Special steel grade

At present, there are nearly 2,000 special steel grades and about 50,000 varieties in the world. In addition to a wide variety of special steels, the specifications also show different characteristics from ordinary steel. In addition to plates, tubes, wires, belts, rods and profiles, there are composites, surface alloys, surface treatments, precision forgings, precision castings, powder metallurgy products, etc.

I. Overview of China's steel number representation method

The steel grade 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 is expressed in accordance with the national standard "Steel Product Brand Representation Method" (GB221-79), using a combination of Chinese Pinyin letters, chemical element symbols and Arabic numerals. Namely: 1 The chemical elements in the steel number are represented by international chemical symbols, such as Si, Mn, Cr, etc. The mixed rare earth element is represented by "RE" (or "Xt"). 2 Product name, use, smelting and pouring methods, etc., generally expressed in abbreviated letters of Chinese Pinyin. The content of major chemical elements (%) in steel 3 is expressed in Arabic numerals.

Second, the classification description of China's steel number representation method

Carbon structural steel

1 consists of Q + number + quality level symbol + deoxygenation method symbol. Its steel number is "Q", which represents the yield point of the steel, and the latter number represents the value of the yield point. The unit is MPa. For example, Q235 represents a carbon structural steel with a yield point (σs) of 235 MPa.

2 If necessary, the symbol of the quality grade and deoxidation method can be marked after the steel number. The quality level symbols are A, B, C, and D, respectively. Deoxidation method symbol: F indicates boiling steel; b indicates semi-killed steel: Z indicates killed steel; TZ indicates special killed steel, and killed steel may not be marked, that is, Z and TZ may not be marked. For example, Q235-AF represents Class A boiling steel.

3 Special-purpose carbon steels, such as bridge steel and marine steel, basically use the expression method of carbon structural steel, but the letters indicating the use are added at the end of the steel number.

2. High quality carbon structural steel

The two digits at the beginning of the steel number indicate the carbon content of the steel, expressed as a few tenths of the average carbon content. For example, steel with an average carbon content of 0.45%, the steel number is “45”, which is not a sequence number, so it cannot be read as 45 steel.

2 High-quality carbon structural steel with high manganese content should be marked with manganese, such as 50Mn.

3Boiling steel, semi-killed steel and special-purpose high-quality carbon structural steel shall be specially marked at the end of the steel number, for example, semi-killed steel with an average carbon content of 0.1%, and its steel number is 10b.

3. Carbon tool steel

1 steel is crowned with “T” to avoid mixing with other steels.

The number in the 2 steel number indicates the carbon content, expressed as a few thousandth of the average carbon content. For example, "T8" means an average carbon content of 0.8%.

3 For those with higher manganese content, “Mn” is marked at the end of the steel number, for example “T8Mn”.

4 The high-quality carbon tool steel has lower phosphorus and sulfur content than ordinary high-quality carbon tool steel. The letter “A” is added at the end of the steel number to distinguish it, for example “T8MnA”.

4. Free cutting steel

1 steel is crowned with "Y" to distinguish it from high quality carbon structural steel.

The number after the 2 letter "Y" indicates the carbon content, expressed as a few tenths of the average carbon content, for example, a free-cutting steel having an average carbon content of 0.3%, and its steel number is "Y30".

3 Those with higher manganese content are also marked with "Mn" after the steel number, such as "Y40Mn".

5. Alloy structural steel

The two digits at the beginning of the steel number indicate the carbon content of the steel, expressed as a few ten thousandths of the average carbon content, such as 40Cr.

2 The main alloying elements in steel, except for individual microalloying elements, are generally expressed in percent. When the average alloy content is <1.5%, the steel symbol is generally only marked with the symbol of the element, and the content is not indicated, but in the special case, it is easy to cause confusion. The element symbol can also be marked with the number "1", for example, the steel number. "12CrMoV" and "12Cr1MoV", the former has a chromium content of 0.4-0.6%, the latter has a 0.9-1.2%, and the remaining 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.

The 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 be marked in the steel number. For example, in 20MnVB steel. The vanadium is 0.07-0.12% and the boron is 0.001-0.005%.

4 high-quality steel should be added "A" at the end of the steel number to distinguish it from ordinary high-quality steel.

5 Special purpose alloy structural steel, steel crown with (or suffix) represents the symbol of the use of the steel. For example, 30CrMnSi steel for rivet screw, steel grade is expressed as ML30CrMnSi.