Techniques for indicating steel number in my country

1. Overview of the representation method of steel grades in my country

The grade of steel, referred to as steel grade, is the name given to each specific steel product and is a common language for people to understand steel. my country’s steel grade expression method is based on national standards

“Steel Product Grade Representation Method” (GB221-79) stipulates that it should be represented by a combination of Chinese pinyin letters, chemical element symbols and Arabic numerals. Right now:

①The chemical elements in the steel grade are represented by international chemical symbols, such as Si, Mn, Cr…etc. Mixed rare earth elements are represented by “RE” (or “Xt”).

②The product name, usage, smelting and pouring methods, etc. are generally represented by the abbreviated letters of Chinese Pinyin.

③The content (%) of the main chemical elements in steel is expressed by Arabic numerals.

d2. Classification explanation of steel grade expression methods in my country

1. Carbon structural steel

①It consists of Q+number+quality grade symbol+deoxidation method symbol. Its steel number is prefixed with “Q”, which represents the yield point of the steel. 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.

② If necessary, symbols indicating the quality grade and deoxidation method can be marked after the steel number. The quality grade symbols are A, B, C, and D respectively. Deoxidation method symbols: F represents boiling steel; b represents semi-killed steel; Z represents killed steel; TZ represents special killed steel. Killed custom stainless steel decorative corner brackets may not be marked with symbols, that is, both Z and TZ may be unmarked. For example, Q235-AF represents Grade A boiling steel.

③Special-purpose carbon steel, such as bridge steel, marine steel, etc., basically uses the representation method of carbon structural steel, but a letter indicating the purpose is appended to the end of the steel number.

2. High quality carbon structural steel

①The 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. For example, for steel with an average carbon content of 0.45%, the steel number is “45”. It is not a sequential number, so it cannot be read as 45 gauge steel.

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

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

3. carbon tool steel

①The steel number is marked with “T” to avoid confusion with other steel types.

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

③ For those with higher manganese content, “Mn” will be marked at the end of the steel number, such as “T8Mn”.

④The phosphorus and sulfur content of high-grade high-quality carbon tool steel is lower than that of ordinary high-quality carbon tool steel. The letter “A” is added at the end of the steel number to indicate the difference, such as “T8MnA”.

4． Free cutting steel

①The steel number is named “Y” to distinguish it from high-quality carbon structural steel.

②The number after the letter “Y” indicates the carbon content, expressed in ten thousandths of the average carbon content. For example, the steel number of free-cutting steel with an average carbon content of 0.3% is “Y30”.

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

5． Alloy structural steel

①The 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.

②The main alloying elements in steel, except for a few microalloying elements, are generally expressed in percentages. When the average alloy content is less than 1.5%, the stainless steel beer brewing equipment enclosure number is generally marked with the element symbol instead of the content. However, in special circumstances that may 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 has a chromium content of 0.9-1.2%, and the rest of the ingredients are the same. When the average content of alloy 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. accordingly. For example 18Cr2Ni4WA.

③Alloying elements such as vanadium V, titanium Ti, aluminum AL, boron B, and rare earth RE in steel are all micro-alloying 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%.

④High-grade high-quality steel should add “A” at the end of the steel number to distinguish it from general high-quality steel.

⑤Special-purpose alloy structural steel, the steel number is preceded (or suffixed) by a symbol representing the purpose of the steel type. For example, 30CrMnSi steel specially used for rivet screws, the steel number is expressed as ML30CrMnSi.

6． low alloy high strength steel

①The expression method of steel grade is basically the same as that of alloy structural steel.

②For professional low-alloy high-strength steel, the steel number should be indicated at the end. For example, 16Mn steel, the special steel type used for bridges is “16Mnq”, the special steel type used for automobile girders is “16MnL”, and the special steel type used for pressure vessels is “16MnR”.

7. spring steel

Spring steel can be divided into two categories according to its chemical composition: carbon spring steel and alloy spring steel. The steel number is expressed in that the former is basically the same as high-quality carbon structural steel, and the latter is basically the same as alloy structural steel.

8. Rolling bearing steel

①The steel number is preceded by the letter “G”, which represents rolling bearing steel.

②The carbon content of high-carbon chromium bearing steel grades is not marked, and the chromium content is expressed in parts per thousand, such as GCr15. The method of expressing the steel grade of carburized bearing steel is basically the same as that of alloy structural steel.

9. Alloy tool steel and high speed tool steel

​ ① When the average carbon content of the alloy tool steel grade is ≥1.0%, the carbon content is not marked; when the average carbon content is <1.0%, it is expressed in thousandths. For example, Cr12, CrWMn, 9SiCr, 3Cr2W8V.

②The method of expressing the content of alloy elements in steel is basically the same as that of alloy structural steel. However, for alloy tool steel grades with lower chromium content, the chromium content is expressed in parts per thousand, and “0” is added before the number indicating the content so that it can be compared with the general element content expressed in percent. distinguish. For example Cr06.

③The steel grade of high-speed tool steel generally does not indicate the carbon content, but only indicates the percentage of the average content of various alloying elements. For example, the steel grade of tungsten high-speed steel is expressed as “W18Cr4V”. Steel grades marked with the letter “C” indicate that their carbon content is higher than general steel grades without “C”.

10. Stainless steel and heat-resistant steel

①The carbon content in the steel grade is expressed in parts per thousand. For example, the average carbon content of “2Cr13” steel is 0.2%; if the carbon content in the steel is ≤0.03% or ≤0.08%, the steel number will be preceded by “00” and “0” respectively, such as 00Cr17Ni14Mo2, 0Cr18 Ni9, etc. .

②The main alloying elements in steel are expressed in percentages, while titanium, niobium, zirconium, nitrogen, etc. are marked according to the above-mentioned expression method of microalloying elements in alloy structural steel.

11. Welding rod steel

Its steel number is preceded by the letter “H” to distinguish it from other steel types. For example, the stainless brass turning welding machine plug wire is “H2Cr13”, which can be distinguished from the stainless steel “2Cr13”.

12. Silicon steel for electricians

①The steel number consists of letters and numbers. The letter DR at the beginning of the steel number indicates hot-rolled silicon steel for electrical applications, DW indicates cold-rolled non-oriented silicon steel for electrical applications, and DQ indicates cold-rolled oriented silicon steel for electrical applications.

②The number after the letter indicates 100 times the iron loss value (W/kg).

③ If the steel number is added with the letter “G” at the end, it means that it was inspected at a high frequency; if “G” is not added, it means that it was inspected at a frequency of 50 cycles.

For example, steel number DW470 indicates that the maximum unit weight iron loss value of cold-rolled non-oriented silicon  custom stainless steel belt tool products for electrical purposes at a frequency of 50 Hz is 4.7W/kg.

13. Pure iron for electricians

① Its grade consists of the letters “DT” and numbers. “DT” represents pure iron for electricians, and the numbers represent the sequence numbers of different grades, such as DT3.

②The letters added after the number indicate the electromagnetic performance: A – advanced, E – special grade, C – super, such as DT8A.