Steel knowledge
Thread Content
Steel Knowledge – Basic Concepts of Steel 2I. Definitions of Terms Related to Steel
I. Eutectoid steel, hypoeutectoid steel, hypereutectoid steel
1. Eutectoid steel: Carbon is dissolved in the crystal lattice of iron to form a solid solution. The solid solution formed when carbon dissolves in α-iron is called ferrite, while that formed when it dissolves in γ-iron is called austenite. Both ferrite and austenite possess good plasticity. When all the carbon in an iron-carbon alloy cannot be dissolved in ferrite or austenite, the remaining carbon forms a compound with iron – iron carbide (Fe3C). The crystal structure of this compound is called cementite; it has extremely high hardness and almost no plasticity. As can be seen from the iron-carbon equilibrium diagram, which shows the relationship between the microstructure of steel, its carbon content, and temperature, phase transformation in this alloy occurs at a constant temperature when the carbon content is exactly 0.77%, meaning that about 12% of the alloy consists of cementite (iron carbide) and about 88% consists of ferrite. That is, at this specific ratio of cementite and ferrite, during phase transformation, if either one disappears, the other also disappears (when heated); if either one appears, the other appears as well. In this regard, this type of structure behaves similarly to the phase transformation in pure metals. For this reason, this two-phase structure with a specific composition is regarded as a single type of structure and named pearlite; such steel is then called eutectoid steel. Steel with a carbon content of exactly 0.77% is called eutectoid steel, and its microstructure is pearlite. 2. Hypoeutectoid steel: Common structural steels have a carbon content of less than 0.5%. Since the carbon content is below 0.77%, the amount of cementite in the microstructure is also less than 12%. As a result, aside from part of the ferrite that combines with cementite to form pearlite, excess ferrite remains, so the microstructure of this type of steel consists of ferrite + pearlite. The lower the carbon content, the smaller the proportion of pearlite in the steel structure, and the lower the strength of the steel; however, its ductility is better. Such steels are collectively referred to as hypoeutectoid steels. 3. Hypereutectoid steel: Tool steels typically have a carbon content of over 0.77%. In such steel, the proportion of cementite exceeds 12%; as a result, in addition to pearlite formed together with ferrite, there is also excess cementite. Therefore, the microstructure of this type of steel consists of pearlite plus cementite. These types of steel are collectively referred to as hypereutectoid steels. II. Terms related to the mechanical properties of steel 1. Yield point (σs) When steel or a specimen is under tension, if the stress exceeds the elastic limit, and the steel or specimen continues to undergo significant plastic deformation even though the stress no longer increases, this phenomenon is known as yield. The minimum stress value at which this yield phenomenon occurs is called the yield point. Let Ps be the external force at the yield point s, and Fo be the cross-sectional area of the specimen; then the yield point σs is given by σs = Ps/Fo (in MPa). MPa stands for megapascals, which is equivalent to N (newtons) per mm2. (1 MPa = 106 Pa, where Pa is pascals, equal to N/m2.) 2. Yield strength (σ0.2): For some metal materials, the yield point is not very distinct, making it difficult to measure it. Therefore, in order to assess the yield properties of such materials, the stress at which a permanent residual plastic deformation equal to a certain value (usually 0.2% of the original length) occurs is defined as the conditional yield strength, or simply yield strength σ0.2. 3. Tensile strength (σb): The maximum stress value that a material reaches from the beginning of tensioning until it breaks. It indicates the degree to which steel resists fracture. Corresponding to tensile strength are compressive strength, bending strength, and so on. Let Pb be the maximum tensile force reached before the material breaks, and Fo be the cross-sectional area of the specimen; then the tensile strength σb = Pb/Fo (MPa). 4. Elongation (δs) The percentage of the plastic elongation length of a material after it is pulled to break, relative to the original length of the sample, is called elongation or stretch. 5. Yield ratio (σs/σb) The ratio of a steel material’s yield point (yield strength) to its tensile strength is called the yield ratio. The higher the yield ratio, the greater the reliability of structural components. Generally, the yield ratio for carbon steel is 0.6–0.65, for low-alloy structural steel it is 0.65–0.75, and for alloy structural steel it is 0.84–0.86. 6. Hardness: Hardness refers to a material’s ability to resist the penetration of a hard object into its surface. It is one of the important performance indicators of metal materials. Generally, the higher the hardness, the better the wear resistance. Common hardness indicators include Brinell hardness, Rockwell hardness, and Vickers hardness. ⑴Brinell hardness (HB) is determined by pressing a hardened steel ball of a certain size (usually with a diameter of 10 mm) onto the surface of a material under a specific load (typically 3000 kg). After holding this pressure for a certain period of time, the load is removed; the ratio of this load to the area of the resulting indentation gives the Brinell hardness value (HB), which is expressed in kilogram-force per mm2 (N/mm2). ⑵Rockwell hardness (HR): When HB>450 or the specimen is too small, the Brinell hardness test cannot be used; instead, Rockwell hardness measurement is employed. It involves using a diamond cone with an apex angle of 120° or steel balls with diameters of 1.59 and 3.18 mm to press against the surface of the material under test; the hardness of the material is determined from the depth of the indentation. Depending on the hardness of the test material, it is expressed using three different scales: HRA: This is the hardness determined using a 60 kg load and a diamond cone indenter, and it is used for materials with extremely high hardness (such as cemented carbides). HRB: It is the hardness obtained using a load of 100 kg and hardened steel balls with a diameter of 1.58 mm; it is used for materials with lower hardness, such as annealed steel and cast iron. HRC: It is the hardness determined using a 150 kg load and a diamond cone indenter, and it is used for materials with very high hardness (such as quenched steel). ⑶Vickers hardness (HV) is determined by using a diamond square pyramid indenter with a load of 120 kg or less and an apex angle of 136° to press into the surface of the material; the Vickers hardness value is then calculated by dividing the surface area of the indentation formed in the material by the load applied. III. Terms related to heat treatment of steel 1. Annealing of steel: Heating steel to a certain temperature and holding it there for a period of time before allowing it to cool down slowly is known as annealing. Annealing of steel is a heat treatment method in which the steel is heated to a temperature at which phase transformation or partial phase transformation occurs, and then cooled slowly after being held at that temperature. The purpose of annealing is to eliminate structural defects, improve the structure by homogenizing the composition, refine the grains, enhance the mechanical properties of the steel, and reduce residual stresses ； It can also reduce hardness, increase plasticity and toughness, and improve machinability. Therefore, annealing serves both to eliminate and improve the structural defects and internal stresses remaining from previous processing steps, as well as to prepare for subsequent processes; hence, annealing is considered a type of heat treatment for semi-finished products, also known as pre-heat treatment. 2. Normalizing of steel: Normalizing is a heat treatment process in which steel is heated above its critical temperature to cause it to transform entirely into uniform austenite, after which it is cooled naturally in air. It can eliminate the reticular cementite in hypereutectoid steel; for hypoeutectoid steel, normalizing can refine the grain structure and improve overall mechanical properties. For parts with modest performance requirements, using normalizing instead of annealing is a more economical option. 3. Quenching of steel: Quenching is a heat treatment method in which steel is heated above its critical temperature, held at that temperature for a certain period of time, and then quickly placed in a quenching agent to cause a sudden drop in its temperature. It is cooled at a rate faster than the critical cooling rate, resulting in an unstable microstructure dominated by martensite. Quenching can increase the strength and hardness of steel, but it reduces its ductility. Common quenching agents used in quenching include water, oil, alkaline solutions, and salt solutions. 4. Tempering of steel: Reheating the quenched steel to a certain temperature and then cooling it using specific methods is called tempering. Its purpose is to eliminate the internal stresses resulting from quenching, reduce hardness and brittleness, in order to achieve the desired mechanical properties. Tempering is divided into three categories: high-temperature tempering, medium-temperature tempering, and low-temperature tempering. Tempering is often used in combination with quenching and normalizing. ⑴Quenching and tempering: The heat treatment method that involves high-temperature tempering after quenching is called quenching and tempering. High-temperature tempering refers to tempering at temperatures between 500-650°C. Quenching and tempering allows for a significant adjustment of the properties and quality of steel; it results in good strength, plasticity, and toughness, as well as excellent overall mechanical properties. ⑵Aging treatment: To prevent changes in the dimensions and shape of precision measuring tools, molds, or parts over time due to long-term use, it is common to reheat the workpieces to 100–150°C after low-temperature tempering (at a temperature of 150–250°C), and hold them at this temperature for 5–20 hours before further finishing. This treatment, aimed at stabilizing the quality of precision components, is known as aging. It is particularly important to carry out aging treatment on steel components under low-temperature or dynamic load conditions in order to eliminate residual stresses and stabilize the structure and dimensions of the steel. 5. Surface heat treatment of steel ⑴ Surface quenching: This involves rapidly heating the surface of a steel part above its critical temperature, and then cooling it quickly before heat has time to reach the interior of the part. As a result, the surface layer is transformed into a martensitic structure, while no phase change occurs in the interior, thereby achieving surface hardening without affecting the interior of the part. Suitable for medium carbon steel. ⑵Chemical heat treatment refers to a heat treatment process in which atoms of chemical elements are implanted into the surface layer of a workpiece, taking advantage of the ability of atoms to diffuse at high temperatures. This process is used to alter the chemical composition and structure of the surface layer, thereby giving the surface layer of the steel the desired structure and properties. Depending on the type of element infiltrated, chemical heat treatment can be divided into four methods: carburizing, nitriding, cyaniding, and metal infiltration. Carburizing: Carburizing refers to the process of allowing carbon atoms to penetrate into the surface layer of steel. It also enables the workpiece made of low-carbon steel to have a surface layer similar to that of high-carbon steel; through quenching and low-temperature tempering, this surface layer gains high hardness and wear resistance, while the core part of the workpiece retains the toughness and ductility of low-carbon steel. Nitriding: Also known as nitration, it refers to the process of introducing nitrogen atoms into the surface layer of steel. Its purpose is to increase the hardness and wear resistance of the surface layer, as well as to enhance fatigue strength and corrosion resistance. The gas nitriding method is commonly used in current production. Cyanidation: Also known as carbonitriding, it refers to the process of simultaneously diffusing carbon atoms and nitrogen atoms into steel. It endows the steel surface with carburizing and nitriding properties. Metal infiltration: refers to the process in which metal atoms penetrate into the surface layer of steel. It involves alloying the surface layer of steel, so that the surface of the workpiece possesses the properties of certain alloy steels and special steels, such as heat resistance, wear resistance, oxidation resistance, and corrosion resistance. Commonly used in production methods include aluminum infiltration, chromium infiltration, boron infiltration, silicon infiltration, etc. II. The method of designating steel grades in China I. Overview of the method of designating steel grades in China The grade of steel, also referred to as the steel grade designation, is the name given to each specific steel product; it serves as a common language for understanding steel. China’s method for denoting steel grades, in accordance with the **standard \"Method for Denoting Steel Product Grades\" (GB221-79), uses a combination of Pinyin letters, chemical element symbols, and Arabic numerals. That is: ① The chemical elements in the steel grade are represented using international chemical symbols, such as Si, Mn, Cr, etc. Mixed rare earth elements are denoted by “RE” (or “Xt”). ②The product name, purpose, smelting and casting methods, etc., are generally represented by abbreviated letters in Pinyin, as shown in the table. ③The contents of major chemical elements in steel (%) are expressed in Arabic numerals. II. Classification explanation of steel grade designation methods in China 1. Carbon structural steel ①Composed of Q + a number + a quality grade symbol + a deoxidation method symbol. Its steel grade is prefixed with “Q”, which denotes the yield strength of the steel; the number that follows indicates the value of this yield strength, in MPa. For example, Q235 refers to a carbon structural steel with a yield strength (σs) of 235 MPa. ②If necessary, symbols indicating the quality grade and deoxidation method can be indicated after the steel grade. The quality grade symbols are A, B, C, and D respectively. Deoxidation method symbol: F denotes boiling steel ； b denotes semi-killed steel: Z denotes killed steel ； TZ denotes special killed steel; killed steel does not require a symbol, meaning neither Z nor TZ is necessary. For example, Q235-AF denotes grade A boiling steel. ③Special-purpose carbon steels, such as bridge steel and marine steel, basically use the designation method for carbon structural steel, but letters indicating the purpose are added at the end of the steel grade. 2. High-quality carbon structural steel: 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, for steel with an average carbon content of 0.45%, the grade is “45”; this is not a sequential number, so it should not be referred to as steel grade 45. 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 grade designation; for example, semi-killed steel with an average carbon content of 0.1% has a grade designation of 10b. 3. Carbon tool steel ① The steel grade is prefixed with “T” to avoid 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”. 4. Free-cutting steel: 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”. 5. Alloy structural steel: 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 is <1.5%, only the element symbols are usually indicated in the steel grade, without specifying the content; however, in cases where confusion might arise, the number \"1\" can also be added after the element symbol. For example, in the steel grades \"12CrMoV\" and \"12Cr1MoV\", the chromium content is 0.4–0.6% in the former and 0.9–1.2% in the latter, with all other components being identical. When the average content of alloying elements is ≥1.5%, ≥2.5%, ≥3.5%..., the content should be indicated after the element symbol, which can be represented as 2, 3, 4..., etc. accordingly. For example, 18Cr2Ni4WA. ③Alloying elements in steel such as vanadium V, titanium Ti, aluminum AL, boron B, and rare earths RE all belong to micro-alloying elements; although their contents are low, they still need to be indicated in the steel grade. For example, in 20MnVB steel. Vanadium is 0.07-0.12%, and boron is 0.001-0.005%. ④High-grade quality steel should have “A” added at the end of its grade designation to distinguish it from ordinary quality steel. ⑤Alloy structural steels for specific purposes have steel grades preceded by (or followed by) symbols indicating the purpose of that steel grade. For example, the 30CrMnSi steel dedicated to rivet screws is denoted by the steel grade ML30CrMnSi. 6. Low-alloy high-strength steel ① The method of designating steel grades is basically the same as that for alloy structural steel. ②For specialty low-alloy high-strength steels, it should be indicated at the end of the steel grade. For example, for 16Mn steel, the special grade used for bridges is “16Mnq”, the special grade for automobile frames is “16MnL”, and the special grade for pressure vessels is “16MnR”. 7. Spring steel: Spring steel can be divided into two categories based on its chemical composition – carbon spring steel and alloy spring steel. The method of designating steel grades is basically the same for the former as that used for high-quality carbon structural steel, while it is similar to that used for alloy structural steel for the latter. 8. Rolling bearing steel ① The steel grade is prefixed with the letter “G” to indicate it belongs to the rolling bearing steel category. ②The carbon content of high-carbon chromium bearing steel grades is not specified, while the chromium content is expressed as a percentage per thousand, for example in GCr15. The method of designating steel grades for carburized bearing steel is basically the same as that for alloy structural steel. 9. Alloy tool steels and high-speed tool steels: ① When the average carbon content of alloy tool steel grades is ≥1.0%, the carbon content is not indicated ； When the average carbon content is <1.0%, it is expressed as a per thousand. Such as Cr12, CrWMn, 9SiCr, 3Cr2W8V. ②The method of expressing the content of alloying elements in steel is basically the same as that for alloy structural steel. However, for alloy tool steels with lower chromium contents, the chromium content is expressed as a few thousandths, and a “0” is added in front of the number indicating the content, in order to distinguish it from the method of expressing the content of other elements as percentages. For example, Cr06. ③The grade of high-speed tool steel generally does not indicate the carbon content; instead, it only shows the percentage average content of various alloying elements. For example, the grade of tungsten-based high-speed steel is denoted as “W18Cr4V”. Steel grades marked with the letter “C” indicate that their carbon content is higher than that of standard steel grades that are not marked with “C”. 10. Stainless steel and heat-resistant steel ①The carbon content in the steel grade is expressed as a percentage per thousand. 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%, the letters “00” and “0” are respectively prefixed to the steel grade, such as 00Cr17Ni14Mo2, 0Cr18Ni9, etc. ②The main alloying elements in steel are expressed as percentages, while titanium, niobium, zirconium, nitrogen, and so on are indicated using the same method used for micro-alloying elements in alloy structural steels. 11. Welding rod steel: Its steel grade is preceded by the letter “H” to distinguish it from other types of steel. For example, the stainless steel welding wire is “H2Cr13”, which can be distinguished from the stainless steel “2Cr13”. 12. Silicon steel for electrical use ① The steel grade is composed of letters and numbers. The initial letters DR in the steel grade designation indicate hot-rolled silicon steel for electrical use, DW indicates cold-rolled non-oriented silicon steel for electrical use, and DQ indicates cold-rolled oriented silicon steel for electrical use. ②The number following the letter represents 100 times the iron loss value (W/kg). ③If the letter “G” is added at the end of the steel grade, it indicates that testing was conducted at high frequencies ； The absence of the “G” indicates that the test was conducted at a frequency of 50 Hz. For example, the steel grade DW470 indicates that for cold-rolled non-oriented silicon steel products used in electrical applications, the maximum iron loss per unit weight at a frequency of 50 Hz is 4.7 W/kg. 13. Pure iron for electrical use ① Its grade is composed of the letters “DT” and numbers; “DT” denotes pure iron for electrical use, while the numbers indicate the sequence number of different grades, such as DT3. ②The letter added after the digit indicates the electromagnetic performance: A—advanced, E—extra premium, C—superior; for example, DT8A. III. Comparison of Some New and Old Steel Grades 1. Comparison of carbon structural steel grades under new and old standards. The new GB700-88 standard is based on the international standard ISO630 \"Structural Steel\", whereas the old GB700-79 standard was primarily based on the former Soviet standard IOCT380. As a result, the methods of designating steel grades in both standards, as well as the technical requirements specified for each grade, differ. The comparison of steel grades under the old and new standards is shown below. GB700-88 standard, GB700-79 standard: Steel grades and technical requirements. Steel grade and technical requirements: Q195 – no grades are specified; its chemical composition and mechanical properties (σs, σb, δ, and cold bending capacity) must be ensured. Steel A1 guarantees specified mechanical properties (σs, σb, δ, and cold bending capacity), while steel B1 has a chemical composition identical to that of Q195. For products such as rolled sheets and bars, the requirements regarding their mechanical properties can be specified separately in relevant standards, depending on the characteristics of the product and its intended uses. The cold bending test for B1 and A1 steels is an additional guarantee condition. Steel No. 1 does not have special grades; Q215 is divided into grades A and B, and both require that the specified chemical composition and mechanical properties be met. The mechanical properties guaranteed for A2 steel are similar to those of Q215 steel, while the chemical composition and mechanical properties guaranteed for C2 steel are also similar to those of Q215 steel. Q215A does not require impact testing. C2 and Q215B must undergo room-temperature impact testing using V-notched specimens. Q235 is divided into grades A, B, C, and D, and all of these grades require that the specified chemical composition and mechanical properties be met. The mechanical properties guaranteed for A3 steel are similar to those of Q235 steel, while the chemical composition and mechanical properties guaranteed for C3 steel are also similar to those of Q235 steel. Q235A does not require impact testing; C3 and A3 steel require additional room-temperature impact testing using U-notched specimens. Q235B must undergo room-temperature impact testing using V-notched specimens. C3 steel requires additional impact testing at room temperature or at -20°C, using the same type of specimens as mentioned above. Q235C and Q235D are used in important welded structures; Q235C requires impact testing at 0°C, while Q235D requires impact testing at -20°C, using the same type of specimens as before. Q255 is divided into grades A and B, and both require that the specified chemical composition and mechanical properties be met. The mechanical properties guaranteed for A4 steel are similar to those of Q255 steel, while the chemical composition and mechanical properties guaranteed for C4 steel are also similar to those of Q255 steel. Q255A does not require impact testing; C4 steel requires additional impact testing using U-notched specimens. Q255B must undergo room-temperature impact testing using V-notched specimens. Q275 has no grades defined, but it still requires that the specified chemical composition and mechanical properties be met. The chemical composition and mechanical properties guaranteed for C5 steel are similar to those of Q275 steel. 2. Low-alloy steels: Currently, GB/T1591-94 replaces GB1591-88. Below is a comparison of some of the old and new grade designations: GB/T1591-94 GB1591-88 Q295 09MnV 09MnNb 12Mn Q345 12MnV 16Mn 16MnRE Q390 15MnV 15MnTi 16MnNb Q420 15MnVN 14MnVTiRE 3. Dimensions and weight of steel products 1. Length dimensions of steel products: The length dimensions of steel products represent the most basic measurements of these materials, including their length, width, height, diameter, radius, inner diameter, outer diameter, and wall thickness. The legal units of measurement for the length of steel are meter (m), centimeter (cm), and millimeter (mm). In current practice, it is also expressed in inches (″), but it is not a legal unit of measurement. 1. Specifying fixed lengths for steel products is an effective measure to save materials. Fixed-length delivery means that the length or length times width must be at least a certain size, or the items are delivered within a specific range of lengths and length times widths. Manufacturing units can produce and supply products according to these size requirements. 2. Variable length (standard length): Products whose dimensions (length or width) fall within the specified standard ranges, without a requirement for a fixed size, are referred to as having variable length. Variable length is also known as normal length (standard length). For metal materials delivered in variable lengths, it is sufficient to deliver them within the specified length range. For example, for ordinary round steel with a diameter not exceeding 25 mm, the standard length is specified as 4–10 meters; round steel within this length range can all be delivered. 3. Fixed length: Cutting to a fixed size as specified in the order is called fixed length. When delivered in fixed lengths, the metal material must have the length specified by the buyer in the order contract. For example, if the contract specifies delivery in lengths of 5m, then all the material delivered must be 5m long; any length that is shorter or longer than 5m is considered unacceptable. But in reality, it is not possible for all deliveries to be 5m in length; therefore, a positive deviation is allowed, while a negative deviation is not permitted. 4. Standard size: Materials that are cut to fixed dimensions as specified in the order, into multiples of a certain value, are referred to as standard size. When delivered in multiples of a standard length, the length of the metal material supplied must be an integer multiple of the length specified by the buyer in the order contract (referred to as the single standard length), plus the cutting edge. For example, if the buyer specifies in the order contract that the length should be 2m per piece, then when cut into double-length pieces the length will be 4m, and when cut into triple-length pieces it will be 6m; in each case, an amount corresponding to one or two cuts must be added. The amount of saw cut is specified in the standards. When delivered in multiples, only positive deviations are allowed; negative deviations are not permitted. 5. Short length: A length that is below the minimum limit for irregular lengths specified by standards, but not less than the permitted shortest length, is called a short length. For example, the standards for steel pipes used in water and gas transmission specify that 10% of the pipes in each batch (based on the number of pipes) may be short pipes measuring 2–4 meters in length. 4m is the minimum length for irregular sizes; the shortest allowable length is 2m. 6. Narrow size: A size whose width is below the lower limit for irregular widths specified by standards, but not below the minimum allowable width, is called a narrow size. When delivering in a reduced size, attention must be paid to the reduced size ratio and the minimum size specified by relevant standards. II. Examples of steel length dimensions 1. Length dimensions of section steel ⑴ The standard lengths for railway rails are 12.5 m and 25 m. ⑵The dimensions of round bars, wires, and steel wires are specified in millimeters (mm) based on their diameter d. ⑶The dimensions of square steel are specified in millimeters (mm) based on the side length a. ⑷The dimensions of hexagonal and octagonal steel are specified in millimeters (mm) as the distance between opposite sides, s. ⑸The dimensions of flat steel are specified in millimeters (mm) for width b and thickness d. ⑹The dimensions of I-beams and channel beams are specified in millimeters (mm) as the web height h, leg width b, and web thickness d. ⑺The dimensions of equal-angle steel are specified in millimeters (mm) as the equal side width b and the side thickness d. The dimensions of unequal angle steel are specified in millimeters (mm) based on the side widths B, b, and the side thickness d. ⑻The dimensions of H-shaped steel are specified in millimeters (mm) as the web height h, flange width b, web thickness t1, and flange thickness t2. 2. Length dimensions of steel plates and steel strips ⑴ Are generally specified in millimeters (mm) based on the thickness d of the steel plate. Steel strips, on the other hand, are specified by their width b and thickness d in millimeters (mm). ⑵There are specified different sizes for single sheets; for example, among hot-rolled steel sheets, there are those that are 1 mm thick, with a width of 600 mm and a length of 2000 mm ； 650×2000 mm ； 700×1420 mm ； 750×1500 mm ； 900×1800 mm ； 1000×2000 mm, etc. 3. Length dimensions of steel pipes ⑴ Are generally specified in millimeters (mm) based on the outer diameter D, inner diameter, and wall thickness S of the steel pipe. ⑵Each type of steel pipe comes in specified dimensions; for example, there are 15 types of seamless steel pipes with an outer diameter of 50 mm and wall thicknesses ranging from 2.5 to 10 mm ； In other words, for a wall thickness of 5 mm, there are 29 types with outer diameters ranging from 32 to 195 mm. For example, for welded steel pipes with a nominal diameter of 25 mm, there are standard pipes with a wall thickness of 3.25 mm, as well as thicker pipes with a wall thickness of 4 mm. III. Weight of steel 1. Theoretical weight of steel The theoretical weight of steel is the weight calculated based on the nominal dimensions and density of the steel; this weight is referred to as the theoretical weight. This is directly related to the length of the steel, its cross-sectional area, and the allowable tolerances for dimensions. Due to the allowable tolerances in the manufacturing process of steel, there is a certain difference between the theoretical weight calculated using formulas and the actual weight; therefore, it is only used as a reference for estimation. 2. Actual weight of steel: The actual weight of steel refers to the weight obtained through actual measurement (weighing), which is known as the actual weight. The actual weight is more accurate than the theoretical weight. 3. Method for calculating the weight of steel ⑴ Gross weight is the opposite of \"net weight\"; it represents the total weight of the steel itself plus the packaging materials. Transportation companies calculate freight based on the gross weight. However, in the purchase and sale of steel, it is calculated based on net weight. ⑵Net weight is the opposite of “gross weight”. The weight of the steel after deducting the weight of the packaging materials, that is, the actual weight, is referred to as the net weight. In the purchase and sale of steel, it is generally calculated based on net weight. ⑶Tare weight refers to the weight of the packaging materials for steel, and is known as tare weight. ⑷Weight ton is a unit of weight used to calculate freight charges based on the gross weight of steel. Its legal unit of measurement is the ton (1000 kg), as well as the long ton (a British unit of weight equal to 1016.16 kg) and the short ton (an American unit of weight equal to 907.18 kg). ⑸Billing weight is also known as “billing ton” or “freight ton”. The weight of the steel for which the transportation department charges a fee. Different modes of transportation have different calculation standards and methods. For full-car railway transportation, the gross weight indicated on the freight car used is generally taken as the charging weight. Road transportation charges are based on the load capacity in tons of the vehicle. For parcel shipments by rail or road, the minimum charging weight is set at a certain number of kilograms based on the gross weight; if this amount is insufficient, it is rounded up. IV. Calculation of the theoretical weight of steel The unit of measurement for calculating the theoretical weight of steel is kilogram (kg). Its basic formula is: W (weight, kg) = F (cross-sectional area, mm2) × L (length, m) × ρ (density, g/cm3) × 1/1000. The density of steel is 7.85 g/cm3. The formulas for calculating the theoretical weight of various types of steel are as follows:
Name (unit), Calculation formula, Meaning of symbols, Example calculation: Round bar, Wire rod (kg/m). W = 0.006165 × d × d, where d is the diameter in mm. To find the weight per meter for a round bar with a diameter of 100 mm. Weight per m = 0.006165 × 1002 = 61.65 kg for deformed steel (kg/m). W = 0.00617 × d × d, where d is the cross-sectional diameter in mm. Determine the weight per meter for deformed steel with a cross-sectional diameter of 12 mm. Weight per m = 0.00617 × 12 × 2 = 0.89 kg. For square steel (kg/m), W = 0.00785 × a × a, where a is the width in mm. Calculate the weight per meter for square steel with a width of 20 mm. Weight per m = 0.00785 × 202 = 3.14 kg. For flat steel (kg/m), W = 0.00785 × b × d, where b is the width in mm and d is the thickness in mm. For flat steel with a width of 40 mm and a thickness of 5 mm, calculate the weight per meter. Weight per m = 0.00785 × 40 × 5 = 1.57 kg. Weight of hexagonal steel (kg/m): W = 0.006798 × s × s, where s is the distance between opposite sides. Calculate the weight per meter for hexagonal steel with a distance of 50 mm between opposite sides. Weight per m = 0.006798 × 502 = 17 kg. Weight of angle steel (kg/m): W = 0.0065 × s × s, where s is the distance between opposite sides. For angle steel with a distance of 80 mm between opposite sides, calculate the weight per meter. Weight per m = 0.0065 × 802 = 41.62 kg. Weight of equilateral angle steel (kg/m) = 0.00785 × b. Side width = d, Side thickness = R, Inner arc radius = r, Outer arc radius = … Calculate the weight per meter for equilateral angle steel with dimensions of 20 mm × 4 mm. From the metallurgical product catalog, it can be found that for equal-angle steel with dimensions of 4 mm × 20 mm, the value of R is 3.5 and r is 1.2; thus, the weight per meter is 0.00785 × 1.15 kg. For irregular-angle steel: W = 0.00785 × B; the length of the long side is b, the length of the short side is d, and the thickness of the side is t. R represents the radius of the inner arc, while r represents the radius of the end arcs. The weight per meter for irregular-angle steel with dimensions of mm × 20 mm × 4 mm is to be calculated. From the metallurgical product catalog, it can be found that for the irregular angle steel with dimensions 30 × 20 × 4, R is 3.5 and r is 1.2; thus, the weight per meter is 0.00785 × = 1.46 kg per meter. For channel steel: W = 0.00785 × h; b = length of the legs; d = thickness of the web; t = average thickness of the legs; R = radius of the inner arc; r = radius of the end arcs. Calculate the weight per meter for channel steel with dimensions 80 mm × 43 mm × 5 mm. From the metallurgical product catalog, it is found that for this channel steel, t is 8, R is 8, and r is 4. Therefore, the weight per meter is 0.00785 × 8 = 8.04 kg per meter. For an I-beam: W = 0.00785 × h; b = width of the legs; d = length of the legs; t = average thickness of the legs; R = radius of the inner arc; r = radius of the end arcs. Calculate the weight per meter for an I-beam with dimensions of 250 mm × 118 mm × 10 mm. According to the metal materials manual, for this I-beam, t is 13, R is 10, and r is 5. The weight per meter is therefore 0.00785 × = 42.03 kg. For steel plates, the weight per m2 is given by W = 7.85 × d, where d is the thickness. For a steel plate with a thickness of 4 mm, what is its weight per m2? Weight per m2 = 7.85 × 4 = 31.4 kg. For steel pipes (including seamless and welded pipes), the weight is given by W = 0.02466 × S × (D – S), where D is the outer diameter and S is the wall thickness. Calculate the weight per meter for a seamless pipe with an outer diameter of 60 mm and a wall thickness of 4 mm. Weight per m = 0.02466 × 4 × (60 – 4) = 5.52 kg. IV. Main types of steel materials (wires and profiles are arranged separately). I. Hot-rolled ribbed steel bars, hot-rolled H-shaped steel, and cold-formed steel. A. Hot-rolled ribbed steel bars 1. Types and specifications: The grade of hot-rolled ribbed steel bars is composed of HRB and the minimum yield strength value of that grade. H, R, and B are respectively the first letters of the English words for Hotrolled, Ribbed, and Bars. Hot-rolled ribbed steel bars are divided into three grades: HRB335 (old grade 20MnSi), HRB400 (old grades 20MnSiV, 20MnSiNb, 20MnTi), and HRB500. 2. Vanadium-containing Grade III threaded steel bars ① The market prospects for vanadium-containing Grade III threaded steel bars are promising. These new Grade III threaded steel bars (20MnSiV, 400Mpa) have alloys such as vanadium, niobium, and titanium added during the production process; compared to ordinary Grade II threaded steel bars, they offer advantages in terms of higher strength, better toughness, as well as improved welding and seismic performance. In developed construction markets such as Europe, grade III deformed steel bars account for 80% of the total amount of such bars; in countries like the United Kingdom, Germany, Australia, and Japan, the use of high-strength vanadium-containing grade III deformed steel bars has reached 80-90%. In our country, the former Ministry of Metallurgy and the Ministry of Construction jointly issued a document in 1995 to promote its use; the Ministry of Construction incorporated the technical specifications for new Grade III threaded rebar into the standard GBJ10-89 \"Code for Design of Concrete Structures\", which came into effect on January 1, 1997. To date, new Grade III threaded rebar has been successfully used in various construction projects such as high-rise buildings, large power plants, bridges, tunnels, and airports, offering broad market prospects. The Ministry of Construction requires that the use of new Grade III rebar account for 50% of the total amount of deformed steel by 2002, and 80% by the end of the 10th Five-Year Plan period. However, due to insufficient promotion efforts, its usage level is still **lower than that of the conventional grade 335Mpa Grade II rebar; therefore, more intensive promotion is needed for the new Grade III rebar. ②Advantages of vanadium-containing Grade III deformed steel bars: A. Cost efficiency: Due to their high strength, the use of new Grade III deformed steel bars allows for a 10-15% reduction in steel usage compared to Grade II deformed steel bars, thereby reducing the construction costs of building projects. B. High strength and good toughness: Thanks to micro-alloying, the yield strength is above 400 Mpa and the tensile strength is above 570 Mpa, representing a 20% increase compared to grade II deformed steel bars. C. Seismic resistance: Vanadium-containing steel bars possess high bending strength and aging resistance, as well as excellent low-cycle fatigue performance; their seismic resistance is significantly better than that of grade II deformed steel bars. D. Easy to weld: With a carbon content of ≤0.54%, it has good weldability, is suitable for various welding methods, and the welding process is simple and convenient. E. Easy construction: The use of new Grade III threaded steel bars increases the construction clearance, ensuring ease of construction and better construction quality. 3. Standards for Hot-Rolled Ribbed Steel Bars for Reinforced Concrete
I. Name: Hot-Rolled Ribbed Steel Bars for Reinforced Concrete
II. Standard Number: GB1499-1998
III. Chemical Composition:
Grade Chemical Composition, 100% C Si Mn P S Ceq
HRB335 0.25 0.80 1.60 0.045 0.045 0.52
HRB400 0.25 0.80 1.60 0.045 0.045 0.54
HRB500 0.25 0.80 1.60 0.045 0.045 0.55
IV. Mechanical Properties
1) The mechanical properties of the steel bars shall comply with the values in the following table:
Grade Nominal Diameter (mm) σs (or σp0.2) MPa σb MPa δ5% Minimum Value
HRB335 6–25 28–25 335 490 16
HRB400 6–25 28–50 400 470 14
HRB500 6–25 28–50 500 630 12
2) The total elongation δgt of the steel bar under maximum stress shall be not less than 2.5%. If the supplier can provide a guarantee, inspection may be waived. 3) At the request of the buyer, steel bars meeting the following conditions can be supplied: a) The ratio of the actual tensile strength to the actual yield strength of the steel bars is not less than 1.25 ； b) The ratio of the actually measured yield strength of the steel bars to the minimum yield strength specified in the table above shall not be greater than 1.30. V. Process Properties 1) Bending Property: After being bent 180 degrees using a bend radius as specified in the table below, no cracks shall appear on the surface of the part of the rebar that is subjected to bending. Grade, Nominal Diameter (mm), Bend Test Bend Diameter: HRB335 – 6-2528-50, 3a4a; HRB400 – 6-2528-50, 4a5a; HRB500 – 6-2528-50, 6a7a. 2) Reverse bend performance: At the request of the client, steel bars can be subjected to reverse bend performance tests. The bend center diameter for the reverse bending test is increased by one rebar diameter compared to that of the bending test. First bend 45 degrees in the forward direction, then bend 23 degrees in the reverse direction, and then bend 23 degrees again in the reverse direction. After the reverse bending test, no cracks shall appear on the surface of the bent portion of the rebar. VI. Surface Quality: The surface of the rebar shall not have cracks, scars, or folds. Bumps are allowed on the surface of the rebar, but they must not exceed the height of the transverse ribs. The depth and height of other defects on the surface of the rebar must not be greater than the allowable tolerances for the dimensions of that area. VII. Dimensions, Shape, Weight, and Allowable Tolerances 1) Nominal diameter range and recommended diameters The nominal diameter range for steel bars is 6–25 mm, with the standard recommended nominal diameters being 6, 8, 10, 12, 16, 20, 25, 32, 40, and 50 mm. 2) Allowable deviations in the surface shape and dimensions of ribbed steel discs. The transverse ribs of ribbed rebar shall comply with the following basic requirements: the angle β between the transverse ribs and the axis of the steel disc shall not be less than 45 degrees; when this angle is not greater than 70 degrees, the directions of the transverse ribs on the opposite sides of the rebar shall be opposite to each other ； The transverse ribs and spacing l shall not be greater than 0.7 times the nominal diameter of the reinforcement ； The angle α between the side of the transverse rib and the surface of the rebar must not be less than 45 degrees ； The total of the gaps between the ends of the transverse ribs on opposite sides of the rebar (including the width of the longitudinal ribs) should not exceed 20% of the nominal perimeter of the rebar ； When the nominal diameter of the rebar is not greater than 12 mm, the relative rib area shall not be less than 0.055 ； For nominal diameters of 14 mm and 16 mm, the relative rib area should not be less than 0.060 ； When the nominal diameter is greater than 16 mm, the relative rib area shall not be less than 0.065. 3) Length and allowable tolerances: a. Length: Rebar is usually delivered in fixed lengths, and the specific delivery length shall be specified in the contract ； When rebar is delivered in coils, each coil should contain a single strand of rebar; however, 5% of the coils in a batch are allowed to consist of two strands each (in cases where the number is less than two coils, two coils can have two strands each). Its disc weight and diameter are determined through negotiation between the supplier and the buyer. b、Allowable length deviation: When reinforced bars are delivered in fixed lengths, the allowable length deviation shall not exceed +50mm. c. Bend and ends: The bending deformation of straight rebar shall not affect its normal use, with the total bend not exceeding 40% of the total length of the rebar ； The ends of the rebar should be cut straight, and any local deformation should not affect its usability. II. Hot-rolled H-beams 1. Notation for hot-rolled H-beams. H-shaped steel is divided into three categories: wide-flange H-shaped steel (HK), narrow-flange H-shaped steel (HZ), and H-shaped steel piles (HU). Its representation is: height H × width B × web thickness t1 × flange thickness t2. For example, H-beams such as Q235 and SS400 with dimensions 200×200×8×12 represent H-beams with a height of 200 mm, a width of 200 mm, a web thickness of 8 mm, and a flange thickness of 12 mm; their grades are Q235 or SS400. 2. Advantages of hot-rolled H-beams H-beams are a new type of economical steel for construction use. The H-shaped steel has a cost-effective cross-sectional shape and excellent mechanical properties; during rolling, the deformation of various points in the cross-section is relatively uniform and internal stresses are low. Compared with ordinary I-beams, it offers advantages such as a higher section modulus, lower weight, and reduced metal usage, enabling building structures to be lighter by 30-40% ； Furthermore, since the inner and outer sides of its legs are parallel and the ends of the legs form right angles, assembling them into components can reduce welding and riveting work by up to 25%. It is commonly used in large buildings that require high load-bearing capacity and good cross-sectional stability (such as factories and high-rise buildings), as well as in bridges, ships, lifting and transportation machinery, equipment foundations, supports, and foundation piles. III. Cold-formed steel sections: Cold-formed steel sections are a type of economical, lightweight thin-walled steel material; they are also known as cold-formed steel profiles or simply cold-formed profiles. It is a type of steel member with various cross-sectional shapes and dimensions, manufactured by bending rolled strips, either hot-rolled or cold-rolled, into the desired shape. Cold-formed steel profiles have the following characteristics: 1. An economically rational cross-section that saves materials. The cross-sectional shape of cold-formed steel can be designed as needed; it has a rational structure, and its cross-sectional coefficient per unit weight is higher than that of hot-rolled steel. Under the same load, it can reduce the weight of components and save materials. Cold-formed steel can save 38-50% of metal compared to hot-rolled steel in building structures, and 15-60% in agricultural machinery and vehicles. It facilitates construction and reduces overall costs. 2. It offers a wide variety of options, enabling the production of various profiles with uniform wall thicknesses and complex cross-sectional shapes that are difficult to manufacture using conventional hot-rolling methods, as well as cold-formed steel products made from different materials. 3. The product features a smooth surface, an attractive appearance, and precise dimensions; its length can also be adjusted flexibly as needed. It is supplied in fixed lengths or in multiples thereof, thereby improving material utilization. 4. In production, it can also be combined with processes such as punching to meet various requirements. There are a wide variety of cold-formed steel products. Classified by cross-sectional shape, they include open, semi-closed, and closed types. The main products include cold-formed channel steel, angle steel, Z-shaped steel, cold-formed corrugated steel sheets, square tubes, rectangular tubes, electric-welded shaped steel tubes, and roller shutter doors. The cold-formed steel products typically produced have a thickness of less than 6 mm and a width of less than 500 mm. The products are widely used in industries such as mining, construction, agricultural machinery, transportation, bridges, petrochemicals, light industry, and electronics. Second, steel plates (including strip steel)
I. Classification of steel plates (including strip steel)
1. By thickness: (1) Thin plates (2) Medium plates (3) Thick plates (4) Extra-thick plates
2. By production method: (1) Hot-rolled steel plates (2) Cold-rolled steel plates
3. By surface characteristics: (1) Galvanized plates (hot-dip galvanized plates, electro-galvanized plates) (2) Tinned plates (3) Composite steel plates (4) Color-coated steel plates
4. By application: (1) Bridge steel plates (2) Boiler steel plates (3) Shipbuilding steel plates (4) Armored steel plates (5) Automotive steel plates (6) Roofing steel plates (7) Structural steel plates (8) Electrical steel sheets (silicon steel sheets) (9) Spring steel plates (10) Others
II. Common Japanese grades for ordinary and mechanical structure steel plates
1. Among the grades of Japanese steel (JIS series), ordinary structural steel mainly consists of three parts: The first part indicates the material; for example, S (Steel) denotes steel, while F (Ferrum) denotes iron ； The second part indicates different shapes, types, and uses; for example, P (Plate) denotes a plate, T (Tube) denotes a tube, and K (Kogu) denotes a tool ； The third part indicates the characteristic value, usually the minimum tensile strength. For example: SS400 – the first S stands for Steel, the second S stands for Structure; 400 represents the minimum tensile strength of 400 MPa, indicating that it is a common structural steel with a tensile strength of 400 MPa. 2. SPHC – The first letter ‘S’ stands for Steel, ‘P’ stands for Plate, ‘H’ stands for Heat, and ‘C’ stands for Commercial; it refers to hot-rolled steel plates and strips that are commonly used. 3. SPHD – refers to hot-rolled steel plates and strips for stamping. 4. SPHE – refers to hot-rolled steel plates and strips for deep drawing. 5. SPCC – refers to commonly used cold-rolled carbon steel sheets and strips, equivalent to China’s Q195-215A grade. The third letter, C, is an abbreviation for Cold. It is necessary to ensure that, for tensile testing, the letter T is added at the end of the grade to denote SPCCT. 6. SPCD – refers to cold-rolled carbon steel sheets and strips for stamping, equivalent to China’s 08Al (13237) high-quality carbon structural steel. 7. SPCE – refers to cold-rolled carbon steel sheets and strips for deep drawing, equivalent to China’s 08Al (5213) deep-drawing steel. To ensure it is not time-sensitive, add N at the end of the grade to get SPCEN. Tempering codes for cold-rolled carbon steel sheets and strips: annealed condition is A, standard tempering is S, 1/8 hard is 8, 1/4 hard is 4, 1/2 hard is 2, and hard is 1. Surface finish code: D for dull finish rolling, B for bright finish rolling. For example, SPCC-SD denotes general-purpose cold-rolled carbon steel sheets with standard quenching and tempering treatment and a matte finish. For example, SPCCT-SB denotes standard quenching and tempering as well as bright finishing, referring to cold-rolled carbon steel sheets for which mechanical properties must be ensured. 8. The notation for steel grades used in mechanical structures according to JIS is: S + carbon content + letter code (C, CK), where the carbon content is expressed as the intermediate value multiplied by 100; the letter C denotes carbon, while K denotes steel used for carburizing. For example, carbon steel coil S20C has a carbon content of 0.18-0.23%. III. Methods for Designating Silicon Steel Sheet Grades in China and Japan 1. Chinese method of grade designation: (1) For cold-rolled non-oriented silicon steel strips (sheets): The designation format is DW + iron loss value (the iron loss per unit weight at a magnetic flux peak value of 1.5 T, with a frequency of 50 Hz and a sine wave shape). ) times 100 plus times 100 times the thickness value. For example, DW470-50 indicates cold-rolled non-oriented silicon steel with an iron loss of 4.7 W/kg and a thickness of 0.5 mm; the new designation for this type is 50W470. (2) Cold-rolled oriented silicon steel strips (sheets): Notation method: DQ + iron loss value (the iron loss per unit weight at a magnetic flux peak of 1.7 T at a frequency of 50 Hz and a sine wave shape). ) times 100 plus times 100 times the thickness value. Sometimes, adding G after the iron loss value indicates a high magnetic flux density. For example, DQ133-30 indicates a cold-rolled oriented silicon steel strip (sheet) with an iron loss value of 1.33 and a thickness of 0.3 mm; the new model designation is 30Q133. (3) Hot-rolled silicon steel sheets are denoted by DR; they are classified into low-silicon steel (silicon content ≤ 2.8%) and high-silicon steel (silicon content > 2.8%) based on their silicon content. Representation method: DR + 100 times the iron loss value (the iron loss per unit weight when magnetized repeatedly at 50Hz and with a sinusoidally varying magnetic flux density of 1.5T) + 100 times the thickness value. For example, DR510-50 denotes a hot-rolled silicon steel sheet with an iron loss value of 5.1 and a thickness of 0.5 mm. The grade of hot-rolled silicon steel sheets for household appliances is denoted by JDR + iron loss value + thickness value, such as JDR540-50. 2. Japanese grade designation method: (1) Cold-rolled non-oriented silicon steel strip: Nominal thickness (value multiplied by 100) + code A + iron loss guarantee value (value obtained by multiplying by 100 the iron loss at a frequency of 50 Hz and a maximum magnetic flux density of 1.5 T). For example, 50A470 denotes a cold-rolled non-oriented silicon steel strip with a thickness of 0.5 mm and an iron loss guarantee value of ≤4.7. (2) Cold-rolled oriented silicon steel strip: nominal thickness (value multiplied by 100) + code G: indicates ordinary material; P: indicates highly oriented material + iron loss guarantee value (value obtained by multiplying the iron loss at a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T by 100). For example, 30G130 denotes a cold-rolled oriented silicon steel strip with a thickness of 0.3 mm and an iron loss guarantee value of ≤1.3. IV. Tin-plated sheets and hot-dip galvanized sheets 1. Tin-plated sheets Tin-plated thin steel sheets and strips, also known as tinplate, have their surfaces coated with tin; they possess excellent corrosion resistance and are non-toxic. They can be used as packaging material for canned goods, as outer and inner coatings for cables, in components for instruments and telecommunications equipment, as well as in small hardware items such as flashlights. Classification methods, category codes: By coating thickness – uniform tin plating: E1, E2, E3, E4; variable thickness tin plating: D1, D2, D3, D4, D5, D6, D7. By hardness grade: T50, T52, T57, T61, T65, T70. By surface finish: smooth surface – G; textured surface – S; rough surface – M. By passivation method: low-chromium passivation – L; chemical passivation – H; cathodic electrochemical passivation – Y. By oil coating amount: light oil coating – Q; heavy oil coating – Z. By surface quality: Group I, Group II. The specifications for uniform and variable thickness tin plating are as follows: Code, nominal tin coating amount in g/m2, minimum average tin coating amount in g/m2: E1 – 5.6 (2.8/2.8), 4.9; E2 – 11.2 (5.6/5.6), 10.5; E3 – 16.8 (8.4/8.4), 15.7; E4 – 22.4 (11.2/11.2), 20.2. D1 – 5.6/2.8, 5.05/2.25; D2 – 8.4/2.8, 7.85/2.25; D3 – 8.4/5.6, 7.85/5.05; D4 – 11.2/2.8, 10.1/2.25; D5 – 11.2/5.6, 10.1/5.05; D6 – 11.2/8.4, 10.1/7.85; D7 – 15.1/5.6, 13.4/5.05. 2. Hot-dip galvanized steel sheets: Zinc is applied to the surface of thin steel sheets and strips through a continuous hot-dip process, which prevents corrosion and rusting on their surfaces. Galvanized steel sheets and strips are widely used in industries such as machinery, light industry, construction, transportation, chemicals, and telecommunications. The classification and symbols for galvanized steel plates and strips are shown in the table below: Classification Method Category Symbol Workability General use PT Mechanical biting JY Deep drawing SC Ultra-deep drawing Age resistance CS Structural use JG Zinc 1 100 200 275 350 450 600 Zinc 1 Iron 90 Alloy 120 Gold 180 By surface structure Normal zinc coating Z Fine zinc coating X Smooth zinc coating GZ Zinc-iron alloy XT By surface quality Group I Ⅰ Group II Ⅱ By dimensional accuracy High precision A Ordinary precision B By surface treatment Chromic acid passivation L Oiling Y Chromic acid passivation plus oiling LY The weight of the zinc coating on grade 001 is less than 100 g/m2. V. Boiled steel plates and killed steel plates 1. Boiled steel plates are steel plates that are hot-rolled from ordinary carbon structural steel of the boiled type. Boiling steel is a type of steel with incomplete deoxidation; only a certain amount of weak deoxidizing agents is used to deoxidize the molten steel, resulting in a high oxygen content in it. When the molten steel is poured into the ingot mold, the carbon-oxygen reaction generates large amounts of gas, causing the molten steel to boil – hence the name boiling steel. Boiling steel has a low carbon content; since no ferrosilicon is used for deoxidation, the silicon content in the steel is also low (Si