Explanation of steel number classification method in China
1. Carbon Structural Steel
① Composed of Q + number + quality grade symbol + deoxidation method symbol. The steel number is prefixed with “Q”, representing the yield strength of the steel, and the following number indicates the yield strength value in MPa. For example, Q235 indicates 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, D. Deoxidation method symbols: F represents boiling steel; b represents semi-finished steel; Z represents dead steel; TZ stands for special dead steel. Dead steel can be unmarked, i.e. both Z and TZ can be unmarked. For example, Q235-AF represents grade A boiling steel.
③ Special-purpose carbon steel, such as bridge steel, marine steel, etc., basically adopts the expression method of carbon structural steel, but a letter indicating the purpose is added to the end of the steel number.
2. High quality carbon structural steel
① The first two digits of the steel number indicate the carbon content of the steel, which is expressed in ten thousandths of the average carbon content. For example, for steel with an average carbon content of 0.45%, the steel number is “45”, which is not a serial number, so it cannot be read as steel number 45.
② High-quality carbon structural steel with high manganese content must mark the element manganese, such as 50Mn.
③ Boiling steel, semi-finished steel and high-quality carbon structural steel for special purposes must be specifically marked at the end of the steel number. For example, the steel number for semi-finished steel with an average carbon content of 0.1% is 10b.
3. Tool carbon steel
① The steel number is prefixed with “T” to avoid confusion with other types of steel.
② The number in the steel number indicates the carbon content, which is expressed in thousandths of the average carbon content. For example, “T8” indicates an average carbon content of 0.8%.
③ If the manganese content is high, “Mn” will be marked at the end of the steel number, such as “T8Mn”.
④ The phosphorus and sulfur content of high-quality carbon tool steel is lower than that of general high-quality carbon tool steel. The letter “A” is added to the end of the steel number to indicate the difference, such as “T8MnA”.
4. Free cutting steels
① Steel grade begins with “Y” to distinguish it from high-quality carbon structural steel.
② The number after the letter “Y” indicates the carbon content, represented as a percentage in ten thousand of the average carbon content. For example, for free cutting steel with an average carbon content of 0.3%, the steel grade would be “Y30”.
③ For those with higher manganese content, “Mn” is also indicated after the steel type, such as “Y40Mn”.
5. Alloy structural steels
① The first two digits of the steel type represent the carbon content of the steel, expressed as a percentage in ten thousand of the average carbon content, such as 40Cr.
② The main alloying elements of steel, except some microalloying elements, are generally represented as a percentage. When the average alloy content is <1.5%, the steel grade typically only marks the element symbol without indicating the content. However, in special cases where confusion may arise, the symbol may be followed by the number “1”, for example, “12CrMoV” and “12Cr1MoV”. The former has a chromium content of 0.4-0.6%, while the latter has a content of 0.9-1.2%, all other components being equal. When the average alloying element content is ≥1.5%, ≥2.5%, ≥3.5%, etc., the content should be indicated after the element symbol, which can be represented as 2, 3, 4, etc. For example, 18Cr2Ni4WA.
③ Steel alloying elements such as vanadium (V), titanium (Ti), aluminum (Al), boron (B) and rare earths (RE) are all considered microalloying elements. Although their levels are very low, they must be indicated in the steel class. For example, in 20MnVB steel, the vanadium content is 0.07-0.12% and the boron content is 0.001-0.005%.
④ High quality steel must have an “A” added at the end of the steel type to distinguish it from general quality steel.
⑤ For specialized purpose alloy structural steels, the steel type must be prefixed (or suffixed) with a symbol that represents the purpose of the steel. For example, 30CrMnSi steel used specifically for rivet bolts would be called ML30CrMnSi.
6. Low-alloy, high-strength steel
① The method of denoting the steel number is fundamentally similar to that of alloy structural steel.
② For specialized low-alloy, high-strength steels, the designation must be appended to the end of the steel number. For example, “16Mnq” is the specific grade for bridge construction, “16MnL” for automotive beams and “16MnR” for pressure vessels, all derived from 16Mn steel.
7. Spring Steel
Spring steel, based on its chemical composition, can be divided into carbon spring steel and alloy spring steel. The representation of its steel numbers is similar to high-quality carbon structural steel and alloy structural steel respectively.
8. Bearing steel
① The steel number is prefixed with the letter “G”, indicating a category of bearing steel.
② The carbon content of bearing steel with high carbon and chromium content is not indicated in the steel number, while the chromium content is expressed in per thousand. For example, GCr15. The representation method for carburizing the steel number of bearing steel is essentially the same as that of alloyed structural steel.
9. Alloy tool steel and high speed tool steel
① When the average carbon content of tool steel alloy is ≥1.0%, it is not indicated; when it is <1.0%, it is expressed in per thousand. For example, Cr12, CrWMn, 9SiCr, 3Cr2W8V.
② The method of representing the content of alloy elements in steel is fundamentally similar to that of alloy structural steel. However, for tool steel alloys with lower chromium content, their chromium content is expressed in per thousand and the number indicating the content is prefixed with “0” to distinguish it from the generally represented percentage of other elements. For example, Cr06.
③ The number of high-speed tool steel generally does not indicate the carbon content, but only the average percentage of various alloying elements. For example, the designation for tungsten high-speed steel is “W18Cr4V”. A steel number prefixed with the letter “C” indicates that its carbon content is higher than the general steel number without the “C” prefix.
10. Stainless steel and heat resistant steel
① The carbon content of steel is represented in thousandths. For example, the average carbon content of “2Cr13” steel is “0.2%. If the carbon content in the steel is ≤0.03% or ≤0.08%, it is indicated by “00” and “0” respectively before the steel number, such as 00Cr17Ni14Mo2, 0Cr18Ni9, etc.
② The main alloying elements of steel are represented in percentages, while titanium, niobium, zirconium, nitrogen, etc. are marked in accordance with the method of indicating microalloy elements in said alloy structural steel.
11. Steel Welding Electrode
The letter “H” is prefixed to the steel number to differentiate it from other types of steel. For example, stainless steel welding wire is “H2Cr13”, which can be distinguished from “2Cr13” stainless steel.
12. Electrical Silicon Steel
① The steel number is composed of letters and numbers. The letters at the beginning of the steel number, DR means hot-rolled silicon steel for electrical use, DW means cold-rolled non-oriented silicon steel for electrical use, and DQ means cold-rolled grain-oriented silicon steel for electrical use. electrical use.
② The numbers after the letters represent 100 times the value of iron loss (w/kg).
③ If the letter “G” is added to the end of the steel number, it indicates that it is inspected with high frequency; if “G” is not added, it indicates that it is inspected at a frequency of 50 Hz. For example, the steel number DW470 indicates that the maximum value of iron loss per unit weight of the cold-rolled non-oriented silicon steel product for use electricity at a frequency of 50 Hz is 4.7 w/kg.
13. Electric Pure Iron
Your brand is made up of the letters “DT” and numbers. “DT” means pure electric iron and the number represents the order number of different brands such as DT3. The letter added after the number represents electromagnetic performance: A – advanced, E – special, C – super, like DT8A.
Introduction to Steel Varieties
Sheets: Cold-rolled coils, cold-rolled sheets, hot-rolled coils, hot-rolled sheets, color coated coils, color coated sheets, medium and thick sheets
Coating: Hot dip galvanized coil, electro galvanized coil, hot dip tinplate coil, tinplate coil, chrome plated coil, plastic composite steel, other coated steel coils, tinplate
Profiles and Bars: Rebar, wire rod, round bars, angles, I beams, flat bars, H beams, rails, special profiles, high quality profiles, other profiles
Stainless steel: Stainless steel plate, stainless steel coil, stainless steel tube, stainless steel profile, stainless steel wire, stainless steel billet, stainless steel products, other stainless steel materials
Tubes: seamless steel tubes, welded steel tubes
Steel Billet: Plate Billet, Square Billet, Tube Billet
Ferroalloys: Ferrosilicon, ferromanganese, ferrovanadium, ferrochrome, ferrotitanium
Other steels: silicon steel sheets, metal products, others
Steel Billet:
Steel billet is a semi-finished product for steel production and generally cannot be used directly in society. Billet is produced through three process methods: first, direct casting of molten steel into billets using continuous casting equipment in the steel production system (see Chapter 4 for details); secondly, semi-finished steel products processed from steel ingots or continuous casting billets produced by the steel production system using the rolling system; third, semi-finished products processed from steel ingots produced by the steel system using forging equipment.
Steel Standards
Carbon Structural Steels GB700-88, replacing GB700-79, this standard is adopted in reference to ISO 630 “Structural Steels”.
1. Scope and Content of this Standard
This standard specifies the technical conditions for carbon structural steels.
This standard is applicable to structural steels in general and hot-rolled steel sheets, steel strips, profiled steel and rolled steel for engineering purposes. These products can be used for welding, riveting and screwing components, generally in the supplied state.
The chemical composition specified in this standard applies to steel ingots (including continuously cast slabs), steel billets and their products.
2. Referenced Patterns
GB222 Sampling method for chemical analysis of steel and allowable deviation of the chemical composition of the finished product
GB223 Methods for chemical analysis of iron, steel and alloys
GB228 Metal Tensile Test Method
GB232 metal bending test method
GB247 General provisions for acceptance, packaging, marking and quality certificates of steel plates and strips
GB2101 General provisions for acceptance, packaging, marking and quality certificates of profiled steel
GB2106 V-Notch Charpy Impact Test Method for Metals
GB2975 Sampling arrangements for testing mechanical and process properties of steel materials
GB4159 Low Temperature Metal Charpy Impact Test Method
GB6397 Metal Tensile Test Samples
3. Steel quality nomenclature, codes and symbols
3.1 Steel Class Nomenclature
The type of steel is sequentially composed of a letter that represents the yield limit, a numerical value for the yield limit, quality grade symbol and deoxidation method symbol.
For example: Q235-A·F
3.2 Symbols
Q – First letter of Chinese Pinyin for the word “yield” in “yield point” for steel;
A, B, C, D – Represent the respective quality levels;
F – First letter of Chinese Pinyin for the word “boil” in “boiling steel”;
b – First letter of Chinese Pinyin for the word “semi” in “semi-dead steel”;
Z – First letter of Chinese Pinyin for the word “dead” in “dead steel”;
TZ – Chinese Pinyin initial letters for the words “special dead” in “special dead steel”.
In the class nomenclature, the symbols “Z” and “TZ” are omitted.
4. Dimensions, shape, weight and permitted deviations
The dimensions, shape, weight and permissible deviations of the steel must comply with the respective standards.
5. Technical Requirements
5.1 Steel Class and Chemical Composition
5.1.1 The type of steel and chemical composition (fusion analysis) must be in accordance with what is stipulated in Table 1.
table 1
| Note | Level | Chemical composition, % | Deoxygenation method | ||||
| W | Mn | Yes | s | P | |||
| ≤ | |||||||
| Q195 | – | 0.06~0.12 | 0.25~0.50 | 0:30 | 0.050 | 0.045 | F, b, z |
| Q215 | A | 0.09~0.15 | 0.25~0.55 | 0:30 | 0.050 | 0.045 | F, b, z |
| B | 0.045 | ||||||
| Q235 | A | 0.14~0.22 | 0.3~0.651 | 0:30 | 0.50 | 0.045 | F, b, z |
| B | 0.12~0.20 | 0.3~0.701 | 0.045 | ||||
| W | ≤0.18 | 0.35~0.80 | 0.040 | 0.040 | Z | ||
| D | ≤0.17 | 0.035 | 0.035 | TZ | |||
| Q255 | A | 0.18~0.28 | 0.40~0.70 | 0:30 | 0.050 | 0.045 | F, b, z |
| B | 0.045 | ||||||
| Q275 | – | 0.28~0.38 | 0.50~0.80 | 0.35 | 0.050 | 0.045 | beauty |
Note: For Q235A and B grade boiling steel, the upper limit of Mn content is 0.60%.
5.1.1.1 The silicon content in boiling steel must be ≤0.07%; in semi-finished steel, it should be ≤0.17%, and the lower limit for silicon content in dead steel is 0.12%.
5.1.1.2 Grade D steel must contain sufficient elements to form a fine-grained structure, such as an acid-soluble aluminum content ≥0.015% or total aluminum content ≥0.020% in the steel.
5.1.1.3 The residual elements of chromium, nickel and copper in the steel should be ≤0.30% each, and the nitrogen content of the oxygen converting steel should be ≤0.008%. If the supplier can guarantee this, no analysis is necessary. With the necessary agreement, the copper content in grade A steel can be ≤0.35%. At this point, the supplier must analyze the copper content and note its quantity on the quality certificate.
5.1.1.4 The residual arsenic content in steel must be ≤0.08%. Steel refined from pig iron smelted with arsenic-containing ore must have its arsenic content agreed between the supplier and the recipient. If the raw materials do not contain arsenic, it is not necessary to analyze the arsenic content in steel.
5.1.1.5 To ensure that the mechanical properties of steel meet this standard, the lower limit of carbon, silicon manganese content in Grade A steel, and the lower limit of carbon, manganese content in other types of steel cannot be used as delivery conditions. However, its content (fusion analysis) must be specified in the quality certificate.
5.1.1.6 When supplying commercial steel ingots (including continuous casting blanks) and steel billets, the supplier shall ensure that the chemical composition (melting analysis) is in accordance with Table 1, but to ensure that the performance of the steel laminate meets the requirements of this standard, the chemical composition of class A and B steel can be adjusted accordingly according to customer needs under a separate agreement.
5.1.2 Allowable deviations in the chemical composition of finished steel and commercial billets shall be in accordance with Table 1 of GB222. No guarantee is given regarding deviation in chemical composition of finished boiling steel products and commercial billets.
5.2 Casting Method
The steel is melted in an oxygen converter, open furnace or electric furnace, unless the customer has special requirements, which must be indicated in the contract. The casting method is usually decided by the supplier.
5.3 Delivery Status
Steel is generally delivered in hot-rolled condition (including controlled rolling). At the customer's request and by mutual agreement, it can also be delivered in a state of standardization treatment (excluding grade A steel).
5.4 Mechanical Properties
5.4.1 The tensile and impact tests of the steel must be in accordance with the specifications in Table 2, and the flexural test must be in accordance with the standards in Table 3.
| σb | Tensile strength | MPa, N/mm 2 |
| σ is | Yield point | MPa, N/mm 2 |
| σ P | Specified non-proportional stretching stress | MPa, N/mm 2 |
| σ P0.2 | Tension is set at a non-proportional stretch rate of 0.2%. | MPa, N/mm 2 |
| δ | Stretching after fracture | ％ |
| δ 5 | Post-break elongation rate of short proportional samples | ％ |
| δ 10 | Post-fracture elongation rate of a long proportional specimen. | ％ |
| δxmm | Post-break elongation rate of standard length sample | ％ |
Table 2: Tensile and impact test of steel
| Note | Level | Traction test | Impact test | |||||||||||||
| Yield point σ is N/mm 2 |
Tensile strengthσ b N/ mm2 |
Elongation Rate δ 5 % |
||||||||||||||
| Steel Thickness (Diameter), mm |
Steel Thickness (Diameter), mm |
|||||||||||||||
| ≤16 | 16~40 | 40 ~ 60 | 60~100 | 100~150 | >150 | ≤16 | 16~40 | 40~60 | 60~100 | 100~150 | >150 | Temperature ℃ |
V-notch impact (longitudinal)J |
|||
| ≤ | ≤ | ≤ | ||||||||||||||
| Q195 | – | (195) | (185) | – | – | – | – | 315-430 | 33 | 32 | – | – | – | – | – | – |
| Q215 | A | 215 | 205 | 195 | 185 | 175 | 165 | 335-450 | 31 | 30 | 29 | 28 | 27 | 26 | – | – |
| B | 20 | 27 | ||||||||||||||
| Q235 | A | 235 | 225 | 215 | 205 | 195 | 185 | 375-500 | 26 | 25 | 24 | 23 | 22 | 21 | – | – |
| B | 20 | 27 | ||||||||||||||
| W | 0 | |||||||||||||||
| D | -20 | |||||||||||||||
| Q255 | A | 255 | 245 | 235 | 225 | 215 | 205 | 410-550 | 24 | 23 | 22 | 21 | 20 | 19 | – | – |
| B | 20 | 27 | ||||||||||||||
| Q275 | – | 275 | 265 | 255 | 245 | 235 | 225 | 490-630 | 20 | 19 | 18 | 17 | 16 | 15 | – | – |
Table 3: Steel Bending Test
| Note | Sample direction | Cold bending test B=2a 180° |
||
| Steel thickness (diameter), mm |
||||
| 60 | >60~100 | >100~200 | ||
| radius of curvature d | ||||
| Q195 | Vertical | 0 | – | – |
| Horizontal | 0.5a | |||
| Q215 | Vertical | 0.5a | 1.5a | 2a |
| Horizontal | The | 2a | 2.5a | |
| Q235 | Vertical | A | 2a | 2.5a |
| Horizontal | 1.5a | 2.5a | 3a | |
| Q255 | / | 2a | 3a | 3.5a |
| Q275 | / | 3a | 4a | 4.5a |
Note: B refers to the width of the sample and a refers to the thickness (diameter) of the steel.
5.4.1.1 The yield strength of class Q195 is for reference only and should not be considered as a condition of delivery.
5.4.1.2 For tensile and bending tests, steel plates and strips shall use transverse specimens, and the elongation rate may decrease by 1% (absolute value) compared with Table 2. Profiled steel shall use longitudinal specimens.
5.4.1.3 Cold bending tests for all Class A steels are carried out only if required by the purchaser. When the cold bending test is passed, the upper limit of tensile strength can be disregarded as a delivery condition.
5.4.2 The Charpy impact test (V-notch) must meet the specifications in Table 2.
5.4.2.1 The value of the Charpy impact function (V-notch) is calculated as the arithmetic mean of a set of three individual sample values, allowing a sample value to be less than the prescribed value, but not less than 70% of the prescribed value.
5.4.2.2 When carrying out an impact test with a small sample size of 5mm x 10mm x 55mm, the test result must be ≥50% of the specified value.
5.4.3 Grade B steel made from boiling steel should generally have a thickness (diameter) ≤25 mm.
5.5 Surface Quality
The surface quality of the steel must be in accordance with the relevant standard specifications.
6. Testing methods
6.1 Inspection items, sample quantities, sampling methods and test methods for each batch of steel must comply with the specifications in Table 4.
| Serial number | Inspection Item | Sample Quantity | Serial number | Inspection Item |
| 1 | Chemical analysis | 1 (Oven batch number) |
GB222 | GB223.1~223.5 GB223.8~223.12 GB223.18~223.19 GB223.23~223.24 GB223.31~223.32 GB233.36 |
| two | Stretching | 1 | GB2975 | GB228 GB6397 |
| 3 | Cold Bending | GB232 | ||
| 4 | Impact on ambient temperature | 3 | GB2106 | |
| 5 | Low temperature impact | GB4159 |
6.1.1 When carrying out the cold bending test for steels with a base diameter thickness greater than 20mm, the sample must be flattened laterally until its thickness reaches 20mm. The diameter of the bending core must be determined according to Table 3. During the test, the unprocessed surface must be outside. If the sample has not been planed, the diameter of the flexural core must be increased by one sample thickness above 'a' relative to the value listed in Table 3.
6.1.2 The longitudinal axis of the impact specimen must be parallel to the rolling direction.
6.1.3 When carrying out the impact test for steel sheets, steel strips, profiles with a thickness of ≥12mm or steel bars with a diameter of less than 16mm, a sample of 5mm×10mm×55mm must be used. For steel plates, steel strips, profiles with a thickness of 6mm to less than 12mm or steel bars with a diameter of 12mm to less than 16mm, a small sample size of 5mm × 10mm × 55mm should be used. The impact specimen may retain a rolling surface.
7. Inspection Rules
7.1 Steel materials must be inspected and accepted by technical supervision.
7.2 Steel materials shall be accepted in batches, each batch consisting of the same type, same furnace burner, same grade, same type, same size and same delivery status. The weight of each batch must not exceed 60t.
For steel billets or continuous casting cast in steel furnaces with rated capacity ≤30t, it is allowed to form a mixed batch of grade A or grade B steel of the same type, same smelting and casting method, but different furnace numbers. However, each batch should not have more than six kiln numbers, and the difference in carbon content between kiln numbers should not exceed 0.02%, and the difference in manganese content should not exceed 0.15%.
7.3 If the results of the Charpy (V-notch) impact test of the steel do not meet the specifications in section 5.4.2, a set of three samples shall be retested from the same batch of steel. The average value of the six samples before and after must not be less than the specified value, but two samples are allowed to be less than the specified value, and only one sample can be 70% of the specified value.
7.4 Reinspection and acceptance rules for other steel inspection items shall comply with the regulations of GB247 and GB2101.
8. Packaging, marking and quality certificate
Steel packaging, marking and quality certificate must meet the requirements of GB247 and GB2101.
