Section steel is a kind of strip steel with certain cross-sectional shape and size.

5. Classification of section steel

According to the different smelting quality of steel, section steel can be divided into ordinary section steel and high-quality section steel. Ordinary section steel is divided into large steel, medium steel and small steel according to the current metal product catalogue. Ordinary section steel can be divided into I-beam, channel steel, angle steel and round steel according to its section shape. The specifications of section steel are expressed by the main external dimensions reflecting its cross-sectional shape. For example, the specifications of round steel are expressed in millimeters in diameter; Round steel with a diameter of 30 mm is recorded as φ 30; The specifications of square steel are expressed in millimeters of side length; The specification of flat steel is expressed by thickness * width mm; The specifications of I-beam and channel steel are expressed by height * leg width * waist thickness, and numbers are also used to express the centimeters of height. For example, I-beams with a height of 10# are I-beams with a height of 100 mm; Angle steel is expressed in millimeters as side width * side width * side thickness, and can also be expressed in numbers. When the same I-beam or channel steel has several different leg widths and waist thicknesses, add A, B and C after the number to distinguish them, such as 32a#, 32b# and 32c#. Ordinary section steel is made of ordinary carbon structural steel and ordinary low-alloy structural steel.

High-quality steel is a profile made of high-quality steel. Although there are many kinds of high-quality steel, the variety is single. Mostly round steel. In addition, there are square steel, flat steel, hexagonal steel and hollow steel.

In addition, section steel also includes cold-formed section steel, which is made of ordinary carbon steel, high-quality carbon steel or low-alloy steel plate or steel strip through certain cold-formed forming.

6. Large section steel: I-beam, channel steel, angle steel and flat steel in large section steel are all hot rolled, while round steel, square steel and hexagonal steel are not only hot rolled, but also forged and cold drawn.

I-beam, channel steel and angle steel are widely used in industrial buildings and metal structures, such as factories, bridges, ships, agricultural machinery and vehicles, transmission towers and transportation machinery. Flat steel is used as bridges, housing frames, fences, power transmission boats, vehicles, etc. Round steel and square steel are used as various mechanical parts, agricultural machinery accessories and tools.

Tractor girder channel steel in special-shaped steel; Steel pile steel is used in water conservancy construction and mine engineering; Tractor construction machinery track shoe, concave flat steel, ball flat steel, etc. Because these special-shaped steels are close to the shape and size of parts or finished products, machining can be greatly reduced, product quality can be guaranteed and metal can be saved.

7. Medium-sized steel: The use of medium-sized steel such as I-beam, groove, angle, round and flat steel is similar to that of large-sized steel.

Special-shaped steels include 9#, 1 1#, 12#, miner steel, 18V, 25V and 29V supporting steels for water conservancy, construction and mining; U-shaped steel, π-shaped steel, all kinds of flat steel, etc. In addition, there are share steel specially used for making agricultural machinery share, elevator guide rail, wheel net steel used for making automobile wheel net, composite flat steel used for making agricultural tools, etc.

8. Small-sized steel: The processing and use of corner, circle, square and flat steel in small-sized steel are similar to those in large-sized steel, and small-diameter circles are often used as building reinforcement.

Special-shaped steel includes retaining ring, horseshoe steel, magnetic pole steel, presser foot, shallow channel steel, small channel steel, T-beam, ball flat steel, feed tooth steel, hot rolled hexagonal steel and so on. There are rivet steel, farm tool steel and window frame steel.

9. Steel bars for reinforced concrete: small steel. Include hot rolled round steel for reinforced concrete, thermo-mechanical steel bars for prestressed concrete and hot rolled ribbed steel bars for reinforced concrete. Cold rolled steel bar. Besides round steel, others are also called rebar. Because the steel surface is rolled into lugs or threaded ribs during the rolling process, it is the steel used for reinforced concrete in the construction industry.

The above steel bars can be used directly. Heat-treated rebar for prestressed concrete Heat-treated threaded rebar has high strength, but it is not suitable for welding and spot welding. Steel bars are made of 40Si2Mn, 48Si2Mn, 45Si2Cr and other steels after heat treatment, with nominal diameters of 6, 8.2 and10 mm. Cold-rolled ribbed bars are made of Q2 15, Q235 and 24MnTi steels with nominal diameters of 4- 12mm. After heat treatment, steel bars shall be transported in rolls in the heat treatment state.

10, agricultural steel: agricultural steel mainly refers to special or semi-special steel used in agricultural production and agricultural machinery, mainly including:

Agricultural tool steel: Agricultural tool steel is generally used to manufacture small farm tools and general civil knives in rural areas. Mainly small section round steel, flat steel and other varieties.

Agricultural composite steel: agricultural composite steel is divided into sickle blank, hoe blank and kitchen knife blank, which is used to manufacture small farm tools such as sickles and hoes and other household knives (such as kitchen knives). This kind of composite steel is made of two carbon steels with the same composition by hot rolling. The outer layer is called bulk steel with low carbon content, which is soft, tough, impact-resistant, good adhesion and easy to polish. There is a layer of blade steel in the middle, which contains high carbon and manganese, and is hard and wear-resistant. After grinding, the cutting edge of the tool is very sharp.

Ploughshare steel: Ploughshares of mechanical plows, horse-drawn plows, main plows and front plows used to make common shallow farming tools are generally made of wear-resistant steel with sufficient strength and toughness. In China, 65Mn and 65SiMnXt steels are generally used for manufacturing.

In addition, special section steel is often used as farm tool steel, such as T-beam, Z-beam, arc beam steel, double-sided reinforced steel, reinforced I-beam, blade steel of grass mower, concave flat steel, ribbed steel bar and so on.

1 1. Cold-formed steel: Cold-formed steel is the main material for making light steel structures, which is formed by cold-forming steel plates or steel belts. Its wall thickness can not only be made very thin, but also greatly simplifies the production process and improves the production efficiency. It can produce all kinds of profiles and cold-formed steel with uniform wall thickness but complex cross-section shape, which are difficult to produce by general hot rolling methods. Cold-formed steel is not only used in various building structures, but also widely used in vehicle manufacturing and agricultural machinery manufacturing.

There are many kinds of cold-formed steel, which are divided into open type, semi-closed type and closed type according to section. According to the shape, there are cold-formed channel steel, angle steel, Z-shaped steel, square pipe, rectangular pipe, special-shaped pipe, rolling door and so on.

According to GB6725-92, cold-formed steel is made of common carbon negative electrode, high-quality carbon structural steel, low-alloy structural steel plate or steel strip.

12, high-quality profiles: high-quality profiles are profiles made of high-quality steel. There are hot-rolled (forged) high-quality profiles and cold-drawn (drawn) high-quality profiles.

Hot rolled (forged) high-quality profiles include carbon structural steel, carbon tool steel, alloy structural steel, spring steel, stainless steel, bearing steel, alloy tool steel, die steel and high-speed tool steel.

Cold-drawn (drawn) high-quality profiles include carbon structural steel, carbon tool steel, alloy structural steel, spring steel, stainless steel, bearing steel, alloy tool steel, high-speed tool steel, free-cutting steel, cold heading steel, S/5A and other varieties. S/5A is a product, which is often used to make shells and bullets.

Other varieties are mainly some special high-quality profiles. Include hollow steel, oxygen cylinder material, cold heading steel, industrial pure iron, hot-rolled free-cutting steel, D60, S/5A, F 18, F 1 1 etc. The latter are all military supplies.

High-quality steel is divided into large, medium and small, and the group spacing between round steel and square steel is divided according to specifications, such as 8- 10mm,1-15mm, 18-20mm, 205-245 mm ... flat steel is large according to the cross-section integral. Hexagons are not grouped. However, the group spacing of high-quality steel cannot replace the specific specifications, which should be filled in the document. High-quality profiles have simple specifications and are mostly round steel. In addition, there are square steel, flat steel, six-row buckle steel, hollow steel, special-shaped steel and so on.

There are two kinds of dimensional deviations of hot-rolled (forged) high-quality round steel, square steel and hexagonal steel: ordinary precision and high precision. Cold-drawn profiles have more accurate dimensions and smoother surfaces, and some surfaces need to be polished. Round steel with polished or polished surface is called silver bright steel. High-quality profiles are rarely used, and most of them need further processing and heat treatment by users. Therefore, in addition to ensuring chemical composition, mechanical properties after heat treatment should also be ensured.

13. Wire rod: mainly refers to hot rolled round steel with a diameter of 5-9mm and rebar with a diameter below 10mm. Most of them are wound into coils by winding machines, also called wire rods or coils.

Wire rods are mainly used as raw materials for reinforced concrete reinforcement, welding structural parts or reprocessing (such as wire drawing, wire drawing, etc.). ).

According to the distribution catalogue of steel products, wires include ordinary low-carbon steel rolling wires, welding wires, blasting wires, quenched and tempered threaded wires and high-quality wires.

The widely used wire rod is mainly ordinary low carbon steel hot rolled wire rod, also known as ordinary wire rod. It is made of common carbon steels Q 195, Q2 15 and Q235 by hot rolling, with a nominal diameter of 5.5- 14.0mm and a weight of 100-200kg per coil. Now it is basically undistorted. Ordinary wire rods are mainly used in construction, wire drawing, packaging, covered electrode and the manufacture of bolts, nuts and rivets.

High quality wire rod, only supply high quality carbon structural steel hot rolled wire rod. Such as 08F, 10, 35Mn, 50Mn, 65, 75Mn, etc. Used as raw materials for metal products such as steel wires and other structural parts, and other high-quality steel rolling wires. Traditionally, more than 8 mm is included in high-quality profiles, and less than 8 mm is included in metal products.

In addition to the strength requirements, the wire should be subjected to cold bending test and dimensional inspection according to the purpose, and the surface should not have cracks, folds, scars, ear marks, delamination, inclusions and other defects.

Generally, steel bars are marked at the factory, indicating the grade. If not, the rebar shall be marked (factory name), specification and grade;

Grade: Grade 1, 2, 3 and 4;

Code name:? 、? 、? 、? ;

Generally expressed as: grade \ logo \ specification.

Building steel bars are mainly classified according to tensile strength.

2400kg/c m tensile strength is 1 grade steel bar, which is indicated by Ф on the drawing;

The tensile strength of 2800kg/cm square also belongs to 1 grade steel bar, and two vertical circles are represented by Ф on the drawing;

16Mn steel with a tensile strength of 3400kg/cm ~ 2 belongs to Grade 2 steel bar, which is indicated by Ф plus horizontal line on the drawing;

25MnSi steel with a tensile strength of 3800kg/cm square belongs to Grade 3 steel bar, which is indicated by Ф in the middle on the drawing, and there are two vertical lines and one horizontal line below.

Now the data is the old standard, and the current standard stress unit is MPa, 1 MPa = 10 kg/cm square, which needs to be converted.

You may be used to first-class steel (that is? ), mixed structural engineering 1 grade steel (Ⅰ? ) is relatively large, such as with foundation, constructional column, ring beam, cast-in-place floor slab or roof slab; Cast-in-place frame structures are widely used in civil or industrial buildings, structures and water conservancy bridges.

But if you analyze it carefully, you will find that it is more economical to use grade III steel than grade I steel. In the case of small plates, the general plates are reinforced by structure, which is controlled by the minimum reinforcement ratio, and the minimum reinforcement ratio is directly related to the grade of steel bars. You will find that the difference between the first-grade steel and the third-grade steel is obvious under the same concrete grade: (For large plates, the superiority of the third-grade steel is more obvious under the condition of controlling stress).

For example: c25 concrete

Grade I steel: ρ min = max {0.20%, 0.45 ft/fy} = max {0.20%, 0.27%} = 0.27%.

Grade III steel: ρ min = max {0.20%, 0.45 ft/fy} = max {0.20%, 0. 16%} = 0.20%.

If the plate thickness:

H = 100 mm

Reinforcement per meter: as1=1000 *100 * 0.27% = 270mm _ _ as3 =1000 *100 * 0.20% = 200mm _

H =120mm

Reinforcement per meter: as1=1000 *120 * 0.27% = 324 mm _ _ as3 =1000 *120 * 0.20% = 240 mm _

This comparison shows the difference between the two, and the prices are similar. Another advantage of using grade 3 steel is that the bearing ribs are not afraid of stepping on them. The bottom reinforcement does not need to be hooked.

Of course, due to the high strength, even the calculation will be saved, not only in the case of structure. "The minimum reinforcement ratio is directly related to the grade of reinforcement" should also be reasonable.

φ is grade I steel.

The round rebar is basically HPB235 grade rebar (Grade I), and its diameter is basically within 10MM (inclusive). Commonly used are φ 6, φ 8, φ 10.

Add a vertical line to the circle of your symbol, and a horizontal line below it is HRB335 grade steel bar (grade II), which is basically steel bar. Commonly used diameters are: 8, 10, 12, 14, 16, 18, 20, 20.

On the basis of the symbol of secondary reinforcement, a vertical line is added to the tertiary reinforcement, which is usually a steel bar with the same diameter as the secondary reinforcement.

The difference between them lies in their different mechanical properties and different compositions. The toughness and ductility of the first-grade steel bar are the best, and the carbon content of the third-grade steel bar is relatively large and brittle, but its strength is high.

Φ is the symbol of diameter, and it also represents the grade of reinforcement: the middle vertical represents the first grade steel, the middle two vertical represents the second grade steel, and the three vertical represents the third grade steel. Generally, there are only three kinds, and there are no more grades.

In fact, the general building steel bars are round steel and rebar, which can also be called ribbed steel bars, both of which are relative to round steel.

Grade I rebar (HPB235) is usually smooth rebar, commonly known as wire rod, and 6- 12 circle is the most common. Buildings are often used to make stirrups, plate distribution bars, stirrups, wall lacing bars and so on.

Secondary reinforcement (HRB335) is a threaded reinforcement with a diameter of 12-25, which is most commonly used in beams, columns and shear walls. No matter how big the diameter is, it is rarely used in industrial and civil buildings, and is mostly used in mass concrete, such as water conservancy projects.

Third-grade steel bars (above HRB400) are also rebar, with the same diameter as second-grade steel bars, higher strength and higher price. They are rarely used in industrial and civil buildings, and are usually used in special buildings. Some people get rich, buy villas for customization, and require all the main bars to be made into bunkers. This is actually a very wasteful and stupid behavior, because the most common cause of building damage is the destruction of concrete, not the destruction of steel bars.