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Steel is a general term for iron-carbon alloys with a carbon content by mass ranging from 0.02% to 2.11%. In actual production, steel often contains different alloying elements depending on its intended use, such as manganese, nickel, vanadium, etc. Today, steel is one of the most widely used materials in the world, thanks to its low cost and reliable performance. So, do you all know the naming rules for steel? Today, I will introduce that in our country, the classification is based on the uses of steel. 1. Carbon structural steel: The notation format is Q + number + (quality grade symbol) + (deoxidation method symbol) + (symbol for specific use). ① The letter “Q” at the beginning of the steel grade indicates the yield strength of the steel; ② The number following “Q” represents the yield strength value, expressed in MPa. For example, Q235 denotes carbon structural steel with a yield strength (σs) of 235 MPa; ③ When necessary, symbols indicating the quality grade and deoxidation method can be added after the steel grade. The quality grade symbols are A, B, C, and D respectively. Symbols for deoxidation methods: F denotes boiling steel; b denotes semi-killed steel; Z denotes killed steel; TZ denotes specially killed steel. Killed steel may not require a symbol, so both Z and TZ can be omitted. For example, Q235-AF denotes grade A boiling steel. Special-purpose carbon steel: such as bridge steel and marine steel, basically uses the designation method for carbon structural steel, but letters indicating the application are added at the end of the steel grade. II. High-quality carbon structural steel – Notation method: digits + (element symbol) + (deoxidation method symbol) + (symbol for specific application). ① The first two digits of the steel grade indicate the carbon content of the steel, expressed as a fraction of ten thousand of the average carbon content. For example, steel with an average carbon content of 0.45% has the grade “45”; this is not a sequential number, so it should not be referred to as “Grade 45” steel. ②For high-quality carbon structural steel with a high manganese content, the manganese element should be specified, such as 50Mn. ③Boiled steel, semi-killed steel, and high-quality carbon structural steels for special purposes should be specifically indicated at the end of their steel grade; for example, semi-killed steel with an average carbon content of 0.1% has a grade of 10b. III. Carbon tool steel – Notation method: Letter T + number + (element symbol) + (quality grade symbol). ① The steel grade is preceded by the letter “T” to prevent confusion with other types of steel. ②The digits in the steel grade indicate the carbon content, expressed as a percentage of the average carbon content. For example, “T8” indicates an average carbon content of 0.8%. ③For grades with a higher manganese content, “Mn” is indicated at the end of the steel grade, such as “T8Mn”. ④The phosphorus and sulfur contents in high-grade high-quality carbon tool steels are lower than those in ordinary high-quality carbon tool steels; the letter “A” is added at the end of the steel grade to indicate this difference, such as “T8MnA”. IV. Free-cutting steel: Notation method: Letter Y + number + (element symbol). ① The steel grade is prefixed with “Y” to distinguish it from high-quality carbon structural steel. ②The number following the letter “Y” indicates the carbon content, expressed as a fraction of ten thousand of the average carbon content. For example, a free-cutting steel with an average carbon content of 0.3% has the designation “Y30”. ③For grades with a higher manganese content, “Mn” is also indicated after the steel grade, such as “Y40Mn”. V. Alloy structural steel – Notation method: (Special-purpose symbol) + number + symbols and numbers of the main alloying elements + symbols of trace alloying elements + (Quality grade symbol) + (Special-purpose symbol). ① The first two digits of the steel grade indicate the carbon content of the steel, expressed as a fraction of ten thousand of the average carbon content; for example, 40Cr. ②The main alloying elements in steel, with the exception of a few micro-alloying elements, are generally expressed as percentages. When the average alloy content