Chromium, nickel, manganese, silicon, phosphorus, and sulfur are often found in 321 stainless steel flanges. Its chromium concentration (18-20%) and nickel content (9-12%) are more significant than 304-grade stainless steel. Other constituents in the alloy, such as molybdenum and titanium, contribute to its corrosion resistance.

Type 321 is a stabilised austenitic stainless steel, identical to type 304, but with titanium added. This titanium additive minimises or eliminates carbide precipitation during welding and in 800 - 1500 °F (427 - 816 °C) use. It also improves the alloy's characteristics at increased temperatures.

Because of its lower nickel content, grade 321 is often less costly than 316 stainless steel. This can make it a more cost-effective solution for some applications while maintaining strong corrosion resistance and high-temperature characteristics. Grade 321 stainless steel incorporates titanium as a stabilising element, which aids in the prevention of sensitisation and grain boundary carbide precipitation during high-temperature exposure. This makes it more suited for applications that need extended exposure to high temperatures, such as heat exchangers and furnace components.