ASTM A729/A729M-17(2022)

Standard Specification for Carbon and Alloy Steel Axles, Heat-Treated, for Mass Transit and Electric Railway Service

ABSTRACT
This specification deals with the standard requirements for heat-treated alloy steel axles and solid design roller bearing axles with machined bodies for mass transit and commuter cars in electric and locomotive hauled railway service. Various axle designs are used for this service including motor and non-motor with either inboard or outboard journals. Materials shall be forged, cooled and heat treated by normalizing, liquid quenching, tempering, and straightening. Steels shall conform to chemical composition requirements specified for each of the seven classes considered here. Conformance to mechanical property requirements such as tensile strength, yield strength, elongation, and reduction of area, shall be evaluated by tensile tests. Details of nondestructive ultrasonic and magnetic particle examination procedures are discussed thoroughly. Final axle products shall conform to purchaser-specified size, shape, and finish. Rough machining shall be free of excessively rough ridges and coarse chatter marks, and the finish machined axle surfaces shall be free of injurious imperfections.
SCOPE
1.1 This specification covers heat-treated carbon and alloy steel axles for mass transit and commuter cars in electric and locomotive hauled railway service.  
1.2 This specification is for solid design roller bearing axles with machined bodies.  
1.3 Various axle designs are used for this service including motor and non-motor with either inboard or outboard journals.  
1.4 Supplementary requirements including those in the general requirements of Specification A788/A788M are provided for use when additional testing or inspection is desired. These shall apply only when specified individually by the purchaser in the order.  
1.5 Unless the order specifies the applicable “M” specification designation, the axles shall be furnished to the inch-pound units.  
1.6 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.  
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Aug-2022
• ICS: 45.040 - Materials and components for railway engineering
• Technical Committee: A01 - Steel, Stainless Steel and Related Alloys
• Drafting Committee: A01.06 - Steel Forgings and Billets

Relations

• Refers: ASTM A388/A388M-23 - Standard Practice for Ultrasonic Examination of Steel Forgings
• Effective Date: 01-Nov-2023
• Refers: ASTM A275/A275M-23 - Standard Practice for Magnetic Particle Examination of Steel Forgings
• Effective Date: 01-Nov-2023
• Refers: ASTM E1426-14(2019)e1 - Standard Test Method for Determining the X-Ray Elastic Constants for Use in the Measurement of Residual Stress Using X-Ray Diffraction Techniques
• Effective Date: 01-Oct-2019
• Refers: ASTM A788/A788M-19 - Standard Specification for Steel Forgings, General Requirements
• Effective Date: 01-May-2019
• Refers: ASTM A788/A788M-18b - Standard Specification for Steel Forgings, General Requirements
• Effective Date: 01-Nov-2018
• Refers: ASTM A788/A788M-18a - Standard Specification for Steel Forgings, General Requirements
• Effective Date: 01-Sep-2018
• Refers: ASTM A788/A788M-18 - Standard Specification for Steel Forgings, General Requirements
• Effective Date: 01-Mar-2018
• Refers: ASTM A788/A788M-17a - Standard Specification for Steel Forgings, General Requirements
• Effective Date: 01-Nov-2017
• Refers: ASTM A788/A788M-17 - Standard Specification for Steel Forgings, General Requirements
• Effective Date: 01-May-2017
• Refers: ASTM A788/A788M-16a - Standard Specification for Steel Forgings, General Requirements
• Effective Date: 01-Dec-2016
• Refers: ASTM A29/A29M-15 - Standard Specification for General Requirements for Steel Bars, Carbon and Alloy, Hot-Wrought
• Effective Date: 01-Nov-2015
• Refers: ASTM A788/A788M-15 - Standard Specification for Steel Forgings, General Requirements
• Effective Date: 01-May-2015
• Refers: ASTM E1426-14 - Standard Test Method for Determining the X-Ray Elastic Constants for Use in the Measurement of Residual Stress Using X-Ray Diffraction Techniques
• Effective Date: 01-Dec-2014
• Refers: ASTM A788/A788M-14a - Standard Specification for Steel Forgings, General Requirements
• Effective Date: 01-Oct-2014
• Refers: ASTM A788/A788M-14 - Standard Specification for Steel Forgings, General Requirements
• Effective Date: 15-May-2014

Overview

ASTM A729/A729M-17(2022) sets the standard specification for heat-treated carbon and alloy steel axles designed for mass transit and electric railway service. Issued by ASTM International, this standard covers axles intended for use in mass transit and commuter cars operated by electric or locomotive-hauled railway service. The specification encompasses solid design roller bearing axles with fully machined bodies and prescribes rigorous requirements for materials, manufacturing processes, heat treatment, mechanical properties, testing, inspection, and finish quality. The goal is to ensure axles demonstrate consistent performance, durability, and safety in demanding railway environments.

Key Topics

This standard addresses several core areas critical to axle performance:

• Material Selection: Specifies the use of carbon and alloy steels, classified into seven classes, each with defined chemical compositions. Steel classes are selected based on required mechanical properties and service conditions.
• Heat Treatment: Outlines comprehensive heat treatment procedures such as normalizing, liquid quenching, tempering, and straightening. Heat treatment methods are tailored to different grades to enhance mechanical properties like strength and ductility.
• Mechanical Properties: Sets minimum requirements for tensile strength, yield strength, elongation, and reduction of area. Mechanical property compliance is verified through tensile testing according to standard methods.
• Nondestructive Testing: Mandates ultrasonic and magnetic particle testing for detecting internal and surface discontinuities. Acceptance criteria are clearly defined to ensure axles are free from injurious imperfections.
• Dimensional Tolerances: Establishes precise requirements for axle length, diameter, and finish, ensuring easy integration and reliable in-service performance.
• Workmanship and Finish: Dictates that axles must be free from rough machining marks, chatter, or surface defects, with finish machining meeting strict smoothness and flaw criteria.

Applications

ASTM A729/A729M-17(2022) is referenced wherever high-reliability railway axles are required, particularly in:

• Mass Transit Systems: Subways, trams, and light rail vehicles that demand dependable performance and long-term durability.
• Commuter Rail Services: Axles for cars serving urban and suburban rail networks, where frequent loads and stops necessitate robust design.
• Locomotive-Hauled Rolling Stock: Axles engineered for both powered (motor) and non-powered (non-motor) car applications, accommodating either inboard or outboard journal designs.
• Railway Fleet Maintenance: Providing standards for axle procurement, inspection, and replacement to ensure continued safe operation of railcars.
• International Railway Projects: Used in global projects where conformance to recognized quality and safety standards is essential for cross-border compatibility and trade.

Related Standards

ASTM A729/A729M-17(2022) is part of a family of railway and forging standards, often referenced together to ensure comprehensive quality control:

• ASTM A788/A788M: General requirements for steel forgings, referenced for additional ordering, testing, and manufacturing details.
• ASTM A29/A29M: Specifications for general requirements for steel bars, relevant to the forging material.
• ASTM A388/A388M: Ultrasonic examination practices for steel forgings, referenced for nondestructive testing procedures.
• ASTM A275/A275M: Magnetic particle examination procedures.
• AAR Manual of Standards and Recommended Practices – Section G: Industry standards specifically for railway wheels and axles.
• ASTM E112, E381, E1426: Test methods for grain size, macroetch testing, and x-ray residual stress determination.

Practical Value

Implementing ASTM A729/A729M-17(2022) ensures railway axles meet internationally recognized quality, safety, and reliability criteria. Adherence to this standard enhances axle life, minimizes risk of failure, ensures regulatory compliance, and provides confidence in procurement and maintenance processes for rail operators and manufacturers worldwide.

Keywords: ASTM A729, alloy steel axles, carbon steel axles, heat-treated railway axles, mass transit axles, electric railway service, rail axles standard, non-destructive testing, steel forgings, railway safety.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: A729/A729M −17 (Reapproved 2022)
Standard Specification for
Carbon and Alloy Steel Axles, Heat-Treated, for Mass Transit
and Electric Railway Service
This standard is issued under the fixed designationA729/A729M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* A29/A29M SpecificationforGeneralRequirementsforSteel
Bars, Carbon and Alloy, Hot-Wrought
1.1 This specification covers heat-treated carbon and alloy
A275/A275M Practice for Magnetic Particle Examination of
steel axles for mass transit and commuter cars in electric and
Steel Forgings
locomotive hauled railway service.
A388/A388M Practice for Ultrasonic Examination of Steel
1.2 This specification is for solid design roller bearing axles
Forgings
with machined bodies.
A788/A788M Specification for Steel Forgings, General Re-
quirements
1.3 Various axle designs are used for this service including
motor and non-motor with either inboard or outboard journals. E112 Test Methods for Determining Average Grain Size
E381 Method of Macroetch Testing Steel Bars, Billets,
1.4 Supplementary requirements including those in the gen-
Blooms, and Forgings
eral requirements of Specification A788/A788M are provided
E1426 Test Method for Determining the X-Ray Elastic
for use when additional testing or inspection is desired. These
Constants for Use in the Measurement of Residual Stress
shall apply only when specified individually by the purchaser
Using X-Ray Diffraction Techniques
in the order.
2.2 Other Standard:
1.5 Unless the order specifies the applicable “M” specifica-
AAR Manual of Standards and Recommended Prac-
tion designation, the axles shall be furnished to the inch-pound
tices Wheels and Axles, Section G
units.
3. Terminology
1.6 The values stated in either SI units or inch-pound units
are to be regarded separately as standard. The values stated in 3.1 Definitions of Terms Specific to This Standard:
3.1.1 class—the set of chemical requirements for the steel to
each system are not necessarily exact equivalents; therefore, to
ensure conformance with the standard, each system shall be be used for the axles to be supplied.
used independently of the other, and values from the two
3.1.2 grade—the designation of the specific set of mechani-
systems shall not be combined.
cal properties selected for the axle(s) to be supplied. The grade
1.7 This international standard was developed in accor- is selected based on the axle design and service requirements.
dance with internationally recognized principles on standard-
3.2 Users of this specification are cautioned that the above
ization established in the Decision on Principles for the
terms may be used differently in other industry standards and
Development of International Standards, Guides and Recom-
purchaser ordering information. Producers and purchasers
mendations issued by the World Trade Organization Technical
should ensure that both parties are in agreement regarding the
Barriers to Trade (TBT) Committee.
specific mechanical and chemical requirements for the axles to
be supplied.
2. Referenced Documents
2.1 ASTM Standards: 4. Ordering Information
4.1 Material supplied to this specification shall conform to
the requirements of Specification A788/A788M, which out-
This specification is under the jurisdiction of ASTM Committee A01 on Steel,
Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee
lines ordering information, manufacturing requirements, test-
A01.06 on Steel Forgings and Billets.
ing and retesting methods and procedures, marking,
Current edition approved Sept. 1, 2022. Published September 2022. Originally
certification,productanalysisvariations,andadditionalsupple-
approved in 1976. Last previous edition approved in 2017 as A729/A729M – 17.
DOI: 10.1520/A0729_A0729M-17R22. mentary requirements.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Available from Association of American Railroads (AAR), 425 3rd St., SW,
the ASTM website. Washington, DC 20024, http://www.aar.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A729/A729M − 17 (2022)
4.1.1 If the requirements of this specification are in conflict 6.3 Heat Treatment:
with the requirements of Specification A788/A788M, then the
6.3.1 Axlesshallbeheat-treatedinaccordancewithTable2.
requirements of this specification shall prevail.
6.3.2 Grades A and F shall be heat-treated by double
4.2 In addition to the ordering information required by normalizing, followed by tempering. After heating to and
Specification A788/A788M, the purchaser should include with
holding at an appropriate temperature in the austenitic range,
the inquiry and order a detailed drawing, sketch or written the axles shall be cooled in still air to under 500 °F [260 °C].
description of the axle showing complete details pertaining to
They shall then be reheated into the austenitic range to the
dimensions, grade, tolerances if more restrictive than those
same or a lower temperature and again air cooled to under
contained in this specification, degree of finish, and location of
500 °F [260 °C]. A furnace charge thus treated is termed a
stamping.
double normalizing charge. After cooling, the axles are then
4.2.1 Unlessthepurchaserdesignatesaclassinthepurchase
tempered as in 6.3.4.
order or contract, the class used shall be at the producer’s
6.3.3 All other Grades shall be liquid quenched and tem-
discretion.
pered. After heating to and holding at an appropriate tempera-
4.3 Supplementary requirements, if needed, including any ture in the austenitic range, the axles shall be quenched in a
that are appropriate from Specification A788/A788M. suitable medium. A furnace charge thus treated is termed a
quenching charge. Following quenching, the axles are tem-
5. Chemical Requirements
pered as in 6.3.4.
5.1 Chemical Composition—The steel shall conform to the
6.3.3.1 Grade H axles require a normalizing cycle prior to
chemical requirements specified in Table 1.
the quenching heat treatment.
6.3.3.2 At the manufacturer’s option for Grade G, a normal-
5.2 Seven classes of steel are included in Table 1. Unless
izing cycle may precede austenitizing for the liquid quenching
otherwisespecifiedbythepurchaser,thechoiceofsteelclassto
be used for any given axle grade is at the option of the operation.
producer.
6.3.4 Tempering—Axles shall be reheated gradually to and
heldatanappropriatesubcriticaltemperature,andshallthenbe
5.3 Classes F, G, and H are referenced in the AAR Manual
allowed to cool under uniform conditions. A furnace charge
ofStandardsandRecommendedPractices,SectionG,Standard
thus treated is termed a tempering charge.
M-101 as Grades F, G, and H and unspecified element
6.3.4.1 When required by Supplementary Requirement S2,
additions to these classes shall be reported.
axles that have been rough machined after heat treatment shall
5.4 The purchaser may use the requirements of Specifica-
be heated to and held for an appropriate time at a temperature
tion A788/A788M for a product analysis.
that is less than the last tempering temperature by at least 50 °F
[10 °C]. Then the axles shall be quenched directly into water
6. Manufacture
with the axle length vertical.
6.1 Forging Practice—The axle may be made direct from
6.3.5 Heat treatment may be performed in either batch-type
the ingot or from blooms, the total reduction in cross-sectional
furnaces or continuous furnaces.
area from ingot or strand cast blooms to axle forging being not
less than 3 to 1, unless otherwise specified.
6.4 Straightening—Straightening, if necessary, shall be
6.2 Cooling and Heating: done before machining and at a temperature between 950 °F
[510 °C] and 100 °F [55 °C] below the final tempering tem-
6.2.1 Blooms and ingots shall be reheated for forging in a
manner that will prevent internal bursts and overheating. perature. Straightening performed at temperatures lower than
950 °F [510 °C] shall be followed by stress relieving or
6.2.2 Axles that are heat-treated directly from forging shall
becooledbelow1000 °F[538°C]andfullytransformedbefore applicable heat treatment. These requirements do not apply to
the start of any reheating operation. straightening performed prior to final heat treatment.
TABLE 1 Chemical Requirements
Composition %
A
Class A Class B Class C Class D Class F ClassesG&H
Carbon 0.43-0.48 0.28-0.33 0.38-0.43 0.28-0.33 0.45-0.59 .
Manganese 0.75-1.00 0.40-0.60 0.75-1.00 0.70 0.90 0.70-1.00 0.60-0.90
Phosphorous 0.035 max 0.035 max 0.035 max 0.035 max 0.035 max 0.035 max
Sulfur 0.040 max 0.040 max 0.040 max 0.040 max 0.040 max 0.040 max
Silicon 0.15-0.35 0.15-0.35 0.15-0.35 0.15-0.35 0.15 min 0.15 min
BB
Nickel . . . 0.40-0.70
BB
Chromium 0.20-0.35 0.80-1.10 0.80-1.10 0.40-0.60
BB
Molybdenum . 0.15-0.25 0.15-0.25 0.15-0.25
B
Vanadium 0.08 max 0.08 max 0.08 max 0.08 max 0.02-0.08
BB
Aluminum 0.04 max 0.04 max 0.04 max 0.04 max
A
Class D meets the requirements of SAE 8630 alloy steel.
B
The manufacturer may add these elements as necessary to meet the specified mechanical properties after the required heat treatment. The actual chemistry shall be
reported.
A729/A729M − 17 (2022)
TABLE 2 Heat Treatment and Tensile Requirements
Yield Strength
Size, Solid Diameter or Thickness, Tensile Strength, Elongation, in Reduction of
Grade Heat Treatment at 0.2 %, min,
in. [mm] psi [MPa], min 2 in. [50 mm], min Area %, min
psi [MPa]
Over Not Over
A, F Double Normalize . 8 [200] 88 000 [605] 50 000 [345] 22 37
and Temper 86 000 [595] 48 000 [330] 21 35
8 [200] 12 [300]
... 4 [100] 105 000 [725] 70 000 [485] 24 45
Quench 4 [100] 7 [175] 100 000 [690] 65 000 [450] 22 45
B, C, D
and Temper
7 [175] 10 [250] 85 000 [585] 50 000 [345] 20 40
10 [250] . 82 500 [570] 48 000 [330] 19 35
... 4 [200] 90 000 [620] 55 000 [380] 20 39
Quench
G 4 [100] 7 [175] 85 000 [585] 50 000 [345] 20 39
and Temper
7 [175] 10 [250] 85 000 [585] 50 000 [345] 19 37
Normalize, Quench, . 7 [175] 115 000 [795] 75 000 [520] 16 35
H
and Temper 7 [175] 10 [250] 105 000 [725] 65 000 [450] 18 35
7. Metallurgical Requirements 8.1.4 The longitudinal axis of the specimen shall be located
at any point midway between the center and surface of the axle
7.1 A specimen, representing each heat in each heat-
orfull-sizedprolongationandshallbeparalleltotheaxisofthe
treatment lot, shall be taken for the heat treated grain size
axle.
determination in accordance with Test Methods E112. This
samplesectionmaybecutfromthelargeundistortedportionof
8.2 Prolongation:
the tension test specimen in such a way as will give a face
8.2.1 To ensure that sufficient material is available for test
transverse to the axis of the axle.
purposes, prolongations shall be attached to at least 5 % of the
axles in each heat in each heat-treating lot.
7.2 The entire specimen shall show a uniform, fine-grained
structure of No. 5 or finer as measured in accordance with Test
8.2.2 If axles with prolongations have been expended, then
Methods E112. axles without prolongations may be used to prepare test
samples. The samples shall be removed from the bearing
7.3 Alternatively, the austenitic fine grain requirements of
journal diameter and radially located per 8.1.4.
Specification A29/A29M may be used in lieu of the heat-
treated grain size described in 7.1. In this case, the grain
8.3 Number of Tests:
refining elements used shall be included in the heat analysis
8.3.1 Unless otherwise specified by the purchaser, mechani-
results.
cal tests shall be made as covered in 8.3.2 and 8.3.3.
8.3.2 Where batch-type furnaces are used, one test per heat
8. Tension Test Requirements
per size classification is required, but each test shall represent
8.1 Tensiontestsshallbetakenfromthetestprolongationor
no more than 70 axles. The axles represented by this test shall
from an axle in accordance with 8.2.
be called a heat-treatment lot.
8.1.1 Axles shall conform to the requirements in Table 2.
8.3.3 Where continuous heat-treating furnaces are used, one
8.1.2 The diameter of the test prolongation of axle forgings
test per heat per size classification is required, but each test
shall be determined by the forged diameter of the journal.
shall represent no more than 70 axles.The axles represented by
8.1.3 Tests shall be made only after final heat treatment.
this test shall be called a heat-treatment lot.
Final heat treatment for purposes of this requirement includes
8.4 Retest:
thesubcriticalquenchrequiredbySupplementaryRequirement
S2, but does not include post-straightening stress relief heat 8.4.1 If the results of the mechanical tests of any lot do not
treatment per 6.4. conform to the requirements specified, the axles may be
FIG. 1 Typical Distance-Amplitude Curve for a Heat-Treated Axle Using a 1 ⁄8 in. [28.6 mm] Diameter 2.25 MHz Quartz Transducer
A729/A729M − 17 (2022)
FIG. 2 Location of Reference Holes in an Axle—Flat Bottom Hole Sizes for a Heat-Treated Axle
retreated, but not more than three additional times and retests 9.4.3 Distance-Amplitude Correction—The amplitude of an
shall be made in accordance with Section 8. ultrasonic indication must be considered in relation to its
distance from the testing surface to evaluate its significance.
9. Nondestructive Testing Requirements
This can be accomplished by an electronic device or by
9.1 Ultrasonic Examination—The purpose of this examina- distance-amplitude curves (DAC), which are described in
9.7.2.
tion is to evaluate the quality of new axles (1) by determining
end face to end face penetrability, and (2) by detecting
9.4.4 In addition to the reportable conditions of Practice
discontinuities that may be harmful to axle service. A388/A388M, indications exceed
...