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Common methods for denoting metal material grades: There are a wide variety of metal materials used in mechanical parts. To facilitate production and management in an orderly manner, relevant standards specify methods for indicating the grades of different metal materials, thereby ensuring consistency and making it easier to adopt and use them. 1. General overview of the standard for indicating steel product grades (referencing GB/T221): The GB/T221 standard was revised by taking into account foreign methods for indicating steel product grades as well as changes in domestic methods for such indication (such as Q345 replacing 16Mn), etc. It was issued on April 1, 2000, and came into effect on November 1, 2000. 2. Changes in the main technical content: (1) Since some steel product grades have their own specific standards, the methods for denoting grades such as ferroalloys, casting alloys, superalloys, precision alloys, corrosion-resistant alloys, as well as cast iron, cast steel, and powder materials, which were included in the original standards, have been removed. (2) The emergence of some new steel products has further improved the original standards. The new standard adds designation methods for grades such as decarburized low-phosphorus granular iron, vanadium-containing pig iron, cast wear-resistant pig iron, steel ensuring hardenability, non-quenched and tempered mechanical structural steel, plastic mold steel, and oriented silicon steel (for telecommunications). (3) Some steel grades that were not suited to technological advancements and were inconsistent with production have been completely changed or modified. For example, carbon structural steel A3 is replaced by Q235, and low-alloy high-strength structural steel 16Mn is replaced by Q34, etc. The notation methods for grades of stainless steel, heat-resistant steel, cold-rolled silicon steel, etc., have also been modified. (4) Table 3, \"Examples of methods for indicating steel product grades\" in the original standard, has been removed as it is not applicable to the new standard. 3. Basic principles for the designation of steel product grades (1) The grades of steel products specified in **national standards and industry standards shall all be written in accordance with the designation method prescribed by the GB/T221 standard. Steel product grades that are not formulated in accordance with the regulations should be revised when the standards are updated, and the grades for some new steel products should also be formulated in this manner. (2) The designation of product grades is generally achieved by combining Pinyin letters, chemical element symbols, and Arabic numerals. (3) When using Pinyin letters to represent the product name, purpose, characteristics, and manufacturing methods, generally the first letter from the Pinyin representing the product name is selected. When the letter used is the same as that of another product, you can use the second or third letter, or select the first pinyin letter from the two Chinese characters. (4) If no suitable Chinese characters or Pinyin are available, symbols in the form of English letters shall be used. 3. Examples and explanations of methods for indicating steel product grades. Method for indicating pig iron grades: Pig iron grades are indicated using the symbols and Arabic numerals specified in Table 1. a. The Arabic numerals indicate the average silicon content (expressed as a percentage per thousand). For example: cast iron with a silicon content of 2.75%–3.25% is designated by the grade “Z30”” ； Steel-making pig iron with a silicon content of 0.85–1.25% is designated by the grade “L10”. b. Vanadium-containing pig iron and decarburized low-phosphorus granular iron; the Arabic numerals indicate the average contents of vanadium and carbon respectively (both expressed as per thousand). For example: Vanadium-containing pig iron with a vanadium content of not less than 0.40% is designated by the grade “40”” ； A decarbonized low-phosphorus granular iron for steelmaking with a carbon content of 1.20%–1.60%, designated by the grade “TL14”. 4. Designation methods for carbon structural steel and low-alloy high-strength structural grades: The steels mentioned above are generally classified into two categories: general-purpose steels and special-purpose steels. a. For general structural steel, the pinyin letter “Q” representing the yield point is used. The yield strength value (in MPa), along with symbols such as quality grade and deoxidation method, sequentially constitute the grade designation. For example: the grades of carbon structural steel are denoted as Q235AF, Q235BZ ； The grades of low-alloy high-strength structural steel are denoted as: Q345C, Q345D. In the designation of carbon structural steel, the symbol “Z” for normalized steel and the symbol “TZ” for specially normalized steel can be omitted. For example, for Q235 steel with quality grades C and D, the designations should be Q235C and Q235DTZ, but they can also be written as Q235C and Q235D. Low-alloy high-strength structural steel includes normalized steel and specially normalized steel, but the symbol indicating the deoxidization method is not included at the end of the grade designation. b. Special structural steel is generally denoted by the symbol “Q” representing the yield strength of the steel, the value of the yield strength, and a symbol indicating the intended use of the product; for example, the steel grade used for pressure vessels is indicated as “Q345R” ； The grade of weathering steel is denoted as Q340NH. c. As required, the grades of general-purpose low-alloy high-strength structural steel can also be composed of two Arabic digits (representing the average carbon content in ten-thousandths) and standard element symbols ； For the grades of dedicated low-alloy high-strength structural steel, in addition to the general composition, the symbols specifying the product’s application as listed in Table 1 shall also be indicated. 5. Designation methods for grades of high-quality carbon structural steel and high-quality carbon spring steel: High-quality carbon structural steel is designated using two Arabic digits (representing the average carbon content on a per ten-thousand basis) or a combination of Arabic digits, element symbols, and specified symbols. a. For boiling steel and semi-killed steel, the symbols “F” and “b” are added at the end of the grade designations, respectively. For example: Boiling steel with an average carbon content of 0.08% is designated by the grade “08F”” ； Semi-killed steel with an average carbon content of 0.10% is designated by the grade “10b”. b. Calming steel (with S and P ≤ 0.035% respectively) generally does not have a symbol indicated. For example, a mild steel with an average carbon content of 0.45% is designated by the grade “45”. c. For high-quality carbon structural steel with a higher manganese content, the symbol for manganese is added after the Arabic numeral indicating the average carbon content. For example, steel with an average carbon content of 0.50% and a manganese content of 0.70%–1.00% is designated by the grade “50Mn”. d. High-grade high-quality carbon structural steel (with S and P each ≤ 0.030%), with the symbol “A” added after the grade designation. For example, high-quality carbon structural steel with an average carbon content of 0.45% is designated by the grade “45A”. e. Extra-high-quality carbon structural steel (S≤0.020%, P≤0.025%), with the symbol “E” added after the grade designation. For example, a high-quality carbon structural steel with an average carbon content of 0.45% is designated by the grade “45E”. The method of designating grades for high-quality carbon spring steel is the same as that for high-quality carbon structural steel (steels such as 65, 70, 85, and 65Mn are specified in both GB/T1222 and GB/T699 standards). 6. Method of designating grades for alloy structural steels and alloy spring steels: The average carbon content (expressed as per ten thousand) is indicated by two Arabic digits, which are placed at the beginning of the grade designation. The method of indicating the content of alloying elements is as follows: when the average content is less than 1.50%, only the element name is indicated in the grade, while the specific content is generally not specified ； When the average alloy content is 1.50%～2.49%, 2.50%～3.49%, 3.50%～4.49%, 4.50%～5.49%, …., the corresponding numbers 2, 3, 4, 5, … are written after the alloying element. For example, in an alloy structural steel with average contents of carbon, chromium, manganese, and silicon at 0.30%, 0.95%, 0.85%, and 1.05% respectively, when the contents of S and P are ≤0.035% each, its grade is denoted as “30CrMnSi”. High-grade high-quality alloy structural steel (with S and P contents of ≤0.025% respectively), indicated by the letter “A” at the end of the grade designation. For example: “30CrMnSiA”. Ultra-high-quality alloy structural steel (S≤0.015%, P≤0.025%), with the symbol “E” added at the end of the grade designation, for example: “30CrMnSiE”. 7. For special alloy structural steel grades, symbols indicating the intended use of the product shall also be added at the beginning (or end) of the grade designation. The method of denoting alloy spring steel grades is the same as that for alloy structural steel. For example, a spring steel with average contents of 0.60% carbon, 1.75% silicon, and 0.75% manganese is denoted by the grade “60Si2Mn”. High-grade high-quality spring steel, with the symbol “A” added at the end of the grade designation; its grade is denoted as “60Si2MnA”. 8. Designation method for free-cutting steel grades: Free-cutting steel is designated using standard chemical element symbols, the symbols specified in Table 1, and Arabic numerals. The Arabic numerals indicate the average carbon content (expressed as parts per ten thousand). a. Sulfurized free-cutting steel and sulfurized/phosphorusized free-cutting steel do not have the symbol for the free-cutting element following the symbol “Y” and the Arabic numeral. For example: a free-cutting steel with an average carbon content of 0.15% is designated as “Y15”. b. For sulfurized or sulfurized-phosphorus free-cutting steels with a higher manganese content, the symbol for manganese is added after the symbol “Y” and the Arabic numeral. For example, a free-cutting steel with an average carbon content of 0.40% and a manganese content of 1.20%–1.55% is denoted by the grade “Y40Mn”. c. Free-cutting steels containing free-cutting elements such as calcium and lead have the symbol of the free-cutting element added after the symbol “Y” and the Arabic numeral. For example: “Y15Pb”, “Y45Ca”. 9. Designation method for grades of non-quenched and tempered mechanical structural steel: For non-quenched and tempered mechanical structural steel, the symbols “YF” and “F” are added at the beginning of the grade designation to indicate machinable non-quenched and tempered mechanical structural steel and non-quenched and tempered mechanical structural steel for hot forging respectively; the other aspects of the grade designation method are the same as those for alloy structural steel. For example: “YF35V”, “F45V”. 10. Method of designating tool steel grades: Tool steels are classified into three categories: carbon tool steels, alloy tool steels, and high-speed tool steels. Carbon tool steel is denoted using standard chemical element symbols, prescribed symbols, and Arabic numerals. The Arabic numerals indicate the average carbon content (expressed as a percentage per thousand). a. Ordinary carbon tool steel with manganese content, indicated by an Arabic numeral following the tool steel symbol “T”. For example, carbon tool steel with an average carbon content of 0.80% is designated by the grade “T 8”. b. For carbon tool steels with a higher manganese content, the symbol for manganese is added after the tool steel symbol “T” and the Arabic numeral. For example: “T8Mn”. c. High-grade high-quality carbon tool steel, with “A” added at the end of the grade designation. For example: T8MnA. 11. Alloy tool steels and high-speed tool steels: The method of designating alloy tool steels and high-speed tool steels is the same as that used for alloy structural steels. It is denoted using the alloy element symbols and Arabic numerals specified by standards; however, the average carbon content is generally not indicated. For example, an alloy tool steel with an average carbon content of 1.60%, and chromium, molybdenum, and vanadium contents of 11.75%, 0.50%, and 0.22% respectively, is designated as “Cr12MoV”” ； A high-speed tool steel with an average carbon content of 0.85%, and contents of tungsten, molybdenum, chromium, and vanadium of 6.00%, 5.00%, 4.00%, and 2.00% respectively, is designated by the grade “W6Mo5Cr4V2”. When the average carbon content is less than 1.00%, the carbon content can be expressed using a single Arabic digit (expressed as a per thousand). For example, an alloy tool steel with an average carbon content of 0.80%, a manganese content of 0.95%, and a silicon content of 0.45% is designated by the grade “8MnSi”. Low-chromium alloy tool steels with an average chromium content of < 1.00% have the digit \"0\" added before the chromium percentage (expressed as a per mille value). For example, an alloy tool steel with an average chromium content of 0.60% is designated by the grade “Cr06”. 12. Method of designating plastic mold steel grades: Apart from the addition of the symbol “SM” at the beginning, the method of designating plastic mold steel grades is the same as that used for high-quality carbon structural steel and alloy tool steel grades. For example: Carbon plastic mold steel with an average carbon content of 0.45% is designated by the grade “SM45”” ； An alloy plastic mold steel with an average carbon content of 0.34%, a chromium content of 1.70%, and a molybdenum content of 0.42%, is designated by the grade SM3Cr2Mo. 13. Method of indicating bearing steel grades. Bearing steels are divided into four main categories: high-carbon chromium bearing steels, carburized bearing steels, high-carbon chromium stainless bearing steels, and high-temperature bearing steels. High-carbon chromium bearing steel is denoted by the symbol “G” at the beginning of its grade designation, but the carbon content is not specified. The chromium content is expressed as a few thousandths, while the other alloying elements are indicated according to the alloy content of structural steel. For example, a bearing steel with an average chromium content of 50% is designated by the grade GCr15. Carbide bearing steel is designated using the naming convention for alloy structural steels, with the symbol “G” added at the beginning of the grade designation. For example: G20 CrNiMo. High-grade, high-quality carburized bearing steel, with “A” added at the end of the grade designation. For example, G20CrNiMoA. High-carbon chromium stainless bearing steel and high-temperature bearing steel are denoted using the designation methods for stainless steel and heat-resistant steel, without the “G” symbol at the beginning of the grade. For example: high-carbon chromium stainless bearing steel “9Cr18” and high-temperature bearing steel 10Cr14Mo.