ASTM E1921-15a
(Test Method)Standard Test Method for Determination of Reference Temperature, To, for Ferritic Steels in the Transition Range
Standard Test Method for Determination of Reference Temperature, T<inf>o</inf>, 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 (16). 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 presume that the test materials are macroscopically homogeneous such that both the tensile and toughness properties are uniform. The fracture toughness evaluation of nonuniform materials is not amenable to the statistical analysis methods employed in the main body of this test method. For example, multipass weldments can create heat-affected and brittle zones with localized properties that are quite different from either the bulk material or weld. Thick section steel also often exhibits some variation in properties near the surfaces. An appendix to analyze the cleavage toughness properties of nonuniform or inhomogeneous materials is currently being prepared. In the interim, users are referred to (6-8) for procedures to analyze inhomogeneous materials. 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 to compare with the bulk material. It is also advisable to measure the toughness properties of these nonuniform regions distinctly from the bulk material.
5.4 Distributions of KJc data from replicate tests can b...
SCOPE
1.1 This test method covers the determination of a reference temperature, To, 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 (3.2.1) 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 To values as a function of specimen type for the same material. To values obtained from C(T) specimens are expected to be higher than To values obtained from SE(B) specimens. Best estimate comparisons of several materials indicate that the average difference between C(T) and SE(B)-derived To values is approximately 10°C (2). C(T) and SE(B) To 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 To results which fall between the To values calculated using solely C(T) or SE(B) specimens. It is therefore strongly recomme...
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E1921 − 15a
StandardTest Method for
Determination of Reference Temperature, T , for Ferritic
o
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
o
1.1 Thistestmethodcoversthedeterminationofareference
results. This recommended reporting is in addition to the
temperature, T , which characterizes the fracture toughness of
o
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 (3.2.1) 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
o o
less strength mismatch relative to that of the base metal.
quasi-static loading rate range with 0.1< dK/dt<2MPa√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.
The dimension on which the proportionality is based is
1.6 The statistical effects of specimen size on K in the
Jc
specimen thickness.
transition range are treated using weakest-link theory (4)
1.3 Median K values tend to vary with the specimen type
applied to a three-parameter Weibull distribution of fracture
Jc
at a given test temperature, presumably due to constraint
toughness values. A limit on K values, relative to the
Jc
differences among the allowable test specimens in 1.2. The
specimen size, is specified to ensure high constraint conditions
degree of K variability among specimen types is analytically
along the crack front at fracture. For some materials, particu-
Jc
2
predicted to be a function of the material flow properties (1)
larly those with low strain hardening, this limit may not be
and decreases with increasing strain hardening capacity for a
sufficient to ensure that a single-parameter (K ) adequately
Jc
given yield strength material. This K dependency ultimately
describes the crack-front deformation state (5).
Jc
leads to discrepancies in calculated T values as a function of
o
1.7 Statistical methods are employed to predict the transi-
specimen type for the same material. T values obtained from
o
tion toughness curve and specified tolerance bounds for 1T
C(T) specimens are expected to be higher than T values
o
specimens of the material tested.The standard deviation of the
obtained from SE(B) specimens. Best estimate comparisons of
datadistributionisafunctionofWeibullslopeandmedianK .
Jc
several materials indicate that the average difference between
The procedure for applying this information to the establish-
C(T) and SE(B)-derived T values is approximately 10°C (2).
o
ment of transition temperature shift determinations and the
C(T) and SE(B) T differences up to 15°C have also been
o
establishment of tolerance limits is prescribed.
recorded (3). However, comparisons of individual, small data-
1.8 This test method assumes that the test material is
sets may not necessarily reveal this average trend. Datasets
macroscopically homogeneous such that the materials have
which contain both C(T) and SE(B) specimens may generate
uniform tensile and toughness properties. The fracture tough-
T results which fall between the T values calculated using
o o
nessevaluationofnonuniformmaterialsisnotamenabletothe
solely C(T) or SE(B) specimens. It is therefore strongly
statistical analysis methods employed in the main body of this
test method. Application of the analysis of this test method to
an inhomogeneous material will result in an inaccurate esti-
1
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue
mate of the transition reference value T and non-conservative
and Fracture and is the direct responsibility of E08.07 on Fracture Mechanics.
o
Current edition approved Oct. 1, 2015. Published February 2016. Originally
confidence bounds. For example, multipass weldments
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.