Corrosion Resistance Classification of Stainless Steels

The European standard EN 1993-1-4 defines the corrosion resistance classes of stainless steels to ensure structural integrity in a variety of environments. The standard classifies stainless steels into several classes based on their resistance to atmospheric and aqueous corrosion.

Class 1 (CR Class 1): This class includes stainless steels with limited corrosion resistance and are typically used in indoor applications or in environments with low corrosion risk. For example, ferritic and martensitic stainless steels such as 1.4003 (X2CrNi12) and 1.4016 (X6Cr17).

Class 2 (CR Class 2): This class of steel offers moderate corrosion resistance and is suitable for rural and urban environments with low pollution levels. Common grades include austenitic stainless steels such as 1.4301 (X5CrNi18-10) and 1.4307 (X2CrNi18-9).

Class 3 (CR Class 3): This grade of stainless steel offers high corrosion resistance and is used in more aggressive environments such as industrial atmospheres or coastal areas with moderate chloride exposure. Typical grades are 1.4401 (X5CrNiMo17-12-2) and 1.4404 (X2CrNiMo17-12-2).

Class 4 (CR Class 4): These steels offer very high corrosion resistance and are suitable for use in highly corrosive environments, including marine atmospheres and chloride-rich environments. For example, 1.4432 (X2CrNiMo17-12-3) and 1.4435 (X2CrNiMo18-14-3). Class 5 (CR Class 5): This highest grade includes stainless steels with excellent corrosion resistance and is used in extremely aggressive environments such as seawater exposure or chemical processing plants. Super-austenitic and duplex stainless steels such as 1.4547 (X1CrNiMoCuN20-18-7) and 1.4462 (X2CrNiMoN22-5-3) belong to this category.

Application examples:

Classes 1 and 2: Structural components in indoor environments, low-risk outdoor applications.

Class 3: Urban infrastructure, moderate industrial environments.

Class 4: Coastal infrastructure, industrial applications with moderate chloride exposure.

Class 5: Offshore structures, chemical processing equipment, highly corrosive industrial environments.

In summary, EN 1993-1-4 provides a systematic classification to guide the selection of stainless steels based on their corrosion resistance, ensuring durability and safety in different environmental conditions.