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Common classification of stainless steel

     Stainless steel is an abbreviation for stainless acid-resistant steel. It is resistant to air, steam, water and other weakly corrosive media or stainless steel. It is called stainless steel; Corrosion resistant steels (acid, alkali, salt, and other chemical etching) are called acid-resistant steels.

     Stainless steel refers to steels resistant to weak corrosive media such as air, steam, and water, and chemically etched media such as acids, alkalis, and salts, and also called stainless acid-resistant steels.In practical applications, steels that are resistant to weak corrosive media are often referred to as stainless steels, and steels that are resistant to chemical corrosion are known as acid-resistant steels.Because of the difference in chemical composition between the two, the former is not necessarily resistant to chemical media corrosion, while the latter is generally non-rust.The corrosion resistance of stainless steel depends on the alloying elements contained in the steel.

Common classification of stainless steel
 

Common categories:


Usually divided into metallographic organizations:


     Generally, 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 a face-centered cubic crystal structure, is non-magnetic, and is mainly strengthened by cold working (and may cause some magnetic properties) in stainless steel. 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, dual-phase 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 mild corrosive environments, materials are required to be high. For strength or high hardness, martensitic stainless steel and precipitation hardened stainless steel can be used.

Common classification of stainless steel

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