ASTM F2328M-17(2022)

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: F2328M − 17 (Reapproved 2022)
Standard Test Method for
Determining Decarburization and Carburization in Hardened
and Tempered Threaded Steel Bolts, Screws, Studs, and
Nuts (Metric)
This standard is issued under the fixed designation F2328M; 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* 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers procedures for measuring,
A574M Specification for Alloy Steel Socket-Head Cap
classifying, and determining the presence of decarburization
Screws (Metric) (Withdrawn 2015)
and carburization in the threaded section of hardened and
E3 Guide for Preparation of Metallographic Specimens
tempered metric steel bolts, screws, studs, nuts and similar
E384 Test Method for Microindentation Hardness of Mate-
parts which have been heated to facilitate fabrication or to
rials
modify their mechanical properties. This test method is not
F835M Specification forAlloy Steel Socket Button and Flat
intendedtoaddressproductswhichareintentionallycarburized
to achieve specific results. Countersunk Head Cap Screws (Metric) (Withdrawn
2015)
1.2 Two routine methods are described for measuring the
F912M Specification for Alloy Steel Socket Set Screws
limits of and determining the presence of decarburization or
(Metric) (Withdrawn 2015)
carburization; the Optical Method and the Microindentation
F1789 Terminology for F16 Mechanical Fasteners
Method 1. Either method is appropriate for routine examina-
tions. The Microindentation Method 2 shall be considered the
3. Terminology
referee method.
3.1 Definitions:
1.3 For the purpose of these tests, there are five classes of
3.1.1 carburization—process or result of increasing the
hardened and tempered steel products for which specific
carbon content of the surface layers of the steel fastener
measurements must be made with respect to their physical
product.
properties.
3.1.2 decarburization—in accordance with Terminology
1.4 The values stated in SI units are to be regarded as F1789,isalossofcarbonfromthesurfacelayerofthefastener,
standard. No other units of measurement are included in this
normally associated with heat treatment.
standard.
3.1.3 gross decarburization—also known as complete
decarburization, is characterized by a sufficient carbon loss to
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the show only clearly defined ferrite grains.
responsibility of the user of this standard to establish appro-
3.1.4 partial decarburization—characterized as a loss of
priate safety, health, and environmental practices and deter-
carbon sufficient to cause a lighter shade of tempered marten-
mine the applicability of regulatory limitations prior to use.
site than that of the immediately adjacent base metal, but as
1.6 This international standard was developed in accor-
being of insufficient carbon loss to show clearly defined ferrite
dance with internationally recognized principles on standard-
grains.
ization established in the Decision on Principles for the
4. Significance and Use
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
4.1 Decarburization and carburization are two surface con-
Barriers to Trade (TBT) Committee.
ditions created, either intentionally or unintentionally, as with
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method is under the jurisdiction of ASTM Committee F16 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Fasteners and is the direct responsibility of Subcommittee F16.01 on Test Methods. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Aug. 1, 2022. Published December 2022. Originally the ASTM website.
approved in 2004. Last previous edition approved in 2017 as F2328M – 17. DOI: The last approved version of this historical standard is referenced on
10.1520/F2328M-17R22. www.astm.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
F2328M − 17 (2022)
a pre-existing condition created during the rod rolling process, 7. Evaluation by the Optical Method
the rod/wire annealing process, or while heat treating threaded
7.1 Etch the mounted specimen (Section 6)ina2to4%
steel products. Too much of either will adversely affect the
nital or picral solution to exhibit the microstructure. Examine
safety and performance of the threaded product. Therefore,
the specimen at 100X magnification using a method capable of
limits have been established for four different product groups:
measuring distances to at least 0.001 in. resolution. The width
the harder and greater the tensile strength of the product, the
of any light-etching band of martensite defines the depth of
more susceptible to failure the product becomes if these limits
decarburization. Compare the image with Fig. 1 for the
are exceeded.
maximum limits for G by taking a measurement on a line
4.2 When testing to a particular product specification that
perpendicular to the flank of the thread midway between the
lists the dimensions and microindentation data to be used, that thread crest and root (pitch diameter).
data shall take precedence over the tables in this test method.
7.2 Interpretation of Results:
4.3 There are only two viable methods available to detect
7.2.1 Allowable limits for partial decarburization shall be in
these deficiencies: either by the visual method or the microin-
accordancewith3.1.4andFig.1,andthemeasuredvaluesshall
dentation method. Both methods are used for routine inspec-
be in accordance with Table 2, when measured in accordance
tionswhenevaluationsareconductedatasinglelocationonthe
with the illustrations in Figs. 2 and 3.
product sample. Because an evaluation at a specific location
7.2.2 Allowablelimitsforgrossdecarburization(G)shallbe
maynotberepresentativeofthewholepart,therefereemethod
in accordance with 3.1.3 and the measured values as defined in
employs the microindentation method taken as an average of
Table 1. The optical method is the only valid method for
evaluationsconductedonfouradjacentthreads.Thisprocedure
evaluating the depth of gross decarburization. Gross decarbur-
significantly reduces random test variables when compared to
ization is prohibited in Class 3 and Class 4 products.
testing on a single thread.
7.2.3 Carburization is identified when the tempered marten-
4.4 Specifying this test method does not specify or imply
siteisadarkershadethantheimmediatelyadjacentbasemetal.
that testing shall be for either decarburization or carburization
If visible evidence of surface carburization is present on the
alone or for both conditions. When either test method is
surface zone, the microindentation hardness method, in accor-
performed, both conditions will be apparent and shall be
dance with Section 8, shall be used.
reported. For example, if an order is placed to test for
7.2.4 The optical method may not be appropriate for speci-
decarburization and none is found but the presence of decar-
mens with certain coatings, such as zinc, where the coating can
burization is detected, it shall be reported on the test report that
affecttheetchingprocessanddistorttheappearanceofthebase
carburization was found.
material microstructure. These coatings shall be removed prior
to mounting if the coating prevents proper etching. Care must
5. Class of Decarburization
also be exercised to not alter the surface condition of the
5.1 Class Determination—These measurements by Class
substrate during the coating removal process.
arepredicatedupontheirrelationshipbetweentheheight(H)of
7.2.5 If the results of the optical method indicate a possible
the external thread at its maximum boundary, disregarding any
nonconformance in the measurement of partial decarburization
surface coating, and N, which is the minimum thread height in
or carburization, or are otherwise inconclusive, the microin-
the non-decarburized zone (see Figs. 1-3). The dimensions for
dentation hardness method (Section 8) shall be performed after
N and H are listed in Table 2 for each Class. Dimension G
the specimens are repolished.
(Table 1 and Fig. 1) represents the maximum
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