The grade of steel is referred to as the steel number, which is the name given to each specific steel product, and is a common language for people to understand steel. China&'s steel number representation method, according to the national standard Steel Product Grade Representation Method(gb221-79), is represented by a combination of Chinese pinyin letters, chemical element symbols and arabic numerals.
1. Carbon structural steel
The steel number of carbon structural steel is prefixed with "q";, which represents the yield point of the steel, and the following number represents the yield point value in mpa. For example, q235 represents a carbon structural steel with a yield point (σs) of 235 mpa.
If necessary, the symbol indicating the quality grade and deoxidation method can be marked behind the steel number. The quality grade symbols are a, b, c, and d, respectively. Symbol of deoxidation method: f means boiling steel; b means semi-killed steel; z means killed steel; tz means special killed steel, and the symbol for killed steel can be omitted, that is, both z and tz can be omitted. For example, q235-af means A-grade boiling steel.
Special purpose carbon steel, such as bridge steel, marine steel, etc., basically adopts the representation method of carbon structural steel, but the letter indicating the purpose is added at the end of the steel number.
2. Alloy Structural Steel
The two digits at the beginning of the steel number indicate the carbon content of the steel, expressed in ten thousandths of the average carbon content, such as 40cr.
The main alloying elements in steel, except for individual microalloying elements, are generally expressed in percent. When the average alloy content is less than 1.5%, only the element symbol is generally indicated in the steel grade, but the content is not indicated. However, in special cases, if it is easy to cause confusion, the number "1"; can also be marked after the element symbol, such as the steel number 12crmov and 12cr1mov, the former has a chromium content of 0.4-0.6%, the latter is 0.9-1.2%, and the rest of the components are all the same. When the average content of alloying elements is ≥1.5%, ≥2.5%, ≥3.5%, the content should be indicated after the element symbol, which can be expressed as 2, 3, 4 etc., for example 18cr2ni4wa.
Alloying elements such as vanadium v, titanium ti, aluminum al, boron b, and rare earth re in steel are all microalloying elements. Although the content is very low, they should still be marked in the steel grade, for example, in 20mnvb steel, vanadium is 0.07-0.12% and boron is 0.001-0.005%.
High quality steel should add a at the end of the steel number to distinguish it from general high-quality steel.
For special purpose alloy structural steel, the steel number is crowned (or suffixed) with a symbol representing the purpose of the steel. For example, the special 30crmnsi steel for riveting screws, the steel number is expressed as ml30crmnsi.
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