The Alloy Casting Institute (ACI) has developed a system for designating stainless and heat resistant casting alloys. As Figure 14 shows, casting designations begin with either a “C” for corrosion resistant materials, or an “H” for heat resistant materials. The second letter in the designation ranges from “A” to “Z” depending upon the nickel content and, to a lesser degree, the chromium content. For example, a corrosion resistant material with no nickel and 12% chromium begins with “CA” (refer to CA15 in the Figure 14). For another example, an alloy with 100% nickel and no chromium begins with “CZ” (refer to material CZ100 in Figure 14). Following the letter designators are numeric digits that indicate the maximum carbon content. Additional letters following the numeric digits indicate the presence of supplementary alloying elements.
Although ACI no longer exists, the system has been adopted by ASTM, and designations for new alloys are being assigned. UNS numbers have also been assigned to many of these alloys; however, the ACI designations are easier to interpret than the UNS designations, which explains the continued popularity of the ACI system.