Common classification of stainless steel

Time: 2018-07-14
Stainless steel is usually classified according to metallographic structure:
According to the metallurgical structure, ordinary stainless steel is classified into three types: austenitic stainless steel, ferritic stainless steel, and martensitic stainless steel. Based on these three types of basic metallurgical structures, dual-phase steels, precipitation-hardening stainless steels, and high-alloy steels containing less than 50% iron were derived for specific needs and purposes.
1. Austenitic stainless steel.
The matrix is mainly composed of an austenite (CY phase) with face-centered cubic crystal structure, is non-magnetic, and is mainly strengthened by cold working (and may result in a certain magnetic properties). The American Iron and Steel Institute is marked with 200 and 300 series numbers, such as 304.
2. Ferritic stainless steel.
The matrix is mainly composed of a ferrite structure with body-centered cubic crystal structure (a phase), which is magnetic and can not generally be hardened by heat treatment, but can be slightly strengthened by cold working. The American Iron and Steel Institute is marked with 430 and 446.
3. Martensitic stainless steel.
The matrix is a martensite (body-centered cubic or cubic), magnetic, stainless steel that can be adjusted by heat treatment to adjust its mechanical properties. The American Iron and Steel Institute is marked with numbers 410, 420, and 440. Martensite has an austenite structure at a high temperature, and when cooled to room temperature at an appropriate rate, the austenite structure can be transformed into martensite (ie, hardened).
4. Austenitic-ferritic (dual phase) stainless steel.
The matrix has both austenite and ferrite two-phase structure, in which the content of less phase matrix is generally greater than 15%, there is magnetic, stainless steel that can be strengthened by cold working, and 329 is a typical duplex stainless steel. Compared with austenitic stainless steels, duplex steels have high strength, resistance to intergranular corrosion, chloride stress corrosion resistance, and pitting corrosion.
5. Precipitation hardening stainless steel.
The substrate is austenitic or martensitic and can be hardened by precipitation hardening stainless steel. The American Iron and Steel Institute is marked with 600 series numbers, such as 630, that is, 17-4PH.
In general, the corrosion resistance of austenitic stainless steels is excellent except for alloys. Ferritic stainless steels can be used in environments with low corrosiveness. In mildly corrosive environments, materials are required to be high. For strength or high hardness, martensitic stainless steel and precipitation hardened stainless steel can be used.