Material Introduction

　　Steel: Steel is a material produced by pressure processing steel ingots, billets, or steel materials into various shapes, sizes, and properties as required. Steel is an essential material for national construction and the realization of the four modernizations. It has a wide range of applications and many varieties. According to the different cross-sectional shapes, steel is generally divided into four major categories: profiles, plates, pipes, and metal products. It is further divided into heavy rails, light rails, large-section steel, medium-section steel, small-section steel, cold-bent steel, high-quality steel, wire rods, medium and thick steel plates, thin steel plates, electrical silicon steel sheets, strip steel, seamless steel pipes, welded steel pipes, and metal products, etc.

　　Characteristics

　　Ferrous Metals: Ferrous metals mainly refer to iron, manganese, chromium, and their alloys.

　　Steelmaking: Steel is obtained by smelting pig iron used for steelmaking in a steelmaking furnace according to a certain process.

　　Non-ferrous Metals: Metals other than ferrous metals are called non-ferrous metals, such as copper, tin, lead, zinc, aluminum, as well as brass, bronze, aluminum alloys, and bearing alloys, etc.

　　Related Terms

　　Carbon Steel: Carbon steel, also known as carbon steel, is an iron-carbon alloy with a carbon content (wc) of less than 2%. In addition to carbon, carbon steel generally contains small amounts of silicon, manganese, sulfur, and phosphorus. According to its use, carbon steel can be divided into three categories: carbon structural steel, carbon tool steel, and free-cutting structural steel. Carbon structural steel can be further divided into two types: structural steel for construction and structural steel for machinery manufacturing. According to the carbon content, carbon steel can be divided into low-carbon steel (wc≤0.25%), medium-carbon steel (wc 0.25%~0.6%), and high-carbon steel (wc >0.6%). According to the phosphorus and sulfur content, carbon steel can be divided into ordinary carbon steel (higher phosphorus and sulfur content), high-quality carbon steel (lower phosphorus and sulfur content), and high-grade high-quality steel (even lower phosphorus and sulfur content). Generally, the higher the carbon content in carbon steel, the higher the hardness and strength, but the lower the plasticity.

　　Carbon Structural Steel: This type of steel mainly ensures mechanical properties, so its grade reflects its mechanical properties, represented by Q+number. "Q" is the first letter of the Pinyin for "Yield Point," and the number represents the yield point value. For example, Q275 indicates a yield point of 275MPa. If the grade is followed by the letters A, B, C, D, it indicates different steel quality grades, with the amounts of S and P decreasing sequentially and the steel quality improving accordingly. If the letter "F" is marked after the grade, it is boiling steel; if "b" is marked, it is semi-killed steel; if neither "F" nor "b" is marked, it is killed steel. For example, Q235-A·F represents grade A boiling steel with a yield point of 235MPa, and Q235-c represents grade C killed steel with a yield point of 235MPa. Carbon structural steel is generally not heat-treated and is used directly in the supply state. Generally, Q195, Q215, and Q235 steels have low carbon mass fractions, good weldability, good plasticity and toughness, and certain strength. They are often rolled into thin plates, steel bars, welded steel pipes, etc., used in bridges, buildings, and other structures, and for manufacturing ordinary rivets, screws, nuts, and other parts. Q255 and Q275 steels have slightly higher carbon mass fractions, higher strength, and better plasticity and toughness, and can be welded. They are usually rolled into shaped steel, bar steel, and steel plates for structural parts and for manufacturing connecting rods, gears, couplings, pins, and other parts of simple machinery.

　　High-Quality Structural Steel: This type of steel must guarantee both chemical composition and mechanical properties. Its grade uses two digits to represent the average carbon mass fraction in ten thousandths (wс×10000). For example, 45 steel indicates that the average carbon mass fraction in the steel is 0.45%; 08 steel indicates that the average carbon mass fraction in the steel is 0.08%. High-quality carbon structural steel is mainly used for manufacturing machine parts. It usually undergoes heat treatment to improve mechanical properties. Different uses exist depending on the carbon mass fraction. 08, 08F, 10, and 10F steels have high plasticity and toughness, excellent cold forming properties, and weldability. They are often cold-rolled into thin plates and used to make instrument casings and cold-pressed parts on automobiles and tractors, such as car bodies and tractor cabs; 15, 20, and 25 steels are used to make smaller, lighter-load parts with wear-resistant surfaces and moderate core strength requirements, such as piston pins and templates; 30, 35, 40, 45, and 50 steels, after heat treatment (quenching + high-temperature tempering), have good comprehensive mechanical properties, i.e., high strength and high plasticity and toughness, and are used to manufacture shaft parts. For example, 40 and 45 steels are often used to manufacture crankshafts, connecting rods, general machine tool spindles, machine tool gears, and other shafts with low stress; 55, 60, and 65 steels, after heat treatment (quenching + medium-temperature tempering), have a high elastic limit and are often used to manufacture small, low-load springs (cross-sectional dimensions less than 12-15mm), such as pressure and speed control springs, plunger springs, and cold-coiled springs.

　　Carbon Tool Steel: Carbon tool steel is a high-carbon steel that is essentially free of alloying elements, with a carbon content in the range of 0.65% to 1.35%. It has a low production cost, easily accessible raw materials, good machinability, and after treatment, it can achieve high hardness and wear resistance. Therefore, it is a widely used steel type, used to manufacture various cutting tools, molds, and measuring tools. However, this type of steel has poor red hardness, i.e., when the working temperature exceeds 250℃, the hardness and wear resistance of the steel will drop sharply and lose its working ability. In addition, if carbon tool steel is made into larger parts, it is difficult to harden and is prone to deformation and cracking.

　　Free-Cutting Structural Steel: Free-cutting structural steel adds some embrittling elements to the steel, making the chips brittle and easy to break into fragments during cutting, thus improving cutting speed and extending tool life. The elements that embrittle the steel are mainly sulfur, and in ordinary low-alloy free-cutting structural steel, lead, tellurium, and bismuth are used. The sulfur content (ws) of this steel is in the range of 0.08% to 0.30%, and the manganese content (wMn) is in the range of 0.60% to 1.55%. The sulfur and manganese in the steel exist in the form of manganese sulfide, which is brittle and has lubricating properties, making the chips easy to break and improving the quality of the processed surface.

　　Alloy steel, in addition to iron, carbon, and small amounts of unavoidable silicon, manganese, phosphorus, and sulfur, also contains a certain amount of alloying elements. The alloying elements in steel include one or more of silicon, manganese, molybdenum, nickel, chromium, vanadium, titanium, niobium, boron, lead, and rare earth elements. This type of steel is called alloy steel. Alloy steel systems vary from country to country depending on their respective resource situations, production, and usage conditions. Foreign countries previously developed nickel-chromium steel systems, while China developed alloy steel systems primarily based on silicon, manganese, vanadium, titanium, niobium, boron, and rare earth elements. Alloy steel accounts for about ten to twenty percent of total steel production and is generally smelted in electric furnaces. According to its use, alloy steel can be divided into eight categories: alloy structural steel, spring steel, bearing steel, alloy tool steel, high-speed tool steel, stainless steel, heat-resistant non-scaling steel, and electrical silicon steel.

　　Ordinary low-alloy steel is a common alloy steel containing a small amount of alloying elements (in most cases, the total amount w does not exceed 3%). This steel has relatively high strength, good overall performance, and possesses corrosion resistance, wear resistance, low-temperature resistance, as well as good machinability and weldability. With significant savings in scarce alloying elements (such as nickel and chromium), 1 ton of ordinary low-alloy steel can typically replace 1.2-1.3 tons of carbon steel, and its service life and application range far exceed that of carbon steel. Ordinary low-alloy steel can be smelted using general smelting methods in open-hearth furnaces and converters, and its cost is also close to that of carbon steel.

　　This refers to alloy steel used in engineering and building structures, including weldable high-strength alloy structural steel, alloy reinforcing steel, railway alloy steel, alloy steel for geological and petroleum exploration, alloy steel for pressure vessels, and high-manganese wear-resistant steel. This type of steel is used for engineering and building structural components. Among alloy steels, this type has a relatively low total alloy content but a large production and usage volume.

　　This type of steel refers to alloy steel suitable for manufacturing machines and mechanical parts. Based on high-quality carbon steel, one or more alloying elements are appropriately added to improve the steel's strength, toughness, and hardenability. This type of steel usually undergoes heat treatment (such as tempering or surface hardening) before use. It mainly includes commonly used alloy structural steel and alloy spring steel, including tempered alloy steel, surface-hardened alloy steel (carburizing steel, nitriding steel, high-frequency surface quenching steel, etc.), and alloy steel for cold plastic forming (steel for cold heading, steel for cold extrusion, etc.). According to the basic chemical composition series, it can be divided into Mn series steel, SiMn series steel, Cr series steel, CrMo series steel, CrNiMo series steel, Ni series steel, and B series steel, etc.

　　The carbon content (wc) of alloy structural steel is slightly lower than that of carbon structural steel, generally in the range of 0.15% to 0.50%. In addition to carbon, it contains one or more alloying elements such as silicon, manganese, vanadium, titanium, boron, nickel, chromium, and molybdenum. Alloy structural steel is easy to harden and is not easily deformed or cracked, making it convenient for heat treatment to improve steel performance. Alloy structural steel is widely used in manufacturing various transmission parts and fasteners for automobiles, tractors, ships, steam turbines, and heavy machine tools. Low-carbon alloy steel generally undergoes carburizing treatment, while medium-carbon alloy steel generally undergoes tempering treatment.

　　Alloy tool steel is medium-to-high carbon steel containing various alloying elements such as silicon, chromium, tungsten, molybdenum, and vanadium. Alloy tool steel is easily hardened, is not prone to deformation or cracking, and is suitable for manufacturing large-sized, complex-shaped cutting tools, molds, and measuring tools. The carbon content of alloy tool steel varies depending on its use. Most alloy tool steels have a carbon content (wc) of 0.5% to 1.5%. Steel for hot deformation molds has a lower carbon content (wc), ranging from 0.3% to 0.6%; steel for cutting tools generally has a carbon content (wc) of around 1%; and steel for cold working molds has a higher carbon content, such as graphite mold steel with a carbon content (wc) of up to 1.5%, and high-carbon, high-chromium cold-working mold steel with a carbon content (wc) as high as 2% or more.

　　High-speed tool steel is high-carbon, high-alloy tool steel. The steel contains 0.7%-1.4% carbon (wc) and alloying elements that can form high-hardness carbides, such as tungsten, molybdenum, chromium, and vanadium. High-speed tool steel has high red hardness; even at high-speed cutting temperatures of 500-600 degrees Celsius, the hardness does not decrease, thus ensuring good cutting performance.

　　Springs are used under impact, vibration, or long-term alternating stress, so spring steel requires high tensile strength, elastic limit, and high fatigue strength. In terms of processing, spring steel requires a certain hardenability, resistance to decarburization, and good surface quality. Carbon spring steel is high-quality carbon structural steel with a carbon content (wc) in the range of 0.6% to 0.9% (including normal and higher manganese content). Alloy spring steel is mainly silicon-manganese steel; their carbon content is slightly lower, and the performance is mainly improved by increasing the silicon content (wSi) (1.3% to 2.8%); there are also chromium, tungsten, and vanadium alloy spring steels. In combination with China's resources and based on the requirements of new technologies in automobile and tractor design, new steel grades have been developed by adding boron, niobium, and molybdenum to silicon-manganese steel, extending the service life of springs and improving spring quality.

　　Bearing steel is used to manufacture ball bearings, roller bearings, and bearing rings. Bearings operate under extremely high pressure and friction, so bearing steel requires high and uniform hardness and wear resistance, as well as a high elastic limit. The uniformity of the chemical composition of bearing steel, the content and distribution of non-metallic inclusions, and the distribution of carbides are all strictly required. Bearing steel is also known as high-carbon chromium steel, with a carbon content (wc) of around 1% and a chromium content (wc) of 0.5% to 1.65%. Bearing steel is divided into six categories: high-carbon chromium bearing steel, chromium-free bearing steel, carburized bearing steel, stainless bearing steel, medium-high temperature bearing steel, and anti-magnetic bearing steel.

　　Electrical silicon steel is mainly used to manufacture electrical silicon steel sheets for the electrical industry. Silicon steel sheets are a type of steel used extensively in motor and transformer manufacturing. According to chemical composition, silicon steel can be divided into low-silicon steel and high-silicon steel. Low-silicon steel contains 1.0% to 2.5% silicon (wSi) and is mainly used for motor manufacturing; high-silicon steel contains 3.0% to 4.5% silicon (wSi) and is generally used for transformer manufacturing. Their carbon content (wc) is ≤0.06% to 0.08%.

　　Rail steelRail steel primarily bears the pressure and impact loads of locomotives and rolling stock; therefore, it requires sufficient strength and hardness, as well as a certain degree of toughness. Commonly used rail steel is open-hearth and converter-melted carbon-killed steel. This steel contains 0.6%~0.8% carbon (Wc), belonging to medium carbon steel and high carbon steel, but the manganese content (WMn) is higher, ranging from 0.6% to 1.1%. Ordinary low-alloy steel rails have been widely adopted, such as high-silicon rails, medium-manganese rails, copper-containing rails, and titanium-containing rails. Ordinary low-alloy steel rails are more wear-resistant and corrosion-resistant than carbon steel rails, significantly improving their service life.

　　Steel for shipbuildingSteel for shipbuilding refers to steel used in the manufacturing of hulls for seagoing vessels and large inland river ships. Since ship hulls are generally manufactured using welding methods, shipbuilding steel is required to have good weldability. In addition, it requires a certain degree of strength, toughness, and low-temperature and corrosion resistance. In the past, low-carbon steel was mainly used as shipbuilding steel. Ordinary low-alloy steel has been widely used, with existing steel grades such as 12Mn ship steel, 16Mn ship steel, and 15MnV ship steel. These steel grades have high strength, good toughness, are easy to process and weld, and are resistant to seawater corrosion, successfully used to manufacture tens of thousands of tons of ocean-going giants.

　　Steel for bridgesRailway or highway bridges bear impact loads from vehicles, requiring bridge steel to have a certain degree of strength, toughness, and good fatigue resistance, and higher requirements for the surface quality of the steel. Bridge steel often uses basic open-hearth killed steel, with the successful application of ordinary low-alloy steel such as 16Mn and 15MnV nitrogen.

　　Boiler steelBoiler steel mainly refers to materials used to manufacture superheaters, main steam pipes, and the heat-receiving surfaces of boiler furnaces. The main performance requirements for boiler steel are good weldability, certain high-temperature strength, and resistance to alkaline corrosion and oxidation. Commonly used boiler steels include open-hearth-melted low-carbon killed steel or electric-furnace-melted low-carbon steel, with a carbon content (Wc) in the range of 0.16% to 0.26%. Pearlitic heat-resistant steel or austenitic heat-resistant steel is used in the manufacture of high-pressure boilers. Ordinary low-alloy steel is also used to build boilers, such as 12Mn, 15MnV, and 18MnMoNb.

　　Steel for welding rodsThis type of steel is specifically used for manufacturing arc welding and gas welding electrodes and wires. The composition of the steel varies depending on the material being welded. According to the needs, it is roughly divided into three categories: carbon steel, alloy structural steel, and stainless steel. The sulfur and phosphorus content (Ws, Wp) of these steels is no more than 0.03%, which is stricter than that of general steel. These steels do not require mechanical property testing; only chemical composition testing is performed.

　　Stainless steelStainless and acid-resistant steel, referred to as stainless steel, is composed of two major parts: stainless steel and acid-resistant steel. Simply put, steel that can resist atmospheric corrosion is called stainless steel, while steel that can resist chemical corrosion (such as acids) is called acid-resistant steel. Generally speaking, steel with a chromium content (Wcr) greater than 12% exhibits the characteristics of stainless steel. Stainless steels can be further divided into five categories according to their microstructure after heat treatment: ferritic stainless steel, martensitic stainless steel, austenitic stainless steel, austenitic-ferritic stainless steel, and precipitation-hardening stainless steel.

　　Heat-resistant steelSteel that exhibits oxidation resistance, sufficient high-temperature strength, and good heat resistance under high-temperature conditions is called heat-resistant steel. Heat-resistant steel includes oxidation-resistant steel and heat-resistant steel. Oxidation-resistant steel is also called scaling-resistant steel. Heat-resistant steel refers to steel that has good oxidation resistance at high temperatures and high high-temperature strength. Heat-resistant steel is mainly used for parts that are used for extended periods at high temperatures.

　　High-temperature alloyHigh-temperature alloys are heat-resistant materials that have sufficient creep strength, thermal fatigue strength, high-temperature toughness, and sufficient chemical stability at high temperatures, used for thermal power components operating at temperatures above 600 degrees Celsius. According to their basic chemical composition, they can be further divided into nickel-based high-temperature alloys, iron-nickel-based high-temperature alloys, and cobalt-based high-temperature alloys.

　　Precision alloyPrecision alloys are alloys with special physical properties. They are indispensable materials in the electrical industry, electronics industry, precision instrument industry, and automatic control systems. Precision alloys are divided into seven categories according to their different physical properties: soft magnetic alloys, deformable permanent magnetic alloys, elastic alloys, expansion alloys, bimetals, resistance alloys, and thermocouple alloys. The vast majority of precision alloys are based on ferrous metals; only a few are based on non-ferrous metals. Note: Wc, Ws, Wmn, and Wp represent the mass fractions of C, S, Mn, and P respectively.

　　Common Terminology

　　1. Standards: Standards are unified regulations for repetitive things and concepts. They are based on the comprehensive achievements of science, technology, and practical experience, agreed upon by relevant parties, approved by the competent authorities, and published in a specific form as commonly observed rules and basis. The standards implemented by China's steel products include national standards (GB, GB/T), industry standards (YB), local standards, and enterprise standards. 2. Technical Conditions: The various performance indicators and quality requirements that a product should meet as stipulated in the standard are called technical conditions, such as chemical composition, external dimensions, surface quality, physical properties, mechanical properties, process properties, internal organization, and delivery status, etc. 3. Assurance Conditions: According to the provisions of the metal material technical conditions, the manufacturer should conduct inspections and ensure that the inspection results meet the specified requirements for performance, chemical composition, internal organization, and other quality indicators, which are called assurance conditions. 4. Quality Certificate: The production of metal materials, like the production of other industrial products, is carried out according to unified standard regulations, implementing product factory inspection systems; unqualified metal materials are not allowed to be delivered. For delivered metal materials, the manufacturer provides a quality certificate to guarantee its quality. The quality certificate of metal materials not only states the name, specifications, number of delivered pieces, weight, etc., of the material, but also provides all the inspection results of the specified guaranteed items. 5. Quality Certificate: The quality certificate is the supplier's confirmation and guarantee of the inspection results of this batch of products, and it is also the basis for the purchaser's re-inspection and use. 5. Quality Grades: According to different requirements for steel surface quality, shape, and dimensional tolerances, the quality of steel is divided into several grades. For example, first-grade products and second-grade products. Sometimes different grades are formulated for a certain requirement, for example, for surface quality, it is divided into first-grade, second-grade, and third-grade; for surface decarburization depth, it is divided into group one, group two, etc., all indicating differences in quality. 6. Accuracy Grades: For some metal materials, the standard stipulates several dimensional tolerances, and according to the different sizes of dimensional tolerances, they are divided into several grades, called accuracy grades. Accuracy grades are divided into ordinary accuracy, higher accuracy, and high accuracy according to the tolerances. The higher the accuracy grade, the smaller the allowable dimensional deviation. When ordering, attention should be paid to including the accuracy grade requirements in the contract and other relevant documents. 7. Grade: The grade of metal materials is the name given to each specific metal material. The grade of steel is also called steel grade. The grade of metal materials in China generally reflects the chemical composition. The grade not only indicates the specific variety of metal materials, but also can roughly judge its quality based on it. In this way, the grade simply provides a common concept of the quality of specific metal materials, thus bringing great convenience to production, use, and management work. 8. Variety: The variety of metal materials refers to products with different uses, shapes, production processes, heat treatment states, and particle sizes, etc. 9. Model: The model of metal materials refers to the code used to represent different shapes and categories of profiles and cemented carbides, etc., using Chinese Pinyin (or Latin) letters and one or more numbers. The number indicates the nominal dimensions of the main parts. 10. Specification: Specification refers to the different dimensions of metal materials of the same variety or the same model. Generally, different dimensions also have different tolerances. In product standards, the specifications of varieties are usually arranged in order from small to large. 11. Surface State: Mainly divided into bright and non-bright. Common in steel wire and steel strip standards, the main difference lies in whether bright annealing or general annealing is used. Polishing, grinding, pickling, and plating are also regarded as surface states. 12. Edge State: Edge state refers to whether the strip steel is trimmed. Trimmed ones are trimmed strip steel, and untrimmed ones are untrimmed strip steel. 13. Delivery State: Delivery state refers to the final plastic deformation processing or final heat treatment state of the product delivery. Those delivered without heat treatment include hot-rolled (forged) and cold-rolled states. Those treated with normalizing, annealing, high-temperature tempering, quenching and tempering, and solid solution are collectively referred to as heat-treated delivery, or according to the heat treatment category, they are respectively called normalizing, annealing, high-temperature tempering, quenching and tempering, etc., delivery states. 14. Material Hardness: This refers to the different hardness obtained by using different heat treatments or degrees of work hardening. In some strip steel standards, it is divided into extra-soft strip steel, soft strip steel, semi-soft strip steel, low-hard strip steel, and hard strip steel. 15. Longitudinal and Transverse: The longitudinal and transverse directions mentioned in steel standards refer to the relative relationship with the rolling (forging) and drawing directions. Those parallel to the processing direction are called longitudinal; those perpendicular to the processing direction are called transverse. Samples taken along the processing direction are called longitudinal samples; samples taken perpendicular to the processing direction are called transverse samples. The fracture on the longitudinal sample is perpendicular to the rolling direction, so it is called the transverse fracture; the fracture on the transverse sample is parallel to the processing direction, so it is called the longitudinal fracture. 16. Theoretical Weight and Actual Weight: These are two different methods for calculating the delivery weight. Those delivered according to the theoretical weight are calculated based on the nominal dimensions and density of the material. Those delivered according to the actual weight are the delivery weight obtained by weighing (weighbridge) the material. 17. Nominal Dimensions and Actual Dimensions: Nominal dimensions refer to the nominal dimensions specified in the standard, which are the ideal dimensions hoped to be obtained during production. However, in actual production, the actual dimensions of steel are often larger or smaller than the nominal dimensions. The dimensions actually obtained are called actual dimensions. 18. Deviation and Tolerance: Because it is difficult to achieve nominal dimensions in actual production, the standard stipulates an allowable difference between the actual dimensions and the nominal dimensions, which is called deviation. A negative difference is called a negative deviation, and a positive difference is called a positive deviation. The sum of the absolute values of the allowable positive and negative deviations stipulated in the standard is called tolerance. Deviation has directionality, i.e., it is represented by "positive" or "negative"; tolerance does not have directionality. 19. Delivery Length: There are four regulations on steel delivery length in the current standard:

　　Fixed length, any steel with a length within the range specified in the standard and without a fixed length is called the usual length. However, for the convenience of packaging, transportation, and measurement, when cutting steel, enterprises should cut it into several different lengths, striving to avoid irregular lengths.

　　The term "short length" refers to a length of 20. The smelting method refers to the type of steelmaking furnace used, such as open-hearth furnace, electric arc furnace, electroslag furnace, vacuum induction furnace, and combined steelmaking. The term "smelting method" in the standard does not include deoxidation methods (such as fully killed steel, semi-killed steel, and rimmed steel) and casting methods (such as top pouring, bottom pouring, and continuous casting).