ASTM B874-96(2023) PDF

ABSTRACT This specification covers the requirements for chromium diffusion of metals applied by pack cementation process. The four classes of chromium diffusion coating, defined by the type of base metal, are as follows: Class I (carbon steels); Class II (low-alloy steels); Class III (stainless steels); and Class IV (nickel-based alloys). Specimens shall adhere to processing requirements such as substrate preparation, materials (masteralloys, activators, and inert fillers), loading, furnace cycle, post cleaning, post straightening, visual inspection, and marking and packaging. Specimens shall also adhere to coating requirements such as diffusion thickness, decarburization, chromium content, appearance, and mechanical properties (tensile strength, and macro- and micro-hardness). SCOPE 1.1 This specification covers the requirements for chromium diffusion of metals by the pack cementation method. Pack diffusion employs the chemical vapor deposition of a metal which is subsequently diffused into the surface of a substrate at high temperature. The material to be coated (substrate) is immersed or suspended in a powder containing chromium (source), a halide salt (activator), and an inert diluent such as alumina (filler). When the mixture is heated, the activator reacts to produce an atmosphere of chromium halides which transfers chromium to the substrate for subsequent diffusion. The chromium-rich surface enhances corrosion, thermal stability, and wear-resistant properties. 1.2 This 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.