Classification of stainless steel

Stainless steel is classified based on its microstructure, chemical composition, and properties. The two main classifications of stainless steel are:

Austenitic Stainless Steel: Austenitic stainless steels are the most common type and are characterized by their face-centered cubic (FCC) crystal structure. They contain high levels of chromium (usually around 18% to 20%) and nickel (typically 8% to 10%) as alloying elements, along with smaller amounts of other elements such as manganese, nitrogen, and molybdenum. Austenitic stainless steels are non-magnetic and offer excellent corrosion resistance, high ductility, and good formability. They are widely used in various industries, including food processing, chemical processing, and medical devices. Common grades include 304 (18-8 stainless steel), 316 (marine grade stainless steel), and 321.

Ferritic Stainless Steel: Ferritic stainless steels have a body-centered cubic (BCC) crystal structure and contain higher levels of chromium (usually between 10.5% and 27%) and lower amounts of nickel compared to austenitic stainless steels. They may also contain other alloying elements such as molybdenum, titanium, or aluminum. Ferritic stainless steels are magnetic and offer good corrosion resistance in mildly corrosive environments. They are often used in automotive applications, architectural trim, and appliances. Common grades include 430 and 446.

Additionally, there is a third category:

Martensitic Stainless Steel: Martensitic stainless steels have a body-centered tetragonal (BCT) crystal structure and contain higher levels of carbon (usually between 0.1% and 1.2%) along with chromium (usually between 12% and 18%). They can be hardened by heat treatment, resulting in high strength and hardness properties. Martensitic stainless steels are magnetic and offer good corrosion resistance in some environments. They are commonly used in cutlery, knives, and industrial applications requiring high strength and wear resistance. Common grades include 410, 420, and 440.

These classifications provide a broad understanding of the different types of stainless steel available, each with its own unique properties and applications. Manufacturers may also produce specialized stainless steel alloys tailored to specific requirements, such as increased corrosion resistance, high-temperature strength, or enhanced form ability.