Chord Method of Evaluating Surface Microstructural Characteristics
This practice provides a method for evaluating microhardness and microstructure very close (0.002 inch (0.051 mm) or less) to the surface of a disk specimen. Specific accept/reject criteria for partial decarburization (3.7.1), inadvertent carburization/nitriding (3.7.3), total decarburization/intergranular oxidation (3.8), and other characteristics evaluated are to be found in the applicable specification where this ARP is referenced.
ARP1820C results from a Five-Year Review and update of this specification with rewritten Introduction and Scope to add clarity, disc surface texture changed from 32 to 18 as it was more desirable but that higher texture may be needed for smaller diameters (3.1), added ASTM E385 for determining Knoop microhardness and allowed for staggered indentations (3.5), changed hardness for Depth of Decarburization to be consistent with AMS2759 (3.6), added clarifying wording for Inadvertent Carburization and Nitriding (3.7.2), and Figures 2, 3, and 4 were replaced with more accurate figures.
Corrosion resistant alloys
Coatings, colorants, and finishes
Also known as: SAE ARP 1820
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