1. Carbon steel
Carbon steel, also called carbon steel, is an iron-carbon alloy with a carbon content of less than 2%. In addition to carbon, carbon steel generally contains small amounts of silicon, manganese, sulfur, and phosphorus.
According to the purpose, carbon steel can be divided into three categories: carbon structural steel, carbon tool steel and free-cutting structural steel. Carbon structural steel can be divided into two types: building structural steel and machine-made structural steel. According to the carbon content, carbon steel can be divided into low carbon steel (ωc≤0.25%), medium carbon steel (ωc=0.25%-0.6%) and high carbon steel (ωc>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 (lower phosphorus and sulfur content) Generally, the higher the carbon content in carbon steel, the higher the hardness and strength, but the plasticity decreases.
2. Carbon structural steel
This type of steel mainly ensures mechanical properties. Therefore, its grade reflects its mechanical properties and is represented by Q+ numbers, where “Q” is the yield point and the prefix of the Chinese pinyin of “Qu”.
The numbers indicate the yield point value. For example, Q275 indicates that the yield point is 275Mpa. If the letters A, B, C, and D are marked after the grade, it means that the quality of the steel is different. The content of S and P decreases in sequence, and the quality of the steel increases in sequence.
If the letter “F” is marked after the grade, it is boiling steel, if it is marked “b”, it is semi-killed steel, and if it is not marked “F” or “b”, it is killed steel. For example, Q235-AF 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 as supplied. Generally, Q195, Q215, and Q235 steels have low carbon mass fraction, good welding performance, good plasticity and toughness, and a certain strength. They are often rolled into thin plates, steel bars, welded steel pipes, etc.
Used in bridges, buildings and other structures and in the manufacture of ordinary rivets, screws, nuts and other parts. Q255 and Q275 steels have a slightly higher carbon mass fraction, higher strength, 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 and couplings of simple machines. Sections, pins and other parts.
3. High-quality structural steel
This type of steel must ensure both chemical composition and mechanical properties. Its grade uses two digits to express the mass fraction of the average carbon in the steel in ten thousand (ωс*10000). For example, 45 steel means that the average carbon mass fraction in the steel is 0.45%; 08 steel means that the average carbon mass fraction in the steel is 0.08%.
High-quality carbon structural steel is mainly used to make machine parts. Generally, heat treatment is required to improve mechanical properties. Depending on the carbon mass fraction, it has different uses.
08, 08F, 10, 10F steel has high plasticity and toughness, excellent cold forming performance and welding performance. It is often cold rolled into thin plates and used to make instrument casings and cold stamping parts on cars and tractors, such as car bodies and tractors. Cab, etc.;
15, 20, and 25 steel are used to make carburized parts that are smaller in size, lighter in load, wear-resistant on the surface, and have low core strength requirements, such as piston pins, templates, etc.;
30, 35, 40, 45 and 50 steel have good comprehensive mechanical properties after heat treatment (quenching + high temperature tempering), that is, they have higher strength, higher plasticity and toughness, and are used to make shaft parts, such as 40 , 45 steel is often used to manufacture crankshafts, connecting rods, general machine tool spindles, machine tool gears and other shaft parts with low stress for automobiles and tractors;
55, 60, and 65 steel have high elastic limit after heat treatment (quenching + medium temperature tempering), and are often used to make springs with low load and small size (section size less than 12~15mm), such as pressure regulating and speed regulating springs, Plunger spring, cold rolled spring, etc.
4. Carbon tool steel
Carbon tool steel is a high-carbon steel that basically does not contain alloy elements. The carbon content is in the range of 0.65%-1.35%. Its production cost is low, the source of raw materials is easy to obtain, and its cutting processability is good. After heat treatment, it can obtain high hardness and It has high wear resistance, so it is a widely used steel type for manufacturing various cutting tools, molds, and measuring tools.
However, this type of steel has poor red hardness, that is, when the working temperature is greater than 250°C, the hardness and wear resistance of the steel will drop sharply and it will lose its working ability. In addition, carbon tool steel is not easy to harden if it is made into larger parts, and is prone to deformation and cracks.
5. Easy-cut structural steel
Free-cutting structural steel is made by adding some elements to the steel that make the steel brittle, so that the steel is easily broken into chips when cutting, which is beneficial to increasing the cutting speed and extending the tool life. The element that makes steel brittle is mainly sulfur. Elements such as lead, tellurium, and bismuth are used in ordinary low-alloy free-cutting structural steel.
The sulfur content of this steel is in the range of 0.08%-0.30%, and the manganese content is in the range of 0.60%-1.55%. Sulfur and manganese in steel exist in the form of manganese sulfide. Manganese sulfide is very brittle and has lubricating properties, making the chips easy to break and helping to improve the quality of the machined surface.
6. Alloy steel
In addition to iron, carbon and a small amount of inevitable silicon, manganese, phosphorus and sulfur elements, steel also contains a certain amount of alloying elements. The alloying elements in steel include silicon, manganese, molybdenum, nickel, chromium, vanadium and titanium. , niobium, boron, lead, rare earth, etc. and one or more of them, this kind of steel is called alloy steel.
The alloy steel systems of various countries vary according to their respective resource conditions, production and use conditions. Foreign countries have developed nickel and chromium steel systems in the past, while our country has developed alloys based on silicon, manganese, vanadium, titanium, niobium, boron and rare earths. steel system.
Alloy steel accounts for about ten percent of the total steel production. It is generally smelted in electric furnaces. Alloy steel can be divided into 8 categories according to its use. They are: alloy structural steel, spring steel, bearing steel, and alloy tools. Steel, high-speed tool steel, stainless steel, heat-resistant peeling steel, silicon steel for electricians.
7. Ordinary low alloy steel
Ordinary low alloy steel is a common alloy steel containing a small amount of alloying elements (the total amount does not exceed 3% in most cases). This kind of steel has relatively high strength, relatively good comprehensive properties, and has corrosion resistance, wear resistance, low temperature resistance, good cutting performance, welding performance, etc. Under the condition of saving a large amount of scarce alloy elements (such as nickel and chromium), it is usually 1t of ordinary low alloy steel can be used as much as 1.2-1.3t of carbon steel, and its service life and use range far exceed that of carbon steel. Ordinary low alloy steel can be smelted in open hearth or converter using general smelting methods, and the cost is close to that of carbon steel.
8. Alloy steel for engineering structures
This refers to alloy steel used in engineering and building structures, including weldable high-strength alloy structural steel, alloy steel, alloy steel for railways, alloy steel for geological oil drilling, alloy steel for pressure vessels, high manganese wear-resistant steel, etc. . This type of steel is used as engineering and construction structural parts. Among alloy steels, the total alloy content of this type of steel is low, but its production and use are large.
9. Alloy steel for mechanical structure
This type of steel refers to alloy steel suitable for manufacturing machines and mechanical parts. It is based on high-quality carbon steel and appropriately adds one or several alloying elements to improve the strength, toughness and hardenability of the steel. This type of steel is usually used after heat treatment (such as quenching and tempering treatment, surface hardening treatment).
It mainly includes two categories: commonly used alloy structural steel and alloy spring steel, including quenched and tempered alloy steel, surface-hardened alloy steel (carburized steel, nitrided steel, surface high-frequency quenched steel, etc.), cold plastic forming Use alloy steel (cold upsetting steel, cold extrusion steel, 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, B series steel, etc.
10. Alloy structural steel
The carbon content of alloy structural steel is lower than that of carbon structural steel, generally in the range of 0.15%-0.50%. In addition to carbon, it also contains one or several alloying elements, such as silicon, manganese, vanadium, titanium, boron and nickel, chromium, molybdenum, etc. Alloy structural steel is easy to harden and not easy to deform or crack, making it easy to heat treat to improve the properties of the steel.
Alloy structural steel is widely used in the manufacture of 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 quenching and tempering treatment.
11. Alloy tool steel
Alloy tool steel is medium and high carbon steel containing a variety of alloying elements, such as silicon, chromium, tungsten, molybdenum, vanadium, etc. Alloy tool steel is easy to harden and is not prone to deformation and cracks. It is suitable for manufacturing cutting tools, molds and measuring tools with large sizes and complex shapes. The carbon content of alloy tool steel is also different for different uses.
The carbon content ωc of most alloy tool steels is 0.5%-1.5%. The carbon content of hot deformation mold steel is lower, ωc is in the range of 0.3%-0.6%; the carbon content of cutting tool steel is generally about ωc1%;
Cold working mold steel has a higher carbon content. For example, graphite mold steel has a carbon content of ωc up to 1.5%, and high carbon and high chromium cold working mold steel has a carbon content of more than 2%.
12. High speed tool steel
High-speed tool steel is a high-carbon high-alloy tool steel. The carbon content ωc in the steel is 0.7%-1.4%. The steel contains alloy elements that can form high-hardness carbides, such as tungsten, molybdenum, chromium, and vanadium.
High-speed tool steel has high red hardness. Under high-speed cutting conditions, the hardness does not decrease even at temperatures as high as 500-600°C, thus ensuring good cutting performance.
13. Spring
Spring is used under impact, vibration or long-term alternating stress, so spring steel is required to have high tensile strength, elastic limit and high fatigue strength. In terms of technology, spring steel is required to have a certain degree of hardenability, be difficult to decarburize, and have good surface quality, etc.
Carbon spring steel is high-quality carbon structural steel with a carbon content ωc in the range of 0.6%-0.9% (including normal and higher manganese content). Alloy spring steel is mainly silicon-manganese steel type. Their carbon content is slightly lower, and their performance is mainly improved by increasing the silicon content ωsi (1.3%-2.8%);
There are also alloy spring steels of chromium, tungsten and vanadium. In recent years, combined with my country’s resources and according to the requirements of new technologies in automobile and tractor design, new steel types have been developed based on silicon-manganese steel with boron, niobium, molybdenum and other elements added, which has extended the service life of springs and improved the performance of springs. Steel quality.
14. Bearing steel
Bearing steel is the steel used to make balls, rollers and bearing rings. Bearings are subjected to great pressure and friction when working, so the bearing steel is required to have high and uniform hardness and wear resistance, as well as high elastic limit. The uniformity of the chemical composition of the bearing steel and the absence of non-metallic inclusions The requirements for content and distribution, and the distribution of carbides are very strict.
Bearing steel is also called high carbon chromium steel, with a carbon content of about 1% and a lead content of 0.5%-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 and high temperature bearing steel and antimagnetic bearing steel.
15. Electrical silicon steel
Silicon steel for the electrical appliance industry is mainly used to make silicon steel sheets for the electrical appliance industry. Silicon steel sheets are a large amount of steel used in the manufacture of motors and transformers. According to chemical composition, silicon steel can be divided into low silicon steel and high silicon steel. Low silicon steel contains silicon ωsi=1.0%-2.5% and is mainly used to make motors; high silicon steel contains silicon ωsi=3.0%-4.5% and is generally used to make transformers. Their carbon content ωc=0.06%-0.08%.
16. Rail steel
Rails mainly bear the pressure and impact load of rolling stock, so. It requires sufficient strength, hardness and certain toughness. The commonly used rails are carbon-killed steel smelted in open hearth and converter furnaces. This steel contains carbon ωC=0.6%-0.8%, which belongs to medium carbon steel and high carbon steel. However, the manganese content ωMn in the steel is relatively high, at 0.6%. -1.1% range. In recent years, ordinary low alloy steel rails have been widely used, such as high silicon rails, medium manganese rails, copper-containing rails, titanium-containing rails, etc. Ordinary low-alloy rails are more wear-resistant and corrosion-resistant than carbon rails, and their service life is greatly improved.
17. Steel for shipbuilding
Shipbuilding steel refers to the steel used to manufacture sea-going ships and large inland river hull structures. Since the hull structure is generally manufactured by welding, shipbuilding steel is required to have good welding performance. In addition, it is also required to have certain strength, toughness and certain low temperature and corrosion resistance. In the past, low carbon steel was mainly used as shipbuilding steel. Recently, ordinary low alloy steel has been widely used, and existing steel types include 12 manganese ships, 16 manganese ships, 15 manganese vanadium ships and other steel types. These steel types have comprehensive properties such as high strength, good toughness, easy processing and welding, and resistance to seawater corrosion, and can be successfully used to manufacture ocean-going ships of 10,000 tons.
18. Bridge steel
Railway or highway bridges bear the impact load of vehicles. Bridge steel is required to have certain strength, toughness and good fatigue resistance, and has high requirements for the surface quality of the steel. Bridge steel often uses alkaline open-hearth killed steel. Recently, ordinary low alloy steels such as 16 manganese, 15 manganese vanadium nitrogen, etc. have been successfully used.
19. Boiler steel
Boiler steel mainly refers to materials used to manufacture superheaters, main steam pipes and boiler fire chamber heating surfaces. The performance requirements for boiler steel are mainly good welding performance, certain high-temperature strength and resistance to alkali corrosion and oxidation. Commonly used boiler steels include low-carbon killed steel smelted by open-hearth furnaces or low-carbon steel smelted by electric furnaces, with carbon content ωc in the range of 0.16%-0.26%. When manufacturing high-pressure boilers, pearlitic heat-resistant steel or austenitic heat-resistant steel is used. In recent years, ordinary low alloy steel has also been used to build boilers, such as 12 manganese, 15 manganese vanadium, 18 manganese molybdenum niobium, etc.
20. Steel for welding rods
This type of steel is specially used to make wire for arc welding and gas welding electrodes. The composition of steel varies with the material being welded. According to needs, it can be roughly divided into three categories: carbon steel, alloy structural steel and stainless steel. The sulfur and phosphorus content ωs and ωp of these steels are not more than 0.03%, which is higher than the requirements for ordinary steel. These steels do not require mechanical properties, but only test chemical composition.
21. Stainless steel
Stainless acid-resistant steel is referred to as stainless steel. It is composed of stainless steel and acid-resistant steel. In short, steel that can resist atmospheric corrosion is called stainless steel, while steel that can resist corrosion by chemical media (such as acids) is called acid-resistant steel. Generally speaking, steel with a chromium content of more than 12% has the characteristics of stainless steel; stainless steel can be divided into five categories according to its microstructure after heat treatment: ferritic stainless steel, martensitic stainless steel, austenitic stainless steel Stainless steel, austenitic-ferritic stainless steel and precipitation hardened stainless steel.
22. Heat-resistant steel
Under high temperature conditions, steel with oxidation resistance, sufficient high temperature strength and good heat resistance is called heat-resistant steel. Heat-resistant steel includes two types: oxidation-resistant steel and heat-strength steel. Anti-oxidation steel is also called anti-corrosion steel. Heat-strength steel refers to steel that has good oxidation resistance at high temperatures and has high high-temperature strength. Heat-resistant steel is mainly used for parts that are used at high temperatures for a long time.
23. High temperature alloy
High-temperature alloy refers to a thermally strong material that has sufficient durable strength, creep strength, thermal fatigue strength, high-temperature toughness and sufficient chemical stability at high temperatures. It is used for thermodynamic components working at high temperatures around 1000°C.
According to their basic chemical composition, they can be divided into nickel-based superalloys, iron-nickel-based superalloys and cobalt-based superalloys.
24. Precision alloy
Precision alloys refer to alloys with special physical properties. It is an indispensable material in the electrical industry, electronic industry, precision instrument industry and automatic control system.
Precision alloys are divided into seven categories according to their different physical properties, namely: soft magnetic alloys, deformed permanent magnet alloys, elastic alloys, expansion alloys, thermal bimetals, resistance alloys, and thermoelectric alloys. The vast majority of precision alloys are based on ferrous metals, and only a few are based on non-ferrous metals.