Stainless Steel Grades
200 Series—Austenitic Chromium-Nickel-Manganese Alloys
300 Series—Austenitic Chromium-Nickel Alloys
Highly ductile, for formed products. Also hardens rapidly during mechanical working. Good weldability. Better wear resistance and fatigue strength than 304.
Same corrosion resistance as 304, with slightly higher strength due to additional carbon.
Easier machining version of 304 via addition of sulfur and phosphorus. Also referred to as "A1" in accordance with International Organization for Standardization ISO 3506
The most common grade; the classic 18/8 stainless steel. Also referred to as "A2" in accordance with International Organization for Standardization ISO 3506.
Better temperature resistance than 304
The second most common grade (after 304); 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 resistance to chloride corrosion compared to type 304. SS316 is often used for building nuclear reprocessing plants. Most watches that are made of stainless steel are made of this grade. Rolex is an exception in that they use Type 904L. 18/10 stainless often corresponds to this grade. Also referred to as "A4" in accordance with International Organization for Standardization ISO 3506.
Similar to 304 but lower risk of weld decay due to addition of titanium. See also 347 with addition of niobium for desensitization during welding.
400 Series—Ferritic and Martensitic Chromium Alloys
heat-resistant; poor corrosion resistance; 11% Chromium, 8% Nickel.
cheapest type; used for automobile exhausts; ferritic (iron/chromium only).
martensitic (high-strength iron/chromium). Wear resistant, but less corrosion resistant.
easy to machine due to additional sulfur
"Cutlery Grade" martensitic; similar to the Brearley's original "rustless steel". Also known as "surgical steel". Excellent polishability.
decorative, e.g., for automotive trim; ferritic. Good formability, but with reduced temperature and corrosion resistance.
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. It can be hardened to Rockwell 58 hardness, making it one of the hardest stainless steels. Also known as "razor blade steel". Available in three grades 440A, 440B, 440C (more common) and 440F (free machinable).
500 Series—Heat Resisting Chromium Alloys
600 Series—Martensitics Precipitation Hardening Alloys
most common PH stainless, better known as 17-4; 17% Chromium, 4% Nickel