5.1 Qualitative measurement of "nodularity" and "nodule count" using visual estimations has been practiced for many years. These methods suffer from poor reproducibility and repeatability. The introduction of computer-aided image analysis enables metallographers to measure and count individual particles of interest in a microstructure with a high degree of precision. This greatly reduces measurement variations compared to visual estimation methods (see, for example, Test Method A247).

5.2 This method defines a procedure for measuring the number of nodules and the quality of nodularity of spherulitic graphite in a cast iron microstructure. The specimen's location in a casting or cast test specimen, and the orientation of the plane-of-polish, are governed by product standards. When a product standard is not defined, choose the test location randomly or at specific systematically chosen depths as needed. The plane-of-polish may be parallel or perpendicular to the solidification direction, or chosen at random, depending upon the needs of the study.

5.3 This test method may be used to determine variations within a given test specimen, within a given location in a casting, between different locations in a casting, or for the same location in different castings over time. Results from this test method may be used to qualify material for shipment in accordance with guidelines agreed upon between purchaser and manufacturer or can be used to monitor process quality or product variations.

5.4 Measurements are performed using a computer-controlled automatic image analysis system.

5.5 A minimum number of specimens and a minimum surface area to be evaluated may be defined by producer-purchaser agreement, provided at least 500 particles meeting the minimum size requirements are measured. The number of particles analyzed shall be indicated in the final analysis report (see 9.6).