Explanation of the categories of steel number expressions in my country

1. Carbon structural steel ① consists of Q + number + quality grade symbol + deoxidation method symbol. Its steel number is prefixed with “Q”, which represents the yield point of the steel. The following number represents the yield point value in MPa. For example, Q235 represents a carbon structural steel with a yield point (σs) of 235 MPa.

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

③Special-purpose carbon steel, such as bridge steel, marine steel, etc., basically uses the representation method of carbon  steel, but a letter indicating the purpose is appended to the end of the steel number.

2. High quality carbon structural steel

①The two digits at the beginning of the steel number indicate the carbon content of the steel, expressed as a few ten thousandths of the average carbon content. For example, for steel with an average carbon content of 0.45%, the steel number is “45”. It is not a sequential number, so it cannot be read as 45 gauge steel.

② For high-quality carbon structural steel with high manganese content, the manganese element should be marked, such as 50Mn.

③ Boiling steel, semi-killed steel and special-purpose high-quality carbon structural steel should be specially marked at the end of the steel number. For example, semi-killed steel with an average carbon content of 0.1% has a steel number of 10b. 3． Carbon tool steel ①The steel number is marked with “T” to avoid confusion with other steels. ②The number in the steel number indicates the carbon content, expressed as a few thousandths of the average carbon content. For example, “T8” means an average carbon content of 0.8%.

③ For those with higher manganese content, “Mn” will be marked at the end of the steel number, such as “T8Mn”.

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

①The steel number is marked with “Y” to distinguish it from high-quality carbon structural steel.

②The number after the letter “Y” indicates the carbon content, expressed in ten thousandths of the average carbon content. For example, the steel number of free-cutting steel with an average carbon content of 0.3% is “Y30”. ③ Those with higher manganese content will also be marked with “Mn” after the steel number, such as “Y40Mn”.

5． Alloy structural steel ① The two digits at the beginning of the steel number indicate the carbon content of the steel, expressed as a few ten thousandths of the average carbon steel, such as 40Cr.

②The main alloying elements in steel, except for a few microalloying elements, are generally expressed in percentages. When the average alloy content is less than 1.5%, the steel number is generally marked with the element symbol instead of the content. However, in special circumstances that may cause confusion, the number “1” can also be marked after the element symbol, such as the steel number. “12CrMoV” and “12Cr1MoV”, the former has a chromium content of 0.4-0.6%, the latter has a chromium content of 0.9-1.2%, and the rest of the ingredients are the same. When the average content of alloy elements is ≥1.5%, ≥2.5%, ≥3.5%…, the content should be indicated after the element symbol, which can be expressed as 2, 3, 4… etc. accordingly. For example 18Cr2Ni4WA. ③Alloying elements such as vanadium V, titanium Ti, aluminum AL, boron B, and rare earth RE in steel are all micro-alloying elements. Although the content is very low, they should still be marked in the steel grade. For example, in 20MnVB steel. Vanadium is 0.07-0.12%, and boron is 0.001-0.005%. ④High-grade high-quality steel should add “A” at the end of the steel number to distinguish it from general high-quality steel.

⑤Special-purpose alloy structural steel, the steel number is preceded (or suffixed) by a symbol representing the purpose of the steel type. For example, the steel number of 30CrMnSi steel specially used for rivet screws is ML30CrMnSi.

6. Low alloy high strength steel ①The expression method of steel grade is basically the same as that of alloy structural steel. ② For professional low-alloy high-strength steel, the steel number should be indicated at the end. For example, 16Mn steel, the special steel type used for bridges is “16Mnq”, the special steel type used for automobile girders is “16MnL”, and the special steel type used for pressure vessels is “16MnR”.

7. Spring steel Spring steel can be divided into two categories according to its chemical composition: torsion spring steel and alloy spring steel. The steel number is expressed in the way that the former is basically the same as high-quality carbon structural steel, and the latter is basically the same as alloy structural steel.

8. Rolling bearing steel ①The steel number is preceded by the letter “G”, which represents rolling bearing steel. ②The carbon content of high-carbon chromium bearing steel grades is not marked, and the chromium content is expressed in parts per thousand. For example GCr15. The method of expressing the steel grade of carburized bearing steel is basically the same as that of alloy structural steel.

9. Alloy tool steel and high-speed tool steel ① When the average carbon content of the alloy tool steel grade is ≥1.0%, the carbon content is not marked; when the average carbon content is <1.0%, it is expressed in thousandths. For example, Cr12, CrWMn, 9SiCr, 3Cr2W8V. ②The expression method of alloy element content in steel is basically the same as that of alloy structural steel. However, for alloy tool steel grades with lower chromium content, the chromium content is expressed in parts per thousand, and “0” is added before the number indicating the content so that it can be compared with the general element content expressed in percent. distinguish. For example Cr06. ③The steel grade of high-speed tool steel generally does not indicate the carbon content, but only indicates the percentage of the average content of various alloying elements. For example, the steel grade of tungsten high-speed steel is expressed as “W18Cr4V”. Steel grades marked with the letter “C” indicate that their carbon content is higher than general steel grades without “C”.

10． Stainless steel and heat-resistant steel ①The carbon content in the steel grade is expressed in thousandths. For example, the average carbon steel of “2Cr13” steel is 0.2%; if the carbon content in the steel is ≤0.03% or ≤0.08%, the steel number will be preceded by “00” and “0” respectively, such as 00Cr17Ni14Mo2, 0Cr18 Ni9, etc. . ②The main alloying elements in the steel are expressed in percentages, while titanium, niobium, zirconium, nitrogen, etc. are marked according to the above-mentioned expression method of micro-alloying elements in alloy structural steel.

11． Welding rod steel: Its steel number is preceded by the letter “H” to distinguish it from other steel types. For example, the stainless steel welding wire is “H2Cr13”, which can be distinguished from the stainless steel “2Cr13”.

12. Silicon steel for electricians ①The steel number consists of letters and numbers. The letter DR at the beginning of the steel number indicates hot-rolled silicon steel for electrical applications, DW indicates cold-rolled non-oriented silicon steel for electrical applications, and DQ indicates cold-rolled oriented silicon steel for electrical applications. ②The number after the letter indicates 100 times the iron loss value (W/kg). ③ If the letter “G” is added to the end of the steel number, it means that it was inspected at a high frequency; if “G” is not added, it means that it was inspected at a frequency of 50 cycles. For example, steel number DW470 indicates that the maximum unit weight iron loss value of cold-rolled non-oriented silicon steel products for electrical applications at a frequency of 50 Hz is 4.7W/kg.

13. Pure iron for electricians ① Its grade consists of the letters “DT” and numbers. “DT” means pure iron for electricians, and the numbers represent the sequence numbers of different grades, such as DT3. ②The letters added after the number indicate the electromagnetic performance: A – advanced, E – special grade, C – super, such as DT8A.

3. Comparison of some new and old steel grades 1. Comparison of new and old standard steel grades of carbon steel. The new standard GB700-88 refers to the international standard ISO630 “Structural Steel”, while the old standard GB700-79 mainly refers to the former Soviet Union IOCT380. Therefore, the methods of expressing steel grades and the technical requirements stipulated for each steel grade are different. Now compare the old and new standard steel grades as follows. GB700-88 standard GB700-79 standard Steel number Technical conditions Steel number Technical conditions Q195 Regardless of grade, its chemical composition and mechanical properties (σs, σb, δ and cold bending) must be guaranteed. For products such as rolled sheets and wire rods, the guarantee conditions for their mechanical properties may be separately stipulated in relevant standards based on product characteristics and usage requirements. A1 B1 The guaranteed mechanical properties of A1 steel (σs, σb, δ and cold bending), the guaranteed chemical composition of B1 steel is the same as Q195. The cold bending test of A1 steel is an additional guarantee condition. No. 1 steel does not have special steel Q215 points A, B Grade, the specified chemical composition and mechanical properties must be guaranteed. Q215A is not subject to impact test. Q215B must be subject to room temperature impact test. The mechanical properties guaranteed by V-notch sample A2 C2 A2 steel, the chemical composition and mechanical properties guaranteed by C2 steel are the same as Q215. Steel is basically the same. Q235 is divided into grades A, B, C, and D. The specified chemical composition and mechanical properties must be guaranteed. Q235A does not conduct impact tests. Q235B requires room temperature impact tests. V-notch samples Q235C and Q235D are used for important welded structures. The former is subjected to an impact test at 0OC, and the latter is subjected to an impact test at -20OC. The specimens are the same as above. A3 C3 The mechanical properties guaranteed by A3 steel, the chemical composition and mechanical properties guaranteed by C3 steel are basically the same as Q235 steel. A3 steel has additional guarantees. Normal temperature impact test, use U-shaped notch sample C3 steel to additionally guarantee normal temperature or -20OC impact test. The sample is the same as above. Q255 is divided into A and B grades. The specified chemical composition and mechanical properties must be guaranteed. Q255A does not undergo impact testing. Q255B requires room temperature impact. Test, use V-notch sample A4 C4 A4 steel to ensure the mechanical properties, C4 steel to ensure the chemical composition and mechanical properties, basically the same as Q255 steel C4 steel additional guarantee impact test, use U-notch sample Q275 regardless of grade, The specified chemical composition and mechanical properties must ensure the chemical composition and mechanical properties guaranteed by C5 C5 steel, which are basically the same as Q275 steel. 2. Low alloy steel currently uses GB/T1591-94 instead of 1591-88. Some new and old steel grades are now The comparison is as follows: GB/T1591-94 GB1591-88 Q295 09MnV 09MnNb 12Mn Q345 12MnV 16Mn 16MnRE Q390 15MnV 15MnTi 16MnNb Q420 15MnVN 14MnVTiRE