18C9

18C9 is a designation used in some metal catalogs and regional standards to refer to a stainless steel alloy with approximately 18% chromium and 9% nickel. In many Western standards this composition is equivalent to 304 stainless steel, which typically contains 18–20% chromium and 8–10.5% nickel, with a maximum carbon of 0.08%. Because exact composition varies by producer and standard, 18C9 is a shorthand rather than a fixed formal grade in all catalogs.

This alloy is austenitic, offering good toughness, formability, and weldability, with high corrosion resistance in ordinary environments. It cannot be hardened by heat treatment; strength is typically increased by cold working. In the annealed state it is usually non-magnetic, though slight magnetism can arise after significant cold deformation.

Common applications include kitchenware such as cookware and flatware, sinks, and other consumer goods, as well as chemical processing equipment and architectural trim, where a combination of corrosion resistance and ease of fabrication is valuable.

Variants and related standards include low-carbon 304L and high-carbon 304H grades. When precision is required, the exact alloy specification should be confirmed against the applicable standard (for example ASTM or EN) rather than relying on the 18C9 designation alone.