Decarburization Detects Surface Losses in Carbon Content
Case Depth: Case hardening may be defined as a process for hardening a ferrous materials in such a manner that the surface layer (known as the case), is substantially harder than the remaining materials (known as the core). This process is controlled through carburizing, nitriding, carbonitriding, cyaniding, induction and flame hardening. The chemical composition, mechanical properties, or both, are effected by these practices. Methods for determining case depth are chemical, mechanical or visual and should be selected on the basis of specific requirements.
Decarburization Measurement: This method is designed to detect changes in the microstructure, hardness, or carbon content at the surface of the steel sections due to carburization. The depth is determined as the depth where a uniform microstructure, hardness, or carbon content, typical of the interior of the specimen is observed. This method will detect surface losses in carbon content due to heating at elevated temperatures, as in hot working or heat treatment.
Coating / Plating Evaluation (ASTM B487, ASTM B748): A coating or plating application is used primarily for protection of the substrate. The thickness is an important factor in the performance of the coating or plating. A portion of the specimen is cut, mounted transversely, a prepared in accordance with acceptable or suitable techniques. The thickness of the cross section is measured with an optical microscope. When the coating or plating is thinner than .00020", the measurement should be taken with the aid of the scanning electron microscope. Cross-sectioned metallographic examinations of substrates with platings, surface evaluations, thickness measurements, weight per volume, and even salt spray testing can aid in the evaluation of platings.
