part 11: Wrought case--hardening steels ISO 4967:1979, Steel -- Determination of content of non--metallic inclusions -- micrographic method using standard diagrams ISO 6336--5:1996, Calculation of load capacity of spur and helical gears -- Part 5: Strength and quality of materials ISO 14104:1995, Surface temper etch inspection after grinding SAE/AMS 2300G, Aircraft--Quality Steel Cleanliness, Magnetic Particle Inspection Procedure SAE/AMS 2301H, Cleanliness, Aircraft Quality Steel Magnetic Particle Inspection Procedure SAE/AMS 2304, Special Aircraft--Quality Steel Cleanliness, Magnetic Particle Inspection Procedure SAE/AMS--S--13165, Shot Peening of Metal Parts SAE J419 Dec 83, Methods of Measuring Decarburization SAE J422 Dec 83, Microscopic Determination of Inclusions in Steels



SAE J423 Dec 83, Methods of Measuring Case Depth SAE J864 May 93, Surface Hardness Testing with Files

3 Definitions The used in this document, wherever applicable, conform to AGMA 904--B89, ANSI/AGMA 1012--F90, and ASTM A919, but they have been modified to cover only those concepts applicable to this document. For definitions of technical not included in this clause, see ANSI/AGMA 1012--F90, ANSI/AGMA 2004--B89, ASTM A919, and ASTM A941. Key used in this document are defined as follows: NOTE: These definitions may differ from those in other AGMA publications. The should not assume that familiar can be used without a careful study of their definitions.

alloy steel: A steel containing specified quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, copper, silicon, sulfur, and phosphorus) added to increase hardenability and to affect changes in mechanical properties. annealing: The heating to and holding at a suitable temperature above the upper transformation temperature and then cooling, typically in the furnace at a suitable rate, for reducing hardness, improving machinability, producing a desired microstructure, or obtaining desired mechanical properties. austenite: A solid solution of one or more elements in face--centered cubic iron. In carbon and low alloy steels this phase is stable only at elevated temperatures and is non--magnetic. austenitizing: The forming of austenite by heating a ferrous material into the transformation range (partial austenitizing) or above the transformation range (complete austenitizing). bainite: An aggregate of ferrite and cementite resulting from the transformation of austenite at temperatures below the pearlite range but above the martensite start temperature. Its appearance is feathery if formed in the upper part of the bainite transformation range and acicular, resembling tempered martensite, if formed in the lower part.


AGMA 923--B05

banding: A segregated structure consisting of alternating, nearly parallel bands of different chemical composition, typically aligned in the direction of primary hot working. Segregation is frequently expressed as a departure from the average chemical composition. Elements which tend to segregate are sulfur, phosphorus, carbon, silicon, and manganese. base hardness: The surface hardness in the tooth area that was developed by through hardening and not changed by subsequent heat treatments. If the material selected has adequate hardenability for the required hardness and section size combination, this surface hardness represents the expected hardness at the intersection of the root circle and the centerline of the tooth at mid--face width. Base hardness is applicable to through hardened, induction hardened, flame hardened, and nitrided gearing, but not to carburize and hardened gearing. bending strength: The bending strength of gear teeth related to their resistance to gear tooth bending failure. Bending failure is a fatigue phenomenon usually resulting in cracking at the tooth root fillet. Typical cracks and fractures are illustrated in ANSI/ AGMA 1010--E95. See standards such as ANSI/ AGMA 2001--C95, ANSI/AGMA 2003--B97, ANSI/AGMA 6002--B93, or ANSI/AGMA 6032--A94. capable of: The producer documents that the material was produced with the processing steps and controls that the producer has established to assure compliance with the specification, but the testing to confirm compliance is not required. carbide: A microstructural phase which is a compound of metal (M) and carbon (C) having the chemical formula of MxCy. See figures 1 through 4 for photomicrographs of various classifications of carbide structures (white constituent) in tempered martensite. carbon potential: A measure of the ability of a furnace environment containing active carbon to alter or maintain, under prescribed conditions, the carbon content of the steel. carbon restoration: Carburizing to replace the carbon lost in the surface layer due to previous thermal processing. carbon steel: A steel having no specified minimum quantity of alloying elements except manganese and silicon.

3

AGMA 923--B05

5% nital etch 400 X mag.

Figure 1 -- Continuous carbide network


Figure 2 -- Semi--continuous carbide network

4



Figure 3 -- Discontinuous carbides


Figure 4 -- Dispersed carbides



carburizing: A heat treatment process in which an austenitized steel is brought into with a carbonaceous atmosphere of sufficient carbon potential to cause adsorption of carbon at the surface and by diffusion to create a concentration gradient. Carburizing is generally followed by quenching and reheating (tempering) of an item to produce a hardened and tempered case. case: The outer portion that has been made harder than the inner portion (see core hardness) as a result of altered composition, microstructure, or both, by treatments such as carburize and hardening, induction hardening, flame hardening, and nitriding. case depth: See the specific type of case depth such as effective or total case depth. case hardening: The generic terminology covering carburize and nitride hardening applicable to steel that change the chemical composition and microstructure of the surface layer by adsorption of carbon, nitrogen, or a mixture of the two and by diffusion, create a chemical composition gradient.

AGMA 923--B05

controlling section: The section size which has the greatest effect in determining the rate of cooling during quenching at a location where the specified hardness is required. Figures 5 through 8 illustrate the controlling section size for various gearing configurations whose teeth are machined after heat treatment and whose hardness must be maintained at the roots of the teeth. The maximum permitted section size for an alloy steel increases with the hardenability of the alloy steel. Teeth

6 in (150 mm)

8 in (200 mm)

6 in (150 mm)

Figure 5 -- Solid on shaft pinion blank

Teeth

Adsorption of carbon processes involve a subsequent quenching to harden, while adsorption of nitrogen does not require quenching to harden. case hardness: For carburize and hardened gearing and induction or flame hardened gearing the hardness is measured at 0.002--0.004 inches (0.05 -0.10 mm) below the surface using a microhardness test technique. For nitriding specifications surface hardness is typically used rather than case hardness.

Controlling section: 8 in (200 mm) diameter

4 in (100 mm) 8 in (200 mm) 12 in (300 mm)

Controlling section: 2 in (50 mm) wall thickness NOTE: If the bore diameter is less than 20 percent of the length of the bore, then the controlling section is determined by figures 5 or 7.

Figure 6 -- Bore style gearing blank Case hardness is not to be confused with surface hardness which is taken directly on the surface using a conventional or portable hardness tester.

Teeth

cementite: A hard compound of iron and carbon, known chemically as iron carbide, having the chemical formula Fe3C. cold treatment: The preferred terminology for cooling carburize and hardened parts to temperatures typically below minus 80°F (minus 60°C) to reduce retained austenite. Cold treatment is also known as sub--zero treatment or deep freezing. If cooled to below minus 300°F (minus 185°C), the correct terminology is deep cryogenic treatment.


12 in (300 mm) 1.5 in (40 mm) 2 in (50 mm)

Controlling section: 2 in (50 mm) thickness

Figure 7 -- Disc style gearing blank

5

AGMA 923--B05

AMERICAN GEAR MANUFACTURERS ASSOCIATION Teeth

the hardness at a specified location such as surface, quarter radius, mid--radius, or centerline. decarburization: The loss of carbon from the near--surface of a ferrous material.

36 in 32 in (900 mm) (800 mm)

Controlling section: 2 in (50 mm) rim thickness

8” (200 mm)

Figure 8 -- Web style gear blank

deoxidizing: The removal of oxygen from molten steel by addition of suitable elements, such as silicon and aluminum which react with oxygen, primarily forming discard slag. direct quenching: The quenching of carburized gearing directly after the carburizing operation, generally from a reduced temperature within the austenitic range.

Note that a flat plate with thickness equal to the diameter of a round bar will cool slower than the bar. The thickness of a plate equivalent in cooling rate to that of a round bar (equivalent controlling section size) is 0.7 times the bar diameter.

effective case depth: The distance from the finished tooth surface to a specific sub--surface hardness value. Stock removal done after heat treating will reduce the as heat treated effective case depth and potentially the surface hardness.

The controlling section size for the selection of an appropriate type of steel and specified hardness combination must consider part configuration at the time of heat treatment. Special stock additional allowances, such as those used to minimize distortion during heat treatment, must be considered.

Carburize and hardened The effective case depth is measured normal to the finished gear surface to a location where the hardness number is 50 HRC (542 HK500 or 515 HV500 min) by conversion from a microhardness test result. Note that ISO 6336--5 uses 550 HV500 min, which converts to 52.4 HRC or 583 HK500, as its criterion for determining the effective case depth. It is recognized that the effective case depth of carburize and hardened gear teeth varies with location on the gear tooth.

converted hardness: The hardness number reported on a scale different from the scale used for hardness testing. For example an actual microhardness test reading of 542 HK500 has a converted hardness of 50 HRC and would be properly reported as 50 HRC (542 HK500) with the hardness number and scale in parentheses representing the actual testing result and method. core hardness: The hardness at the intersection of the root circle and the centerline of the tooth at mid--face width that was developed during the hardening of carburized gearing. An alternative location is given by ISO 6336--5, table 4, item 8. The material must have adequate hardenability for the required hardness and section size combination for the required core hardness to be achieved. The quench severity must also be adequate in order to achieve the required core hardness. The term core hardness is applicable to carburize and hardened gearing. Induction, flame, and nitride hardened gearing may use the term base hardness. The core hardness of non--tooth portions (such as journal areas of carburize and hardened gearing), is

6

Induction and flame hardened For Grades 1 and 2 gearing, the effective case depth is measured from the finished surface to a location where the hardness number is equivalent to 10 HRC numbers below the specified minimum surface hardness. Grade 3 induction hardened gearing uses the carburize and hardened definition for its effective case depth definition. Note that ISO 6336--5 uses the distance from the surface to the location where the hardness is equal to 80% of the specified minimum surface hardness as its criterion for determining the effective case depth. Nitrided The effective case depth is measured from the finished surface to a location where the hardness number is equivalent to 40.8 HRC (421 HK500 or 400 HV500 min) by conversion from a microhardness test result. If the core hardness is more than 38.9 HRC (391 HK500 or 380 HV500 min), core hardness plus 54 HK500 or 50 HV500 min (4.6 HRC) may be used as the



AGMA 923--B05

definition of nitrided effective case depth. Note that this is the same definition used in ISO 6336--5.

hardness: See specific kind of hardness such as base, case, core or surface.

ferrite: A solid solution of one or more elements in body--centered cubic iron. In carbon and alloy steels this phase is stable at room temperature.

hardness conversion chart: A published document for use in converting from one hardness testing scale to another.

flame hardening: A case hardening process in which only the surface layer of the work piece is heated by a flame to above the upper transformation temperature and immediately quenched.

Hardness conversion charts should be used with great caution since discrepancies of 0.3 HRC numbers at 30 HRC to 3.9 HRC numbers at 60 HRC, have been noted between various published conversion charts. Therefore, it is suggested that the conversion chart used for testing and reporting be specified. Some of the more popular hardness conversion charts are found in ASTM A370, ASTM E140, ISO 6336--5, and certain individual corporate documents and standards. For this document, ASTM A370 is used and should be used whenever no other document is specified.

free ferrite: The ferrite that is formed directly during cooling without simultaneous formation of carbide. grain size: The dimensions of the grains, or crystals, in a polycrystalline metal exclusive of twinned regions and sub--grains when present. The ASTM grain size is a designation bearing a relationship to average intercept distance at 100 diameters magnification. Commercial grain size is categorized as either coarse (grain size 1--4) or fine (grain size 5 or finer). hardenability: The property of a ferrous alloy that determines the depth and distribution of hardness induced by quenching. hardened depth: For induction or flame hardened gearing, alternative terminology for effective case depth.

induction hardening: A surface hardening process in which only the surface layer of the work piece is heated by electrically induced currents to above the upper transformation temperature and immediately quenched. intergranular oxidation (IGO): The preferential oxidization of certain alloying elements along grain boundaries during gas carburizing. See figure 9 for a photomicrograph of intergranular oxides (black constituent).

Unetched 400 X mag.

Figure 9 -- Intergranular oxidation in carburized gearing


7

AGMA 923--B05


linear indication: An indication with length at least three times its width. marquench: Quenching into a liquid media whose temperature is above the martensite start transformation temperature, typically 300 -- 500°F (150 -260°C), held at this temperature until temperature is uniform throughout, and then cooled to form martensite. Marquenching is used to achieve reduced distortion when compared to conventional quenching. martensite: A generic term for microstructures formed by the diffusionless phase transformation of austenite. Martensite is characterized by an acicular or needle--like pattern in the microstructure and is the hardest of the austenitic transformation products in steel. microsegregation: The non--uniform distribution of alloying elements, impurities, or phases observed primarily in the microstructure of the material. nitriding: The introduction of nascent nitrogen into a suitable solid ferrous alloy by holding at a suitable temperature in with a nitrogenous material. Adsorption of nascent nitrogen produces case hardening without quenching.

non--martensitic structures: Inclusive terminology for ferrite, carbide, retained austenite, pearlite, and bainite due to incomplete transformation to martensite or incomplete austenization. Retained austenite is not included in the quantitative metallographic measurement of non--martensitic structures. non--martensitic transformation products: Inclusive terminology for ferrite, cementite, pearlite, and upper bainite in the surface microstructure of carburize hardened gearing due to incomplete transformation to martensite. See figure 10 for a photograph of non--martensitic transformation products in martensite. normalizing: The heating of a ferrous alloy to a suitable temperature above the transformation range and then cooling, typically in air, to a temperature substantially below the transformation range. pearlite: A microstructural constituent consisting of lamellar ferrite and cementite resulting from the transformation of austenite at temperatures above the bainite range.


Figure 10 -- Non--martensitic transformation products in carburized gearing

8



pitting resistance: Endurance limit adequate to resist fatigue. Initial pitting and progressive pitting are illustrated and discussed in ANSI/AGMA 1010--E95. See standards such as ANSI/AGMA 2001--C95, ANSI/AGMA 2003--B97, ANSI/AGMA 6002--B93, or ANSI/AGMA 6032--A94. process control test coupon: For carburize and hardened gearing or nitrided gearing, a test coupon used primarily to monitor the consistency of the heat treatment process in of carbon or nitrogen penetration and case microstructure. Sometimes called a standardized test coupon. For procedures associated with process control test coupons, see 4.2.1. Due to differences in quench cooling rates and hardenability, the microstructure and hardness of process control test coupons used for carburize and hardened gearing may not be the same as that of the finished gear tooth. reduction ratio: In forging and rolling, the ratio of the cross sectional area of the rough cast ingot or continuously cast billet to the final cross--sectional area. The reduction ratio is calculated by the following equation: RR = A C E F B D G H

(1)

where RR

is reduction ratio;

A

is the cross sectional area of the cast ingot or continuous cast billet, in2 (mm2).

For bar stock and forged shafting including step shafts for solid on shaft pinion blanks as in figure 5: B

is the cross sectional area at the finished largest forging diameter in the area where the teeth will be, in2 (mm2); and,

C, D, E, F, G and H = 1. For upset forged gearing blanks as in figures 7 and 8: B

is the cross sectional area of the billet prior to upsetting, in2 (mm2);

C

is the height of the cutoff ingot prior to upsetting, inch (mm);

D

is the height of the finish forged upset blank before piercing, inch (mm); and

E, F, G and H = 1.


AGMA 923--B05

For forged or rolled rings: B

is the cross sectional area of the billet prior to upsetting, in2 (mm2);

C

is the height of the cutoff ingot prior to upsetting, inch (mm);

D

is the height of the upset blank after upsetting before piercing, inch (mm);

E

is the height of the upset blank after piercing, inch (mm);

F

is the wall thickness of the upset blank after piercing, before any bore expansion associated with piercing, inch (mm);

G

is the height of the finish forged or rolled ring, inch (mm);

H

is the wall thickness of the finish forged or rolled ring, inch (mm).

representative test coupon: A test coupon designed to represent the quenching rate of the finished gearing tooth. If the coupon is to be used only to determine the case properties, it can be smaller than one used to determine the core properties of the gear tooth. A representative test coupon sized for determining the core hardness and microstructure can also be used for determining the case properties or as a process control test coupon. A representative test coupon sized for determining the case properties can also be used as a process control test coupon but not for determining core properties unless substantiated by documented test data. For procedures associated with representative test coupons, see 4.2.2. retained austenite: The metastable austenite retained within a quenched microstructure. The amount of retained austenite is a function of carbon content, alloy content (especially nickel and manganese), quench temperature and subsequent thermal or mechanical treatments. See figures 11, 12 and 13 for examples of visual estimates of retained austenite (white constituent) in tempered martensite. More precise measurements of retained austenite can be obtained by X--ray diffraction techniques. shot peening: A cold working process performed by bombarding the surface of a part with small spherical media. This results in a thin layer of high magnitude residual surface compressive stress and generally improves the bending strength in the roots of gear teeth. Shot peening should not be confused with grit blasting or shot blasting which are cleaning operations.

9

AGMA 923--B05

5% nital etch 400X mag. Figure 11 -- Tempered martensite and 5% retained austenite in carburized gearing


5% nital etch 400X mag. Figure 13 -- Tempered martensite and 30% retained austenite in carburized gearing specialty nitriding steel: A steel typically alloyed with 1% aluminum to provide higher surface hardness after nitriding than normally attained with nitrided through hardening steels. standardized test coupon: Alternate terminology for a process control test coupon. subcritical anneal: Reheating to a temperature below the transformation range. For carburized gearing the temperature is typically 1200--1250°F (650--675°C) and is done after carburizing and before hardening. surface hardening: The generic terminology for selective induction or flame heating of a surface layer and then quenching that layer to produce a hardened surface layer that may be thinner than the heated area, but is harder than the unheated base material. With induction or flame hardening there is no significant alteration of the chemical composition of the surface layer.

5% nital etch 400X mag. Figure 12 -- Tempered martensite and 20% retained austenite in carburized gearing

10

surface hardness: The hardness measured directly on the functional surface, after appropriate surface preparation. Surface hardness is not to be confused with case hardness, which is taken on a



AGMA 923--B05

metallographic cross section using a microhardness tester.

Banding -- See microsegregation.

tempering: The reheating of a hardened ferrous alloy part to a temperature below the transformation range, and then cooling it at any rate.

Case hardness

test bar: A sample used for tensile or impact strength testing. Also used as alternate terminology for a test coupon used for hardness and microstructure testing. test coupon: See specific type of test coupon such as process control or representative. total case depth: For carburized gearing the maximum depth of diffused carbon. The total case depth for induction or flame hardened gearing is usually assumed to be the same as the hardened and effective case depths. The total case depth for nitrided gearing is the distance from the surface to the depth at which the HRC hardness number is 110% of the hardness number for the core. total nominal alloy content: The sum of the mid--points of the specified ranges for all alloying elements added to increase hardenability (e.g., Mn, Cr, Ni, Mo). transformation temperature: The temperature at which a phase change occurs. traveling indication: An uninterrupted ultrasonic testing signal on the display which moves horizontally on the sweep line as the transducer is moved on the scanning surface. Travel of the signal indicates varied depth of the discontinuity from the scanning surface, often indicative of a crack.

4 Procedures 4.1 Recommended test methods The test methods listed in this clause are to be used when no other method is clearly defined or specified. These are the methods to be used for evaluations to the requirements of clause 5. Testing of the actual part is preferred and should always be used whenever practical. However, properly selected test coupons can also be used. The dimensions in this document are always to be measured normal (not oblique) to the surface.


Carbon -- See surface carbon.

For carburize and hardened gearing, unless otherwise specified, the case hardness is determined at a location 1/2 of tooth height (or from a representative test coupon). For induction or flame hardened gearing, unless otherwise specified, the case hardness is determined at a location 1/4 of tooth height above the root. For nitrided gearing, unless otherwise specified, the case hardness is determined at a location 1/2 of tooth height (or from a process control or representative test coupon). Chemistry -- Analyzed per ASTM A751. Core hardness -- Per a standard or superficial hardness testing method listed under “hardness”. Decarburization -- Per any of three methods: Method 1 -- File hardness The flanks of a tooth are file hardness tested per SAE J864 or ISO 6336--5, annex D with lack of file hardness indicating possible decarburization or non--martensitic structures. Method 2 -- Reduction of hardness Surface hardness readings are taken in the same area using two different hardness testing loads, such as HRC and HR15N with major loads of 150 kg and 15 kg respectively. The two sets of readings are compared using a standard hardness conversion chart, such as ASTM A370, ASTM E140 or ISO 6336--5, annex C. Decarburization is indicated by a lower converted hardness for the lighter load compared to that from the heavier load, presuming that proper hardness testing techniques were used for both sets of tests. Method 3 -- Metallographic evaluation A metallographic specimen is prepared per ASTM E3, etched per ASTM E407, and evaluated per ASTM E1077 or SAE J419. Effective case depth -- Per SAE J423 microhardness test method. For carburize and hardened gearing and nitrided gearing, unless otherwise specified, the effective case depth is determined at a location 1/2 of tooth height (or from a representative test coupon). For induction or flame hardened gearing, unless otherwise specified, the effective case depth is

11

AGMA 923--B05

determined at a location 1/4 of tooth height above the root. Grain size -- Per ASTM E112 or ISO 643.


of three points HRC from actual HRC measurements per ASTM E18. The significance and interpretation of those results needs to be agreed upon between the parties.

Hardenability -- Per ASTM A255 or ISO 642 end--quench test or by hardenability calculation per ASTM A255.

Intergranular oxides -- In the unetched condition, see metallography and figure 9.

Hardness -- Listed below are each method and the associated processes which are tested by that method.

Magnetic particle -- Per ASTM E1444 regardless of form, or alternatively ASTM E125 for raw castings, ASTM A275 for raw forgings, or ASTM E709 for finished gearing.

ASTM E10, Brinell hardness testing --

Through hardened parts

-- Base hardness of flame, induction, or nitride hardened parts

--


--

Carburize and hardened parts

Metallography -- Performed at a magnification of 400 -- 600 diameters. Metallographic samples shall be prepared per ASTM E3 and etched per ASTM E407, except for intergranular oxidation which shall be evaluated in the unetched condition.

--

Flame and induction hardened parts

Microhardness -- See hardness.

--

Nitrided parts

ASTM E18, Rockwell hardness testing

--


Microsegregation -- Analyzed per ASTM A534. Acceptance criteria is not specified but is to be agreed upon.

--


Microstructure -- See metallography.

--


--

Nitrided parts

Nonmetallic inclusions -- Per any of the following methods:

ASTM E92, Vicker’s hardness testing

ASTM E384, Microhardness testing

--

SAE/AMS 2301, for aircraft steels

--

ASTM A534, for carburizing bearing steels

--


--


-- ASTM A866, for through hardening bearing steels

--

Nitrided parts

--

If standard bench top hardness testing cannot be accomplished as stated in ASTM E10 or ASTM E18, portable testing may be accomplished by ASTM E110 or other appropriate methods. Measurement of surface hardness per ASTM E18 is used as a nondestructive method to evaluate the conformity of individual work pieces to the surface hardness requirements. The measurement method should be appropriate for the size and configuration of the work pieces. The teeth area requirements for hardness measurements include the root of the tooth. Alternate methods of hardness measurement, including file testing in accordance with SAE J864 or ISO 6336--5, annex D, may be used. Due to the state of the art of alternate microhardness testing methods, results may vary by the equivalent

12

Mechanical testing -- Per ASTM E8 for tensile testing and ASTM E23 for impact testing (also see hardness).

ASTM E45, for inclusion count

-- ISO 4967, by comparison to micrographic diagrams, Method B, Plate II with 0.3 in2 (200 mm2) inspection area -- SAE J422, by comparison to micrographic diagrams Surface carbon -- Per one of the following methods: Method 1 -- Spectrometric Per ASTM E415. Method 2 -- Combustion The combustion method utilizes chips from a machining cut of 0.001 -- 0.004 inch (0.02 -- 0.10 mm) in thickness on a carbon control specimen. The chips from this cut are collected and analyzed by combustion for carbon content per ASTM E350. The specimen should be machined dry with high



speed cutting tools on centers, and at least one gram of clean chips free of contamination should be used for analysis. Both methods require that prior to carburizing the process control specimen, sufficient stock be machined from the surface to be carburized, in order to remove all material with non--uniform surface chemistry. Surface temper -- Per ANSI/AGMA 2007--B92 or ISO 14104. Test coupons -- Microstructure, microhardness and core hardness characteristics may be determined from either actual parts or test coupons. See 4.2 for the specific type of test coupon (process control or representative). Ultrasonic inspection -- Ultrasonic inspection is recommended for large parts to detect flaws before incurring the expense of machining. When ultrasonic inspection is specified, the following guidelines shall apply: -- For wrought products the straight beam procedures described in ASTM A388 shall apply. Either the flat bottom hole or back reflection method may be used. The sensitivity for the flat bottom hole method shall utilize standard test blocks per ASTM E428 with the reflector size as specified in tables 1 through 4 of this information sheet. The metal test distance for the blocks shall be 4.000 inches (101.6 mm). This sensitivity shall be used when radially scanning the portion of the wrought material that will comprise the tooth area. The tooth area includes only those portions of the gearing material where the teeth will be located to a depth below the finished tooth tips of at least 1.5 times the tooth height. The balance of the part may be scanned using a distance amplitude correction curve (DAC) whose construction is detailed in ASTM A388. -- For cast products the straight beam procedures described in ASTM A609 shall apply. The back reflection method shall be used. 4.2 Test coupons 4.2.1 Process control test coupons Process control test coupons are used to monitor various heat treatment process parameters, their variation, their interactions, and to that these parameters are maintained within their expected


AGMA 923--B05

control range. The process control test coupons may be made of various steel grades, different sizes, and differing geometry depending on the parameter to be monitored and the heat treat facility’s quality control plan. Process control test coupons are not intended to be used for final acceptance. The properties of a process control coupon may be correlated by experience to the properties of the finished gearing with regard to hardness and case depth. The process control test coupon microstructure may be correlated to the condition of the finished gear. The method of correlation should be documented. Process control test coupons may be used to determine surface carbon concentration, carbon penetration, carbon gradients, nitride depth, white layer thickness, intergranular oxidation depth, and process repeatability. Shim stock is often used to monitor atmospheric carbon potential. Variations from expected process control limits are used as indicators of unacceptable heat treat process variations. As long as the process control test coupons are within expected control limits, the parts being heat treated should have the expected metallurgical properties. The process control test coupon for carburize and hardening should have minimum dimensions of 5/8 inch (16 mm) diameter by 2 inches (50 mm) long and is suitable for gearing 4.5 normal diametral pitch (5.6 module) and finer. A 1 inch (25 mm) diameter by 2 inches (50 mm) long coupon may be used for coarser pitch (module) carburized gearing to 1.5 normal diametral pitch (17 mm module). The size of the coupon for coarser than 1.5 normal diametral pitch (17 module) gearing should be agreed upon, and should approximate the inscribed diameter at mid height of the tooth cross section. The coupon length should be a minimum of 2 times the diameter. Test disks or plates may be used whose minimum thickness is 70 percent of the appropriate test bar diameter. The minimum inscribed diameter on a test disc (or plate dimensions) should be three times its thickness. For determination of case hardness, case depth, and case microstructure, the process control test coupon should be examined on a section normal to its axis and at least one diameter from the end of the test coupon. Case hardness is to be measured by a microhardness method at a depth 0.002 to 0.004 inch (0.05 to 0.10 mm) below the surface. Any post--heat treat stock removal must be considered.

13

AGMA 923--B05

4.2.2 Representative test coupon The representative test coupon shall be from the same grade of alloy steel with similar hardenability as the production part, but need not necessarily be from the same heat of steel. Representative test coupon proportions of a minimum diameter of 6 divided by the normal diametral pitch (6 times module) but not less than 5/8 inch diameter (16 mm), and a minimum length 2 times its diameter, as used in ISO 6336--5, are recommended. A representative test coupon may contain a tooth form that will be used to the heat treat process. With customer approval, representative test coupon proportions of a minimum diameter of 3 divided by the normal diametral pitch (3 times module) but not less than 5/8 inch diameter (16 mm), and a minimum length 2 times its diameter, as used in ISO 6336--5, are recommended. A representative test coupon should have the same heat treat condition prior to carburizing as the part(s) represented. This coupon should remain with the part(s) represented throughout the entire heat treat process, with the possible exception of heat treatments prior to carburizing. The representative test coupon, when positioned in a heat treat load in the same general area but separate from the piece part, is intended to represent the metallurgy of the heat treated tooth section. The microstructure at the center of the minimum size representative test coupon approximates the core microstructure of the tooth section.

5 Metallurgical requirements The metallurgical characteristics identified in the tables of this clause are intended to be used for all steel gearing. Metallurgical characteristics defined in the tables of this clause are intended to assure the quality of the finished gear teeth. Individual AGMA rating standards may have specific modifications to the metallurgical characteristics grading; but the intent is to formalize the assumptions and definitions on which the various AGMA standards are based. These characteristics should be compatible, wherever possible, with ISO 6336--5. s of this document must be aware that the Grade 1, Grade 2 and Grade 3 gearing produced by different heat treatment processes have different

14


ratings. Refer to the applicable gear rating standards for specific gear ratings. Individual customers and manufacturers may have specific modifications to the metallurgical grade requirements or special material and processing conditions that are not covered in these tables. These modifications and special conditions are permissible with mutual agreement. The following tables establish reasonable minimum limits for each material and metallurgical characteristic that will allow gearing, which meet dimensional tolerances, to meet the minimum expectations of the gear rating design standards. As individual gearing designs increase in size and complexity of features, they become more difficult to manufacture, heat treat, and inspect. This document, as a general rule, does not differentiate based on gearing size. However, where necessary, specific notation is made to reflect the special processing methods, techniques and inspections required for large gear manufacturing. All requirements for a metallurgical quality grade must be met in order to use the stress value, from the AGMA rating standard, for that grade. This can be accomplished by specifically certifying each requirement where necessary, or by establishing practices and procedures to obtain the requirements on a production basis. It is not the intent of this document that all requirements for metallurgical quality grade be certified, but that practices and procedures be established for their compliance on a production basis. Intermediate values are not classified since the effect of deviations from the quality standards cannot be evaluated easily. Specific sampling plans and test methods need to be addressed by either the manufacturer, the customer, or both. The various characteristics are listed in the order in which that characteristic is typically evaluated during the manufacturing sequence. Each individual characteristic has the same item number in tables 1, 2, 3 and 4 whenever it is used, regardless of which table it appears. Some characteristics are only applicable to specific heat treat methods. Therefore, some item numbers are not used in some tables. Characteristics that are typically evaluated at the same time are grouped by having the same number before the decimal point, and modified with different numbers after the decimal point for the individual characteristics evaluated at that time. 5.1 Through hardened gearing The major metallurgical characteristics that affect through hardened gearing performance are shown



in table 1. The minimum acceptable requirements for each factor for metallurgical quality Grades 1 and 2 are specified. All criteria in any given grade must

AGMA 923--B05

be met to qualify for the stress number associated with that metallurgical quality grade.

Table 1 -- Metallurgical characteristics for through hardened gearing Item Characteristic1) 2) 1 Material chemistry

Grade 1 Not specified verified.

2

Grain size

Verification required.

3

Hardenability

Not specified.

4

Non--metallic inclusions Not specified. (cleanliness, steelmaking) 3)

5.1

Material form

5.2

Material reduction (wrought only)

6

Heat treatment

7

Mechanical properties heat treatment6)

8

Microstructure3)

ratio Notl specified. Not specified.

or

Grade 2 Test report only. Medium carbon alloy steel. 0.025% maximum sulfur.

not

Predominantly 5 or finer. Test report only.

A minimum hardenability which is appropriate for part size and quench severity should be specified. Wrought gearing Capable of meeting (certification not required) SAE/AMS 2301, ASTM A866 or SAE J422 S2--O2 Cast gears Only permissible if primarily round (Type 1) sulfide inclusions. Forgings per either ASTM A290 or ASTM A291 Bar stock per ASTM A29, ASTM A304 or ISO 683--1 Castings per ASTM A148 Tubing per ASTM A519 -- At least 7 to 1 for strand or continuous cast -- At least 3 to 1 for ingot cast4) 5) Quench and temper 900°F (480°C) minimum temper.

after Hardness testing is required. Other mechanical testing is required only if specified. Not specified.

Sound metallurgical practice dictates that the microstructure requirements in the tooth area should be predominantly tempered martensite with limited upper transformation products (ferrite, upper bainite and fine pearlite). The microstructure shall be free of blocky ferrite (due to incomplete austenization) with the following limits for non--martensitic upper transformation products: Controlling section size, Non--martensitic structures, inch maximum at least less than ---5 5% 5 10 10% 10 15 20% 15 ---Hardness must be obtained at roots with 900°F minimum temper Controlling section size, mm at least less than ---125 125 250 250 375 375 ----

9

Ultrasonic inspection3) 5) Wrought material. Either method is acceptable. -- Flat bottom hole (FBH) Not specified. technique

Non--martensitic structures, maximum 5% 10% 20% Hardness must be obtained at roots with 480°C minimum temper

Inspection recommended to the following limits: -- No indications giving a signal response greater than an 8/64 inch (3.18 mm) reference standard. -- No indications giving a signal response greater than 50% of the same reference standard if accompanied by a 50% loss of back reflection. -- No indications which are continuous over an area twice the diameter of the search unit.

(continued)


15

AGMA 923--B05


Table 1 (concluded) Item Characteristic1) 2) 9 (continued) -- Back reflection technique

Not specified.

-- No indications giving a signal response greater than 15% of back reflection. -- No multiple indications that lower the amplitude of the first back reflection by more than 40%. -- No traveling indications whose amplitude is greater than 10% of back reflection and length is greater than 0.75 inch (19 mm).

Castings -- Back reflection technique

Not specified.

-- ASTM A609 Level 1 from outside surface to 1.5 times tooth height below finished tooth tips. -- ASTM A609 Level 2 greater than 1.5 times tooth height below finished tooth tips.

16

Surface microstructure considering subsequent stock removal

16.3

Decarburization. Any of the following methods are acceptable

Grade 1

Should meet the following surface related characteristic:

-- Method 1. File testing. Not applicable. -- Method 2. Reduction of Not specified. surface hardness by two load method.6)

Not applicable. Maximum 2 HRC points or equivalent by conversion.

-- Method 3. evaluation.

No total or partial decarburization apparent on the finished gear tooth.

Metallographic Not specified.

21

Surface cracks7) 8)

22

Magnetic particle inspection of finished gearing5) 7) 8) 9) -- Below the pitch line Not specified. -- Above the pitch line Normal diametral pitch Module at less more at least than than most ---3 8 ---3 10 2.5 8 10 ------2.5

23

Grade 2

Shot peening10)

Cracks, bursts, seams and laps are not permissible in functional areas of finished gearing.

Not specified.

Inspection recommended to the following limits: No indications.

Indication, maximum inch mm 1/8 3.2 3/32 2.4 1/16 1.6

Shot peening per SAE/AMS--S--13165 may be used to increase surface residual compressive stress.

NOTES: 1) See clause 3 for definitions and clause 4 for test methods. 2) The metallurgical requirements assume homogeneous composition. In practice, microsegregation and banding occurs in steels. This microsegregation can produce variations in microstructure and properties that need to be assessed. 3) The grade requirements for non--metallic inclusion, ultrasonic and microstructure characteristics apply only to those portions of the gearing material where the teeth will be located to a depth below the finished tooth tip of at least 1.5 times the tooth height. 4) A 7 to 1 minimum reduction ratio is recommended. For large gearing where this reduction ratio is not physically obtainable, lesser reduction ratios may be used down to a minimum of 3 to 1. 5) In--process ultrasonic and/or magnetic particle inspection of gearing blanks is recommended for large diameter parts to detect flaws before incurring the expense of further machining. 6) See ASTM A370, ASTM E140 or ISO 6336--5, annex C for hardness conversion tables. 7) Removal of defects that exceed the stated limits is acceptable, provided the integrity of the gear is not compromised. 8) Cracks in non--functional areas require engineering disposition. 9) Limits: maximum of one indication per inch (25 mm) of face width with a maximum of five such indications on any one tooth flank. Indications less than 1/32 inch (0.8 mm) are not considered. 10) It is recommended that ANSI/AGMA 2004--B89 be reviewed to determine if the benefits of surface residual compressive stress achieved by shot peening may be beneficial to the particular application. Shot peening of the flanks of gear teeth should be reviewed to ensure that no detrimental effects are caused to the gear set.

16



5.2 Carburize and hardened gearing The major metallurgical characteristics that affect carburize and hardened gearing performance are shown in table 2. Neither carbonitrided nor nitrocarburized gearing is covered by this document. The

AGMA 923--B05

minimum acceptable requirements for each factor for metallurgical quality Grades 1, 2 and 3 are specified. All criteria in any given grade must be met to qualify for the stress number associated with that metallurgical quality grade.

Table 2 -- Metallurgical characteristics for carburize and hardened gearing Item Characteristic1) 2) 1 Material chemistry 2 3

Grain size Hardenability

4

Non--metallic inclusions (cleanliness, steelmaking)3) 4)

5.1

Material form

5.2

Material reduction ratio (wrought only)

Grade 1 Specified, but not verified. Verification not required. Not specified. p

Grade 2 Test report only. Alloy steel. 0.025% maximum sulfur.3)

Grade 3 Test report only. Alloy steel. 0.015% maximum sulfur.3)

Predominantly 5 or finer. Test report only. A minimum hardenability which is appropriate for part size and quench severity should be specified. Wrought gearing Alternative A: -- Capable of meeting bearing quality per ASTM A534 Alternative B, all of the following: -- The steel must be certified: -- electric furnace practice -- ladle refined -- deoxidized -- vacuum degassed -- bottom poured ingot or strand casted -- protected from reoxidation during teeming or casting -- capable of oxygen content of 20 ppm maximum -- capable of cleanliness confirmation by either ASTM E45 or ISO 4967 Method B Plate II with 0.3 inch2 (200 mm2) inspection area. Acceptable if does not exceed: Type Fine Thick A (sulfide) 3.0 3.0 B (alumina) 2.5 1.5 C (silicate) 2.5 1.5 D (globular oxide) 2.0 1.5 Alternative C: Capable of meeting SAE/AMS 2301 or SAE J422, S2--O2 Alternative D:5) Magnetic particle inspection of finished gearing to the requirements of Item 22, Grade 3. Cast gears Only permissible if primarily round (Type 1) sulfide inclusions.

Wrought gearing Alternative A: -- Certified ASTM A534 Alternative B, all of the following: -- The steel must be certified: -- electric furnace practice -- ladle refined -- deoxidized -- vacuum degassed -- bottom poured ingot -- protected from reoxidation during teeming or casting -- oxygen content of 20 ppm maximum -- certified cleanliness by either ASTM E45 or ISO 4967 Method B Plate II with 0.3 inch2 (200 mm2) inspection area. Acceptable if does not exceed: Type Fine Thick A (sulfide) 2.5 1.5 B (alumina) 2.0 1.0 C (silicate) 0.5 0.5 D (globular oxide) 1.0 1.0 Alternative C: Certified SAE/AMS 2300 or SAE/AMS 2304.

Cast gears Not permitted.

Forgings per ASTM A837 and either ASTM A290 or ASTM A291 Bar stock per ASTM A29, ASTM A304 or ISO 683--11 Tubing per ASTM A519 Not specified.

Castings per ASTM A148. Castings not permitted. -- At least 7 to 1 for strand or continuous cast -- At least 3 to 1 for ingot cast 6) 7)

(continued)


17

AGMA 923--B05


Table 2 (continued) Characteristic1) 2)

Item 9

Grade 1

Grade 2

Grade 3

inspection4) 7)

Ultrasonic Wrought material. Either method is acceptable.

Inspection recommended to the Inspection required to the following following limits: limits:

-- Flat bottom hole (FBH) Not specified. technique

-- Back reflection technique

-- No indications giving a signal response greater than an 8/64 inch (3.18 mm) reference standard. -- No indications giving a signal response greater than 50% of the reference standard if accompanied by a 50% loss of back reflection. -- No indications which are continuous over an area twice the diameter of the search unit.

-- No indications giving a signal response greater than a 5/64 inch (1.98 mm) reference standard. -- No indications giving a signal response greater than 50% of the reference standard if accompanied by a 50% loss of back reflection. -- No indications which are continuous over an area twice the diameter of the search unit.

Not specified.



Not specified.


Recommended.

Required.


11

Tempering after case hardening

12

Surface hardness in tooth area. Should meet the following characteristics: Alternative method of inspection is case hardness.8) 9) 10) -- Tooth flank

55--64 HRC equivalent

or

58--64 HRC or equivalent

58--64 HRC or equivalent

-- Normal diametral pitch 3 53 HRC minimum or (module 8) and coarser equivalent

56 HRC minimum or equivalent


-- Normal diametral finer than 3 (module 8)



-- Tooth root

13

pitch 55 HRC minimum or equivalent

Case depth considering subsequent stock removal

Should meet the following characteristics:

13.1

Effective case depth in finished Minimum and maximum effective case depth requirements for the tooth should be specified in condition 10) 11) accordance with the appropriate rating standard.

13.2

Effective case depth minimum Not specified. at root radius, as determined by bending strength rating.10) 11)

50% of minimum specified effective 66% of minimum specified effective case at 1/2 tooth height case at 1/2 tooth height recommended. recommended.

Core hardness after case hardening 12) 13) -- For pitting resistance rating Not specified. -- For bending strength rating 21 HRC minimum

21 HRC minimum 25 HRC minimum

12)

14

21 HRC minimum 30 HRC minimum14)

(continued)

18



AGMA 923--B05

Table 2 (continued) Item Characteristic1) 2) 15 Surface carbon (typical)15)

Grade 1

For up to 2.5% total nominal 0.60 -- 1.10%C alloy content 2.5% to 3.5% total nominal 0.60 -- 1.10%C alloy content Over 3.5% total nominal alloy 0.60 -- 1.10%C content 16

16.1

16.2

Grade 2

Grade 3

0.60 -- 1.10%C

0.60 -- 1.00%C

0.60 -- 1.00%C

0.60 -- 1.00%C

0.65 -- 0.95%C

0.65 -- 0.95%C

Surface microstructure consid- The first 0.002 -- 0.003 inch (0.05 -- 0.08 mm) of case microstructure in the tooth area should ering subsequent stock remov- meet the surface hardness requirement of the specific grade and also meet the following sural 12) 16) face related characteristics and the requirements of Item 17: Intergranular oxidation (IGO) Not specified. (see figure 9) Minimum specified effective case depth inch (mm) at less at less least than least than ---0.030 ---(0.75) 0.030 0.060 (0.75) (1.50) 0.060 0.090 (1.50) (2.25) 0.090 0.120 (2.25) (3.00) 0.120 ---(3.00) ----

Maximum allowable depth inch (mm) 0.0007 (17) 0.0010 (25) 0.0015 (38) 0.0020 (50) 0.0025 (60)




Non--martensitic transforma- Not specified. tion products (see figure 10)17) Minimum specified effective case depth inch at less least than ---0.030 0.030 0.060 0.060 0.090 0.090 0.120 0.120 ----

16.3

(mm) at less least than ---(0.75) (0.75) (1.50) (1.50) (2.25) (2.25) (3.00) (3.00) ----

Decarburization. Any of the following methods are acceptable. -- Method 1. File testing.

Not specified.

-- Method 2. Reduction of sur- Not specified. face hardness by two load method or reduction of case hardness.10)

Maximum 3 HRC points or equivalent below maximum measured hardness by conversion, but measuring at least 58 HRC or equivalent by conversion in the finished state.

Maximum 1.5 HRC points or equivalent below maximum measured hardness by conversion, but measuring at least 58 HRC or equivalent by conversion in the finished state.


No partial decarburization apparent on active tooth profile. No ferrite (total decarburization) is permissible in the case microstructure of the gear tooth.

No partial decarburization apparent on the gear tooth. No ferrite (total decarburization) is permissible in the case microstructure of the gear tooth.


Minimum specified effective case depth inch (mm) at less at less least than least than ---0.030 ---(0.75) 0.030 0.060 (0.75) (1.50) 0.060 0.090 (1.50) (2.25) 0.090 0.120 (2.25) (3.00) 0.120 ---(3.00) ---17

Gear tooth surfaces must be file hard to the minimum surface hardness.

Maximum allowable depth in root inch (mm) 0.0007 (17) 0.0010 (25) 0.0015 (38) 0.0020 (50) 0.0025 (60)

Case microstructure consider- The microstructure of the first 20% of the minimum specified effective case depth should be preing subsequent stock removal, dominantly tempered martensite. Additional requirements for the case microstructure are given disregarding corner effects 12) in Item 16 and the following case related characteristics:

(continued)


19

AGMA 923--B05



Item

Grade 1

Grade 2

Grade 3 Discontinuous carbides per figure 3 are not acceptable, but dispersed carbides per figure 4 are acceptable.

17.1

Carbide precipitation in the Continuous carbide case. network per figure 1 is not acceptable, but semi--continuous carbide network per figure 2 is acceptable.

Semi--continuous carbide network per figure 2 is not acceptable, but discontinuous carbides per figure 3 are acceptable. Maximum acceptable length of any carbide is 0.0008 inch (0.02 mm).

17.2

Retained case.9)

Retained austenite 30% maximum determined metallographically by comparison with figure 13. Rejection of piece parts shall only be based on case hardness. The minimum microhardness at 0.004 inch (0.1 mm) or through the area of highest retained austenite shall be 58 HRC (690 HK500).10) 16)

17.3

Microstructure of the case to a depth of 0.010 inch (0.25 mm) or the first 20% of the minimum specified effective case depth, whichever is smaller, along the flank (for pitting resistance rating). 18)

17.4

Microstructure of the case from Untempered mara depth of 0.010 inch (0.25 mm) tensite is acceptor the first 20% of the minimum able. specified effective case depth, whichever is smaller, to a depth equal to 40% of the minimum specified effective case depth along the flank (for pitting resistance rating). 18)

austenite

in

the Not specified.

Primarily tempered martensite with 5% maximum non--martensitic structures, carbide precipitation per Item 17.1, retained austenite per Item 17.2, and other surface microstructures as defined under Items 16.1 through 16.3.

Primarily tempered martensite with only trace non--martensitic structures permissible, carbide precipitation per Item 17.1, retained austenite per Item 17.2, and other surface microstructures as defined under Items 16.1 through 16.3.

-- Normal diametral pitch 3 Not specified. (module 8) and coarser.

Not specified.

Not specified.

-- Normal diametral pitch finer Not specified. than 3 (module 8).

5% maximum structures.

17.5

Microstructure of the case to a Not specified. Undepth of 0.010 inch (0.25 mm) tempered martenor the first 20% of the minimum site is acceptable. specified effective case depth, whichever is smaller, at the root fillet (for bending strength rating). 18)



17.6

Microstructure of the case from Untempered mara depth of 0.010 inch (0.25 mm) tensite is acceptor the first 20% of the minimum able. specified effective case depth, whichever is smaller, to a depth equal to 40% of the minimum specified effective case depth at the root fillet (for bending strength rating). 18) -- Normal diametral pitch 3 Not specified. (module 8) and coarser.

Not specified.

Not specified.

-- Normal diametral pitch finer Not specified. than 3 (module 8).

10% maximum non--martensitic 5% maximum structures. structures.

17.7

Not specified. Untempered martensite is acceptable.

Microcracks in case (cracks Not specified. across more than one platelet)

non--martensitic Only trace structures.

non--martensitic

non--martensitic

10 maximum per 0.0001 in2 (0.064 mm2) field. 9) 19)

(continued)

20



AGMA 923--B05

Table 2 (continued) Item Characteristic1) 2) 18 Core microstructure4) 12)

20 21

22

23

Grade 2 Grade 3 Sound metallurgical practice dictates that the core microstructure requirements are maintained in the tooth area to a depth of twice the minimum specified effective case depth or 0.100 inch (2.5 mm), whichever is less, below the minimum specified effective case depth. The microstructure in this zone should be predominantly tempered martensite. This microstructure zone should be free of blocky ferrite, pearlite, and measurable bainite. Below this zone the core microstructure should be free of blocky ferrite and be primarily tempered martensite with some acicular ferrite and bainite permissible. Surface temper etch inspection Not specified. FB2, which allows light tempering FB1, which allows light tempering of ground teeth on 25% of functional area. on 10% of functional area. Surface cracks20) Cracks, bursts, seams and laps are not permissible in Cracks, bursts, seams and laps are functional areas of finished gearing.21) not permissible in any area of finished gearing. Magnetic particle inspection of Inspection recommended to the Inspection required to the following finished gearing 7) 20) 21) 22) following limits: limits: -- Below the pitch line Not specified. No indications. No indications. -- Above the pitch line Normal diametral pitch Module Indication, maximum Indication, maximum at less more at inch mm inch mm least than than most 1/8 3.2 3/32 2.4 ---3 8 -- -Not specified. 3/32 2.4 1/16 1.6 3 10 2.5 8 1/16 1.6 1/32 0.8 10 ----- -2.5 Shot peening 23)

Grade 1 Not specified.

Shot peening per SAE/AMS--S--13165 may be used to increase surface residual compressive stress.

NOTES: 1) See clause 3 for definitions and clause 4 for test methods. 2) The metallurgical requirements assume homogeneous composition. In practice, microsegregation and banding occurs in steels. This microsegregation can produce variations in microstructure and properties that need to be assessed. 3) Intentional additions of calcium or calcium alloys for deoxidation or inclusion and shape control are not permitted unless specifically approved by the purchaser. The use of lime or fluorspar, or both, in the steelmaking slag is acceptable. 4) The grade requirements for non--metallic inclusion, ultrasonic, and microstructure characteristics apply only to those portions of the gear material where the teeth will be located to a depth below the finished tooth tip of at least 1.5 times the tooth height. 5) Care should be exercised when using Alternative D because of the risk of rejection after the expense of further manufacturing processes. 6) A 7 to 1 minimum reduction ratio is recommended. For large gearing where this reduction ratio is not physically obtainable, lesser reduction ratios may be used down to a minimum of 3 to 1. 7) In--process ultrasonic and/or magnetic particle inspection of gearing blanks is recommended for large diameter parts to detect flaws before incurring the expense of further machining. 8) Root hardness may be less than flank hardness, depending on the size of the gear and the quench process. 9) If cold treatment is performed, it is recommended that it be preceded by tempering at 300°F (150°C) minimum in order to minimize formation of microcracks. Retempering is required after cold treatment. Cold treatment should not be used to transform large amounts of retained austenite (e.g., 50%) to gain excessive improvements in hardness, even with prior tempering. 10) See ASTM A370, ASTM E140 or ISO 6336--5, annex C for hardness conversion tables. 11) When specifying minimum case depth, note that the “optimum” values for pitting resistance and bending strength capacity are not the same. A maximum case depth is prescribed in order to minimize the risk of embrittlement in the tooth area, including the tips. 12) See clauses 3 and 4 for a discussion of test coupons. 13) Core hardness requirements for pitting resistance and bending strength are considered independently. The gear rating may be limited by either pitting resistance or bending strength for the selected metallurgical quality grade and its core hardness requirement. 14) Minimum hardness of 30 HRC for Grade 3 may be difficult to achieve on coarse pitch gearing. Due to the tooth section size of 3 normal diametral pitch (8 module) gearing and coarser, the alternate (ISO) core hardness test location may be used provided documented testing or experience is available.

(continued)


21

AGMA 923--B05


Table 2 (concluded) NOTES: 15) Optimum pitting resistance is best achieved at surface carbon levels above the eutectoid carbon for a given alloy chemistry. 16) If excessive, salvage may be possible by processes such as shot peening per Item 23 or by grinding provided the integrity of the gearing is not compromised. 17) At maximum allowable depths the surface may not be file hard and may not have the expected residual stress profile. 18) Bainite, observable at 200X, that extends from the core microstructure into the case area is considered a ratable characteristic. This bainite is the result of slower heat extraction rates due to part section size, mass of furnace load, marginal agitation, elevated quenchant temperatures, and generally follows alloy segregation and material flow lines. The bainite that results in a fine pepper structure at 400 -- 600X, but is still not resolvable at 800X, is considered nonratable (trace). 19) Maximum limit of microcracks (Item 17.5) for Grade 3 gearing may be difficult to achieve if cold treatment is used to transform the retained austenite level to 30% maximum. 20) Removal of defects that exceed the stated limits is acceptable, provided the integrity of the gear is not compromised. 21) Cracks in nonfunctional areas require engineering disposition. 22) Limits: maximum of one indication per inch (25 mm) of face width with a maximum of five such indications on any one tooth flank. Indications less than 1/32 inch (0.8 mm) are not considered. 23) It is recommended that ANSI/AGMA 2004--B89 be reviewed to determine if the benefits of surface residual compressive stress achieved by shot peening may be beneficial to the particular application. Shot peening of the flanks of gear teeth should be reviewed to ensure that no detrimental effects are caused to the gear set.

5.3 Induction or flame hardened gearing The major metallurgical characteristics that affect induction or flame hardened gearing performance are shown in table 3. The minimum acceptable requirements for each factor for metallurgical quality

Grades 1, 2 and 3 are specified. Grade 3 is restricted to contour spin induction Type A (Contour) hardening only. All criteria in any given grade must be met to qualify for the stress number associated with that metallurgical quality grade.

Table 3 -- Metallurgical characteristics for induction or flame hardened gearing Item

1

2

3 4

Characteristic1) 2)

Grade 1

Grade 2

Grade 3 Spin induction Type A (Contour) only Material chemistry Not specified or Test report only. Test report only. verified. 0.025% maximum sulfur for 0.015% maximum sulfur for wrought. wrought. Grain size Predominantly 5 Predominantly 5 or finer. Test report only. or finer. Verification not required. Hardenability Not specified. A minimum hardenability which is appropriate for part size and quench severity should be specified. Non--metallic inclusions Not specified. Wrought gearing Wrought gearing (cleanliness, steelmaking) 3) Capable of meeting (certification Capable of meeting (certification not required) SAE/AMS 2301, not required) SAE/AMS 2301, ASTM A866 or SAE J422 S2--O2 ASTM A866 or SAE J422 S2--O2 Cast gears Cast gears Only permissible if primarily Not permitted

round (Type 1) sulfide inclusions. 5.1

5.2 6

Material form

Forgings per either ASTM A290 or ASTM A291 Bar stock per ASTM A29, ASTM A304 or ISO 683--1 Tubing per ASTM A519 Castings per ASTM A148. Castings not permitted. Material reduction ratio Not specified. -- At least 7 to 1 for strand or continuous cast (wrought only) -- At least 3 to 1 for ingot cast4) 5) Heat treatment prior to surface Not specified. Quench and temper hardening 900°F (480°C) minimum temper.

(continued)

22



AGMA 923--B05

Table 3 (continued) Item

Characteristic1) 2)

Grade 1

7

Mechanical properties prior to Not specified. surface hardening. See also Item 14. 6) 7)

8

Microstructure prior to surface Not specified. hardening3)

Grade 2

Grade 3 Spin induction Type A (Contour) only 28 HRC minimum. Other mechani- 30 HRC minimum. Other mechanical testing is required only if speci- cal testing is required only if specified. fied. Sound metallurgical practice dictates that the core microstructure requirements are maintained in the tooth area to a depth twice the minimum specified effective case depth or 0.100 inch (2.5 mm), whichever is less, below the minimum specified effective case depth. The microstructure in this zone should be predominantly tempered martensite that is free of blocky ferrite, pearlite, and measurable bainite observable at 400--600X. Below this zone the core microstructure should be primarily tempered martensite and free of blocky ferrite with the following limits: Controlling section size, inch at least less than ---5 5 10 10 15 15 ---Controlling section size, mm at least less than ---125 125 250 250 375 375 ----

9

Non--martensitic structures, maximum 5% 10% 20% Hardness must be obtained at roots with 900°F minimum temper Non--martensitic structures, maximum 5% 10% 20% Hardness must be obtained at roots with 480°C minimum temper

Ultrasonic inspection3) 5) Wrought material. Either method is acceptable.



-- No indications giving a signal response greater than an 8/64 inch (3.18 mm) reference standard. -- No indications giving a signal response greater than 50% of the reference standard if accompanied by a 50% loss of back reflection. -- No indications which are continuous over an area twice the diameter of the search unit. -- No indications giving a signal response greater than 15% of back reflection. -- No multiple indications that lower the amplitude of the first back reflection by more than 40%. -- No traveling indications whose amplitude is greater than 10% of back reflection and length is greater than 0.75 inch (19 mm).

-- Back reflection technique

Not specified.


Not specified.

-- No indications giving a signal response greater than a 5/64 inch (1.98 mm) reference standard. -- No indications giving a signal response greater than 50% of the reference standard if accompanied by a 50% loss of back reflection. -- No indications which are continuous over an area twice the diameter of the search unit. -- No indications giving a signal response greater than 10% of back reflection. -- No multiple indications that lower the amplitude of the first back reflection by more than 20%. -- No traveling indications whose amplitude is greater than 10% of back reflection and length is greater than 0.50 inch (13 mm).


(continued)


23

AGMA 923--B05


Table 3 (continued) Item

10 11 12

13

13.1

13.2

14

17

17.3

17.5

19

20 21 22

Characteristic1) 2)

Grade 1

Grade 2

Grade 3 Spin induction Type A (Contour) only Overheating, especially at the Avoid surface temperatures that result in grain growth, incipient melting or unfavorable tooth tips and end faces 8) residual stresses. Larger chamfers minimize this problem. Tempering after surface 1 hour minimum at temperature furnace temper is required.9) hardening Surface hardness on a repre- 50 HRC minimum or 54 HRC minimum as required by 58--64 HRC or equivalent sentative surface. Alternative rating standard. method of inspection is case hardness. 7) 8) Case depth considering subseShould meet the following characteristics: quent stock removal. Also see Item 19. 7) 8) 10) Effective case depth in finished Minimum and maximum effective case depth should be Minimum and maximum effective condition specified in accordance with the rating standard. A case depth should be specified in hardening pattern per figure 14 shall be specified. accordance with the rating standard. Figure 14 Type A contour pattern only shall be specified. Effective case depth minimum Not specified. 50% of minimum specified effective 100% of minimum specified effecat root radius, or on representacase at 1/4 tooth height above the tive case at 1/4 tooth height above tive sample with same root recommended. the root recommended, and 66% of geometry and material as work minimum specified effective case piece, as determined by at the root. bending strength rating. Base hardness after surface Not specified. 28 HRC minimum 30 HRC minimum hardening. Also see Item 7. 6) 7) 8) 10) Case microstructure consider- The first 20% of the case microstructure should be predominantly tempered martensite. The ing subsequent stock removal, microstructure should be free of undissolved pearlite observable at 100X and measurable disregarding corner bainite observable at 400 -- 600X. effects8) 10) 11) The following case microstructure characteristics for each grade must be met: Microstructure of case along Primarily fine Primarily fine acicular tempered Primarily fine acicular tempered flank (for pitting resistance acicular marten- martensite. Non--martensitic struc- martensite with no non--martensitic rating). site. tures anywhere in the case should structures. not exceed 5%. Microstructure at root (for Primarily fine Primarily fine acicular tempered Primarily fine acicular tempered bending strength rating). acicular marten- martensite. Non--martensitic struc- martensite. Non--martensitic strucsite. tures anywhere in the case should tures anywhere in the case should not exceed 10%. not exceed 5%. Heat affected zone. Also see Induction and flame hardening heat treatments have a characteristic heat affected zone that Item 13. 8) 10) is caused by the surface heating process. This zone can have lower hardness and different microstructure than the base material. The case depth specification should be established to avoid gear failure which might initiate in this zone. Surface temper etch inspection Not specified. FB2, which allows light tempering FB1, which allows light tempering of ground teeth on 25% of functional area. on 10% of functional area. Surface cracks 12) 13) Cracks, bursts, seams and laps are not permissible in functional areas of finished gearing. Magnetic particle inspection of Inspection to the following limits: finished gearing5) 12) 13) 14) -- Below the pitch line Not specified. No indications. No indications. -- Above the pitch line Normal diametral pitch Module Indication, maximum Indication, maximum at less more at inch mm inch mm least than than most 1/8 3.2 3/32 2.4 ---3 8 -- -Not specified. 3/32 2.4 1/16 1.6 3 10 2.5 8 1/16 1.6 1/32 0.8 10 ----- -2.5

(continued)

24



AGMA 923--B05

Table 3 (concluded) Item

23

Characteristic1) 2) Shot peening 15)

Grade 1

Grade 2

Grade 3 Spin induction Type A (Contour) only Shot peening per SAE/AMS--S--13165 may be used to increase surface residual compressive stress.

NOTES: 1) See clause 3 for definitions and clause 4 for test methods. 2) The metallurgical requirements assume homogeneous composition. In practice, microsegregation and banding occurs in steels. This microsegregation can produce variations in microstructure and properties that need to be assessed. 3) The grade requirements for non--metallic inclusion, ultrasonic, and microstructure characteristics apply only to those portions of the gear material where the teeth will be located to a depth below the finished tooth tip of at least 1.5 times the tooth height. 4) A 7 to 1 minimum reduction ratio is recommended. For large gearing where this reduction ratio is not physically obtainable, lesser reduction ratios may be used down to a minimum of 3 to 1. 5) In--process ultrasonic and/or magnetic particle inspection of gearing blanks is recommended for large diameter parts to detect flaws before incurring the expense of further machining. 6) Mechanical properties, including core hardness, may not be the same after induction or flame hardening as they were before induction or flame hardening. 7) See ASTM A370, ASTM E140 or ISO 6336--5, annex C for hardness conversion tables. 8) See clauses 3 and 4 for a discussion on test coupons. 9) Induction tempering is recommended for Grade 3 as a crack preventing stress relief heat treatment prior to furnace tempering. 10) The hardness pattern, depth, facilities and process method must be established, documented and verified to be repeatable. The process equipment and methods must be sufficiently accurate to reproduce the specified results. Excessive case depth can generate unfavorable residual stress conditions. 11) Microstructure analysis of induction hardened test specimens have shown indications of undissolved pearlite or “ghost pearlite”. This is especially true with rapid (short) heating cycles. This “ghost pearlite” should not be present. 12) Removal of defects that exceed the stated limits is acceptable, provided the integrity of the gear is not compromised. 13) Cracks in non--functional areas require engineering disposition. 14) Limits: maximum of one indication per inch of face width with a maximum of five such indications on any one tooth flank. Indications less than 1/32 inch (0.8 mm) are not considered. 15) It is recommended that ANSI/AGMA 2004--B89 be reviewed to determine if the benefits of surface residual compressive stress achieved by shot peening may be beneficial to the particular application. Shot peening of the flanks of gear teeth should be reviewed to ensure that no detrimental effects are caused to the gear set.


25

AGMA 923--B05


Inductor coil

Spin hardening Induction coil or flame head

Type A (Contour) Grades 1, 2 and 3

Type A (Non--contour) Grades 1 and 2 only

Induction coil or flame head

Type B Grades 1 and 2 only

Flank hardening (tooth to tooth) Inductor or flame head

Inductor or flame head



Flank and root hardening (tooth to tooth) Inductor or flame head

Top lands are not fully hardened

Type A Grades 1 and 2 only NOTE: -- Type A indicates that flanks and roots are hardened for contour or non--contour patterns. -- Only spin hardening Type A (Contour) is applicable to Grade 3. -- Type B indicates that the flanks are hardened only to the form diameter. -- For Type B the full active profile must be hardened with the transition zone not in the root fillet area.

Figure 14 -- Variations in hardening pattern obtainable on gear teeth with flame or induction hardening 5.4 Nitrided gearing The major metallurgical characteristics that affect nitrided gearing performance are shown in table 4. These characteristics are not necessarily applicable to carbonitrided or nitrocarburized gearing, neither

26

of which are covered by this document. The minimum acceptable requirements for each factor for metallurgical quality Grades 1, 2 and 3 are specified. All criteria in any given grade must be met to qualify for the stress number associated with that metallurgical quality grade.



AGMA 923--B05

Table 4 -- Metallurgical characteristics for nitrided gearing Item

Characteristic1) 2) chemistry3)

Grade 1

Grade 2

Grade 3

Not specified or verified.

Test report only. Medium carbon alloy steel. 0.025 % maximum sulfur .

Test report only. Medium carbon alloy steel. 0.015 % maximum sulfur .

1

Material

2

Grain size

3

Hardenability

4

Non--metallic inclusions Not specified. (cleanliness, steelmaking) 4)

5.1

Material form

5.2

Material reduction (wrought only)

Predominantly 5 or finer. Test report only. Not specified.

A minimum hardenability which is appropriate for part size and quench severity should be specified.

A minimum hardenability verified by certification, calculation or test which is appropriate for part size and quench severity should be specified.

Wrought gearing Wrought gearing Capable of meeting (certification Certified to SAE/AMS 2304, not required) SAE/AMS 2301, ASTM A866 or SAE J422 S2--O2 ASTM A866 or SAE J422 S2--O2 Cast gears Cast gears Not permitted. Not permitted. Forgings per either ASTM A290 or ASTM A291 Bar stock per ASTM A29, ASTM A304 or ISO 683--1 Tubing per ASTM A519 Castings not permitted.

ratio Not specified.

-- At least 7 to 1 strand or continuous cast -- At least 3 to 1 ingot cast5) 6)

6

Heat treatment prior to case Quench and temper with tempering temperature 900°F (480°C) minimum and 50F° (28C°) hardening minimum above the nitriding temperature.

7

Mechanical properties prior to case hardening. Also see Item 14.7) 8)

8

Microstructure prior to case Not specified. hardening. Also see Item 16.3.4)

Hardness testing is required. Other mechanical testing required only if specified.

Sound metallurgical practice dictates that the core microstructure requirements are maintained in the tooth area to a depth twice the minimum specified effective case depth or 0.100 inch (2.5 mm), whichever is less, below the minimum specified effective case depth. The microstructure in this zone should be predominantly tempered martensite. This microstructure should be free of blocky ferrite, pearlite, and measurable bainite observable at 400--600X. Below this zone the core microstructure should be free of blocky ferrite and be primarily tempered martensite with the following limits: Controlling section size, inch at least less than ---5 5 10 10 15 15 ---Controlling section size, mm at least less than ---125 125 250 250 375 375 ----

Non--martensitic structures, maximum 5% 10% 20% Hardness must be obtained at roots with 900°F minimum temper Non--martensitic structures, maximum 5% 10% 20% Hardness must be obtained at roots with 480°C minimum temper

(continued)


27

AGMA 923--B05



Item 9

Grade 1

Grade 2

Grade 3

inspection4) 6)

Ultrasonic Wrought material. Either method is acceptable.



-- No indications giving a signal re- -- No indications giving a signal response greater than an 8/64 inch sponse greater than a 5/64 inch (3.18 mm) reference standard. (1.98 mm) reference standard. -- No indications giving a signal -- No indications giving a signal response greater than 50% of the response greater than 50% of the reference standard if accompanied reference standard if accompanied by a 50% loss of back reflection. by a 50% loss of back reflection.

-- No indications which are -- No indications which are continuous over an area twice the continuous over an area twice the diameter of the search unit. diameter of the search unit. -- Back reflection technique

12

Not specified.


Surface hardness on a representative surface. Alternative method of inspection is case hardness. 7) -- Specialty nitriding steels9)

13


Either 89 -- 93 HR15N, 650 -- 900 HV or 690 -- 900 HK

-- Through hardening steels

Either 83 min HR15N, 450 min HV or 470 min HK

Case depth considering subsequent stock removal10)

Should meet either of the following characteristics:

13.1

Effective case depth in finished Minimum effective case depth requirements for the tooth should be specified in accordance condition with the appropriate rating standard.

13.3

Total case depth in finished Minimum total case depth requirements for the tooth should be specified in accordance with condition the appropriate rating standard.

14

Core hardness after case hardening. Also see item 7.7)

16

Surface microstructure The first 0.002 -- 0.003 inch (0.05 -- 0.08 mm) of case microstructure in the tooth area should considering subsequent stock meet the surface hardness requirement of the specific grade and also meet the following surremoval 10) face related characteristics and the requirements of Item 17:

16.3

28 HRC minimum

Decarburization.

32 HRC minimum

No decarburization permitted on surface to be nitrided.

-- Method 1. Not applicable.

16.4

-- Method 2. Reduction of hard- Not specified. ness by two load method. 7)

Maximum 2 HRC points or equiva- No reduction in hardness below lent below maximum measured maximum measured hardness by hardness by conversion. conversion is permissible.


No partial decarburization appar- No partial ent except in unground roots. apparent.


decarburization

Epsilon (Á) nitride (white layer) along flank or in root Minimum specified effective case depth inch at less least than ---0.015 0.015 ----

(mm) at less least than ---(0.37) (0.37) ----

M i Maximum allowable depth inch (mm) 0.0010 (0.025) 0.0010 (0.025)

Maximum allowable depth inch (mm) 0.0008 (0.019) 0.0008 (0.019)

Maximum allowable depth inch (mm) 0.0005 (0.012) 0.0008 (0.019)

(continued)

28



AGMA 923--B05

Table 4 (concluded) Characteristic1) 2)

Item 17 Case microstructure considering subsequent stock removal, disregarding corner effects 20 Surface temper inspection

21

22

Grade 1 Grade 2 Grade 3 The first 20% of the case microstructure should be predominantly tempered martensite with interspersed Á nitride. The microstructure should be free of blocky ferrite, pearlite, and measurable bainite. The normal inspection methods, as defined in ANSI/AGMA 2007--B92 or ISO 14104, are not applicable to nitrided gearing. Care must be taken when grinding nitrided surfaces to ensure that no harmful surface conditions are produced in the grinding process. 11) 12) Surface cracks Cracks, bursts, seams and laps are not permitted in Cracks, bursts, seams and laps are functional areas of finished gearing. not permitted in any area of finished gearing. Magnetic particle inspection of Inspection recommended to the Inspection required to the finished gearing 6) 11) 12) 13) following limits: following limits: -- Below the pitch line -- Above the pitch line Normal diametral pitch Module at less more at least than than most -- -3 8 -- -3 10 2.5 8 10 -- --- -2.5

Not specified.

Not specified.

No indications.

Indication, maximum inch mm 1/8 3.2 3/32 2.4 1/16 1.6 Not recommended.

No indications.

Indication, maximum inch mm 3/32 2.4 1/16 1.6 1/32 0.8

23 Shot peening NOTES: 1) See clause 3 for definitions and clause 4 for test methods. 2) The metallurgical requirements assume homogeneous composition. In practice, microsegregation and banding occurs in steels. This microsegregation can produce variations in microstructure and properties that need to be assessed. 3) Chemistry must include adequate nitridable alloying elements such as chromium, aluminum, vanadium or molybdenum. 4) The grade requirements for nonmetallic inclusion, ultrasonic and microstructure characteristics apply only to those portions of the gear material where the teeth will be located to a depth below the finished tooth tip of at least 1.5 times the tooth height. 5) A 7 to 1 minimum reduction ratio is recommended. For large gearing where this reduction ratio is not physically obtainable, lesser reduction ratios may be used down to a minimum of 3 to 1. 6) In--process ultrasonic and/or magnetic particle inspection of gearing blanks is recommended for large diameter parts to detect flaws before incurring the expense of further machining. 7) See ASTM A370, ASTM E140 or ISO 6336--5, annex C for hardness conversion tables. 8) Mechanical properties including core hardness may not be the same after nitride hardening as they were before nitride hardening. 9) Specialty nitriding steels are typically alloyed with 1% aluminum to provide higher surface hardness after nitriding than normally attained with nitrided through hardening steels. 10) For a discussion of test coupons see clauses 3 and 4. 11) Removal of defects that exceed the stated limits is acceptable, provided the integrity of the gear is not compromised. 12) Cracks in non--functional areas require engineering disposition. 13) Limits: maximum of one indication per inch (25 mm) of face width with a maximum of five such indications on any one tooth flank. Indications less than 1/32 inch (0.8 mm) are not considered.


29

AGMA 923--B05


(This page is intentionally left blank.)

30



AGMA 923--B05

Bibliography

The following documents are either referenced in the text of AGMA 923--B05, Metallurgical Specifications for Steel Gearing, or indicated for additional information.

ANSI/AGMA 6033--B98, Materials for Marine Propulsion Gearing ASM Handbook, Volume 1 -- Properties and selection: Irons, steels and high--performance alloys, ASM International, Materials Park, Ohio, 1990 ASM Handbook, Volume 4 -- Heat treating, ASM International, Materials Park, Ohio, 1991 Boyer, Howard E., Ed., Hardness Testing, ASM International, Materials Park, Ohio, 1987 Doane, D.V. and Semchyshen, M., Modern carburized nickel alloy steel, Nickel Development Institute, Toronto, 1990 Heat Treater’s Guide -- Practices and procedures for irons and steels, ASM International, Materials Park, Ohio, 1995


Kern, Roy F. and Suess, Manfred E., Steel Selection -- A guide for improving performance and profits, John Wiley & Sons, New York, 1979 Krauss, G., Steels: Heat Treatment and Processing Principles, ASM International, Materials Park, Ohio, 1996 Parish, Geoffrey, Carburizing: Microstructures and Properties, ASM International, Materials Park, Ohio, 1999 Practical Data for Metallurgists, 14th edition, The Timken Company, Canton, Ohio, 1999 Reed--Hill, R.E., Physical Metallurgy Principles, D. Van Nostrand, New York, 1973 Totten, G.E., and Howes, M.A.H., Steel Heat Treatment Handbook, Marcel Dekker, New York, 1997

31

PUBLISHED BY AMERICAN GEAR MANUFACTURERS ASSOCIATION 500 MONTGOMERY STREET, SUITE 350 ALEXANDRIA, VIRGINIA 22314

Agma-923-b05 681o6b

Overview 1s532p

More details 6h715l

More Documents from "Prakash" 5p1w27

Siddhar Korakkar's 7 Medical Writings 12616b

Astm E 186.pdf 45244l

Prodex-tech-en.pdf 3w35x

Gost 380-2005 555f2x

Kathiruntha Kanavu By Ramya 413q11

Agma-923-b05 681o6b