How Many Types of Stainless Steel Are There?

Materials Knowledge: Stainless Steel Classification (1)
How Many Types of Stainless Steel Are There?

Stainless steel is short for stainless and acid-resistant steel. Steel that resists corrosion from weak media such as air, steam, and water is called stainless steel, while steel that resists corrosion from chemical media (such as acids, alkalis, and salts) is called acid-resistant steel.

In practice, steel resistant to weak corrosive media is often referred to as stainless steel, while steel resistant to chemical media is called acid-resistant steel. Due to differences in their chemical composition, the former is not necessarily resistant to chemical media, while the latter typically has stainless properties. The corrosion resistance of stainless steel depends on the alloying elements it contains.

Classification by Composition:

Stainless steels can be categorized by composition into:

Cr Series (400 Series): Chromium stainless steels

Cr-Ni Series (300 Series): Chromium-nickel stainless steels

Cr-Mn-Ni Series (200 Series): Chromium-manganese-nitrogen stainless steels

Heat-resistant Chromium Alloy Steels (500 Series)

Precipitation Hardening Series (600 Series)

200 Series: Chromium-Manganese-Nickel

201, 202: Nickel is partly replaced by manganese, resulting in lower corrosion resistance. Widely used in China as a cost-effective substitute for the 300 series.

300 Series: Chromium-Nickel Austenitic Stainless Steel

301: Good ductility, suitable for forming. Work hardens rapidly. Good weldability. Better wear and fatigue strength than 304.

302: Similar corrosion resistance to 304 but higher strength due to higher carbon content.

303: Improved machinability compared to 304 by adding small amounts of sulfur and phosphorus.

304: Most common type; also known as 18/8 stainless steel (18% Cr, 8% Ni). Used in containers, cutlery, furniture, railings, and medical devices. Non-magnetic and cannot be hardened by heat treatment. Chinese designation: 0Cr18Ni9.

304L: Low-carbon version of 304 with better corrosion resistance and improved weldability, but lower mechanical strength.

304N: A nitrogen-enhanced version of 304 for increased strength.

309: Better heat resistance than 304, up to 980°C.

309S: Higher Cr and Ni content, offering excellent heat and oxidation resistance. Applications: heat exchangers, boiler components, jet engines.

310: Excellent high-temperature oxidation resistance. Maximum operating temperature: 1200°C.

316: Second most widely used stainless steel after 304. Common in food processing, watches, pharmaceuticals, and surgical instruments. The addition of molybdenum enhances corrosion resistance, especially against chlorides. Known as "marine grade" stainless steel. SS316 is also used in nuclear fuel reprocessing. The 18/10 grade typically meets this standard.

316L: Low-carbon version of 316 for improved corrosion resistance and weldability. Used in chemical processing equipment, nuclear generators, and cryogenic storage.

321: Similar to 304 but with added titanium to reduce weld corrosion sensitivity.

347: Contains niobium for stabilization; suitable for welding and aerospace/chemical equipment.

400 Series: Ferritic and Martensitic Stainless Steels

Contains no manganese and in some cases can be a substitute for 304.

408: Good heat resistance but poor corrosion resistance. Contains 11% Cr and 8% Ni.

409: The cheapest grade (in the UK/US), mainly used in automotive exhaust systems. Ferritic stainless steel (chromium steel).

410: Martensitic (high-strength chromium steel) with good wear resistance but lower corrosion resistance.

416: Sulfur added to improve machinability.

420: "Cutlery-grade" martensitic steel, similar to early high-chromium stainless steels. Used in surgical blades and can be polished to a mirror finish.

430: Ferritic stainless steel for decorative applications (e.g., automotive trim). Good formability but lower heat and corrosion resistance.

440: High-strength cutlery steel with higher carbon content. With proper heat treatment, it can achieve a hardness of up to 58 HRC—among the hardest stainless steels. Commonly used in razor blades. Main types: 440A, 440B, 440C, and 440F (free-machining version).

500 Series: Heat-Resistant Chromium Alloy Steels

600 Series: Martensitic Precipitation-Hardening Stainless Steels