【国外标准】 Standard Practice for Detection of Large Inclusions in Bearing Quality Steel by the Ultrasonic Method

6.1 Comparison with Other Inclusion Rating Methods—Because the test is performed on a volumetric rather than a surface-examination basis, the ultrasonic method is inherently better able to detect infrequently occurring large inclusions or clusters of small inclusions than eddy current, magnetic particle, microscopical, or macroscopic examination procedures.6.2 Limitation of Inclusion Size and Type—A limitation of the method is that it will not detect all inclusions. Inclusion chemistry, size, shape, location, and distribution may limit the ability of the method to provide indications distinct from those generated by the surrounding metallurgical structure. The recommended practice is only meaningfully applicable to examination of steel wherein the inclusion size and type are within the detection capabilities of the method. For steel wherein inclusion size, dispersion, and chemistry prevent optimum inclusion detection by ultrasonics, microscopical methods detailed in Test Methods E45 may be applied.1.1 This practice covers a procedure for the rating of rectangular steel sections by immersion ultrasonic techniques. Its purpose is to provide information on the content of large inclusions or clusters of small inclusions for determining the suitability of a steel lot for bearing applications. This practice in no manner defines or establishes limits of acceptability.1.2 For this document, large inclusions are defined in ultrasonic terms as those having a reflecting area equivalent to or larger than a 1/64 in. diameter flat-bottom hole in a steel reference block of similar properties and thickness. In metallographic terms, large inclusions, defined in this way, are of approximately the same size as the smallest detectable sizes revealed by the macroscopic methods of Test Methods E45. In some cases, inclusions smaller than those described previously can be detected either individually or in clusters, depending on their type, chemical composition, orientation to the ultrasonic beam and distance from the sound entry surface of the specimen.1.3 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.1.4 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.