Basic classification of carbon steel

1. Carbon steel

Carbon steel, also known as carbon steel, is an iron-carbon alloy with carbon content of ωc less than 2%. In addition to carbon steel generally contains a small amount of silicon, manganese, sulfur, phosphorus.

According to the use of carbon steel can be divided into carbon structural steel, carbon tool steel and free cutting structural steel three types. Carbon structural steel can be divided into building structural steel and machine manufacturing structural steel two kinds. 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 amount of phosphorus and sulfur, carbon steel can be divided into ordinary carbon steel (phosphorus, sulfur is higher), high quality carbon steel (phosphorus, sulfur is lower) and senior high quality steel (phosphorus, sulfur is lower). The higher the carbon content of general carbon steel, the higher the hardness is higher, the strength is high, but the plasticity is reduced.

2. Carbon structural steel

This kind of steel mainly guarantees mechanical properties. Therefore, its brand reflects its mechanical properties. Q+ number is used to represent the "Q" is the Chinese pinyin prefix of the yield point "Qu" character.

The number indicates 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 indicates that the steel quality grade is different, and the amount containing S and P decreases successively, while the steel quality increases successively.

If the letter "F" is marked after the grade, it is boiling steel; if "b" is marked, it is semi-sedated steel; if "F" or "b" is not marked, it is sedated steel. For example, Q235 -- AF represents grade A boiling steel with a yield point of 235MPa, and Q235 -- C represents grade C calm steel with a yield point of 235MPa.

Carbon structural steel is generally used in supply without heat treatment. Usually Q195, Q215, Q235 steel carbon quality fraction is low, good welding performance, plasticity, toughness, a certain strength, often rolled into sheet, steel bar, welded steel pipe, etc.

Used for Bridges, buildings and other structures and manufacturing common rivets, screws, nuts and other parts. Q255 and Q275 steel carbon quality fraction is slightly higher, higher strength, plasticity, toughness is better, can be welded, usually rolled into steel, strip steel and steel plate for structural parts and manufacturing of simple machinery connecting rod, gear, coupling, pin and other parts.

3. High quality structural steel

This kind of steel must have both chemical composition and mechanical properties. Its brand is a two-digit representation of the average carbon mass fraction in steel ten thousand points (ω) *10000). For example, 45 steel indicates that the average mass fraction of carbon in steel is 0.45%; 08 steel indicates that the average mass fraction of carbon in steel is 0.08%.

High quality carbon structural steel is mainly used to make machine parts. It is generally heat treated to improve mechanical properties. Depending on the carbon mass fraction, it has different uses.

08, 08F, 10, 10F steel, high plasticity, toughness, has excellent cold forming performance and welding performance, often cold rolled into sheet, used to make instrument shell, automobile and tractor cold stamping parts, such as car body, tractor cab;

15, 20, 25 steel is used for the production of small size, light load, surface requirements of wear resistance, core strength requirements are not high carburized parts, such as piston pin, template, etc.

30, 35, 40, 45, 50 steel after heat treatment (quenching + high temperature tempering) has good comprehensive mechanical properties, that is, has high strength and high plasticity, toughness, used to make shaft parts, such as 40, 45 steel is often used in the manufacture of automobile, tractor crankshaft, connecting rod, general machine tool spindle, machine tool gear and other small force shaft parts;

55, 60, 65 steel has a high elastic limit after heat treatment (quenching + moderate temperature tempering), often used to make the load is not large, small size (section size is less than 12~15mm) of the spring, such as pressure and speed regulating spring, plunger spring, cold coil spring.

4. Carbon tool steel

Carbon tool steel is basically no alloy elements of high carbon steel, carbon content in the range of 0.65%-1.35%, its production cost is low, raw material sources are easy to obtain, good machinability, after heat treatment can get high hardness and high wear resistance, so it is widely used for manufacturing a variety of cutting tools, molds, measuring tools.

But the red hardness of this kind of steel is poor, that is, when the working temperature is greater than 250℃, the hardness and wear resistance of steel will drop sharply and lose the ability to work. In addition, carbon tool steel, such as large parts, is not easy to harden, and easy to produce deformation and crack.

5. Easy cutting structural steel

Easy cutting structural steel is to add some elements to make the steel brittle, so that the steel cutting is easy to break into debris, so as to improve the cutting speed and prolong the life of the tool. Sulfur is the main element that makes steel brittle. Lead, tellurium, bismuth and other elements are used in common low-alloy and easy cutting structural steel.

The sulfur content of this steel ranges from 0.08% to 0.30%, and manganese content ranges from 0.60% to 1.55%. The sulfur and manganese in the steel exist in the form of manganese sulfide, manganese sulfide is very brittle and has lubricating effect, so that the chip is easy to break, and is conducive to improving the quality of the processed surface.

6. Alloy steel

In addition to containing iron, carbon and a small amount of unavoidable silicon, manganese, phosphorus, sulfur elements, but also contains a certain amount of alloy elements, alloy elements in steel silicon, manganese, molybdenum, nickel, chromium, vanadium, titanium, niobium, boron, lead, rare earth and one or several, this steel is called alloy steel.

Alloyed steel systems of different countries vary with their respective resources, production and using conditions. Nickel and chromate system was previously developed abroad, while our country is mainly developed in the form of silicon, manganese, vanadium, titanium, niobium, boron and rare earth.

Alloy steel accounts for about ten percent of the total output of steel, generally smelting in electric furnace according to the use of alloy steel can be divided into 8 categories, they are: alloy structural steel, spring steel, bearing steel, alloy tool steel, high-speed tool steel, stainless steel, heat-resistant non-peeling steel, electrical silicon steel.

7. Ordinary low alloy steel

Common low alloy steel is a common alloy steel containing a small amount of alloying elements (in most cases the total amount does not exceed 3%). The strength of this steel is relatively high, the comprehensive performance is relatively good, and has corrosion resistance, wear resistance, low temperature resistance and better cutting performance, welding performance in a large number of scarce alloying elements (such as nickel, chromium) conditions, usually 1t ordinary low alloy steel can top 1.2-1.3t carbon steel use, its service life and use range is far more than carbon steel. Ordinary low alloy steel can be smelted in open hearth or converter by ordinary smelting method, and the cost is close to that of carbon steel.

8. Alloy steel for engineering structure

This refers to alloy steels used in engineering and building structures, including weldable high-strength alloy structural steel, alloy reinforcement steel, alloy steel for railway, alloy steel for geological oil drilling, alloy steel for pressure vessels, high-manganese wear-resisting steel, etc. This kind of steel is used in engineering and building structures. In alloy steel, the total amount of this kind of steel alloy is low, but the production and use of large.

9. Alloy steel for mechanical structure

This type of steel is alloy steel suitable for making machinery and machine parts. It is on the basis of high quality carbon steel, appropriate to add one or several alloy elements, used to improve the strength, toughness and hardenability of steel. This kind of steel is usually used after heat treatment (e.g. tempering treatment, surface hardening treatment).

It mainly includes commonly used alloy structural steel and alloy spring steel, including alloy steel with tempering treatment, alloy steel with surface hardening treatment (carburizing steel, nitriding steel, surface high frequency hardening steel, etc.), alloy steel with cold plastic forming (cold top forging steel, cold extrusion steel, etc.).

According to the basic chemical composition series can be divided into Mn steel, SiMn steel, Cr steel, CrMo steel, CrNiMo steel, Ni steel, B steel and so on.

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, nickel, chromium, molybdenum and so on. Alloy structural steel is easy to harden and not easy to deform or crack, so it is easy to improve the properties of steel by heat treatment.

Alloy structural steel is widely used in the manufacture of automobiles, tractors, ships, steam turbines, heavy machine tools of various transmission parts and fasteners. Low carbon alloy steel is generally carburized, and medium carbon alloy steel is generally tempered.

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, not easy to produce deformation and crack, suitable for manufacturing large size, complex shape of cutting tools, die and measuring tools, the carbon content of alloy tool steel is different.

The carbon content of most alloy tool steels is 0.5%-1.5%, and the carbon content of hot deformation die steels is lower, and ωc is in the range of 0.3%-0.6%. Cutting tool steel generally contains carbon ωc1%;

The carbon content of cold working die steel is higher, such as the carbon content of graphite die steel ωc is up to 1.5%, and the carbon content of high carbon and high chromium cold working die steel is up to more than 2%.

12. High speed tool steel

High-speed tool steel is high carbon and high alloy tool steel, the carbon content of ωc in steel is 0.7% to 1.4%, steel contains alloy elements that can form high hardness carbide, such as tungsten, molybdenum, chromium, vanadium.

High speed tool steel has high hardness, in high speed cutting conditions, the temperature up to 500-600℃ hardness does not reduce, so as to ensure good cutting performance

13. Spring

The spring is used under impact, vibration or long-term alternating stress, so the spring steel is required to have high tensile strength, elastic limit and high fatigue strength. In the process, spring steel is required to have certain hardenability, not easy to decarbonize, good surface quality, etc

Carbon spring steel is the carbon content of ωc in the range of 0.6%-0.9% of high-quality carbon structural steel (including normal and higher manganese content). Alloy spring steel is mainly silicon manganese series steel, their carbon content is slightly lower, mainly by increasing the silicon content of ωsi (1.3%-2.8%) to improve the performance;

In addition, chromium, tungsten, vanadium alloy spring steel. In recent years, combining with Chinese resources and according to the requirements of automobile and tractor design technology, a new type of steel with boron, niobium, molybdenum and other elements on the basis of silicon manganese steel has been developed, which extends the service life of spring and improves the quality of spring steel.

14. Bearing steel

Bearing steel is used to make balls, rollers and bearing rings. Bearing is under great pressure and friction when working, so bearing steel is required to have high and uniform hardness and wear resistance, as well as high elastic limit. The uniformity of chemical composition, the content and distribution of nonmetallic inclusions and the distribution of carbide of bearing steel are very strict.

Bearing steel, also known as high carbon chromium steel, contains carbon ωc is about 1%, lead content ωcr is 0.5%-1.65%. Bearing steel is divided into six categories: high carbon chromium bearing steel, no chromium bearing steel, carburized bearing steel, stainless bearing steel, high temperature bearing steel and anti-magnetic bearing steel.

15, electrical silicon steel

Silicon steel for electrical industry is mainly used to manufacture silicon steel sheet for electrical industry. Silicon steel sheet is a large amount of steel used in the manufacture of motors and transformers. According to the chemical composition of silicon steel can be divided into low silicon steel and high silicon steel. Low silicon steel silicon content of ωsi=1.0%-2.5%, mainly used to manufacture motor; High silicon steel silicon content of ωsi=3.0%-4.5%, generally used to manufacture transformers. Their carbon content is ωc=0.06%-0.08%.

16. Rail steel

The rail mainly bears the pressure and impact load of the rolling stock, so. It requires sufficient strength and hardness and certain toughness. Usually used rail is open furnace and converter smelting carbon sedated steel, this steel contains carbon ωC=0.6%-0.8%, belongs to carbon steel and high carbon steel, but the manganese content of ωMn in steel is higher, in the range of 0.6%-1.1%. In recent years, the common low alloy steel rail has been widely used, such as high silicon rail, medium manganese rail, copper rail, titanium rail and so on. Ordinary low alloy rail than carbon rail wear resistance, corrosion resistance, the service life is greatly improved.

17. Shipbuilding steel

Shipbuilding steel refers to the steel used in the manufacture of sea ships and large inland river hull structures. Because the ship structure is generally manufactured by welding, the shipbuilding steel is required to have better welding performance. In addition, it also requires a certain strength, toughness and a certain low temperature resistance and corrosion performance. In the past mild steel was mainly used as shipbuilding steel. Recently, a large number of ordinary low alloy steel has been used, and we have steel such as 12 manganese ship, 16 manganese ship, 15 manganese vanadium ship and other steel. These kinds of steel have high strength, good toughness, easy processing and welding, corrosion resistance and other comprehensive characteristics, and can be successfully used to manufacture ten thousand tons of ocean ships.

18. Bridge steel

Railway or highway bridge bearing the impact load of vehicles, bridge steel requires a certain strength, toughness and good fatigue resistance, and the surface quality of steel requirements are higher. Basic open-hearth steel is often used for bridge steel. Recently, common low alloy steels such as 16 manganese and 15 manganese vanadium nitrogen have been successfully used.

19. Boiler steel

Boiler steel mainly refers to the material used in the manufacture of superheater, main steam pipe and boiler chamber heating surface. The performance requirements of boiler steel are mainly good welding performance, high temperature strength and alkali parts corrosion resistance, oxidation resistance. The commonly used boiler steel is low carbon calm steel smelted by open furnace or low carbon steel smelted by electric furnace. The carbon content of ωc is in the range of 0.16% to 0.26%. In the manufacture of high pressure boilers, pearlite or austenitic heat resistant steels are used. In recent years, boilers are also built with common low-alloy steel, such as 12 manganese, 15 manganese vanadium, 18 manganese molybdenum niobium, etc.

20. Steel for welding rod

This type of steel is specially used in the manufacture of arc and gas welding electrode wire. The composition of steel varies with the material of welding. According to the need to roughly divided into carbon steel, alloy structural steel and stainless steel three types. These steel sulfur, phosphorus content of ωs, ωp is not more than 0.03%, higher than the general steel requirements. These steels are not required for mechanical properties, but only for chemical composition.

21. Stainless Steel

Stainless steel referred to as stainless steel, it is composed of stainless steel and acid steel two parts. In short, the steel that can resist atmospheric corrosion is called stainless steel, and the steel that can resist the corrosion of chemical media (such as acids) is called acid resistant steel. Generally speaking, the chromium content of ωcr more than 12% steel has the characteristics of stainless steel; According to the microstructure of stainless steel after heat treatment can be divided into five categories: ferritic stainless steel, martensitic stainless steel, austenitic stainless steel, austenitic - ferritic stainless steel and precipitation-hardened stainless steel.

22. Heat resistant steel

Under high temperature conditions, the steel with oxidation resistance, sufficient high temperature strength and good heat resistance is called heat resistant steel. Heat resistant steel includes oxidation resistant steel and heat strength steel. Antioxidant steel is also known as non-peeling steel. Thermal strength steel is steel with good oxidation resistance and high temperature strength at high temperature. Heat-resistant steel is mainly used for parts used at high temperature for a long time.

23. Superalloy

Superalloy is a kind of thermal strong material with sufficient lasting strength, creep strength, thermal fatigue strength, high temperature toughness and sufficient chemical stability at high temperature. It is used for thermal power components working at high temperature of about 1000℃.

According to the different basic chemical composition, it can be divided into nickel base superalloy, iron nickel base superalloy and cobalt base superalloy.