1. Carbon structural steel

① Composed of Q+number+quality level symbol+deoxygenation method symbol. Its steel grade is prefixed with "Q", representing the yield point of the steel. The following numbers represent the yield point value, in MPa. For example, Q235 represents the yield point（ σ s) 235 MPa carbon structural steel.

② If necessary, symbols indicating quality level and deoxidation method can be marked after the steel grade. The quality level symbols are A, B, C, and D. Symbol for deoxygenation method: F represents boiling steel; B represents semi killed steel; Z represents killed steel; TZ represents special killed steel, and killed steel may not be marked with symbols, that is, both Z and TZ may not be marked. For example, Q235-AF represents A-grade boiling steel.

③ Carbon steel for specialized purposes, such as bridge steel, shipbuilding steel, etc., is generally represented by carbon structural steel, but a letter indicating the purpose is added at the end of the steel grade.

2. High quality carbon 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. For example, for steel with an average carbon content of 0.45%, the steel grade is "45", which is not a sequential number and cannot be read as 45 grade steel.

② High quality carbon structural steel with high manganese content should be labeled with manganese elements, such as 50Mn.

③ Boiling steel, semi killed steel, and high-quality carbon structural steel for specialized purposes should be specially marked at the end of the steel grade, such as semi killed steel with an average carbon content of 0.1%, which has a steel grade of 10b.

3. Carbon tool steel

① The steel grade is prefixed with "T" to avoid mixing with other steel grades.

② The numbers in the steel grade represent the carbon content, expressed in thousandths of the average carbon content. For example, "T8" represents an average carbon content of 0.8%.

③ For those with higher manganese content, indicate "Mn" at the end of the steel grade, such as "T8Mn".

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

4. Free cutting steel

① The steel grade is labeled with "Y" to distinguish it from high-quality carbon structural steel.

② The number after the letter "Y" represents the carbon content, expressed in tens of thousands of parts of the average carbon content. For example, for a free cutting steel with an average carbon content of 0.3%, its steel grade is "Y30".

③ For those with higher manganese content, "Mn" is also indicated after the steel grade, such as "Y40Mn".