ASTM A668/A668M-23

Standard Specification for Steel Forgings, Carbon and Alloy, for General Industrial Use

ABSTRACT
This specification deals with the standard requirements for untreated and heat-treated carbon and alloy steel forgings for general industrial use. This specification covers six classes of carbon steels (Class A to F) and seven classes of alloy steels (Class G, H, and J to N). Materials shall be forged by hot mechanical work. Except for Class A, all forgings shall be heat treated, depending on class, by the following techniques: annealed, or normalized, or normalized and tempered (Classes B, C, D, and G); normalized and tempered, or double-normalized and tempered (Class E); quenched and tempered, or normalized, quenched, and tempered (Classes F); normalized and tempered (Class H); normalized and tempered, or normalized, quenched, and tempered (Class J); and normalized, quenched, and tempered (Classes K, L, M, and N). Steel specimens shall undergo heat and product analyses, and shall conform to required chemical compositions for manganese, phosphorus, and sulfur. Steel forgings shall also be tested on their conformance to the following tensile requirements: tensile strength, yield point, yield strength, elongation, reduction of area, and Brinell hardness.
SCOPE
1.1 This specification covers untreated and heat-treated carbon and alloy steel forgings for general industrial use. Other ASTM specifications for forgings are available for specific applications such as pressure vessels, railroad use, turbine generators, gearing, and others involving special temperature requirements.  
1.2 Hot-rolled or cold finished bars are not within the scope of this specification.  
1.3 Six classes of carbon steel and seven classes of alloy steel forgings are listed (see Section 7), which indicate their required heat treatments, as well as mechanical properties.  
1.4 Provision, with the suffix H for certification and marking, for the supply of forgings after hardness testing only.  
1.5 Supplementary requirements, including those in Specification A788/A788M, of an optional nature are provided. These shall apply only when specified by the purchaser.  
1.6 Appendix X1 lists the current classes corresponding to the various classes of Specifications A235, A237, and A243, which have been superseded by this specification.  
1.7 The values stated in either SI units or inch-pound units are to be regarded separately as standard; within the text and tables, the SI units are shown in brackets. 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.  
1.8 Unless the order specifies the applicable “M” specification, the forgings shall be furnished to the inch-pound units.  
1.9 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: 30-Apr-2023
• ICS: 77.140.85 - Iron and steel forgings
• Technical Committee: A01 - Steel, Stainless Steel and Related Alloys
• Drafting Committee: A01.06 - Steel Forgings and Billets

Relations

• Refers: ASTM A370-24 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Mar-2024
• Refers: ASTM E340-23 - Standard Practice for Macroetching Metals and Alloys
• Effective Date: 15-Nov-2023
• Refers: ASTM A275/A275M-23 - Standard Practice for Magnetic Particle Examination of Steel Forgings
• Effective Date: 01-Nov-2023
• Refers: ASTM A388/A388M-23 - Standard Practice for Ultrasonic Examination of Steel Forgings
• Effective Date: 01-Nov-2023
• Refers: ASTM A370-19 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Jul-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 A370-17a - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 15-Nov-2017
• 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 A370-17 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Jan-2017
• Refers: ASTM A788/A788M-16a - Standard Specification for Steel Forgings, General Requirements
• Effective Date: 01-Dec-2016
• Refers: ASTM A370-15 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products
• Effective Date: 01-Nov-2015

Overview

ASTM A668/A668M-23, published by ASTM International, is the standard specification for untreated and heat-treated carbon and alloy steel forgings intended for general industrial use. This specification designates the technical requirements for six classes of carbon steels (Class A through F) and seven classes of alloy steels (Class G, H, and J through N). The standard defines forging processes, heat treatments, chemical and mechanical property requirements, testing methods, and marking processes, ensuring the safety, durability, and consistency of steel forgings across a wide range of industries.

Key Topics

• Scope and Applicability

  • Covers hot mechanical worked carbon and alloy steel forgings
  • Includes requirements for both untreated and various heat-treated conditions
  • Excludes hot-rolled or cold-finished bars and forgings for pressure vessels, railroad, and specific temperature service, which are covered by other ASTM standards

• Material and Classes

  • Six carbon steel classes: A (untreated) to F (quenched and tempered)
  • Seven alloy steel classes: G, H, J, K, L, M, N (various heat treatments)
  • Provision for “H” suffix when supplied and certified after hardness testing only

• Heat Treatment and Mechanical Properties

  • Specifies mandatory and optional heat treatment methods for each class, including annealing, normalizing, tempering, and quenching
  • Mechanical property requirements include: tensile strength, yield strength or point, elongation, reduction of area, and Brinell hardness
  • Testing locations and sample extraction methods are precisely defined for reliable property verification

• Testing and Analysis

  • Requires chemical composition analysis for manganese, phosphorus, and sulfur
  • Product and heat analysis as per project and manufacturer requirements
  • Includes supplementary testing options such as magnetic particle and ultrasonic testing

• Marking and Certification

  • Marking requirements for traceability, including manufacturer, class, and potentially, additional marking as requested by the purchaser

• Optional and Supplementary Requirements

  • Purchaser may specify requirements for additional analysis, testing, rough machining, or special procedures, referencing other standards such as ASTM A788/A788M

Applications

ASTM A668/A668M-23 is extensively used in industries requiring robust and reliable steel forgings for:

• General Industrial Equipment
  • Shafts, gears, couplings, rings, and structural components
• Heavy Machinery and Construction
  • Components subject to diverse loading and wear conditions
• Agricultural Equipment
  • Durable parts exposed to demanding environments
• Automotive and Transportation
  • Non-specific components in vehicles and heavy trucks
• Energy, Mining, and Processing Facilities
  • General-purpose forged components not subject to pressure vessel or special temperature service

The specification’s comprehensive classification and heat treatment groupings allow end-users to select appropriately balanced properties for strength, ductility, and hardness, maximizing performance and safety.

Related Standards

• ASTM A788/A788M - General requirements for steel forgings, often referenced for supplementary provisions.
• ASTM A275/A275M - Magnetic particle examination for steel forgings.
• ASTM A370 - Mechanical testing methods for steel products.
• ASTM A388/A388M - Ultrasonic examination standards for steel forgings.
• AASHTO M 102M/M 102 - Equivalent standard recognized by the American Association of State Highway and Transportation Officials.

Practical Value

Using ASTM A668/A668M-23 ensures:

• Consistent Quality: Standardized mechanical and chemical properties bolster safety and reliability.
• Traceability: Detailed marking and certification support process control and accountability.
• Flexibility: Multiple steel classes and optional requirements address a wide range of industrial needs.
• International Compliance: Developed under WTO principles, the standard aligns with global trade and industry best practices.

For procurement, engineering, and inspection teams, adherence to ASTM A668/A668M-23 provides assurance of forging performance in general industrial applications, facilitating seamless integration into supply chains and finished products.

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: A668/A668M − 23 American Association State
Highway and Transportation Officials Standard
AASHTO No.: M 102M/M 102
Standard Specification for
Steel Forgings, Carbon and Alloy, for General Industrial
Use
This standard is issued under the fixed designation A668/A668M; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 1.9 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.1 This specification covers untreated and heat-treated
ization established in the Decision on Principles for the
carbon and alloy steel forgings for general industrial use. Other
Development of International Standards, Guides and Recom-
ASTM specifications for forgings are available for specific
mendations issued by the World Trade Organization Technical
applications such as pressure vessels, railroad use, turbine
Barriers to Trade (TBT) Committee.
generators, gearing, and others involving special temperature
requirements.
2. Referenced Documents
1.2 Hot-rolled or cold finished bars are not within the scope
2.1 ASTM Standards:
of this specification.
A275/A275M Practice for Magnetic Particle Examination of
1.3 Six classes of carbon steel and seven classes of alloy
Steel Forgings
steel forgings are listed (see Section 7), which indicate their
A370 Test Methods and Definitions for Mechanical Testing
required heat treatments, as well as mechanical properties.
of Steel Products
A388/A388M Practice for Ultrasonic Examination of Steel
1.4 Provision, with the suffix H for certification and
Forgings
marking, for the supply of forgings after hardness testing only.
A788/A788M Specification for Steel Forgings, General Re-
1.5 Supplementary requirements, including those in Speci-
quirements
fication A788/A788M, of an optional nature are provided.
E290 Test Methods for Bend Testing of Material for Ductil-
These shall apply only when specified by the purchaser.
ity
1.6 Appendix X1 lists the current classes corresponding to
E340 Practice for Macroetching Metals and Alloys
the various classes of Specifications A235, A237, and A243,
which have been superseded by this specification.
3. Terminology
1.7 The values stated in either SI units or inch-pound units
3.1 The terminology section of Specification A788/A788M
are to be regarded separately as standard; within the text and
is applicable to this specification.
tables, the SI units are shown in brackets. The values stated in
3.2 Definitions of Terms Specific to This Standard:
each system are not necessarily exact equivalents; therefore, to
3.2.1 class, n—a description of steel forgings based on heat
ensure conformance with the standard, each system shall be
treatment, mechanical properties and composition.
used independently of the other, and values from the two
3.2.2 controlling cross section thickness (T ), n—the diam-
C
systems shall not be combined.
eter of the largest theoretical sphere which can be inscribed
1.8 Unless the order specifies the applicable “M”
within the volume of the forging.
specification, the forgings shall be furnished to the inch-pound
3.2.3 rough machining, n—machining performed after the
units.
heat treatment cycle used to obtain the stated mechanical
property requirements of Table 2.
This specification is under the jurisdiction of ASTM Committee A01 on Steel,
Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee
A01.06 on Steel Forgings and Billets. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2023. Published May 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1972. Last previous edition approved in 2022 as A668/A668M – 22. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/A0668_A0668M-23. the ASTM website.
*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
A668/A668M − 23
3.2.3.1 Discussion—Rough machining is performed by the 6.4 Product Analysis—An analysis may be made by the
forging supplier or forging supplier representative. It does not purchaser according to the requirements of Specification A788/
include machining used to create detailed features such as gear A788M. If a standard grade has been used to manufacture the
teeth, splines, threads, or keyways and typically does not forging the permissible variations in composition of Specifi-
produce the surface finish or dimensional tolerances the part cation A788/A788M shall apply. If a non-standard grade of
will have when put in service. steel has been used, and composition limits have not been
supplied, the product analysis can be used only to confirm the
3.2.4 T , n—designates prolongations which have a size
P
type of steel supplied.
other than the controlling cross section thickness (T ).
C
7. Mechanical Properties
4. Ordering Information and General Requirements
7.1 Tensile Requirements:
4.1 Material supplied to this specification shall conform to
7.1.1 The material shall conform to the tensile and hardness
the requirements of Specification A788/A788M which outlines
properties prescribed in Table 2. See Test Methods and
additional ordering information, manufacturing requirements,
Definitions A370.
testing and retesting methods and procedures, marking,
7.1.2 All Forgings—The dimensions of the controlling cross
certification, product analysis variations and additional supple-
section thickness (T ) of the forging at time of heat treatment
mentary requirements. C
determine the mechanical properties to be met within each
4.1.1 If the requirements of this specification are in conflict
class (see Table 2) except as noted in 7.1.4.2.
with the requirements of Specification A788/A788M, the
7.1.3 Number of Tests—Unless the purchaser specifies that
requirements of this specification shall prevail.
forgings shall be furnished in accordance with the requirements
4.2 When this specification is to be applied to an inquiry,
of 7.3, the number of tension tests performed shall be as
contract, or order, the purchaser should furnish the following
follows:
information:
7.1.3.1 For all classes of heat-treated forgings with as-heat
4.2.1 The ordering information required by Specification
treated weights (excluding test prolongations) less than 5000 lb
A788/A788M,
[2250 kg] each, one test shall be made from each controlling
4.2.2 The class of forging desired as listed in Table 1,
cross section thickness (T ) represented in each heat and
C
4.2.3 Location(s) of areas of significant loading if test
heat-treating charge. For untreated forgings (Class A) weighing
specimens are to be located in accordance with 7.1.4.5,
less than 5000 lb [2250 kg] each, one test from each heat shall
4.2.4 The options which may be selected as found in 5.3.2,
be made.
6.1, and 7.3, and
7.1.3.2 On all classes, for forgings with as-heat treated
4.2.5 Any applicable supplementary requirements.
weights (excluding test prolongations) of 5000 lb [2250 kg] or
more, at least one test from each forging shall be made.
5. Materials and Manufacture
7.1.3.3 On all classes, for forgings with as-heat treated
5.1 Discard—Sufficient discard shall be made from each
weights (excluding test prolongations) of 7000 lb [3200 kg] or
ingot to secure freedom from piping and undue segregation.
more, two tests will be taken: on ring and disk forgings 180°
apart; on shafts and long hollow cylinders (over 80 in. [2.0 m]
5.2 Forging Process:
5.2.1 The forging shall be brought as close as practical to in length excluding test material), one from each end and offset
180°. Shafts and cylinder forgings 80 in. [2.0 m] or less in
finished shape and size by hot mechanical work.
5.2.2 Supplementary Requirements S2, S14, and S15 may length (excluding test material) may have both tests located at
one end 180° apart.
be specified by the purchaser to satisfy concerns about the
utility of the proposed forging. 7.1.3.4 When forgings are made in multiple as a single
forging, that is, forged as one piece and divided after heat
5.3 Heat Treatment:
treatment, the multiple forging shall be considered as one
5.3.1 All forgings, other than Class A, shall be heat treated.
forging, and the number of tests required shall be as designated
See Section 7.
in 7.1.3.1, 7.1.3.2, and 7.1.3.3.
5.3.2 Where options exist within a class, the choice of heat
7.1.4 Prolongations:
treatment shall be left to the discretion of the manufacturer,
7.1.4.1 A sufficient number of the forgings shall have
unless the purchaser specifies one of the available options.
prolongations for extracting specimens for testing. Examples
of test locations for various forging configurations are shown in
6. Chemical Composition
Figs. 1 and 2.
6.1 The steel shall conform to the requirements prescribed
NOTE 1—Figures provided demonstrate the concept of controlling cross
in Table 1.
section thickness (T ) but do not encompass all possible test prolongation
C
6.2 The choice of chemical composition is left to the
configurations which meet the requirements of Section 7.
discretion of the manufacturer, unless otherwise specified by
7.1.4.2 For all forgings of non-uniform cross section in
the purchaser. See Appendix X2.
classes A, B, C, D, E, G, H, and J (when class J is provided in
6.3 Heat Analysis: the normalized and tempered condition): the prolongation(s)
6.3.1 An analysis of each heat shall be made by the may be extensions of sections other than the controlling cross
manufacturer. section thickness (T ), that is T ≠ T . In this case, the
C P C
A668/A668M − 23
dimension of T shall determine the mechanical properties to 7.1.7 Yield point shall be determined on carbon steel Grades
P
be met within each class. In the case of forgings requiring A through F, and yield strength on alloy steel Grades G through
prolongations on both ends, the prolongations may or may not N. For carbon steel grades not showing a yield point, the yield
have the same T . If T is not the same, and the prolongations strength at 0.2 % offset shall be reported.
P P
fall into different size categories, the manufacturer may elect to
7.2 Hardness Tests—Brinell hardness tests shall be per-
work to either the larger or smaller set of mechanical properties
formed and reported per Test Methods and Definitions A370.
for both prolongations. It is not necessary for a forging with
Hardness testing shall be performed after heat treatment
prolongations falling into two different size classifications to
(except on Class A forgings) and rough machining on each
meet the requirements of both size classifications. When T ≠
P
forging weighing under 7000 lb [3200 kg] at the time of heat
T , T shall not have more reduction than the smallest cross
C P
treatment and each multiple forging made weighing under
section to be qualified.
7000 lb [3200 kg] at the time of heat treatment. Weight at time
(1) For annealed, normalized, or normalized and tempered
of heat treatment excludes test prolongations.
forgings in classes A, B, C, D, E, G, H, and J, the center of the
7.2.1 Hardness testing on forgings in excess of 7000 lb
gage length axis of tension test specimens shall be ⁄4 the
[3200 kg] at the time of heat treatment may be omitted
controlling cross section thickness (T ) from one surface
C
provided they meet the tensile requirements of Table 2.
except as noted in 7.1.4.2 (2).
7.2.2 When forgings are made in multiple as a single
(2) If the prolongation thickness (T ) is less than the
P
forging, that is, forged as one piece and divided after heat
controlling cross section thickness (T ) the center of the gage
C
treatment, the multiple forging shall be considered as one
length axis of the tension test shall be ¼ of the prolongation
forging and the number of tests shall be as described in 7.2.5
thickness (T ) from one surface.
P
and 7.2.6.
7.1.4.3 For quenched forgings in Classes F, J, K, L, M, and
7.2.3 When ordered without rough machining, hardness
N, the center of the gage length axis of the tension test
measurements shall be conducted on the forgings after heat
specimen shall be at a minimum ⁄4 (T ) from one quenched
C
treatment. Due consideration should be provided for the
surface and 3 ⁄2 in. [90 mm] from the nearest second surface.
removal of oxidation and decarburization to ensure accuracy of
For forgings in the aforementioned classes with (T ) of 7 in.
C
hardness results when forgings which have not been rough
[180 mm] or less, the test shall be taken at ⁄4 (T ) from the
C
machined are evaluated.
nearest quenched surface, and at least (T /2) from all other
C
7.2.4 The average value of the hardness readings on each
quenched surfaces exclusive of the (T ) dimension surfaces.
C
forging shall fall within the hardness ranges specified in Table
7.1.4.4 In place of prolongations, the manufacturer may: (1)
2. The permissible variation in hardness in any forging over
elect to submit a representative forging(s) to represent each test
250 lb [110 kg] at time of heat treatment (excluding test
lot; in this event, the representative forging must be made from
prolongations) shall not exceed 30 Brinell Hardness for Classes
the same heat of steel, must not receive more reduction than the
A through E, 40 Brinell Hardness for Classes F through J, 50
forging it represents, must receive the same type of hot
Brinell Hardness for Classes K through N.
working it represents, be of the same controlling cross section
7.2.5 At least two hardness tests shall be taken on each flat
thickness (T ), and have been heat treated in the same
C face of disks, rings, and hollow forgings over 250 lb [110 kg]
heat-treating charge as the forging(s) it represents; or (2) obtain
at time of heat treatment (excluding test prolongations) ap-
the test specimen from the trepanned material of transverse or
proximately at mid-radius for disk forgings and mid-wall for
radial holes, provided the required depth is met.
ring and hollow forgings. When it is impractical to check
7.1.4.5 With prior purchaser approval, test specimens may
hardness on the face of hollow forgings these checks shall be
be taken at a depth (t) corresponding to the distance from the
made at each end on the OD or the ID at a distance equivalent
area of significant stress to the nearest heat-treated surface and
to ⁄2 the wall thickness from each end of the forging. Hardness
at least twice this distance (2t) from any second surface.
checks shall be 180° apart, for example, at the 3:00 and 9:00
However, the test depth shall not be nearer to one heat-treated
positions on one face, and 6:00 and 12:00 positions on the
surface than ⁄4 in. [19
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: A668/A668M − 22 A668/A668M − 23 American Association State
Highway and Transportation Officials Standard
AASHTO No.: M 102M/M 102
Standard Specification for
Steel Forgings, Carbon and Alloy, for General Industrial
Use
This standard is issued under the fixed designation A668/A668M; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This specification covers untreated and heat-treated carbon and alloy steel forgings for general industrial use. Other ASTM
specifications for forgings are available for specific applications such as pressure vessels, railroad use, turbine generators, gearing,
and others involving special temperature requirements.
1.2 Hot-rolled or cold finished bars are not within the scope of this specification.
1.3 Six classes of carbon steel and seven classes of alloy steel forgings are listed (see Section 7), which indicatesindicate their
required heat treatments, as well as mechanical properties.
1.4 Provision, with the suffix H for certification and marking, for the supply of forgings after hardness testing only.
1.5 Supplementary requirements, including those in Specification A788/A788M, of an optional nature are provided. These shall
apply only when specified by the purchaser.
1.6 Appendix X1 lists the current classes corresponding to the various classes of Specifications A235, A237, and A243, which
have been superseded by this specification.
1.7 The values stated in either SI units or inch-pound units are to be regarded separately as standard; within the text and tables,
the SI units are shown in brackets. 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.
1.8 Unless the order specifies the applicable “M” specification, the forgings shall be furnished to the inch-pound units.
1.9 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.
This specification is under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee A01.06
on Steel Forgings and Billets.
Current edition approved May 15, 2022May 1, 2023. Published May 2022May 2023. Originally approved in 1972. Last previous edition approved in 20212022 as
A668/A668MA668/A668M – 22.-21a. DOI: 10.1520/A0668_A0668M-22.10.1520/A0668_A0668M-23.
*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
A668/A668M − 23
2. Referenced Documents
2.1 ASTM Standards:
A275/A275M Practice for Magnetic Particle Examination of Steel Forgings
A370 Test Methods and Definitions for Mechanical Testing of Steel Products
A388/A388M Practice for Ultrasonic Examination of Steel Forgings
A788/A788M Specification for Steel Forgings, General Requirements
E290 Test Methods for Bend Testing of Material for Ductility
E340 Practice for Macroetching Metals and Alloys
3. Terminology
3.1 The terminology section of Specification A788/A788M is applicable to this specification.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 class, class—n—a description of steel forgings based on heat treatment, mechanical properties and composition.
3.2.2 controlling cross section thickness (T )—), n—the diameter of the largest theoretical sphere which can be inscribed within
C
the volume of the forging.
3.2.3 rough machining, n—machining performed after the heat treatment cycle used to obtain the stated mechanical property
requirements of Table 2.
3.2.3.1 Discussion—
Rough machining is performed by the forging supplier or forging supplier representative. It does not include machining used to
create detailed features such as gear teeth, splines, threads, or keyways and typically does not produce the surface finish or
dimensional tolerances the part will have when put in service.
3.2.4 T —, n—designates prolongations which have a size other than the controlling cross section thickness (T ).
P C
4. Ordering Information and General Requirements
4.1 Material supplied to this specification shall conform to the requirements of Specification A788/A788M which outlines
additional ordering information, manufacturing requirements, testing and retesting methods and procedures, marking, certification,
product analysis variations and additional supplementary requirements.
4.1.1 If the requirements of this specification are in conflict with the requirements of Specification A788/A788M, the requirements
of this specification shall prevail.
4.2 When this specification is to be applied to an inquiry, contract, or order, the purchaser should furnish the following
information:
4.2.1 The ordering information required by Specification A788/A788M,
4.2.2 The class of forging desired as listed in Table 1,
4.2.3 Location(s) of areas of significant loading if test specimens are to be located in accordance with 7.1.4.5,
4.2.4 The options which may be selected as found in 5.3.2, 6.1, and 7.3, and
4.2.5 Any applicable supplementary requirements.
5. Materials and Manufacture
5.1 Discard—Sufficient discard shall be made from each ingot to secure freedom from piping and undue segregation.
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 the ASTM website.
A668/A668M − 23
5.2 Forging Process:
5.2.1 The forging shall be brought as close as practical to finished shape and size by hot mechanical work.
5.2.2 Supplementary Requirements S2, S14, and S15 may be specified by the purchaser to satisfy concerns about the utility of the
proposed forging.
5.3 Heat Treatment:
5.3.1 All forgings, other than Class A, shall be heat treated. See Section 7.
5.3.2 Where options exist within a class, the choice of heat treatment shall be left to the discretion of the manufacturer, unless the
purchaser specifies one of the available options.
6. Chemical Composition
6.1 The steel shall conform to the requirements prescribed in Table 1.
6.2 The choice of chemical composition is left to the discretion of the manufacturer, unless otherwise specified by the purchaser.
See Appendix X2.
6.3 Heat Analysis:
6.3.1 An analysis of each heat shall be made by the manufacturer.
6.4 Product Analysis—An analysis may be made by the purchaser according to the requirements of Specification A788/A788M.
If a standard grade has been used to manufacture the forging the permissible variations in composition of Specification
A788/A788M shall apply. If a non-standard grade of steel has been used, and composition limits have not been supplied, the
product analysis can be used only to confirm the type of steel supplied.
7. Mechanical Properties
7.1 Tensile Requirements:
7.1.1 The material shall conform to the tensile and hardness properties prescribed in Table 2. See Test Methods and Definitions
A370.
7.1.2 All Forgings—The dimensions of the controlling cross section thickness (T ) of the forging at time of heat treatment
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determine the mechanical properties to be met within each class (see Table 2) except as noted in 7.1.4.2.
7.1.3 Number of Tests—Unless the purchaser specifies that forgings shall be furnished in accordance with the requirements of 7.3,
the number of tension tests performed shall be as follows:
7.1.3.1 For all classes of heat-treated forgings with as-heat treated weights (excluding test prolongations) less than 5000 lb [2250
kg] each, one test shall be made from each controlling cross section thickness (T ) represented in each heat and heat-treating
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charge. For untreated forgings (Class A) weighing less than 5000 lb [2250 kg] each, one test from each heat shall be made.
7.1.3.2 On all classes, for forgings with as-heat treated weights (excluding test prolongations) of 5000 lb [2250 kg] or more, at
least one test from each forging shall be made.
7.1.3.3 On all classes, for forgings with as-heat treated weights (excluding test prolongations) of 7000 lb [3200 kg] or more, two
tests will be taken: on ring and disk forgings 180° apart; on shafts and long hollow cylinders (over 80 in. [2.0 m] in length
excluding test material), one from each end and offset 180°. Shafts and cylinder forgings 80 in. [2.0 m] or less in length (excluding
test material) may have both tests located at one end 180° apart.
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7.1.3.4 When forgings are made in multiple as a single forging, that is, forged as one piece and divided after heat treatment, the
multiple forging shall be considered as one forging, and the number of tests required shall be as designated in 7.1.3.1, 7.1.3.2, and
7.1.3.3.
7.1.4 Prolongations:
7.1.4.1 A sufficient number of the forgings shall have prolongations for extracting specimens for testing. Examples of test locations
for various forging configurations are shown in Figs. 1 and 2.
NOTE 1—Figures provided demonstrate the concept of controlling cross section thickness (T ) but do not encompass all possible test prolongation
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configurations which meet the requirements of Section 7.
7.1.4.2 For all forgings of non-uniform cross section in classes A, B, C, D, E, G, H, and J (when class J is provided in the
normalized and tempered condition): the prolongation(s) may be extensions of sections other than the controlling cross section
thickness (T ), that is T ≠ T . In this case, the dimension of T shall determine the mechanical properties to be met within each
C P C P
class. In the case of forgings requiring prolongations on both ends, the prolongations may or may not have the same T . If T is
P P
not the same, and the prolongations fall into different size categories, the manufacturer may elect to work to either the larger or
smaller set of mechanical properties for both prolongations. It is not necessary for a forging with prolongations falling into two
different size classifications to meet the requirements of both size classifications. When T ≠ T , T shall not have more reduction
P C P
than the smallest cross section to be qualified.
(1) For annealed, normalized, or normalized and tempered forgings in classes A, B, C, D, E, G, H, and J, the center of the gage
length axis of tension test specimens shall be ⁄4 the controlling cross section thickness (T ) from one surface except as noted in
C
7.1.4.2 (2).
(2) If the prolongation thickness (T ) is less than the controlling cross section thickness (T ) the center of the gage length axis
P C
of the tension test shall be ¼ of the prolongation thickness (T ) from one surface.
P
7.1.4.3 For quenched forgings in Classes F, J, K, L, M, and N, the center of the gage length axis of the tension test specimen shall
1 1
be at a minimum ⁄4 (T ) from one quenched surface and 3 ⁄2 in. [90 mm] from the nearest second surface. For forgings in the
C
aforementioned classes with (T ) of 7 in. [180 mm] or less, the test shall be taken at ⁄4 (T ) from the nearest quenched surface,
C C
and at least (T /2) from all other quenched surfaces exclusive of the (T ) dimension surfaces.
C C
7.1.4.4 In place of prolongations, the manufacturer may: (1) elect to submit a representative forging(s) to represent each test lot;
in this event, the representative forging must be made from the same heat of steel, must not receive more reduction than the forging
it represents, must receive the same type of hot working it represents, be of the same controlling cross section thickness (T ), and
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have been heat treated in the same heat-treating charge as the forging(s) it represents; or (2) obtain the test specimen from the
trepanned material of transverse or radial holes, provided the required depth is met.
7.1.4.5 With prior purchaser approval, test specimens may be taken at a depth (t) corresponding to the distance from the area of
significant stress to the nearest heat-treated surface and at least twice this distance (2t) from any second surface. However, the test
3 1
depth shall not be nearer to one heat-treated surface than ⁄4 in. [19 mm] and to the second heat-treated surface than 1 ⁄2 in. [38
mm]. Sketches showing the exact test locations shall be approved by the purchaser when this method is used.
7.1.5 Tests for acceptance shall be made after final heat treatment of the forgings. Thermal cycling after mechanical testing is
complete shall not exceed 50 °F [30 °C] less than the temperature used to establish mechanical properties.
7.1.6 Test specimen orientation relative to the axis of major metal flow is to be at the discretion of the manufacturer provided the
requirements of Table 2 are met. Test specimen orientation shall be reported.
7.1.7 Yield point shall be determined on carbon steel Grades A through F, and yield strength on alloy steel Grades G through N.
For carbon steel grades not showing a yield point, the yield strength at 0.2 % offset shall be reported.
7.2 Hardness Tests—Brinell hardness tests shall be performed and reported per Test Methods and Definitions A370. Hardness
testing shall be performed after heat treatment (except on Class A forgings) and rough machining on each forging weighing under
7000 lb [3200 kg] at the time of heat treatment and each multiple forging made in accordance with 7.1.3.3weighing under 7000 lb
[3200 kg] at the time of heat treatment. Weight at time of heat treatment excludes test prolongations.
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7.2.1 Hardness testing on forgings in excess of 7000 lb [3200 kg] at the time of heat treatment may be omitted provided they meet
the tensile requirements of Table 2. For additional exceptions see 7.1.3.4 and 7.3.
7.2.2 When forgings are made in multiple as a single forging, that is, forged as one piece and divided after heat treatment, the
multiple forging shall be considered as one forging and the number of tests shall be as described in 7.2.5 and 7.2.6.
7.2.3 When ordered without rough machining, hardness measurements shall be conducted on the forgings after heat treatment.
Due consideration should be provided for the removal of oxidation and decarburization to ensure accuracy of hardness results when
forgings which have not been rough machined are evaluated.
7.2.4 The average value of the hardness readings on each forging shall fall within the hardness ranges specified in Table 2. The
permissible variation in hardness in any forging over 250 lb [110 kg] at time of heat treatment (excluding test prolongations) shall
not exceed 30 Brinell Hardness for Classes A through E, 40 Brinell Hardn
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