What are the basic classifications of carbon steel?

1.Carbon steel

Carbon steel is also called carbon steel, which is carbon contentωcLess than2%Iron-carbon alloy. Carbon steel generally contains a small amount of silicon, manganese, sulfur, and phosphorus in addition to carbon.

Carbon steel can be divided into three types: carbon structural steel, carbon tool steel and free-cutting structural steel according to its purpose. Carbon structural steel can be divided into two types: building structural steel and machine-made structural steel. Carbon steel can be divided into low carbon steel according to carbon content (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 (higher phosphorus and sulfur), high-quality carbon steel (lower phosphorus and sulfur) and high-quality high-quality steel (lower phosphorus and sulfur) Generally, the higher the carbon content in carbon steel, the higher the hardness and the higher the strength, but the lower the plasticity.

2,Carbon structural steel

This type of steel mainly guarantees mechanical properties. Therefore, its grade reflects its mechanical properties.Q+The number means "Q"Is the initial Chinese pinyin of the word "qu" at the yield point.

The number indicates the value of the yield point, for exampleQ275Indicates that the yield point is275Mpa, If the letter is marked after the gradeA,B,C,D, It means that the quality of steel is different, includingS,PThe amount of steel is successively reduced, and the quality of steel is successively improved.

If the letter is marked after the grade"F"Is boiling steel, marked"b"Semi-killed steel, not marked"F"or"b"Sedated steel. For exampleQ235—AFIndicates that the yield point is235MPaofAGrade rimmed steel,Q235—CIndicates that the yield point is235MPaofCGrade killed steel.

Carbon structural steel is generally not subjected to heat treatment, but is directly used in the supply state. usuallyQ195,Q215,Q235Steel carbon has low mass fraction, good welding performance, good plasticity, toughness, and certain strength. It is often rolled into thin plates, steel bars, welded steel pipes, etc.

Used in bridges, buildings and other structures and manufacturing common rivets, screws, nuts and other parts.Q255withQ275Steel carbon has a slightly higher mass fraction, higher strength, better plasticity and toughness, and can be welded. It is usually rolled into section steel, bar steel and steel plate as structural parts and to manufacture simple mechanical connecting rods, gears, couplings, and pins. And other parts.

3, High-quality structural steel

This type of steel must ensure both chemical composition and mechanical properties. The grade is the ten-thousandth fraction of the average carbon mass fraction in steel using two digits (ωс*10000). E.g45Steel indicates that the average carbon mass fraction in steel is0.45%；08Steel indicates that the average carbon mass fraction in steel is0.08%.

High-quality carbon structural steel is mainly used to manufacture machine parts. Generally, heat treatment is required to improve mechanical properties. According to the different carbon mass fraction, there are different uses.

08,08F,10,10FSteel, with high plasticity and toughness, has excellent cold forming properties and welding properties. It is often cold rolled into thin plates and used to make cold stamping parts on instrument housings, automobiles and tractors, such as automobile bodies, tractor cabs, etc.;

15,20,25Steel is used to make carburized parts with small size, lighter load, wear-resistant surface, and low core strength requirements, such as piston pins,Model etc.;

30,35,40,45,50The steel is heat-treated (quenched)+After high temperature tempering), it has good comprehensive mechanical properties, that is, it has higher strength, higher plasticity and toughness, and is used to make shaft parts, such as40,45Steel is often used to manufacture crankshafts, connecting rods of automobiles and tractors, general machine tool spindles, machine tool gears and other shaft parts with little force;

55,60,65Steel heat treatment (quenching+After tempering at medium temperature, it has a high elastic limit, and is often used to make small loads and small sizes (the cross-sectional size is less12~15mm) Springs, such as pressure and speed regulating springs, plunger springs, cold coil springs, etc.

4, Carbon tool steel

Carbon tool steel is a high-carbon steel that basically does not contain alloying elements, and the carbon content is in0.65%-1.35%Within the scope, its production cost is low, the source of raw materials is easy to obtain, the machinability is good, and high hardness and high wear resistance can be obtained after heat treatment. Therefore, it is a widely used steel for manufacturing various cutting tools, molds, and measuring tools.

But the red hardness of this kind of steel is poor, that is, when the working temperature is greater than250At ℃, the hardness and wear resistance of steel will drop sharply and lose work ability. In addition, carbon tool steel is not easy to harden if it is made into larger parts, and it is prone to deformation and cracks.

5, Free-cutting structural steel

Free-cutting structural steel is the addition of some elements that make the steel brittle, which makes the steel brittle and breaks into chips during cutting, which is beneficial to increase the cutting speed and extend the life of the tool. The element that makes steel brittle is mainly sulfur. Lead, tellurium, bismuth and other elements are used in ordinary low-alloy free-cutting structural steel.

The sulfur content of this steel is0.08%-0.30%Within the range, the manganese content is in0.60%-1.55%Within range. Sulfur and manganese in steel exist in the form of manganese sulfide. Manganese sulfide is very brittle and has a lubricating effect, which makes the chips easy to break and helps to improve the quality of the processed 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 with their respective resource conditions, production and use conditions. Foreign countries have developed nickel and chromium steel systems in the past, while China 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 output of steel. Generally, it is smelted in an electric furnace and can be divided into alloy steels according to their purpose.8Major categories, they are: alloy structural steel, spring steel, bearing steel, alloy tool steel, high-speed tool steel, stainless steel, heat-resistant non-skinned steel, and silicon steel for electrical engineering.