5. Alloy structural steel

① The two digits at the beginning of the steel grade indicate the carbon content of the steel, expressed in tens of thousands of parts of the average carbon content, such as 40Cr.

② The main alloying elements in steel, except for individual microalloying elements, are generally expressed in percentage. When the average alloy content is less than 1.5%, only the element symbol is generally indicated in the steel grade, without indicating the content. However, in special cases, those that are prone to confusion can also be marked with the number "1" after the element symbol, such as steel grades "12CrMoV" and "12Cr1MoV", where the chromium content is 0.4-0.6% and 0.9-1.2% respectively, and all other components 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 represented as 2, 3, 4..., etc. For example, 18Cr2Ni4WA.

③ The alloying elements such as vanadium V, titanium Ti, aluminum AL, boron B, and rare earth RE in steel are all microalloyed elements, and although their content is very low, they should still be marked in the steel grade. For example, in 20MnVB steel. Vanadium is 0.07-0.12%, boron is 0.001-0.005%.

④ High quality steel should be distinguished from general quality steel by adding "A" at the end of the steel grade.

⑤ Alloy structural steel for specialized purposes, with a steel grade followed by a symbol (or suffix) representing the purpose of the steel grade. For example, the special 30CrMnSi steel for riveting is represented as ML30CrMnSi.

6. Low alloy high-strength steel

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

② For professional low-alloy high-strength steel, it should be indicated at the end of the steel grade. For example, 16Mn steel, the special steel used for bridges is "16Mnq", the special steel used for automotive beams is "16MnL", and the special steel used for pressure vessels is "16MnR".

7. Spring steel

Spring steel can be divided into two categories based on chemical composition: carbon spring steel and alloy spring steel. The steel grade representation method is basically the same as high-quality carbon structural steel, while the latter is basically the same as alloy structural steel.

8. Rolling bearing steel

① The steel grade is prefixed with the letter "G" to indicate the rolling bearing steel category.

② The carbon content of high carbon chromium bearing steel grades is not indicated, and the chromium content is expressed in thousandths. For example, GCr15. The steel grade representation method for carburized bearing steel is basically the same as that for alloy structural steel.