High-alloy cast steels are most often specified on the basis of composition using the designation system, which has been replaced by the Alloy Casting Institute (ACI), which formerly administered these designations. Features: Corrosion resistance. Alloys are also used for special services at temperatures up to 650°C. Alloys are grouped as chromium steels, chromium-nickel steels in which chromium is the predominant alloying element, and nickel-chromium steels in which nickel is the predominant alloying element. Mechanical properties: Hardness and tensile strength. 20 to 30% Cr Ni. Do not show the phase changes observed in plain carbon and low-alloy steels during heating or cooling between room temperature and the melting point.