ASTM E1921-03
(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, <i>T<sub>o'</sub></i>, for Ferritic Steels in the Transition Range
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) 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 recommended that the specimen type be reported along with the derived To value in all reporting, analysis, and discussion of 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 KJc data populations.
1.5 The statistical effects of specimen size on KJc in the transition range are treated using weakest-link theory (4) applied to a three-parameter Weibull distribution of fracture toughness values. A limit on KJc 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 (KJc) adequately describes the crack-front deformation state (5).
1.6 Statistical methods are employed to predict the transition toughness curve and specified tolerance bounds for 1T specimens of the material tested. The standard deviation of the data distribution is a function of Weibull slope and median KJc. The procedure for applying this information to the establishment of transition temperature shift determinations and the establishment of tolerance limits is prescribed.
1.7 The fracture toughness evaluation of nonuniform material is not amenable to the statistical analysis methods employed in this standard. Materials must have macroscopically uniform tensile and toughness properties. 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. Metallography and initial screening may be necessary to verify the applicability of these and similarly graded materials. Paticular notice should be given to the 2% and 98% tolerance bounds on KJc presented in 9.3. Data falling outside these bounds...
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Designation: E 1921 – 03
Standard Test 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope T results which fall between the T values calculated using
o o
solely C(T) or SE(B) specimens. It is therefore strongly
1.1 Thistestmethodcoversthedeterminationofareference
recommended that the specimen type be reported along with
temperature, T , which characterizes the fracture toughness of
o
thederivedT valueinallreporting,analysis,anddiscussionof
ferritic steels that experience onset of cleavage cracking at o
results. This recommended reporting is in addition to the
elastic, or elastic-plastic K instabilities, or both. The specific
Jc
requirements in 11.1.1.
types of ferritic steels (3.2.1) covered are those with yield
1.4 Requirements are set on specimen size and the number
strengths ranging from 275 to 825 MPa (40 to 120 ksi) and
of replicate tests that are needed to establish acceptable
weld metals, after stress-relief annealing, that have 10% or
characterization of K data populations.
Jc
less strength mismatch relative to that of the base metal.
1.5 The statistical effects of specimen size on K in the
1.2 The specimens covered are fatigue precracked single- Jc
transition range are treated using weakest-link theory (4)
edge notched bend bars, SE(B), and standard or disk-shaped
applied to a three-parameter Weibull distribution of fracture
compact tension specimens, C(T) or DC(T). A range of
toughness values. A limit on K values, relative to the
Jc
specimen sizes with proportional dimensions is recommended.
specimen size, is specified to ensure high constraint conditions
The dimension on which the proportionality is based is
along the crack front at fracture. For some materials, particu-
specimen thickness.
larly those with low strain hardening, this limit may not be
1.3 Median K values tend to vary with the specimen type
Jc
sufficient to ensure that a single-parameter (K ) adequately
Jc
at a given test temperature, presumably due to constraint
describes the crack-front deformation state (5).
differences among the allowable test specimens in 1.2. The
1.6 Statistical methods are employed to predict the transi-
degree of K variability among specimen types is analytically
Jc
2
tion toughness curve and specified tolerance bounds for 1T
predicted to be a function of the material flow properties (1)
specimens of the material tested.The standard deviation of the
and decreases with increasing strain hardening capacity for a
datadistributionisafunctionofWeibullslopeandmedianK .
Jc
given yield strength material. This K dependency ultimately
Jc
The procedure for applying this information to the establish-
leads to discrepancies in calculated T values as a function of
o
ment of transition temperature shift determinations and the
specimen type for the same material. T values obtained from
o
establishment of tolerance limits is prescribed.
C(T) specimens are expected to be higher than T values
o
1.7 The fracture toughness evaluation of nonuniform mate-
obtained from SE(B) specimens. Best estimate comparisons of
rial is not amenable to the statistical analysis methods em-
several materials indicate that the average difference between
ployed in this standard. Materials must have macroscopically
C(T) and SE(B)-derived T values is approximately 10°C (2).
o
uniform tensile and toughness properties. For example, multi-
C(T) and SE(B) T differences up to 15°C have also been
o
pass weldments can create heat-affected and brittle zones with
recorded (3). However, comparisons of individual, small
localizedpropertiesthatarequitedifferentfromeitherthebulk
datasetsmaynotnecessarilyrevealthisaveragetrend.Datasets
material or weld. Thick section steel also often exhibits some
which contain both C(T) and SE(B) specimens may generate
variation in properties near the surfaces. Metallography and
initialscreeningmaybenecessarytoverifytheapplicabilityof
1
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue theseandsimilarlygradedmaterials.Paticularnoticeshouldbe
and Fracture and is the direct responsibility of E08.08 on Elastic-Plastic Fracture
giventothe2%and98%toleranceboundsonK presentedin
Jc
Mechanics Technology.
9.3.Datafallingoutsidetheseboundsmayindicatenonuniform
Current edition approved Nov. 1, 2003. Published December 2003. Originally
material properties.
approved in 1997. Last previous edition approved in 2002 as E1921–02.
2
Theboldfacenumbersinpare
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