Steel is an iron-carbon alloy with a carbon content ranging from 0.0218% to 2.11%. To ensure its toughness and ductility, the carbon content generally does not exceed 1.7%. In addition to iron and carbon, the main
Elements of steel include silicon, manganese, sulfur, and phosphorus. There are various classification methods for steel—today we will explore the nomenclature rules for steel grades.
Expression method: Q + number + (quality grade symbol) + (deoxidation method symbol) + (special purpose symbol).
① The steel grade is prefixed with "Q", representing the yield point of the steel.
② The number following "Q" indicates the yield point value in MPa. For example, Q235 denotes carbon structural steel with a yield point (σs) of 235 MPa.
③ When necessary, symbols indicating quality grade and deoxidation method can be added after the steel grade. Quality grade symbols are A, B, C, and D respectively.
④ Deoxidation method symbols: F for rimmed steel; b for semi-killed steel; Z for killed steel; TZ for special killed steel. Killed steel may omit the symbol (both Z and TZ can be omitted). For example, Q235-AF represents grade A rimmed steel.
⑤ Carbon steel for special purposes (e.g., bridge steel, shipbuilding steel) basically adopts the expression method of carbon structural steel, but with a letter indicating the purpose added at the end of the steel grade.
Expression method: Number + (element symbol) + (deoxidation method symbol) + (special purpose symbol).
① The first two digits at the beginning of the steel grade indicate the carbon content, expressed as a fraction of ten-thousandths of the average carbon content. For example, steel with an average carbon content of 0.45% is designated as "45"—this is not a serial number, so it should not be read as "No. 45 steel".
② High-quality carbon structural steel with high manganese content should be marked with the manganese element, e.g., 50Mn.
③ Rimmed steel, semi-killed steel, and high-quality carbon structural steel for special purposes shall be specially marked at the end of the steel grade. For example, semi-killed steel with an average carbon content of 0.1% is designated as 10b.
Expression method: Letter T + number + (element symbol) + (quality grade symbol).
① The steel grade is prefixed with "T" to distinguish it from other steel types.
② The number in the steel grade indicates the carbon content, expressed as a fraction of one-thousandth of the average carbon content. For example, "T8" denotes an average carbon content of 0.8%.
③ For steel with high manganese content, "Mn" is marked at the end of the steel grade, e.g., "T8Mn".
④ High-grade high-quality carbon tool steel has lower phosphorus and sulfur contents than general high-quality carbon tool steel, and is distinguished by adding the letter "A" at the end of the steel grade, e.g., "T8MnA".
Expression method: Letter Y + number + (element symbol).
① The steel grade is prefixed with "Y" to distinguish it from high-quality carbon structural steel.
② The number following "Y" indicates the carbon content, expressed as a fraction of ten-thousandths of the average carbon content. For example, free-cutting steel with an average carbon content of 0.3% is designated as "Y30".
③ For steel with high manganese content, "Mn" is also marked at the end of the steel grade, e.g., "Y40Mn".
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