A UNS number only identifies a range of chemical compositions, and establishes no requirements for material properties, heat treatment, form, or quality. That is why a UNS, in itself, is not a material specification. The sources you just provided confirm that Ampco 18 is indeed a proprietary material specification for UNS C95400. The material is not corrosion proof, but useful in certain cases. 2: Corrosion rate over 1.0 mm/year. Serious corrosion. The material is not usable. p, P: Risk (severe risk) of pitting and crevice corrosion. c, C: Risk (Severe risk) of crevice corrosion. Used when there is a risk of localised corrosion only if crevices are present.