Significance and Use
These test methods are used to detect surface losses in carbon content due to heating at elevated temperatures, as in hot working or heat treatment.
Results of such tests may be used to qualify material for shipment according to agreed upon guidelines between purchaser and manufacturer, for guidance as to machining allowances, or to assess the influence of processing upon decarburization tendency.
Screening tests are simple, fast, low-cost tests designed to separate non-decarburized samples from those with appreciable decarburization. Based on the results of such tests, the other procedures may be utilized as applicable.
Microscopical tests require a metallographically pol-ished cross section to permit reasonably accurate determina-tion of the depth and nature of the decarburization present. Several methods may be employed for estimation of the depth of decarburization. The statistical accuracy of each varies with the amount of effort expended.
Microindentation hardness methods are employed on polished cross sections and are most suitable for hardened specimens with reasonably uniform microstructures. This procedure can be used to define the depth to a specific minimum hardness or the depth to a uniform hardness.
Chemical analytical methods are limited to specimens with simple, uniform shapes and are based on analysis of incremental turnings or after milling at fixed increments.
Microscopical tests are generally satisfactory for determining the suitability of material for intended use, specification acceptance, manufacturing control, development, or research.
Scope
1.1 These test methods cover procedures for estimating the depth of decarburization of steels irrespective of the composition, matrix microstructure, or section shape. The following basic procedures may be used:
1.1.1 Screening methods.
1.1.2 Microscopical methods.
1.1.3 Microindentation hardness methods.
1.1.4 Chemical analysis methods.
1.2 In case of a dispute, the rigorous quantitative or lineal analysis method (see 7.3.5 and 7.3.6) shall be the referee method. These methods can be employed with any cross-sectional shape. The chemical analytical methods generally reveal a greater depth of decarburization than the microscopical methods but are limited to certain simple shapes and by availability of equipment. These techniques are generally reserved for research studies. The microindentation hardness method is suitable for accurate measurements of hardened structures with relatively homogeneous microstructures.
1.3 The values stated in SI units are to be regarded as standard. The inch-pound equivalents are in parentheses and may be approximate.
1.4This 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 and health practices and determine the applicability of regulatory limitations prior to use.
