1、Overview of methods for denoting steel codes in China
   
The brand code of steel is referred to as steel code, which is the name for every specific steel product, and acts as a common language for people to get information of steel. According to the regulations in the national standard “Method for denoting the brand code of steel products” （GB221-79）, letters of Han-Yu Pin-Yin, chemical element symbols, and Arabic numbers should be combined together to denote every specific steel product, i.e.
 
①The chemical elements in the steel code is denoted by international chemical symbols, e.g., Si, Mn, Cr, etc.. Mixture of rare earth elements are denoted by “RE”（or“Xt”）.
②Product name, usage, method of smelting and casting are usually denoted by the first letter of Han-Yu Pin-Yin, as shown in the table.
③The content （%）of main chemical elements in steel are denoted by Arabic numbers.

Table:Letters used in GB standard steel codes and its meaning.

2、Illustration of classification of methods for denoting steel codes in China

1． Carbon structural steel

① Composed by Q + numbers + quality grade symbol + deoxidization method symbol. “Q” at the beginning of its steel code stands for the yield point of steel, the numbers afterwards stand for the value of the yield point, with a Unit of MPa, e.g., Q235 stands for a carbon structural steel with yield point （σs） of 235 MPa.
②If necessary, label out symbols for quality grade and deoxidization method at the end of steel codes.Symbols for quality grades are A, B, C, D. Symbols for deoxidization methods are: F stands for rimmed steel；b stands for semi killed steel：Z stands for killed steel; TZ stands for special killed steel. Killed steel can go without deoxidization symbols, i.e., Z and TZ are not necessarily labeled, e.g., Q235-AF stands for grad-A rimmed steel.
③ special carbon steel, e.g., bridge steel, and ship steel, etc., are basically using the denoting method of carbon structural steel; however, the letter for usage should be added at the end of the steel code.

2． Quality carbon structural steel
①The first two numbers at the beginning of the steel code stands for the carbon content of the steel, expressed by 10000 times the average carbon content, e.g., for steel with an average carbon content of 0.45%，the steel code would be “45”，which is not a number of order, therefore, do not read as number 45 steel.
② For quality carbon structural steel with high Mn content, label Mn out, e.g., 50Mn。
③ Rimmed steel, semi killed steel, and quality carbon structural steel for special use should be labeled out at the end of the steel numbers, e.g., for semi-killed steel with an average carbon content of 0.1%，its steel number is 10b.

3．Carbon tool steel
① Write a “T” at the beginning of the steel code to differentiate it from other type of steel.
② The numbers in the code stand for carbon content，expressed by 1000 times the average carbon content, e.g., “T8” stands for an average carbon content of 0.8%。
③ For steel with high Mn content, write “Mn” at the end of the code，e.g., “T8Mn”。
④The contents of phosphorus and sulfur in super quality carbon tool steel are lower than those in commercial quality carbon tool steel, therefore, write an “A” at the end of the code in order to mark the difference, e.g., “T8MnA”.

4． Free-machining steel
①Write a “Y” at the beginning of the code, to differentiate it from quality carbon structural steel.
② The numbers after the letter “Y” stand forcarbon content, expressed by 10000 times the average carbon content, e.g., for free-machining steel with an average carbon content of 0.3%, its code is “Y30”.
③If Mn content is high, also write “Mn” at the end of the code, e.g., “Y40Mn”.

5．Alloy structural steel
① The two numbers at the beginning of the steel code stand for the carbon content in steel, expressed by 10000 times the average carbon content, e.g. 40Cr.
②Main alloy elements in steel, except for a few micro alloy elements, are usually denoted by the percentages. If the average alloy content is ＜1.5%, usually only write the symbol of element in the code, without writing the content symbol. However, under special circumstances where it is easy to get confused, the number “1” can also be written after the element symbol, e.g., for codes “12CrMoV” and “12Cr1MoV”, Cr content is 0.4-0.6% for the former, and 0.9-1.2% for the latter, with identical contents of other elements. If the average content of several alloy elements ≥1.5%, ≥2.5%, and ≥3.5%, etc., write the symbols of contents immediately after the element symbols as 2, 3, and 4, etc., e.g., 18Cr2Ni4WA.
③Some alloy elements in steel such as vanadium (V), Titanium(Ti), Aluminum (Al), boron(B), and rare earth elements (RE), etс., all belong to micro alloy elements,which should be labeled in the code, although their contents are low, e.g., for steel 20MnVB, V content is 0.07-0.12%, and B content is 0.001-0.005%.
④Write an “A” at the end of the code for super quality steel, in order to differentiate it from commercial quality steel.
⑤For special alloy structural steel, writethe symbol for the usage at the beginning (or end) of the code, e.g., steel 30CrMnSi dedicated for rivet steel, is denoted by ML30CrMnSi。

6．Low alloy content high-strength steel
①The denoting method is basically the same as that of alloy structural steel.
②For low alloy content high-strength steel for special use, write the symbol of usage at the end of the code, e.g., steel 16Mn dedicated for bridge is denoted by “16Mnq”, dedicated for automobile beam is denoted by “16MnL”, dedicated for pressure container is denoted by “16MnR”.
 
7．Spring steel
Spring steel can be classified according to the chemical compositions into carbon spring steel and alloy spring steel, the denoting method of the former is basically the same as that of quality carbon structural steel, of the latter is basically the same as that of alloy structural steel.
 
8．Rolling bearing steel
① “G” at the beginning of the code stands for rolling bearing steel.
② For high carbon content chromium bearing steel, carbon content does not have to be labeled in the code, while the symbol of Cr content is expressed by 1000 times the actual Cr content, e.g., GCr15. The denoting method of cementite bearing steel is basically the same as that of the alloy structural steel.
 
9．Alloy tool steel and high-speed tool steel
 ① If the average carbon content of alloy tool steel is ≥1.0%, do not write carbon content symbol；if the average carbon content is ＜1.0%, denoted it by 1000 times the average content, e.g. Cr12, CrWMn, 9SiCr, 3Cr2W8V.
② The denoting method of alloy content in steel is basically the same as that of alloy structural steel. However, for alloy tool steel with low Cr content, the symbol of Cr content is expressed by 1000 times the average Cr content, and add “0” before the Cr content symbol, in order to differentiate it from normal element content symbol which is expressed by 100 times the content, e.g. Cr06.
③ The carbon content of high speed tool steel is usually not labeled in the code. Only label the symbol of content expressed by 100 times the average contents of different kinds of alloy element, e.g., the code of Tungsten high-speed steel is “W18Cr4V”. If the first letter of the code is “C”, it means that the carbon content is higher than that in normal steels of codes without “C” at the beginning.
 
10． Stainless steel and heat resistant steel
 ① The carbon content symbol in the code is expressed by 1000 times the average content, e.g., “2Cr13”steel has an average carbon content of 0.2%; if steel has a carbon content ≤0.03% or ≤0.08%, write “00” or “0” at the beginning of the code to denote it, e.g., 00Cr17Ni14Mo2, and 0Cr18 Ni9, etc.
 ② The main alloy element contents symbols in the code are expressed by 100 times the average contents, while for the denoting method of Ti, Nb, Zr, and N, etc., use the denoting method of the contents of micro alloy elements in alloy structural steel.
 
11． Welding bar steel
Write “H” at the beginning of the code, in order to differentiate it from other steels, e.g., stainless steel welding wire is denoted by “H2Cr13”，to differentiate it from stainless steel “2Cr13”.
 
12． Silicon steel for electrical use
①The code is composed of letters and numbers. The DR at the beginning of the code stands for hot rolled silicon steel for electrical use, DW stands for cold rolled non-oriented silicon steel for electrical use, and DQ stands for cold rolled oriented silicon steel for electrical use.
② The numbers after the letters stand for the iron loss value（W/kg）multiplied by 100.
③“G” at the end of the code stands for that it is tested under high frequency; if there is no “G”, that means it is tested under the frequency of 50 Hz.
e.g., code DW470 stands for cold rolled non-oriented silicon steel product for electrical use, and the maximum unit weight iron loss is 4.7W/kg tested at a frequency of 50 Hz。
 
13．Pure iron for electrical use
① Its code is composed of the letters “DT” and numbers, where “DT” stands for pure iron for electrical use, and the numbers stands for the order of different brand codes, e.g. DT3.
② Letter after the numbers stands for the electromagnetic properties: A—— good quality, E——special quality, C——super quality, e.g. DT8A.

3、Comparison between some new codes and old codes

1、 Comparison between some new codes and old codes for carbon structural steel.
GB700-88 is the new standard which is compiled in accordance with “structural steel ” in the international standard ISO630, while GB700-79 is the old standard which is compiled in accordance with the former USSR standard IOCT380, therefore, some of the denoting methods are different, and some of the technical requirements for steel with certain codes are also different. The comparison between codes of the new standard and the old standard are as follows:

2、Use GB/T1591-94 to replace 1591-88 for low alloy steels. Comparison between some of the new codes and the old codes are as follows: