【国外标准】 Standard Test Method for Determining Decarburization and Carburization in Hardened and Tempered Threaded Steel Bolts, Screws, Studs, and Nuts (Metric)

4.1 Decarburization and carburization are two surface conditions created, either intentionally or unintentionally, as with a pre-existing condition created during the rod rolling process, the rod/wire annealing process, or while heat treating threaded steel products. Too much of either will adversely affect the safety and performance of the threaded product. Therefore, limits have been established for four different product groups: the harder and greater the tensile strength of the product, the more susceptible to failure the product becomes if these limits are exceeded.4.2 When testing to a particular product specification that lists the dimensions and microindentation data to be used, that data shall take precedence over the tables in this test method.4.3 There are only two viable methods available to detect these deficiencies: either by the visual method or the microindentation method. Both methods are used for routine inspections when evaluations are conducted at a single location on the product sample. Because an evaluation at a specific location may not be representative of the whole part, the referee method employs the microindentation method taken as an average of evaluations conducted on four adjacent threads. This procedure significantly reduces random test variables when compared to testing on a single thread.˙4.4 Specifying this test method does not specify or imply that testing shall be for either decarburization or carburization alone or for both conditions. When either test method is performed, both conditions will be apparent and shall be reported. For example, if an order is placed to test for decarburization and none is found but the presence of decarburization is detected, it shall be reported on the test report that carburization was found.1.1 This test method covers procedures for measuring, classifying, and determining the presence of decarburization and carburization in the threaded section of hardened and tempered metric steel bolts, screws, studs, nuts and similar parts which have been heated to facilitate fabrication or to modify their mechanical properties. This test method is not intended to address products which are intentionally carburized to achieve specific results.1.2 Two routine methods are described for measuring the limits of and determining the presence of decarburization or carburization; the Optical Method and the Microindentation Method 1. Either method is appropriate for routine examinations. The Microindentation Method 2 shall be considered the referee method.1.3 For the purpose of these tests, there are five classes of hardened and tempered steel products for which specific measurements must be made with respect to their physical properties.1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.5 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.1.6 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.