Standard
Active
Last Updated: May 29, 2025
Track Document
ASTM E1921-25
Standard Test Method for Determination of Reference Temperature, T0, for Ferritic Steels in the Transition Range
Standard Test Method for Determination of Reference Temperature, T0 , for Ferritic Steels in the Transition Range
E1921-25
ASTM|E1921-25|en-US
Standard Test Method for Determination of Reference Temperature, T0 , for Ferritic Steels in the Transition Range
Standard
E1921 Standard Test Method for Determination of Reference Temperature, T0 , for Ferritic Steels in the Transition Range>
new
BOS Vol. 03.01 Committee E08
$
108.00
In stock
ASTM International
Significance and Use
5.1 The property T0 determined by this test method characterizes the fracture toughness resistance of ferritic steels to cleavage cracking. T0 is determined by statistical analysis of sets of fracture toughness data. Historically, estimation of fracture toughness resistance to cleavage cracking has been based on correlative testing of Charpy and nil-ductility specimens, or by conducting extensive testing over a wide temperature range and then subjectively characterizing the ductile to brittle transition curve. The statistical methods detailed in this test method eliminate the need for a correlative approach and reduce this subjectivity and the number of specimens necessary to characterize the fracture toughness resistance of ferritic steels to cleavage cracking.
5.2 Shifts in T0 are a measure of transition temperature change caused, for example, by metallurgical damage mechanisms.
5.3 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 (9). This results in a distribution of fracture toughness values that is amenable to characterization using the statistical methods in this test method.
5.4 The statistical methods in this test method assume that the data set represents a macroscopically homogeneous material, such that the test material has both uniform tensile and fracture 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 contain 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 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 set fails the screening criterion in 10.6, the homogeneity of the material and its fracture toughness can be more accurately assessed using the analysis methods described in Appendix X5.
5.5 Distributions of KJc data are characterized in this test method using a Weibull function that is coupled with weakest-link statistics (10). An upper limit on constraint loss and a lower limit on test temperature are defined between which weakest-link statistics can be used. For some materials, particularly those with low strain hardening, the value of T0 may be influenced by specimen size due to a partial loss of crack-tip constraint (1). When this occurs, the value of T0 may be lower than the value that would be obtained from a data set of KJc values derived using larger specimens.
5.6 There is an expected bias among T0 values as between SE(B) and C(T)/DC(T) specimen types. The magnitude of the bias may increase inversely to the strain hardening ability of the test material at a given yield strength, as the average crack-tip constraint of the data set decreases (11). On average, T0 values obtained from C(T) specimens are higher than T0 values obtained from SE(B) specimens. Best estimate comparison indicates that the average difference between C(T) and SE(B)-derived T0 values is approximately 10 °C (12). However, individual C(T) and SE(B) datasets may show much larger T0 differences (13, 14, 15), or the SE(B) T0 values may be higher than the C(T) values (12) . On the other hand, 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.
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 (3.2.5) 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 KJc 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 KJc data populations. As indicated in 10.3, a minimum of 6 test specimens is required.
1.6 T0 is dependent on the K-rate. T0 is evaluated for a quasi-static loading K-rate range with 0.5 < 
< 2 MPa√m/s. Slowly loaded specimens ( 
< 0.5 MPa√m) can be considered valid if environmental effects are known to be negligible. Provision is also made for higher K-rates ( 
> 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 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 (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 T0 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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.10 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.