ASTM E208-2017 pdf free download

ASTM E208-2017 pdf free download.Standard Test Method for Conducting Drop-Weight Test to Determine Nil-Ductility Transition Temperature of Ferritic Steels
4. Summary of Test Method
4.1 The drop-weight test employs simple beam specimens specially prepared to create a material crack in their tensile surfaces at an early time interval of the test. The test is conducted by subjecting each of a series (generally four to eight) of specimens of a given material to a single impact load at a sequence of selected temperatures to determine the maximum temperature at which a specimen breaks. The impact load is provided by a guided, free-falling weight with an energy of 250 to 1400 ft lbf (340 to 1900 J) depending on the yield strength of the steel to be tested. The specimens are prevented by a stop from deflecting more than a few tenths of an inch.4.2 The usual test sequence is as follows: After the prepa- ration and temperature conditioning ofthe specimen, the initial drop-weight test is conducted at a test temperature estimated to be near the NDT temperature. Depending upon the results of the first test, tests of the other specimens are conducted at suitable temperature intervals to establish the limits within 10°F (5°C) for break and no-break performance. A duplicate test at the lowest no-break temperature of the series is conducted to confirm no-break performance at this tempera- ture. 4.3 In 1984, the method of applying the crack-starter weld bead was changed from a two-pass technique to the current single-pass procedure, and the practice ofrepair-welding ofthe crack-starter weld bead was prohibited. For steels whose properties are influenced by tempering or are susceptible to temper embrittlement, the nil-ductility transition (NDT) tem- perature obtained using the single-pass crack-starter weld bead may not agree with that obtained using the previous two-pass crack-starter weld bead, or when the crack-starter bead was repaired.
5. Significance and Use
5.1 The fracture-strength transitions offerritic 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 ofthis 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. 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 tempera- ture established by the drop-weight test. Validation of the NDT concept has been documented by correlations with numerous service failures encountered in ship, pressure vessel, machinery component, forged, and cast steel applications.
6. Apparatus
6.1 The drop-weight machine is of simple design based on the use of readily available structural steel products. 2 The principal components ofa drop-weight machine are a vertically guided, free-falling weight, and a rigidly supported anvil which provides for the loading of a rectangular plate specimen as a simple beam under the falling weight. Fig. 2(a) illustrates a typical drop-weight machine built of standard structural shapes. 6.2 A rail, or rails, rigidly held in a vertical position and in a fixed relationship to the base shall be provided to guide the weight. The weight shall be provided with suitable devices which engage the rail, or rails, and ensure that it will drop freely in a single, vertical plane. The weight may be raised by any convenient means. A weight-release mechanism, function- ing similarly to that shown in Fig. 2(b), shall be provided to release the weight quickly without affecting its free fall. The weight shall be made in one piece, or ifmade ofseveral pieces, its construction shall be rigid to ensure that it acts as a unit when it strikes the specimen. The striking tup of the weight shall be a steel cylindrical surface with a radius of 1 in. (25.4 mm) and a minimum hardness of HRC 50 throughout the section. The weight shall be between 50 and 300 lb (22.7 and 136 kg). The rails and hoisting device shall permit raising the weight various fixed distances to obtain potential energies of 250 to 1400 ft lbf (340 to 1900 J).