ASTM E1921-23a
(Test Method)Standard Test Method for Determination of Reference Temperature, T0, for Ferritic Steels in the Transition Range
Standard Test Method for Determination of Reference Temperature, <emph type="bdit">T<inf >0</inf></emph>, for Ferritic Steels in the Transition Range
SIGNIFICANCE AND USE
5.1 Fracture toughness is expressed in terms of an elastic-plastic stress-intensity factor, KJc, that is derived from the J-integral calculated at fracture.
5.2 Ferritic steels are microscopically inhomogeneous with respect to the orientation of individual grains. Also, grain boundaries have properties distinct from those of the grains. Both contain carbides or nonmetallic inclusions that can act as nucleation sites for cleavage microcracks. The random location of such nucleation sites with respect to the position of the crack front manifests itself as variability of the associated fracture toughness (13). This results in a distribution of fracture toughness values that is amenable to characterization using the statistical methods in this test method.
5.3 The statistical methods in this test method assume that the data set represents a macroscopically homogeneous material, such that the test material has both the uniform tensile and toughness properties. The fracture toughness evaluation of nonuniform materials is not amenable to the statistical analysis procedures employed in this test method. For example, multi-pass weldments can create heat-affected and brittle zones with localized properties that are quite different from either the bulk or weld materials. Thick-section steels also often exhibit some variation in properties near the surfaces. Metallographic analysis can be used to identify possible nonuniform regions in a material. These regions can then be evaluated through mechanical testing such as hardness, microhardness, and tensile testing for comparison with the bulk material. It is also advisable to measure the toughness properties of these nonuniform regions distinctly from the bulk material. Section 10.6 provides a screening criterion to assess whether the data set may not be representative of a macroscopically homogeneous material, and therefore, may not be amenable to the statistical analysis procedures employed in this test method. If the data ...
SCOPE
1.1 This test method covers the determination of a reference temperature, T0, which characterizes the fracture toughness of ferritic steels that experience onset of cleavage cracking at elastic, or elastic-plastic KJc instabilities, or both. The specific types of ferritic steels (3.2.2) 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 The specimens covered are fatigue precracked single-edge notched bend bars, SE(B), and standard or disk-shaped compact tension specimens, C(T) or DC(T). A range of specimen sizes with proportional dimensions is recommended. The dimension on which the proportionality is based is specimen thickness.
1.3 Median KJc values tend to vary with the specimen type at a given test temperature, presumably due to constraint differences among the allowable test specimens in 1.2. The degree of KJc variability among specimen types is analytically predicted to be a function of the material flow properties (1)2 and decreases with increasing strain hardening capacity for a given yield strength material. This KJc dependency ultimately leads to discrepancies in calculated T0 values as a function of specimen type for the same material. T0 values obtained from C(T) specimens are expected to be higher than T0 values obtained from SE(B) specimens. Best estimate comparisons of several materials indicate that the average difference between C(T) and SE(B)-derived T0 values is approximately 10°C (2). C(T) and SE(B) T0 differences up to 15 °C have also been recorded (3). However, comparisons of individual, small datasets may not necessarily reveal this average trend. Datasets which contain both C(T) and SE(B) specimens may generate T0 results which fall between the T0 values calculated using solely C(T) or SE(B) specimens. It is therefore strongl...
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Designation: E1921 − 23a
Standard Test Method for
Determination of Reference Temperature, T , for Ferritic
0
1
Steels in the Transition Range
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.
1. Scope recommended that the specimen type be reported along with
the derived T value in all reporting, analysis, and discussion of
0
1.1 This test method covers the determination of a reference
results. This recommended reporting is in addition to the
temperature, T , which characterizes the fracture toughness of
0
requirements in 11.1.1.
ferritic steels that experience onset of cleavage cracking at
elastic, or elastic-plastic K instabilities, or both. The specific
1.4 Requirements are set on specimen size and the number
Jc
types of ferritic steels (3.2.2) covered are those with yield of replicate tests that are needed to establish acceptable
strengths ranging from 275 MPa to 825 MPa (40 ksi to 120 ksi)
characterization of K data populations.
Jc
and weld metals, after stress-relief annealing, that have 10 % or
1.5 T is dependent on the K-rate. T is evaluated for a
0 0
less strength mismatch relative to that of the base metal.
¯
˙
quasi-static K-rate range with 0.5 < K < 2 MPa√m/s. T values
I 0
1.2 The specimens covered are fatigue precracked single-
¯
˙
for slowly loaded specimens (K < 0.5 MPa√m) can be
I
edge notched bend bars, SE(B), and standard or disk-shaped
considered valid if environmental effects are known to be
compact tension specimens, C(T) or DC(T). A range of
¯
˙
specimen sizes with proportional dimensions is recommended.
negligible. Provision is also made for higher K-rates (K > 2
I
The dimension on which the proportionality is based is MPa√m/s) in Annex A1. Note that this threshold K-rate for
specimen thickness.
application of Annex A1 is a much lower threshold than is
required in other fracture toughness test methods such as E399
1.3 Median K values tend to vary with the specimen type
Jc
and E1820.
at a given test temperature, presumably due to constraint
differences among the allowable test specimens in 1.2. The
1.6 The statistical effects of specimen size on K in the
Jc
degree of K variability among specimen types is analytically
transition range are treated using the weakest-link theory (4)
Jc
2
predicted to be a function of the material flow properties (1)
applied to a three-parameter Weibull distribution of fracture
and decreases with increasing strain hardening capacity for a
toughness values. A limit on K values, relative to the
Jc
given yield strength material. This K dependency ultimately
specimen size, is specified to ensure high constraint conditions
Jc
leads to discrepancies in calculated T values as a function of
along the crack front at fracture. For some materials, particu-
0
specimen type for the same material. T values obtained from
larly those with low strain hardening, this limit may not be
0
C(T) specimens are expected to be higher than T values
sufficient to ensure that a single-parameter (K ) adequately
0
Jc
obtained from SE(B) specimens. Best estimate comparisons of
describes the crack-front deformation state (5).
several materials indicate that the average difference between
1.7 Statistical methods are employed to predict the transi-
C(T) and SE(B)-derived T values is approximately 10°C (2).
0
tion toughness curve and specified tolerance bounds for 1T
C(T) and SE(B) T differences up to 15 °C have also been
0
specimens of the material tested. The standard deviation of the
recorded (3). However, comparisons of individual, small data-
data distribution is a function of Weibull slope and median K .
Jc
sets may not necessarily reveal this average trend. Datasets
The procedure for applying this information to the establish-
which contain both C(T) and SE(B) specimens may generate
ment of transition temperature shift determinations and the
T results which fall between the T values calculated using
0 0
establishment of tolerance limits is prescribed.
solely C(T) or SE(B) specimens. It is therefore strongly
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
1
This test method is under the jurisdiction of ASTM Committee E08 on Fatigue
toughness properties. Application of this test method to an
and Fracture and is the direct responsibility of E08.07 on Fracture Mechanics.
Current edition approved Nov. 1, 2023. Published March 2024. Originally
inhomogeneous material will result in an inaccurate estim
...
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: E1921 − 23 E1921 − 23a
Standard Test Method for
Determination of Reference Temperature, T , for Ferritic
0
1
Steels in the Transition Range
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.
1. Scope
1.1 This test method covers the determination of a reference temperature, T , which characterizes the fracture toughness of ferritic
0
steels that experience onset of cleavage cracking at elastic, or elastic-plastic K instabilities, or both. The specific types of ferritic
Jc
steels (3.2.2) 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 The specimens covered are fatigue precracked single-edge notched bend bars, SE(B), and standard or disk-shaped compact
tension specimens, C(T) or DC(T). A range of specimen sizes with proportional dimensions is recommended. The dimension on
which the proportionality is based is specimen thickness.
1.3 Median K values tend to vary with the specimen type at a given test temperature, presumably due to constraint differences
Jc
among the allowable test specimens in 1.2. The degree of K variability among specimen types is analytically predicted to be a
Jc
2
function of the material flow properties (1) and decreases with increasing strain hardening capacity for a given yield strength
material. This K dependency ultimately leads to discrepancies in calculated T values as a function of specimen type for the same
Jc 0
material. T values obtained from C(T) specimens are expected to be higher than T values obtained from SE(B) specimens. Best
0 0
estimate comparisons of several materials indicate that the average difference between C(T) and SE(B)-derived T values is
0
approximately 10°C (2). C(T) and SE(B) T differences up to 15 °C have also been recorded (3). However, comparisons of
0
individual, small datasets may not necessarily reveal this average trend. Datasets which contain both C(T) and SE(B) specimens
may generate T results which fall between the T values calculated using solely C(T) or SE(B) specimens. It is therefore strongly
0 0
recommended that the specimen type be reported along with the derived T value in all reporting, analysis, and discussion of
0
results. This recommended reporting is in addition to the requirements in 11.1.1.
1.4 Requirements are set on specimen size and the number of replicate tests that are needed to establish acceptable characterization
of K data populations.
Jc
1.5 T is dependent on loadingthe rate.K-rate. T is evaluated for a quasi-static loading rate range with 0.1< dK/d-rate range with
0 0
¯ ¯
˙ ˙
0.5 < K < 2 MPa√m/s. tT < 2 MPa√m/s. Slowly loaded specimens (dvalues for slowly loaded specimens (K K/dt < 0.10.5
I 0 I
MPa√m) can be analyzed considered valid if environmental effects are known to be negligible. Provision is also made for higher
¯
˙
loading rates (dK/d-ratest (K > 2 MPa√m/s) in Annex A1. Note that this threshold loadingK rate -rate for application of Annex
I
A1 is a much lower threshold than is required in other fracture toughness test methods such as E399 and E1820.
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, 2023Nov. 1, 2023. Published July 2023March 2024. Originally approved in 1997. Last previous edition approved in 20222023 as
E1921 – 22a.E1921 – 23. DOI: 10.1520/E1921-23.10.1520/E1921-23A.
2
The boldface numbers in parentheses refer to the list of references at the end of this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
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E1921 − 23a
1.6 The statistical effects of specimen size on K in the transition range are treated using the weakest-link theory (4) applied to
Jc
a three-parameter Weibull distribution of fracture toughness values. A limit on K values, relative to the specimen size, is specified
Jc
to ensure high constraint conditions along the crack front at fracture. For some materials, particularly those with low strain
hardening,
...
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