Stainless Steel Grades

Stainless Steel Grades

The AISI defines the following grades among others:

- 200 Series

• Austenitic iron-chromium-nickel-manganese alloys

- 300 Series

• Austenitic iron-chromium-nickel alloys

• Type 301: Highly ductile, for formed products. Also hardens rapidly during mechanical working.

• Type 303: Free machining version of 304 via addition of sulfur

• Type 304: The most common; the classic 18/8 stainless steel.

• Type 316: The next most common; for food and surgical stainless steel uses; Alloy addition of molybdenum prevents specific forms of corrosion. Also known as "marine grade" stainless steel due to its increased ability to resist saltwater corrosion compared to type 304. SS316 is often used for building nuclear reprocessing plants.

- 400 Series

• Ferritic and martensitic alloys

• Type 408: Heat-resistant; poor corrosion resistance; 11% chromium, 8% nickel.

• Type 409: Cheapest type; used for automobile exhausts; ferritic (iron/chromium only).

• Type 410: Martensitic (high-strength iron/chromium).

• Type 420: "Cutlery Grade" martensitic; similar to the Brearley's original "rustless steel". Also known as "surgical steel".

• Type 430: Decorative, e.g. for automotive trim; ferritic.

• Type 440: A higher grade of cutlery steel, with more carbon in it, which allows for much better edge retention when the steel is heat treated properly.

- 600 Series

• Martensitic precipitation hardening alloys

• Type 630: Most common PH stainless, better known as 17-4; 17% chromium, 4% nickel