Stainless steel is primarily classified into the 200, 300, and 400 series based on its composition and microstructure. The key differences lie in nickel content, metallurgical structure, magnetic properties, corrosion resistance, and cost.

200 Series (Manganese-Substituted, Low-Nickel Austenitic)

Composition: Uses manganese and nitrogen to partially replace nickel. Nickel content is only about 1%–5%, with chromium at approximately 13%–17%.

Characteristics: Non-magnetic (or weakly magnetic); its appearance is extremely difficult to distinguish from 304 stainless steel. Corrosion resistance is moderate; it is not resistant to acids or chlorides and is prone to rusting. Due to its higher manganese content, there may be a risk of manganese leaching with prolonged contact with acidic foods.

Cost: Least expensive; price is less affected by fluctuations in nickel prices.

Applications: Indoor decoration, furniture, structural components in dry environments.

Common Grades: 201, 202.

300 Series (High-Chromium, High-Nickel Austenitic)

Composition: Contains 8%–10% nickel and approximately 18% chromium, offering the best overall performance.

Characteristics: Non-magnetic in the annealed state (cold working may induce slight magnetism, which is normal). Excellent corrosion resistance, suitable for prolonged contact with water, weak acids, and weak alkalis. Good weldability and formability.

Cost: Most expensive; price is highly sensitive to fluctuations in nickel prices.

Applications: Kitchenware, food processing equipment, medical devices, outdoor architecture, chemical equipment, and other applications with high anti-rust requirements.

Common Grades: 304 (general-purpose), 316 (contains molybdenum, resistant to seawater/salt spray).

400 Series (Ferritic/Martensitic, Essentially Nickel-Free)

Composition: Primarily composed of chromium (11%–18%), with almost no nickel.

Characteristics: Magnetic; often referred to as "stainless iron." Moderate corrosion resistance (inferior to the 300 series but superior to carbon steel). Ferritic grades offer high strength, heat resistance, and good thermal conductivity. Martensitic grades can be hardened by heat treatment (quenching), providing excellent wear resistance.

Cost: Low to moderate; price is relatively stable.

Applications: Ferritic (e.g., 430) used for appliance exteriors, heat-resistant components, and decorative applications; Martensitic (e.g., 410, 420) used for cutlery, bearings, and mechanical parts.