ASTM E1921 - 25a 测定过渡范围内铁素体钢参考温度T0的标准试验方法

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Designation: E1921 −25a
Standard Test Method for
Determination of Reference Temperature, T
0
, for Ferritic
Steels in the Transition Range
1
This standard is issued under the ﬁxed designation E1921; 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.
NOTE—Fig. 7 (previously Fig. 6) and Eq 13 were corrected editorially as balloted on June 24, 2025.
1. Scope
1.1 This test method covers the determination of a reference
temperature, T
0
, which characterizes the fracture toughness of
ferritic steels that experience onset of cleavage cracking at
elastic, or elastic-plastic K
Jc
instabilities, or both. The speciﬁc
types of ferritic steels (3.2.5) covered are those with yield
strengths ranging from 275 MPa to 825 MPa (40 ksi to 120 ksi)
and weld metals, after stress-relief annealing, that have 10 % or
less strength mismatch relative to that of the base metal.
1.2 Testing under Test Method E1820 is generally required
for use of Test Method E1921 with notable exceptions on
speciﬁc aspects of the testing that need to be more tightly
controlled within Test Method E1921. Those unique provisions
are speciﬁcally called out in Test Method E1921.
1.3 The specimens included are fatigue precracked single-
edge bend bars, SE(B), and compact tension, C(T), or disk-
shaped compact tension, DC(T), specimens as described in
Test Method E1820.
1.4 Median K
Jc
values at a given temperature tend to vary
between SE(B) and C(T)/DC(T) specimen types at a given test
temperature, presumably due to constraint differences among
the allowable test specimens in 1.3.
1.5 Requirements are set on specimen size (7.5) and the
number of replicate tests (10.3) that are needed to establish
acceptable characterization of K
Jc
data populations. As indi-
cated in 10.3, a minimum of 6 test specimens is required.
1.6 T
0
is dependent on the K-rate. T
0
is evaluated for a
quasi-static loading K-rate range with 0.5 < K
˙
¯
I
< 2 MPa√m/s.
Slowly loaded specimens (K
˙
¯
I
< 0.5 MPa√m) can be considered
valid if environmental effects are known to be negligible.
Provision is also made for higher K-rates (K
˙
¯
I
> 2 MPa√m/s) in
Annex A1. Note that this threshold K-rate for application of
Annex A1 is a much lower threshold than is required in other
fracture toughness test methods such as E399 and E1820.
1.7 A limit on K
Jc
values, relative to the specimen size, is
speciﬁed to ensure high constraint conditions along the crack
front at fracture. For some materials, particularly those with
low strain hardening, this limit may not be sufficient to ensure
that a single-parameter (K
Jc
) adequately describes the crack-
front deformation state (1).
2
1.8 The procedures described in this test method assume
that the data set represents a macroscopically homogeneous
material, such that the test material has uniform tensile and
toughness properties. A screening method (10.6) is provided to
determine if the material may be inhomogeneous and methods
are provided in Appendix X5 to evaluate such materials.
Application of this test method to an inhomogeneous material
may result in an inaccurate estimate of the transition reference
value T
0
and nonconservative conﬁdence bounds.
1.9 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.10 This international standard was developed in accor-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
3
E4 Practices for Force Calibration and Veriﬁcation of Test-
ing Machines
1
This test method is under the jurisdiction of ASTM Committee E08 on Fatigue
and Fracture and is the direct responsibility of E08.07 on Fracture Mechanics.
Current edition approved June 1, 2025. Published February 2026. Originally
approved in 1997. Last previous edition approved in 2025 as E1921 – 25. DOI:
10.1520/E1921-25A.
2
The boldface numbers in parentheses refer to a list of references at the end of
this standard.
3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at www.astm.org/contact. For Annual Book of
ASTM Standards volume information, refer to the standard’s Document Summary
page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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.
1

E8/E8M Test Methods for Tension Testing of Metallic Ma-
terials
E111 Test Method for Young’s Modulus, Tangent Modulus,
and Chord Modulus
E177 Practice for Use of the Terms Precision and Bias in
ASTM Test Methods
E399 Test Method for Linear-Elastic Plan-Strain Fracture
Toughness K
Ic
of Metallic Materials
E561 Test Method for K
R
Curve Determination
E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
E1820 Test Method for Measurement of Fracture Toughness
E1823 Terminology Relating to Fatigue and Fracture Testing
2.2 ASME Standards:
4
ASME Boiler and Pressure Vessel Code, Section II, Part D
3. Terminology
3.1 Terminology from E1823 is applicable to this test
method. Terminology from Test Method E1820 is also gener-
ally applicable to Test Method E1921 and is generally not
replicated in this section. This section is intended to highlight
terminology that is important to this test method.
3.2 Deﬁnitions:
3.2.1 control force, P
m
[F]—a calculated value of maximum
force, used in 7.8.1 to stipulate allowable precracking limits.
3.2.2 effective modulus, E
eff
[FL
–2
]—an elastic modulus that
allows a theoretical (modulus normalized) compliance to
match the experimentally measured compliance for the initial
crack size, a
0
.
3.2.3 elastic constraint modulus, E' [FL
–2
]—a linear-elastic
factor relating stress to strain, the value of which is dependent
on the degree of constraint. For plane stress, E' =Eis used, and
for plane strain, E/(1 – v
2
) is used, with Ebeing Young’s
modulus and vbeing Poisson’s ratio.
3.2.4 elastic modulus, E [FL
–2
]—the ratio of stress to
corresponding strain below the proportional limit.
3.2.4.1 Discussion—The term “Young’s Modulus” is com-
monly used for materials that conform to Hooke’s Law.
3.2.5 ferritic steels—typically carbon, low-alloy, and higher
alloy grades.
3.2.5.1 Discussion—Typical microstructures are bainite,
tempered bainite, tempered martensite, and ferrite and pearlite.
All ferritic steels have body centered cubic crystal structures
that display ductile-to-cleavage transition temperature fracture
toughness characteristics.
3.2.5.2 Discussion—This deﬁnition is not intended to imply
that all ferritic steels have been veriﬁed as being amenable to
analysis by this test method.
3.2.6 J-integral, J [FL
–1
]—a mathematical expression; a
line or surface integral that encloses the crack front from one
crack surface to the other; used to characterize the local
stress-strain ﬁeld around the crack front (2). See Terminology
E1823 for further discussion.
3.2.6.1 Discussion—In this test method, J
c
, (elastic-plastic
J-integral) corresponds to the onset of cleavage fracture. This
deﬁnition differs from Test Method E1820, which deﬁnes J
c
as
the fracture toughness of materials at fracture instability prior
to the onset of signiﬁcant stable tearing crack extension.
3.2.7 pop-in—a discontinuity in a force versus displacement
test record (3).
3.2.7.1 Discussion—A pop-in event is usually audible and is
a sudden cleavage crack initiation event followed by crack
arrest. The test record will show increased displacement and
drop in applied force if the test frame is stiff. Subsequently, the
test record may continue to higher forces and increased
displacements.
3.2.8 precracked Charpy-type, PCC, specimen—SE(B)
specimen with W=B= 10 mm (0.394 in.).
3.2.9 stress-intensity factor, K [FL
– 3/2
]—the magnitude of
the mathematically ideal, crack-tip stress ﬁeld (stress ﬁeld
singularity) for a particular mode in a homogeneous, linear-
elastic body.
3.2.9.1 Discussion—In this test method, Mode I is assumed.
See Terminology E1823 for further discussion.
3.2.9.2 Discussion—An elastic-plastic equivalent stress-
intensity factor, K
J
, is derived from the J-integral.
3.2.9.3 Discussion—In this test method, K
J
also implies a
stress-intensity factor determined at the test termination point
under conditions that require censoring the data according to
8.9.2.
3.2.9.4 Discussion—an elastic-plastic equivalent stress-
intensity factor, K
Jc
, is derived from the J-integral at the point
of onset of cleavage fracture, J
c
.
3.2.9.5 Discussion—K
Jc
~
med
!
eq
is an equivalent value of the
median toughness for a multi-temperature data set.
3.2.10 yield strength, σ
YS
[FL
−2
]—the stress at which a
material exhibits a speciﬁc limiting deviation, expressed in
terms of strain, from the proportionality of stress to strain at the
test temperature.
3.2.10.1 Discussion—Yield strength shall be determined in
accordance with Test Method E8/E8M.
3.3 Deﬁnitions of Terms Speciﬁc to This Standard:
3.3.1 average stress-intensity-factor rate K
˙
¯
I
[FL
-3/2
T
-1
]—
average rate of increase of applied stress-intensity factor up to
K
Jc
.
3.3.1.1 Discussion—It is evaluated as the ratio between K
Jc
and the corresponding time to cleavage. For tests where partial
unloading/reloading sequences are used to measure
compliance, an equivalent time to cleavage (t
c
) shall be used to
calculate the stress-intensity-factor rate (that is, K-rate). The
value of t
c
is calculated as the ratio between the value of
load-line displacement at cleavage and the load-line displace-
ment rate applied during the monotonic loading portions of the
test (that is, the periods between partial unloading/reloading
sequences used for compliance measurement). Additionally, in
such tests, the total time of unloading/loading sequences
should be shorter than the total time of monotonic loading.
4
Available from American Society of Mechanical Engineers (ASME), ASME
International Headquarters, Two Park Ave., New York, NY 10016-5990, http://
www.asme.org.
E1921 − 25a
2

3.3.2 cumulative failure probability, p
f
—the probability that
a single selected specimen chosen at random from a population
of specimens will fail at or before reaching the K
Jc
value of
interest.
3.3.3 extent of slow-stable cracking prior to cleavage
initiation, ∆a
sc
[L]—the average amount of any ductile crack
growth that precedes rapid cleavage failure or test termination.
3.3.4 load-line displacement rate, ∆
˙
LL
[LT
-1
]—rate of in-
crease of specimen load-line displacement.
3.3.5 provisional reference temperature, T
0Q
[°C]—
provisional T
0
value calculated using the standard test method
described herein.
3.3.5.1 Discussion—T
0Q
is validated as T
0
in 10.5.
3.3.6 reference temperature, T
0
[°C]—The test temperature
at which the median of the K
Jc
distribution from 1T size
specimens equals 100 MPa√m (91.0 ksi√in.).
3.3.7 specimen size, nT—a code used to deﬁne specimen
dimensions, where nis expressed in multiples of 1 in.
3.3.7.1 Discussion—In this method, specimen proportional-
ity is required. For compact specimens and bend bars, speci-
men thickness B = n inches. The metric equivalent of ncan
either be deﬁned as 25.4 mm or rounded down to 25 mm.
3.3.8 time to control force, t
m
[T]—time to P
m
.
3.3.9 Weibull ﬁtting parameter, K
0
—a scale parameter cor-
responding to the 63.2 % cumulative failure probability level
(4).
3.3.9.1 Discussion—K
Jc
= K
0
when p
f
= 0.632.
3.3.10 Weibull slope, b—slope of the p
f
versus K
Jc
ﬁtting
line in a Weibull plot where data pairs are plotted in linearized
coordinates
3.3.10.1 Discussion—values of p
f
are calculated by means
of Eq 22.
3.3.10.2 Discussion—A ﬁtting line with slope bdeﬁnes the
characteristic of the typical scatter of K
Jc
data.
3.3.10.3 Discussion—A Weibull slope of 4 is used exclu-
sively in this test method.
4. Summary of Test Method
4.1 This is a general overview of the major aspects associ-
ated with determining T
0
for a ferritic steel. It is not intended
to provide a prescriptive method to be rigorously followed
sequentially. The general steps necessary for conducting a test
are provided within the following sub-sections. A graphical
overview of the test method is presented in Fig. 1 in the form
of a ﬂowchart.
5
4.2 Select the conﬁguration and dimensions of the test
specimens, 7.1-7.3. This test method covers C(T), DC(T), and
SE(B) specimens. The specimen dimension requirement, based
on the maximum K
Jc
capacity of a specimen K
Jclimit
,Eq 3, is
provided in 7.5, and depends on the values of σ
YS
and Eof the
steel at the test temperature.
4.3 Select the test temperature(s) for the initial test(s) within
a temperature range where K
Jc(med)
for the specimen size tested
is approximately 100 MPa√m, 8.4. If available, Charpy
V-notch data can be used to establish the initial test
temperature(s), 8.4.1 and Table 3. When using small specimens
(precracked Charpy or smaller), it is generally advisable to test
below the expected T
0
,8.5.
4.4 Establish the number of test specimens, based on the
available material and the requirements for obtaining a valid
T
0
,10.3. A minimum of six tests are required by this test
method, (5)and results are weighted based on the difference
between test temperatures and T
0
, Table 4. An iterative
procedure is suggested in 10.3.1 for identifying an appropriate
sequence of test temperatures.
4.5 Precrack specimens by fatigue, 7.8. Methods to promote
early crack initiation are provided in 7.8.1, which also includes
maximum values for the control force, P
m
,Eq 5 or Eq 6. The
fatigue precracking procedure is provided in 7.8.2. Specimens
may be optionally side-grooved in accordance with 7.7, pref-
erably after precracking, in order to limit the curvature of the
initial crack front and avoid tunneling, hence fulﬁlling the
crack curvature requirements of 8.9.1.
4.6 Perform initial test(s) at the temperature(s) selected in
4.3. Tests shall be performed in accordance with the procedure
outlined in Section 8, and the corresponding provisions given
in Test Method E1820 (8.5 for Optical Crack Size
Measurements, 8.3.1 for Bend Testing, and 8.3.2 for Compact
Testing). Provisions for temperature control and measurement
are given in 8.6. Requirements for quasi-static loading rate are
provided in 8.7.1. For loading rates outside the quasi-static
range, refer to 8.7.2 (slow loading rates) or Annex A1 (elevated
loading rates).
4.7 For each test performed, calculate the J-integral at the
onset of cleavage fracture, J
c
, for the relevant specimen type as
prescribed in 9.1.1-9.1.4. Determine the corresponding value
K
Jc
according to 9.1.5. If a signiﬁcant pop-in is observed or
suspected, establish its signiﬁcant in accordance with 8.9.4 and
9.2.
4.8 If the K
Jc
value exceeds K
Jclimit
in Eq 3 and/or the
ductile crack extension limit, K
Jc∆a
(see 8.9.2) is violated,
perform data censoring according to 8.9.2 and 10.2.2. If
cleavage fracture does not occur, refer to 8.9.3.
4.9 Size correct each K
Jc
value to 1T equivalence using the
measured specimen thickness in Eq 22,10.2.3.
4.10 Determine the provisional reference temperature, T
0Q
,
following the iterative procedure in 10.2.4 (tests performed at
multiple temperatures) or 10.4 (tests performed at a single
temperature), and accounting for the T
0Q
650 °C test
temperature requirement in 10.2.4.
4.11 If necessary, adjust test temperature(s) and perform
additional tests (if possible, given the number of remaining
specimens). For each additional test performed, calculate J
c
and K
Jc
according to Section 9. If needed, censor (8.9.2 and
5
The ﬂowchart illustrated in Fig. 1 is only meant to capture the principal
components of an analysis conducted in accordance with this test method, and not
to address all possible outcomes and requirements. Other pathways through the
standard are possible and appropriate, given the constraints and objectives of a
speciﬁc analysis.
E1921 − 25a
3

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标签： #铁素体 #钢 #标准试验

摘要：

ASTM E1921-25a 是测定铁素体钢在韧脆过渡区内参考温度 T0 的标准试验方法，最新版更新了测试流程、数据处理与有效性判据。该方法通过示波冲击试验或断裂韧性试验获取一系列试样在过渡区的断裂韧性值，并基于统计模型将数据归一到 1 英寸（25.4 mm）厚度等效的 KJC 值，从而确定表征材料断裂韧性的参考温度 T0。T0 作为材料韧性-温度曲线在过渡区的位置参数，是评估核反应堆压力容器、船舶、桥梁及低温压力容器等钢结构安全性和完整性，以及开展缺陷评定、寿命预测与延性断裂遏制分析的关键输入

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