Chinese steel grade designation method

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1. 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. The method of designating steel grades consists of the pinyin letters representing the yield point or yield strength of the steel, the numerical value of the yield point or yield strength, the quality grade of the steel, and in some cases, the degree of deoxidation; in fact, it is composed of 4 parts. ①General structural steel is denoted by the pinyin letter “Q” representing the yield point. The grade is composed in sequence of the yield strength value (in MPa), the quality grades specified in Table 1 (A, B, C, D, E), and the deoxidation methods (F, b, Z, TZ) and other symbols. 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. Q235BZ refers to normalized carbon structural steel with a yield strength of ≥235 MPa and a quality grade of B. Q235 and Q345 are the most typical grades of engineering steel, with the highest production volume and widest range of applications. These two grades are available in almost all countries around the world. 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, Q235 steel with quality grades C and D should be denoted as Q235CZ and Q235DTZ respectively, but it 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. ②Special 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 ； Q295HP steel grade for welding gas cylinders ； Q390g boiler steel grade ； Q420q is a steel grade for bridges. ③As required, the grade of general low-alloy high-strength structural steel can also be represented by two Arabic digits (indicating the average carbon content in ten-thousandths) and chemical element symbols, in order ； The grade of specialized low-alloy high-strength structural steel can also be indicated by two Arabic digits (representing the average carbon content in parts per ten thousand), chemical element symbols, as well as certain symbols specified to represent the product’s intended use, arranged in sequence. 2. Designation methods for high-quality carbon structural steel and high-quality carbon spring steel grades: High-quality carbon structural steel is designated using two Arabic digits (expressing the average carbon content as a fraction per ten thousand) or a combination of Arabic digits and element symbols. ①For 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”. ②Calmed steel (with S and P ≤ 0.035% respectively) is generally not marked with a symbol. For example, a mild steel with an average carbon content of 0.45% is designated by the grade “45”. ③For 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 denoted by the grade “50Mn”. ④High-grade quality carbon structural steel (where S and P are each ≤0.030%); the symbol “A” is 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”. ⑤Super-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 (steel grades such as 65, 70, 85, and 65Mn are specified in both standards GB/T1222 and GB/T699). 3. Designation methods for alloy structural steel and alloy spring steel grades: ① Alloy structural steel grades are denoted by Arabic numerals and standard chemical element symbols. The average carbon content (expressed as per ten thousand) is indicated in two Arabic digits and 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%, …., 2, 3, 4, 5, … are respectively written after the alloying elements. 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 symbol “A” at the end of the grade designation. For example: “30CrMnSiA”. Super-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”. For special alloy structural steel grades, symbols indicating the intended use of the product as specified in Table 1 should be added at the beginning (or end) of the grade designation. For example, the 30CrMnSi steel specifically used for rivets and screws is designated as ML30CrMnSi. ②The notation method for 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”. 4. Designation method for free-cutting steel grades: Free-cutting steel is denoted using standard chemical element symbols, specified symbols, and Arabic numerals. The Arabic numerals indicate the average carbon content (expressed as per ten thousand). ①For sulfurized free-cutting steel and sulfurized-phosphorus free-cutting steel, the symbol for the free-cutting element is not added after the symbol “Y” and the Arabic numeral. For example, a free-cutting steel with an average carbon content of 0.15% is designated by the grade “Y15”. ②Sulfurized or sulfurized-phosphorus free-cutting steels with higher manganese content have the manganese symbol 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”. ③Free-cutting steels containing free-cutting elements such as calcium and lead have the symbol “Y” and an Arabic numeral followed by the symbol of the free-cutting element. For example: “Y15Pb”, “Y45Ca”. 5. 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”. 6. Method of indicating tool steel grades: Tool steels are divided into three categories: carbon tool steels, alloy tool steels, and high-speed tool steels. ①Carbon 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, an Arabic numeral follows the tool steel symbol “T”. For example, carbon tool steel with an average carbon content of 0.80% is designated by the grade “T8”. b. Carbon tool steels with a higher manganese content have the symbol for manganese 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”. ②Alloy 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 designating alloy structural steels. The symbols for alloying elements and Arabic numerals specified in the standards are used for representation; however, the average carbon content is generally not indicated. For example, for 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, its grade is denoted as “Cr12MoV”” ； 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 (average chromium content < 1.00%) alloy tool steels have the digit “0” added before the chromium content expressed as a percentage. For example: Alloy tool steel with an average chromium content of 0.60% is designated as “Cr06”. 7. Notation for plastic mold steel grades: Apart from the addition of the symbol “SM” at the beginning, the notation method for plastic mold steel grades is the same as that for high-quality carbon structural steels and alloy tool steels. For example: Carbon plastic mold steel with an average carbon content of 0.45% is designated by the grade “SM45”” ； This alloyed plastic mold steel has an average carbon content of 0.34%, chromium content of 1.70%, and molybdenum content of 0.42%. Its grade designation is “SM3Cr2Mo”. 8. Notation for bearing steel grades: Bearing steels are classified into four main categories: high-carbon chromium bearing steels, carburizing bearing steels, high-carbon chromium stainless bearing steels, and high-temperature bearing steels. ①For high-carbon chromium bearing steel, the symbol “G” is added at the beginning of the grade designation; however, the carbon content is not indicated. The chromium content is expressed in thousandths, while other alloying elements are indicated according to the alloy content in alloy structural steels. For example: Bearing steel with an average chromium content of 1.50% is designated as “GCr15”. ②Carbide 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: “G20CrNiMo”. High-quality advanced carburized bearing steel, with “A” added at the end of the grade designation. For example: “G20CrNiMoA”. ③High-carbon chromium stainless bearing steels and high-temperature bearing steels are designated using the naming conventions for stainless steels and heat-resistant steels, without the “G” symbol at the beginning of the grade designation. For example: high-carbon chromium stainless bearing steel “9Cr18” and high-temperature bearing steel “10Cr14Mo”. 9. Designation method for grades of stainless steel and heat-resistant steel: The grades of stainless steel and heat-resistant steel are indicated using the alloy element symbols and Arabic numerals specified by standards; for machinable stainless steel and free-cutting heat-resistant steel, the letter “Y” is added at the beginning of the grade designation. The average carbon content is generally expressed as a single Arabic digit (on a per thousand basis) ； When the average carbon content is ≥1.00%, it is expressed in two Arabic digits ； When the upper limit of carbon content is <0.10%, it is indicated as “0” for the carbon content ； When the upper limit of carbon content is ≤0.03% or >0.01% (ultra-low carbon), the carbon content is indicated by “03” ； When the upper carbon content limit is ≤0.01% (i.e., extremely low carbon), the carbon content is indicated as “01”. When no lower limit for carbon content is specified, the upper limit value of the carbon content is expressed in Arabic numerals. The method for expressing the content of alloying elements is the same as that for alloy structural steel. For example: Stainless steel with an average carbon content of 0.20% and a chromium content of 13% is designated by the grade “2Cr13”” ； Chromium-nickel stainless steel with a maximum carbon content of 0.08%, an average chromium content of 18%, and a nickel content of 9%, is designated by the grade “0Cr18Ni9”” ； A sulfurized free-cutting chromium stainless steel with a maximum carbon content of 0.12% and an average chromium content of 17%, is designated by the grade “Y1Cr17”” ； High-carbon chromium stainless steel with an average carbon content of 1.10% and a chromium content of 17%, whose grade is denoted as “11Cr7”” ； It is an ultra-low carbon stainless steel with a maximum carbon content of 0.03%, an average chromium content of 19%, and a nickel content of 10%; its grade is denoted as “03Cr19Ni10”” ； It is an ultra-low carbon stainless steel with a maximum carbon content of 0.01%, an average chromium content of 19%, and a nickel content of 11%; its grade is designated as “01Cr19Ni11”. The current domestic standards for stainless heat-resistant steel are revised with reference to JIS standards, but the method of denoting stainless heat-resistant steel grades differs from those in countries such as Japan. We use alloying elements and the average carbon content to denote it, while Japan uses letters indicating the application along with Arabic numerals. For example, stainless steel grades SUS202, SUS316, SUS430; S-steel (steel); U-use (application); S-stainless (stainless steel). For example, heat-resistant steel grades SUH309, SUH330, SUH660, H-Heatresistins. Different numbers in the grade designation represent various types of stainless heat-resistant steel. Japan states that for various types of stainless heat-resistant steel products, corresponding letters are added after the grade; for example, stainless steel rods are denoted as SUS-B, and hot-rolled stainless steel plates as SUS-HP ； Heat-resistant steel rod SUHB, heat-resistant steel plate SUHP. In Western countries such as the UK and the US, the method of denoting stainless heat-resistant steel grades is basically the same as that in Japan; they are primarily indicated using Arabic numerals, and the numbers used are identical, meaning the grades are the same. Because Japan’s stainless heat-resistant steel is based on American technology. 10. Method of designating steel grades for welding. Welding steels include carbon steel for welding, alloy steel for welding, and stainless steel for welding, etc. The method of designating their grades is to add the symbol “H” at the beginning of the grade designation for each type of welding steel. For example: “H08”, “H08Mn2Si”, “H1Cr18Ni9”. High-quality steel for advanced welding, with the symbol “A” added at the end of the grade designation. For example: “H08A”, “08Mn2SiA”. 11. Designation method for silicon steel grades used in electrical engineering: The grade consists of numbers, letters, and digits. The alphabetical codes for non-oriented and oriented silicon steel are “W” and “Q” respectively. The thickness is placed first, the alphabetical code comes next, and the iron loss value is placed last; for example, 30Q113. In oriented silicon steel, the letters representing high magnetic permeability, “G” and “Q”, are used together; for example, the digits following the letter in 30QG113 indicate 100 times the value of iron loss in W/kg. The letter “G” indicates that it has been tested at high frequencies ； The absence of the “G” indicates that the test was conducted at a frequency of 50 Hz. 30Q113 indicates that the maximum loss per unit weight of cold-rolled oriented silicon steel products for electrical use at a frequency of 50 Hz is 1.13 W/kg. The notation for cold-rolled silicon steel is consistent with the Japanese standard (JISC2552), except for the alphabetical symbols; for example, the grade for oriented silicon steel is 27Q140, while the corresponding JIS grade is 27G140. For 30QG110, the corresponding JIS grade is 30P110 (G denotes ordinary material, while P denotes high orientation). The grade for non-oriented silicon steel is 35W250; the corresponding JIS grade is 35A250.