ASTM-E588:03(R2020) pdf free download – Standard Practice for Detection of Large Inclusions in Bearing Quality Steel by the Ultrasonic Method.
8.6 System Reference Block—A system reference block (defined dimensionally in Section .2) is required for initial adjustments and operational testing of the equipment. This sample should be selected to provide reflection signals at all counting levels. Depth distribution of inclusions in the selected reference block should make its response characteristics relatively insensitive to minor focal length variations between different search units. The reference block should give a minimum change in total counts of 10 % for each 10 % increase or decrease in amplitude setting. A maximum of 30 % change in count for each 10 % change in amplitude setting should not he exceeded. It should he suitably protected from corrosion to assure its longevity.
9. Test Specimens
9.1 General—Test specimens must he either in the rolled or forged condition. If forged. upset forging is prohibited in order to maintain the rolling direction. Care should he taken not to overheat the forging to avoid spurious ultrasonic indications. Specimen location and frequency shall he as agreed upon between the supplier and the purchaser.
9.2 Specimen Size and Shape—Specimens shall have a minimum cross-sectional dimension after preparation of 3V2 in. (88.9 mm). The area scanned shall he sufficient to permit testing of a minimum of 25 in.3 (410 cm3) of the specimen. The tested volume equals the scanned area multiplied by the gated depth. If special consideration is given, thinner samples may be tested.
9.3 Entry Suiface Finish—The test surface through which the sound enters the specimen shall be machined and ground. This finish in any direction over the surface shall be preferably 10 iin. to 80 j.iin. (0.25 I.IIn to 2.0 iim). Final material removal may require a dressed grinding wheel to avoid spurious. near-surface indications. All four sides are to he ground.
9.4 1-leat Treatment—Thermal conditioning of the specimens is required to minimize acoustic anomalies. Typical heat treatment may consist of normalizing or quenching and tempering, depending on steel type. to meet the ultrasonic penetrability requirement of Section 9.5. Certain steels may require special thermal treatment such as a double temper to obtain suitable acoustic properties.
9.5 Ultrasonic Penetrability—The ultrasonic penetrability shall be determined to be suitable for the inspection. The penetrability is acceptable if the third back reflection of the specimen is 25 % of full screen height, over the center of the billet specimen, at standard test conditions and test sensitivity.
10. Procedure
1 0. 1 Geiie rat.
10. 1 . 1 Operating frequency—The operating frequency for most bearing steels is 10 MHz. Ten megahertz is recommended as the highest practical frequency available within existing manufacturing capabilities to produce search units with uniform performance characteristics. Higher frequencies give better resolution, while lower frequencies give better penetration.