Chuxing Municipal Facilities — Common Classifications of Stainless Steel
August 10, 2026
Usually, ordinary stainless steels are classified into three categories according to their metallographic structures: austenitic stainless steel, ferritic stainless steel and martensitic stainless steel. Based on these three basic metallographic structures, duplex steel, precipitation‑hardening stainless steel and high‑alloy steel with iron content below 50% have been developed to meet specific requirements and purposes.
-
Austenitic Stainless SteelIt is a stainless steel whose matrix is mainly composed of austenite (γ‑phase) with face‑centered cubic crystal structure, non‑magnetic. It is mainly strengthened by cold working (which may bring certain magnetism). It is designated by the American Iron and Steel Institute (AISI) with the 200 and 300 series numbers, e.g. 304.
-
Ferritic Stainless SteelIt is a stainless steel whose matrix is mainly composed of ferrite (α‑phase) with body‑centered cubic crystal structure, magnetic. It generally cannot be hardened by heat treatment, yet it can be slightly strengthened by cold working. It is designated by AISI as 430 and 446.
-
Martensitic Stainless SteelIt is magnetic stainless steel with martensitic matrix (body‑centered cubic or cubic structure), whose mechanical properties can be adjusted by heat treatment. AISI designates it with numbers 410, 420 and 440. Martensite features austenitic structure at high temperature. When cooled down to room temperature at an appropriate rate, the austenitic structure transforms into martensite (namely quenching hardening).
-
Austenite‑Ferrite (Duplex) Stainless SteelIts matrix contains both austenite and ferrite phases, and the minor‑phase matrix content is generally more than 15%. It is magnetic and can be strengthened by cold working. Grade 329 is a typical duplex stainless steel. Compared with austenitic stainless steel, duplex stainless steel delivers higher strength, improved resistance to intergranular corrosion, chloride stress corrosion and pitting corrosion.
-
Precipitation‑Hardening Stainless SteelIts matrix is austenite or martensite, and it can be hardened by precipitation‑hardening treatment. AISI marks it with the 600‑series numbers, for example 630 (i.e. 17‑4PH).
Generally speaking, except for composite materials, austenitic stainless steel has good corrosion resistance. Ferritic stainless steel can be adopted in low‑corrosive environments. For mildly corrosive environments where high strength or high hardness is required, martensitic stainless steel and precipitation‑hardening stainless steel are recommended.
