Austenitic, Ferritic, Martensitic, Duplex, and Precipitation Hardening

Chromium (Cr): 16-26%

Nickel (Ni): 6-22%

Carbon (C): <0.08% in most grades (some low-carbon versions, like 304L, have <0.03% carbon)

Molybdenum (Mo): 2-3% in some grades (e.g., 316) for enhanced corrosion resistance.

Notes: High chromium and nickel content improve corrosion resistance and flexibility, making austenitic steels non-magnetic and ideal for chemical processing and food-grade equipment.

Austenitic stainless steel is the most common type, comprising over 70% of global stainless steel production. It is high in chromium and nickel, giving it exceptional corrosion resistance and ductility. Due to its non-magnetic nature, austenitic stainless steel is used in various applications, such as kitchenware, chemical processing, and food and beverage equipment.

Key Grades: 304. 316

Chromium (Cr): 10.5-18%

Nickel (Ni): Typically low (≤1%)

Carbon (C): ≤0.12%

Notes: Lower nickel content makes ferritic steels more cost-effective. With high chromium but low carbon, ferritic steels are moderately corrosion-resistant, making them suitable for indoor applications and decorative features.

Ferritic stainless steels are magnetic, with a high chromium content but low carbon and nickel. These steels offer good resistance to corrosion and oxidation, though they are generally less ductile than austenitic stainless steels. Ferritic stainless steels are often used in automotive exhaust systems and decorative applications due to their lower cost and reliable performance in non-structural parts.

Key Grades: 430. 409

Chromium (Cr): 12-18%

Nickel (Ni): Very low or none

Carbon (C): 0.1-1.2% (higher than other types for increased hardness)

Notes: High carbon content makes martensitic steels hardenable through heat treatment, providing excellent wear resistance. However, they are less corrosion-resistant than austenitic grades, suitable for cutlery, surgical tools, and structural components requiring high strength.

Martensitic stainless steel is known for its hardness and strength, thanks to a higher carbon content and a martensitic crystalline structure. It is magnetic and heat-treatable, making it ideal for applications that require high strength and wear resistance. Martensitic steels are commonly used in cutlery, surgical instruments, and turbine blades.

Key Grades: 410. 420

Chromium (Cr): 19-32%

Nickel (Ni): 1-7%

Molybdenum (Mo): 0.3-4% in some grades, providing enhanced resistance to pitting and crevice corrosion

Notes: The balanced structure of ferritic and austenitic phases gives duplex stainless steel higher strength and resistance to chloride stress corrosion cracking, making it ideal for marine and chemical environments.

Duplex stainless steels combine the benefits of both austenitic and ferritic steels, offering high strength and superior corrosion resistance, especially in chloride environments. Duplex grades are frequently used in the oil, gas, and chemical industries where their resistance to stress corrosion cracking and high strength are highly valued.

Key Grades: 2205. 2507

Chromium (Cr): 15-17%

Nickel (Ni): 3-7%

Copper (Cu): 3-5%, sometimes with small additions of aluminum and titanium to form hardening precipitates

Notes: The addition of copper and other elements allows these steels to be hardened through a precipitation process, providing an outstanding strength-to-weight ratio. Common in aerospace and high-strength applications requiring both durability and corrosion resistance.

Precipitation Hardening (PH) stainless steels are known for their incredible strength-to-weight ratio, achieved through a unique hardening process. They are suitable for high-stress applications such as aerospace, defense, and other heavy-duty environments where both strength and corrosion resistance are required.

Key Grades: 17-4 PH