① The grade of high quality steel means that it is A after the grade, such as 40CrAH.
② The final number of the unified numeric code of high quality steel is 7, and the rest of the capitalized Latin letters are the same as the first four Arabic numerals, such as the unified numeric code of 40CrAH is A20407.
③ Quality carbon structural steel: P≤ 0.035%，S≤0.035%，Cu≤0.25%，Cr≤0.25%，Ni≤0.30%
High-quality carbon structural steel: P≤ 0.030%，S≤0.030%，Cu≤0.25%，Cr≤0.25%，Ni≤0.30%
Quality alloy structural steel: P≤ 0.035%，S≤0.035%，Cu≤0.30%，Cr≤0.30%，Ni≤0.30%
High-quality alloy structural steel: P≤ 0.025%，S≤0.025%，Cu≤0.25%，Cr≤0.30%，Ni≤0.30%
④ According to the requirements of the demander, the sulfur content (mass fraction) in the steel can also be in the range of 0.02% to 0.035%. At this time, the sulfur content (mass fraction) allows a deviation of ±0.005%, and S is added before H in the brand name, such as 16CrMnSH.