ASTM A320/A320M-24

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: A320/A320M − 22a A320/A320M − 24
Standard Specification for
Alloy-Steel and Stainless Steel Bolting for Low-Temperature
Service
This standard is issued under the fixed designation A320/A320M; 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 alloy and stainless steel bolting materials and bolting components for pressure vessels, valves,
flanges, and fittings for low-temperature service. See Specification A962/A962M for the definition of bolting. The bars shall be
hot-wrought and may be further processed by centerless grinding or by cold drawing. Austenitic stainless steel may be solution
annealed or annealed and strain-hardened. When strain hardened austenitic stainless steel is ordered, the purchaser should take
special care to ensure that Appendix X1 is thoroughly understood.
1.2 Several grades are covered, including both ferritic and austenitic steels designated L7, B8, etc. Selection will depend on
design, service conditions, mechanical properties, and low-temperature characteristics. The mechanical requirements of Table 1
indicate the diameters for which the minimum mechanical properties apply to the various grades and classes, and Table 2 stipulates
the requirements for Charpy impact energy absorption. The manufacturer should determine that the material can conform to these
requirements before parts are manufactured. For example, when Grade L43 is specified to meet the Table 2 impact energy values
at −150 °F [−101 °C], additional restrictions (such as procuring a steel with lower P and S contents than might normally be
supplied) in the chemical composition for AISI 4340 are likely to be required.
NOTE 1—The committee formulating this specification has included several grades of material that have been rather extensively used for the present
purpose. Other compositions will be considered for inclusion by the committee from time to time as the need becomes apparent. Users should note that
hardenability of some of the grades mentioned may restrict the maximum size at which the required mechanical properties are obtainable.
1.3 The following referenced general requirements are indispensable for application of this specification: Specification
A962/A962M.
1.4 Nuts for use with bolting are covered in Section 10 and the nut material shall be impact tested.
1.5 Supplementary Requirements are provided for use at the option of the purchaser. The supplementary requirements shall apply
only when specified in the purchase order or contract.
1.6 This specification is expressed in both inch-pound units and SI units; however, unless the purchase order or contract specifies
the applicable M specification designation (SI) units, the inch-pound units shall apply.
This specification is under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee A01.22
on Steel Forgings and Wrought Fittings for Piping Applications and Bolting Materials for Piping and Special Purpose Applications.
Current edition approved Nov. 1, 2022March 1, 2024. Published November 2022April 2024. Originally approved in 1948. Last previous edition approved in 2022 as
A320/A320M – 22.A320/A320M – 22a. DOI: 10.1520/A0320_A0320M-22A.10.1520/A0320_A0320M-24.
For ASME Boiler and Pressure Vessel Code applications, see related Specification SA-320 in Section II of that Code.
*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
A320/A320M − 24
TABLE 1 Mechanical Requirements
Minimum Tensile Yield Strength, Elongation
Reduction
Tempering Strength, min, ksi in 2 in. Hardness,
Class and Grade, Diameter, in. [mm] Heat Treatment of Area,
Temperature, min, ksi [MPa] (0.2 % or 50 max
min, %
°F [°C] [MPa] offset) mm, min, %
Ferritic Steels
L7, L7A, L7B, L7C, L70, L71, L72, L73 125 105 16 50 321 HBW or 35
HRC
A
2 ⁄2 [65] and under quenched and tempered 1100 [860] [725]
[593]
L43 125 105 16 50 321 HBW or 35
HRC
A
4 [100] and under quenched and tempered 1100 [860] [725]
[593]
B
L7M 100 80 18 50 235 HBW or
99 HRB
A
2 ⁄2 [65] and under quenched and tempered 1150 [690] [550]
[620]
L1 125 105 16 50 . . .
A
1 [25] and under quenched and tempered [860] [725]
C
Austenitic Steels
D
Class 1: B8, B8C, B8M, B8P, carbide solution treated 75 30 30 50 223 HBW or
96 HRB
B8F, B8T, B8LN, B8MLN, all diameters [515] [205]
Class 1A: B8A, B8CA, B8MA, B8PA, carbide solution treated in the 75 30 30 50 192 HBW or 90
B8FA, B8TA, B8LNA, finished condition [515] [205] HRB
B8MLNA, all diameters
Class 2: B8, B8C, B8P, B8F, B8T: carbide solution treated and strain
hardened
⁄4 [20] and under 125 100 12 35 321 HBW or 35
[860] [690] HRC
over ⁄4 to 1 [20 to 25], incl 115 80 15 35 321 HBW or 35
[795] [550] HRC
over 1 to 1 ⁄4 [25 to 32], incl 105 65 20 35 321 HBW or 35
[725] [450] HRC
A
1 1
over 1 ⁄4 to 1 ⁄2 [32 to 40], incl 100 50 28 45 321 HBW or 35
[690] [345] HRC
Class 2: B8M: carbide solution treated and strain
hardened
⁄4 [20] and under 110 95 15 45 321 HBW or 35
[760] [655] HRC
over ⁄4 to 1 [20 to 25], incl 100 80 20 45 321 HBW or 35
[690] [550] HRC
over 1 to 1 ⁄4 [25 to 32], incl 95 65 25 45 321 HBW or 35
[655] [450] HRC
A
1 1
over 1 ⁄4 to 1 ⁄2 [32 to 40], incl 90 50 30 45 321 HBW or 35
[620] [345] HRC
A
These upper diameter limits were established on the basis that these were the largest sizes commonly available that consistently met specification property limits. They are not intended as absolute limits beyond which
bolting materials could no longer be certified to the specification.
B
To meet the tensile requirements, the Brinell hardness shall not be less than 200 HBW or 93 HRB.
C
Class 1 products are made from solution-treated material. Class 1A products are solution treated in the finished condition for corrosion resistance; heat treatment is critical for enhancing this physical property and meeting
the mechanical property requirements. Class 2 products are made from solution-treated material that has been strain hardened. Austenitic steels in the strain-hardened condition may not show uniform properties
throughout the cross section, particularly in sizes over ⁄4 in. [20 mm] in diameter.
D
For sizes ⁄4 in. [20 mm] in diameter and smaller, a maximum hardness of 241 HBW (100 HRB) is permitted.

A320/A320M − 24
TABLE 2 Impact Test Temperatures and Properties
Test Temperature CVN Specimen Section Min Average Impact Min Impact Value of a Single
Size, mm Toughness of Three Test Specimen of Set of Three,
Grade
Specimens, ft-lbf [J] ft-lbf [J]
°F °C
10 × 10 20 [27] 15 [20]
L7M, L70, L71, L72, L73 –100 –73 10 × 7.5 16 [22] 12 [16]
10 × 10 20 [27] 15 [20]
L7, L7A, L7B, L7C, L43 –150 –101 10 × 7.5 16 [22] 12 [16]
10 × 10 40 [54] 30 [41]
L1 –100 –73 10 × 7.5 32 [44] 24 [32]
1.7 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
1.8 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.
2. Referenced Documents
2.1 ASTM Standards:
A194/A194M Specification for Carbon Steel, Alloy Steel, and Stainless Steel Nuts for Bolts for High Pressure or High
Temperature Service, or Both
A962/A962M Specification for Common Requirements for Bolting Intended for Use at Any Temperature from Cryogenic to the
Creep Range
E566 Practice for Electromagnetic (Eddy Current/Magnetic Induction) Sorting of Ferrous Metals
F436/F436M Specification for Hardened Steel Washers Inch and Metric Dimensions
F606/F606M Test Methods for Determining the Mechanical Properties of Externally and Internally Threaded Fasteners,
Washers, Direct Tension Indicators, and Rivets
2.2 ASME Standards:
B1.1 Screw Threads
B18.21.1 Washers: Helical Spring-Lock, Tooth Lock, and Plain Washers (Inch Series)
3. Ordering Information
3.1 It is the purchaser’s responsibility to specify in the purchase order all information necessary to purchase the needed materials.
Examples of such information include, but are not limited to, the following:
3.1.1 Quantity and size,
3.1.2 Heat-treated condition, that is, for the austenitic stainless steels, solution-treated (Class 1); solution-treated after finishing
(Class 1A); and annealed and strain-hardened (Class 2),
3.1.3 Description of items required (bars, bolts, screws, or studs),
3.1.4 Nuts and washers, if required by the purchaser, in accordance with Section 10, and
3.1.5 Special requirements, in accordance with 5.1.1, 5.1.3, 5.1.4, and 13.1.
4. Common Requirements
4.1 Bolting materials and bolting components supplied to this specification shall conform to the requirements of Specification
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American Society of Mechanical Engineers (ASME), ASME International Headquarters, Two Park Ave., New York, NY 10016-5990, http://
www.asme.org.
A320/A320M − 24
A962/A962M. These requirements include test methods, finish, thread dimensions, macroetch (carbon and alloy steels only)
marking, certification, optional supplementary requirements, and others. Failure to comply with the requirements of Specification
A962/A962M constitutes nonconformance with this specification. In case of conflict between the requirements in this specification
and Specification A962/A962M, this specification shall prevail.
5. Materials and Manufacture
5.1 Heat Treatment:
5.1.1 Bolting materials shall be allowed to cool to room temperature after rolling or forging. Grades L7, L7A, L7B, L7C, L7M,
L43, L1, L70, L71, L72, and L73 shall be reheated to above the upper critical temperature and liquid quenched and tempered.
Grades B8, B8C, B8M, B8T, B8F, B8P, B8LN, and B8MLN shall receive a carbide solution treatment. Products made from such
material are described as Class 1. This shall consist of holding the bolting material for a sufficient time at a temperature at which
the chromium carbide will go into solution and then cooling in air or in a liquid medium at a rate sufficient to prevent
reprecipitation of the carbide. Bolting material thus treated is described as Class 1. If specified in the purchase order, bolting
material shall be solution treated in the finished condition and shall be described as Class 1A.
5.1.2 Use of water quenching is prohibited for any ferritic grade when heat treatment is performed after heading or threading.
5.1.3 When increased mechanical properties are desired, austenitic bolting shall be solution annealed and strain hardened if
specified in the purchase order; material so treated is identified as Class 2.
5.1.4 If scale-free bright finish is required, this shall be specified in the purchase order.
5.1.5 For L7M bolting, the final heat treatment, which may be the tempering or stress-relieving operation conducted at 1150 °F
[620 °C] minimum, shall be done after machining or rolling of the threads and any type of cutting.
6. Mechanical Requirements
6.1 Tensile Properties:
6.1.1 Bolting material as represented by the tension specimens shall conform to the requirements as to tensile properties prescribed
in Table 1 at room temperature after heat treatment (see 5.1.1). Alternatively, Class 2 Strain Hardened Headed Bolting Components
shall be tested full size after strain hardening to determine tensile strength and yield strength and shall conform to the requirements
prescribed in Table 1. Should the results of full size tests conflict with results of tension specimen tests, full size test results shall
prevail.
6.1.2 Number of Tests:
6.1.2.1 For heat-treated bars, one tension test and one impact test consisting of three specimens shall be made for each diameter
of each heat represented in each tempering charge. When heat treated without interruption in continuous furnaces, the material in
a lot shall be the same heat, same prior condition, same size, and subjected to the same heat treatment. Not fewer than two tensile
tests and two impact tests are required for each lot containing 20 000 lbs [9000 kg] or less. Every additional 10 000 lbs [4500
kg] or fraction thereof requires an additional tensile test and impact test.
6.1.2.2 For studs, bolts, screws, etc., one tension test and one set of three impact specimens shall be made for each diameter of
each heat involved in the lot. Each lot shall consist of the following:
Diameter, in. [mm] Lot Size, lb [kg]
1 ⁄8 [30] and under 1500 [680] or fraction thereof
1 3
Over 1 ⁄8 [30] to 1 ⁄4 [45], 4500 [2040] or fraction
incl thereof
3 1
Over 1 ⁄4 [45] to 2 ⁄2 [65], 6000 [2700] or fraction
incl thereof
Over 2 ⁄2 [65] 100 pieces or fraction thereof
6.1.2.3 Full Size Specimens, Headed Bolting Components—Headed bolts or screws 1 ⁄2 in. in body diameter and smaller, with
body length three times the diameter or longer, and that are produced by upsetting or forging (hot or cold) shall be subjected to
A320/A320M − 24
full size testing in accordance with 6.1.3. This testing shall be in addition to tensile testing as specified in 6.1.1. Wedge tensile
testing shall be limited to product with socket head cap screw, hexagon, square, hex flange, or twelve point flange heads. The lot
size shall be shown in 6.1.2.2. Failure shall occur in the body or threaded section with no failure, or indications of failure, such
as cracks, at the junction of the head and shank. Wedge tensile testing is not required for flat countersunk head or socket button
products.
6.1.3 Full Size Bolting Components, Wedge Tensile Testing—When applicable, see 6.1.2.3. Headed components shall be wedge
tested full size. The minimum full size load applied (lbf or kN) for individual sizes shall be as follows:
W 5 T ×A (1)
s t
where:
W = minimum wedge tensile load without fracture,
T = tensile strength specified in ksi or MPa in Tables 2 and 3, and
s
A = stress area of the thread section, square inches or square millimetres, as shown in the Cone Proof Load Tables in
t
Specification A962/A962M.
6.2 Impact Properties:
6.2.1 Requirements:
6.2.1.1 Impact tests are required for the grades shown in Table 3. Class 1, 1A, and 2 austenitic steels for temperatures above –325
°F [–200 °C]; Class 1 and 1A austenitic Grades B8, B8A, B8P, B8PA, B8C, B8CA, B8LN, and B8LNA above –425 °F [–255 °C];
and ferritic or austenitic bolting ⁄2 in. [12.5 mm] and smaller, are exempt from impact testing, unless Supplementary Requirement
S1 is specified in the purchase order (see 1.4). All other material furnished under this specification shall be tested. Material of
Grades L7, L7A, L7B, L7C, L7M, L43, L70, L71, L72, and L73 shall show a minimum impact energy absorption of 20 ft · lbf
[27 J] and of Grade L1 a minimum impact energy absorption of 40 ft · lbf [54 J] at the specified test temperature.
6.2.1.2 The temperature of the coolant used for chilling the test specimens shall be controlled within 62 °F [1 °C]. Test
temperatures for ferritic grades are listed in Table 2. Exceptions to this requirement are permissible, and the impact tests may be
made at specified temperatures different than those shown in Table 2, provided the test temperature is at least as low as the intended
service temperature and the bolting is suitably marked to identify the reported test temperature. When impact testing is required
for austenitic grades, test criteria shall be agreed upon between the supplier and purchaser.
6.2.1.3 The impact test requirements for standard and subsize Charpy V-notch (CVN) test specimens are prescribed in Table 2.
If the material is impact tested at a temperature lower than the specified test temperature with impact energy absorption results
equal to or greater than the specified required impact energy absorption for that product, the material can be considered suitable
for the specified test temperature.
NOTE 2—As an example, the purchase order or contract requires an L-grade bolt to have an average 15 ft-lbs at –50 °F. If the Charpy V-notch testing
indicates
...