【国外标准】 Standard Test Method for Conducting Drop-Weight Test to Determine Nil-Ductility Transition Temperature of Ferritic Steels

5.1 The fracture-strength transitions of ferritic steels used in the notched condition are markedly affected by temperature. For a given “low” temperature, the size and acuity of the flaw (notch) determines the stress level required for initiation of brittle fracture. The significance of this test method is related to establishing that temperature, defined herein as the NDT temperature, at which the “small flaw” initiation curve, Fig. 1, falls to nominal yield strength stress levels with decreasing temperature, that is, the point marked NDT in Fig. 1.FIG. 1 Generalized Fracture Analysis Diagram Indicating the Approximate Range of Flaw Sizes Required for Fracture Initiation at Various Levels of Nominal Stress, as Referenced by the NDT Temperature3 , 4CAT (crack arrest temperature)–the temperature of arrest of a propagating brittle fracture. CAT curve is thus a stress versus temperature curve as related to crack arrest.FTE (fracture transition elastic) temperature–the crack arrest temperature for a stress level equal to the yield strength thus marks the highest temperature of fracture propagation for purely elastic loads.FTP (fracture transition plastic) temperature–the temperature above which fractures are entirely shear, that is, show no center regions of cleavage fracture, and the stress required for fracture approximates the tensile strength of the steel.5.2 Interpretations to other conditions required for fracture initiation may be made by the use of the generalized flaw-size, stress-temperature diagram shown in Fig. 1. The diagram was derived from a wide variety of tests, both fracture-initiation and fracture-arrest tests, as correlated with the NDT temperature established by the drop-weight test. Validation of the NDT temperature has been documented by correlations with numerous service failures encountered in ship, pressure vessel, machinery component, forged, and cast steel applications.5.3 Lists of Selected References Relating to Development of Drop-Weight Test. Selected References Relating to Correlation of NDT temperature to Service Failures, and Selected References Relating to Neutron Irradiation Embrittlement are presented following Section 17 on Precision and Bias.1.1 This test method covers the determination of the nil-ductility transition (NDT) temperature of ferritic steels, 5/8 in. (15.9 mm) and thicker.1.2 This test method may be used whenever the inquiry, contract, order, or specification states that the steels are subject to fracture toughness requirements as determined by the drop-weight test.1.3 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.1.4 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.1.5 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.