1. Scope

1.1 This test method covers the determination of a reference temperature, T o , which characterizes the fracture toughness of ferritic steels that experience onset of cleavage cracking at elastic, or elastic-plastic K Jc instabilities, or both. The specific types of ferritic steels () 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 Jc values tend to vary with the specimen type at a given test temperature, presumably due to constraint differences among the allowable test specimens in . The degree of K Jc 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 K Jc dependency ultimately leads to discrepancies in calculated T o values as a function of specimen type for the same material. T o values obtained from C(T) specimens are expected to be higher than T o values obtained from SE(B) specimens. Best estimate comparisons of several materials indicate that the average difference between C(T) and SE(B)-derived T o values is approximately 10C (2) . C(T) and SE(B) T o differences up to 15C 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 T o results which fall between the T o 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 T o value in all reporting, analysis, and discussion of results. This recommended reporting is in addition to the requirements in .

1.4 Requirements are set on specimen size and the number of replicate tests that are needed to establish acceptable characterization of K Jc data populations.

1.5 The statistical effects of specimen size on K Jc in the transition range are treated using weakest-link theory () applied to a three-parameter Weibull distribution of fracture toughness values. A limit on K Jc 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 ( K Jc ) adequately describes the crack-front deformation state () .

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 K Jc . 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 K Jc presented in . Data falling outside these bounds may indicate nonuniform material properties.

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 and health practices and determine the applicability of regulatory limitations prior to use.

2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

ASTM Standards

E4 Practices for Force Verification of Testing Machines

E8/E8M Test Methods for Tension Testing of Metallic Materials

E23 Test Methods for Notched Bar Impact Testing of Metallic Materials

E74 Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines

E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods

E208 Test Method for Conducting Drop-Weight Test to Determine Nil-Ductility Transition Temperature of Ferritic Steels

E399 Test Method for Linear-Elastic Plane-Strain Fracture Toughness K Ic of Metallic Materials

E436 Test Method for Drop-Weight Tear Tests of Ferritic Steels

E561 Test Method for K-R Curve Determination

E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

E1820 Test Method for Measurement of Fracture Toughness

E1823 Terminology Relating to Fatigue and Fracture Testing

Keywords

temperature;

ICS Code

ICS Number Code 77.040.10 (Mechanical testing of metals)

DOI: 10.1520/E1921-05

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