ASTM E1921-21a
(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 to 825 MPa (40 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 strongly recomm...
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Designation: E1921 − 21a
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.Anumber 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
thederivedT valueinallreporting,analysis,anddiscussionof
0
1.1 Thistestmethodcoversthedeterminationofareference
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
Jc 1.4 Requirements are set on specimen size and the number
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 to 825 MPa (40 to 120 ksi) and
characterization of K data populations.
Jc
weld metals, after stress-relief annealing, that have 10% or
1.5 T is dependent on loading rate. T is evaluated for a
0 0
less strength mismatch relative to that of the base metal.
quasi-static loading rate range with 0.1< dK/dt < 2 MPa√m/s.
1.2 The specimens covered are fatigue precracked single-
Slowly loaded specimens (dK/dt < 0.1 MPa√m) can be
edge notched bend bars, SE(B), and standard or disk-shaped
analyzed if environmental effects are known to be negligible.
compact tension specimens, C(T) or DC(T). A range of
Provision is also made for higher loading rates (dK/dt>2
specimen sizes with proportional dimensions is recommended.
MPa√m/s) in Annex A1. Note that this threshold loading rate
The dimension on which the proportionality is based is
for application of AnnexA1 is a much lower threshold than is
specimen thickness.
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
1.6 The statistical effects of specimen size on K in the
Jc
differences among the allowable test specimens in 1.2. The
transition range are treated using the weakest-link theory (4)
degree of K variability among specimen types is analytically
Jc
2 applied to a three-parameter Weibull distribution of fracture
predicted to be a function of the material flow properties (1)
toughness values. A limit on K values, relative to the
Jc
and decreases with increasing strain hardening capacity for a
specimen size, is specified to ensure high constraint conditions
given yield strength material. This K dependency ultimately
Jc
along the crack front at fracture. For some materials, particu-
leads to discrepancies in calculated T values as a function of
0
larly those with low strain hardening, this limit may not be
specimen type for the same material. T values obtained from
0
sufficient to ensure that a single-parameter (K ) adequately
Jc
C(T) specimens are expected to be higher than T values
0
describes the crack-front deformation state (5).
obtained from SE(B) specimens. Best estimate comparisons of
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-
datadistributionisafunctionofWeibullslopeandmedianK .
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 ofASTM 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 Oct. 1, 2021. Published February 2022. Originally
inhomogeneousmaterialwillresultinaninaccurateestimateof
approved in 1997. Last previous edition approved in 2021 a
...
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 − 21 E1921 − 21a
Standard Test Method for
Determination of Reference Temperature, T , for Ferritic
o0
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
o0
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 to 825 MPa (40 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 o0
material. T values obtained from C(T) specimens are expected to be higher than T values obtained from SE(B) specimens. Best
o0 o0
estimate comparisons of several materials indicate that the average difference between C(T) and SE(B)-derived T values is
o0
approximately 10°C (2). C(T) and SE(B) T differences up to 15 °C have also been recorded (3). However, comparisons of
o0
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
o0 o0
recommended that the specimen type be reported along with the derived T value in all reporting, analysis, and discussion of
o0
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 loading rate. T is evaluated for a quasi-static loading rate range with 0.1< dK/dt < 2 MPa√m/s. Slowly
o0 o0
loaded specimens (dK/dt < 0.1 MPa√m) can be analyzed if environmental effects are known to be negligible. Provision is also
made for higher loading rates (dK/dt > 2 MPa√m/s) in Annex A1. Note that this threshold loading 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.
1.6 The statistical effects of specimen size on K in the transition range are treated using the weakest-link theory (4) applied to
Jc
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 May 15, 2021Oct. 1, 2021. Published August 2021February 2022. Originally approved in 1997. Last previous edition approved in 20202021 as
E1921 – 20.E1921 – 21. DOI: 10.1520/E1921-21.10.1520/E1921-21A.
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 − 21a
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, this limit may not be sufficient to ensure that a single-parameter (K ) adequately describes the crack-front deformation
Jc
state (5).
...
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