The standard "ASTM E45 Standard Test Methods for Determining Inclusion Content in Steel," developed by the American Society for Testing and Materials (ASTM), describes a number of methods for determining the nonmetallic inclusion (intracellular non-living matter) content of wrought steel. Macroscopic methods include macroabrasion, fracturing, step reduction, and magnetic particle testing. Microscopic methods include five inspection systems. In these microscopic methods, inclusions are assigned to a category based on similarity in morphology and not necessarily chemical identity. This standard includes metallographic methods that allow simple discrimination between morphologically similar inclusions. While these methods are primarily designed to grade inclusions, components such as carbides, nitrides, carbonitrides, borides, and intermetallic phases can be graded using some microscopic methods. In some cases, alloys other than steels may be graded using one or more of these methods.
These test methods cover the procedures for performing JK-type inclusion gradings using automated image analysis in accordance with microscopic methods A and D. Depending on the steel type and the required properties, a macroscopic or microscopic method, or a combination of the two, may be found satisfactory for determining inclusion content. These test methods relate only to the recommended test methods, and nothing in them should be construed as defining or establishing the limits of acceptability for any steel grade.
For the purposes of this standard, in addition to the terms and definitions given in ASTM E7, the following definitions apply:
These test methods include four macroscopic and five microscopic test methods (manual and image analysis) to express the inclusion content of steel and the test results.
Inclusions are characterized by size, shape, concentration, and distribution rather than chemical composition. Although compositions are not defined, microscopic methods place inclusions into one of several compositional categories (sulfides, oxides, and silicates). This standard describes a metallographic method to facilitate inclusion discrimination. Only inclusions present on the test surface can be detected.
Macroscopic testing methods evaluate larger surface areas than microscopic testing methods, and because inspection is performed visually or at low magnification, these methods are best suited for detecting larger inclusions. These methods are not suitable for detecting inclusions smaller than approximately 0,40 mm in length and do not separate inclusions by type.
Macroscopic test methods include:
Microscopic testing methods are used to characterize inclusions formed as a result of deoxidation or limited solubility in solid steel. These microscopic testing methods rank the severity and type of inclusions by morphological type, that is, size, shape, concentration, and distribution, but not specifically by composition. These inclusions are characterized by morphological type, that is, size, shape, concentration, and distribution, but not specifically by composition.
Microscopic methods are not designed to assess the content of exogenous inclusions. In cases of disagreement about whether an inclusion is native or exogenous, microanalytical methods such as energy dispersive X-ray spectroscopy (EDS) can be used to help determine the nature of the inclusion. However, experience and knowledge of the casting process and production materials, such as deoxidation, desulfurization, and inclusion shape control additives, as well as refractory and furnace lining compositions, must be used in conjunction with microanalytical results to determine whether an inclusion is native or exogenous.
Because the inclusion population in a given steel batch varies by location, the batch must be statistically sampled to assess inclusion content. The sampling rate must be adequate for the batch size and its specific properties. Materials with very low inclusion content can be graded more accurately using automated image analysis, which allows for more precise microscopic grading.
Macroscopic testing methods are used to characterize the size, distribution, number, and type of inclusions on a polished sample surface.
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