I. Overview of steel grade representation in China
The abbreviation for the designation of steel is “steel grade”, representing the name given to each specific steel product and serving as a common language for understanding steel.
The method of representing steel grades in China, as stipulated in the national standard “Method for Representing Grades of Steel Products” (GB221-79), employs a combination of Pinyin letters, chemical element symbols and Arabic numerals. Specifically:
1. In steel type, chemical elements are represented using international chemical symbols such as Si, Mn, Cr, etc. Mixed rare earth elements are denoted as “RE” (or “Xt”).
2. Product names, uses, casting and casting methods, etc., are generally represented by abbreviated Pinyin letters, as shown in the table.
3. The content of the main chemical elements (%) in steel is represented in Arabic numerals.
II. Classification of steel numbering systems in China
1. Carbon Structural Steel
I. Composed of Q+ number + quality grade symbol + deoxygenation method symbol. The steel number is prefixed with “Q”, denoting the yield strength of the steel, followed by a number representing the yield strength value in MPa. For example, Q235 denotes a carbon structural steel with a yield point (σs) of 235 MPa.
ii. If necessary, symbols indicating the grade of quality and the method of deoxygenation can be attached to the steel number. The quality grade symbols are A, B, C and D, respectively.
The symbols for the deoxygenation method are: F for boiling steel; B for semi-finished steel; Z for dead steel; TZ for special steels. Dead steel requires no symbol, meaning neither Z nor TZ need to be marked. For example, Q235-AF represents grade A boiling steel.
iii. Carbon steels for specific purposes, such as bridge steel or marine steel, are usually displayed using the carbon structural steel notation, but a letter indicating the intended use is added to the end of the steel number.
2. High quality carbon structural steel
I. The first two numbers of the steel number indicate the carbon content of the steel, expressed as a percentage of the average carbon content. For example, steel with an average carbon content of 0.45% has the steel number “45”. It is not a sequential number, so it should not be read as “steel number 45”.
ii. High-quality carbon structural steels with high manganese content must feature the element manganese, such as 50Mn.
iii. Boiling steel, semi-finished steel and high-quality carbon structural steel for specific purposes must be specially marked at the end of the steel number. For example, the steel number for semi-finished steel with an average carbon content of 0.1% is 10b.
3. Tool carbon steel
① The steel type is prefixed with “T” to differentiate it from other steel types.
② The number in the steel grade indicates the carbon content, expressed as a percentage 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 added at the end of the steel grade, such as “T8Mn”.
④ High-quality premium carbon tool steel with lower phosphorus and sulfur content than standard premium carbon tool steel is indicated by adding an “A” at the end of the steel grade, for example, “T8MnA” .
4. Free cutting steel
① The steel grade is prefixed with “Y”, distinguishing it from premium carbon structural steel.
② The number after the letter “Y” indicates the carbon content, represented as a percentage of the average carbon content. For example, free cutting steel with an average carbon content of 0.3% has the steel grade “Y30”.
③ For those with higher manganese content, “Mn” is added to the steel grade, such as “Y40Mn”.
5. Alloy structural steel
① The first two digits of the steel type indicate the carbon content, represented as a percentage of the average carbon content, such as 40Cr.
② The primary alloying elements in steel are generally expressed as a percentage, excluding certain microalloying elements. When the average alloy content is <1.5%, only the element symbol is normally indicated on the steel type, without specifying the content.
However, in cases prone to confusion, the element symbol may be followed by the number “1”, such as “12CrMoV” and “12Cr1MoV”. The former has a chromium content of 0.4-0.6%, while the latter has 0.9-1.2%, all other components being identical.
When the average alloy content is ≥1.5%, ≥2.5%, ≥3.5%, etc., the content should be indicated after the element symbol, which can be correspondingly represented as 2, 3, 4 , etc., for example, 18Cr2Ni4WA.
③ Steel alloying elements such as vanadium (V), titanium (Ti), aluminum (Al), boron (B) and rare earth (RE) are all microalloying elements. Despite the low content, they must still be indicated in the steel class. For example, in 20MnVB steel, vanadium accounts for 0.07-0.12%, and boron accounts for 0.001-0.005%.
④ High-quality premium steel must have an “A” attached to the steel type to distinguish it from standard premium steel.
⑤ For specialized structural steel alloys, the steel grade is prefixed (or suffixed) with a symbol that represents its specific use. For example, the 30CrMnSi steel grade, used specifically for rivet bolts, is called ML30CrMnSi.
6. Low-alloy, high-strength steels
① The method of representing the type of steel essentially aligns with that of alloyed structural steels.
② For professional grade high strength low alloy steels, the intended application should be indicated at the end of the steel grade. For example, 16Mn steel specialized for bridge construction is designated as “16Mnq”; for automobile long beams it is “16MnL” and for pressure vessels it is “16MnR”.
7. Spring steels
Spring steels can be categorized into carbon spring steels and alloy spring steels based on their chemical composition. The method of representing steel type is generally the same as that of high-quality carbon structural steels for the former and alloy structural steels for the latter.
8. Bearing steels
① The steel type is prefixed with the letter “G”, meaning it is a bearing steel.
② For steels with high carbon and chromium content, the carbon content is not specified in the steel type; Chromium content is represented in parts per thousand. For example, GCr15. The method of representing steel type for carburizing bearing steels is fundamentally the same as for alloyed structural steels.
9. Alloy tool steels and high speed tool steels
① For tool alloy steels, when the average carbon content is ≥1.0%, it is not specified; when the average carbon content is <1.0%, it is represented in parts per thousand. For example, Cr12, CrWMn, 9SiCr, 3Cr2W8V.
② The method of representing the content of alloy elements in steel is generally the same as that of alloy structural steels. However, for tool steel alloys with lower chromium content, the chromium content is represented in parts per thousand and is prefixed with “0” to distinguish it from the typical representation in percentage terms. For example, Cr06.
③ For high-speed tool steels, the steel grade generally does not specify the carbon content, only the average percentage content of various alloying elements. For example, a tungsten series high-speed steel is called “W18Cr4V”. Steel grades prefixed with the letter “C” indicate a higher carbon content than steel grades without the “C” prefix.
10. Stainless steel and heat resistant steel
① The carbon content in the steel grade is expressed in thousandths. For example, the average carbon content in “2Cr13” steel is 0.2%. If the carbon content in the steel is ≤0.03% or ≤0.08%, it will be indicated by “00” and “0” respectively before the steel type, as in 00Cr17Ni14Mo2 and 0Cr18Ni9.
② Primary alloy elements in steel are represented in percentages, while titanium, niobium, zirconium, nitrogen, etc., are marked according to the method of representing microalloy elements in said structural steel alloy.
11. Steel Welding Rod
Its steel type is prefixed with the letter “H” to distinguish it from other types of steel. For example, “H2Cr13” stainless steel welding wire can be differentiated from “2Cr13” stainless steel.
12. Electrical Silicon Steel
① The steel grade consists of letters and numbers. The prefix “DR” indicates hot-rolled silicon steel for electrical use, “DW” means cold-rolled non-oriented silicon steel, and “DQ” indicates cold-rolled silicon steel with oriented grains.
② The numbers after the letters represent 100 times the value of iron loss (W/kg).
③ If the steel class ends with the letter “G”, it means that it has been tested at high frequency; If it does not end with “G”, it means it was tested at a frequency of 50 Hz.
For example, steel grade DW470 indicates that the maximum value of iron loss per unit weight of the non-oriented cold-rolled silicon steel product is 4.7 W/kg at a frequency of 50 Hz.
13. Electric Pure Iron
① Your note is made up of the letters “DT” and numbers. “DT” stands for Pure Electric Iron and the numbers indicate the sequential number of different grades, for example, DT3.
② Letters added after numbers indicate electromagnetic properties: A–Advanced, E–Superior, C–Supreme, for example, DT8A.
