Unified Numbering System for Ferrous Metals and Alloys

The Unified Numbering System (UNS) for Metals and Alloys is established to correlate several internationally used alloy and metal numbering systems, which are now commonly used by trade associations, societies and producers and users of alloys and metals. This system does not create the confusion caused due to usage of previous sysyems that used the same number for different metals or alloys or different identification numbers for the the same metal or alloy. The UNS system can be mainly used for maintaining record, efficient indexing, cross-referencing and storing and retrieving data.

CA-UNS designation is a unified identifier of an alloy or a metal. The controlling limits for the alloys and metals have been identified in specifications. Since it avoids the need for form, property, quality or condition, it is not itself a specification.

The UNS constitutes nine series of designations for ferrous metals and alloys. Each designation includes a single-letter prefix and five digits. The letter is identified from the family of metals in many cases, for example, T for tool steel, F for cast irons and S for stainless steels.

Few digits in certain UNS designation family have specific assigned meanings. Each series of UNS designations is independent from each other with respect to the importance of digits, thus eliminating the lengthy and complicated UNS designations and achieving better flexibility.

The identification numbers identified from the existing systems are integrated into the UNS designations in order to ensure user convenience, for example, carbon steel identified by the American Iron and Steel Institute is designated as AISI 1020 and covered by the UNS designation as G10200.

The trade associations had initially used their own designation systems for alloys and metals, but now they have established UNS designation assignments for some of the metals and alloys. The Society of Automotive Engineers (SAE) is in charge of these assignments. The assigners are responsible for assigning specific UNS series of designations, and also consider the request regarding the assignment of new UNS designations. The assigners inform the applicants regarding the action taken against the assignment. The UNS designation assigners immediately report the details of the new assignments to the office of the UNS for Metals and Alloys in order to include these details into the UNS system.

Table 1 shows that the listed cross-referenced specifications are representative only and are not necessarily a complete list of specifications applicable to a particular UNS designation.

Table 1. UNS designations for ferrous metals and alloys.