The Three Families of Stainless Steel and How to Pick One

Austenitic Stainless Steels

These are the most frequently used stainless steels. They carry high chromium compared with other steel alloys, which gives them higher corrosion resistance. They also tend to be non magnetic, although they can become magnetic after cold working. 304, 316, 316L, 317, 321 and 310S all sit in this family.

Related product: 304 Stainless Steel Pipe

Ferritic Stainless Steels

Ferritic grades are the second most common family. As the name implies they are magnetic. They can be hardened through cold working, and they tend to be less expensive because they contain less nickel. Grade 409, the titanium stabilised exhaust grade, belongs here.

Related product: 409 Stainless Steel Plate and Sheet

Martensitic Stainless Steels

Martensitic grades are the least common family. Their corrosion resistance is lower than either ferritic or austenitic alloys, but they reach high hardness. They suit applications that need very high tensile strength and impact resistance, and where corrosion resistance is also needed they may be used with a protective polymer coating. Grade 410 is the basic martensitic stainless steel.

Related product: 410 Stainless Steel Bar

Duplex as a Fourth Route

Duplex grades combine austenite and ferrite in roughly equal proportion, which is why they read as a separate class. They bring austenitic corrosion resistance together with strength closer to a ferritic grade, at a lower nickel content.

Related product: 2205 Duplex Stainless Steel Sheet

Using the Families as a Filter

Ask three questions before reaching for a grade number. Does the part need to be hardened by heat treatment, which rules out everything but martensitic. Does it need to be non magnetic, which points at annealed austenitic. Is the budget driven by nickel content, which pushes toward ferritic or duplex.