Steels with various geometrical cross-sections rolled from heated billets. According to the different shape of the section steel, it is divided into three types: simple section, complex section or special-shaped section and periodic section.
①The characteristic of simple section is that the tangent line made at any point on the periphery of the section generally does not intersect in the section, such as round steel, square steel, hexagonal steel, flat steel, triangular steel, bow-shaped steel and elliptical steel.
② Complex sections include angle steel, I-beam, channel steel, T-beam, H-beam, Z-beam, rail, sheet pile, window frame steel and other miscellaneous section steel;
③ Periodic section is the periodic change in the shape and size of the section along the length of the steel, such as threaded steel bars, axles and ploughshares.
According to the size of the section size of the section steel, it is divided into three types: large section steel, medium section steel and small section steel.
Hot-rolled steel for construction in China is currently mainly made of ordinary carbon steel grade A No. 3 steel (carbon content 0.14-0.22%), which is characterized by easy smelting, low cost, moderate strength, good plasticity and weldability, suitable for Used in construction projects.
Most of the low-alloy steel hot-rolled sections are hot-rolled threaded bars and sections rolled with 16Mn, and special-shaped section sections are rarely used. Compared with ordinary I-beam, H-beam has the advantages of large section modulus, light weight, less steel, and easy combination and connection with other components.
In China, according to the size of the section steel, hot rolled steel has become one of the most widely used materials in various basic constructions, such as rebar, axle and plowshare steel. Machinery, chemical industry, shipbuilding, mining, petroleum and railway sectors all use various types of hot-rolled steel. In construction engineering, hot-rolled steel is mainly used for industrial and civil houses, load-bearing skeletons of bridges (beams, columns, trusses, etc.), tower mast structures, high-voltage transmission line supports, etc.
H-beam has two production methods: hot-rolled forming and welding combined forming.
When the specifications and materials are the same, the hot-rolled H-beam can completely replace the welded H-beam, and the quality of the former is better than that of the latter. Under normal circumstances, in the structural design, hot-rolled H-beam should be used for multi-high-rise buildings. For light steel workshops with portal rigid frame structures, welded variable-section H-beams are used, and the steel consumption index is better, but the project cost cannot be The reason for saving how much is that the processing volume of hot-rolled H-beam is small and the construction period is slightly shorter. If the comprehensive economic benefits (including the project after the project is put into use) are calculated, in the case where the construction period plays a decisive role, the hot-rolled H-beam can be selected. However, when the construction period requirements are not strict or some image projects, the welded H-beam can be selected based on the principle of saving resources.
Application of steel structure industry
Hot-rolled galvanizing is mainly used in light steel structure houses and workshops in the steel structure industry. The main building skeletons are made of galvanized cold-formed steel, mainly C-shaped steel, Z-shaped steel, floor bearing plates and steel gutter manufacturing. Thickness specifications Mainly 1.5-3.5mm. Steel structure buildings are environmentally friendly "green building materials" due to their light weight, high strength, beautiful appearance, fast construction, less pollution, and good wind and earthquake resistance. In developed countries, the use of steel structures in factories and residential buildings has become the trend of building development. In my country, steel structures are still in their infancy and have great potential for development. According to data from Taiwan, the ratio of color-coated panels and hot-dip galvanizing in construction is generally 5:1. Based on this calculation, the demand of my country's hot-dip galvanized sheet market is about 600,000 tons. Since there is currently no domestic production capacity of hot-rolled galvanized sheet, and imported products are far from meeting the market demand, the most widely used galvanized sheet in the market is the steel strip galvanized sheet produced by small galvanizing plants. Due to technical limitations, its products cannot meet market demands in terms of surface quality, galvanized quantity control, corrosion resistance and mechanical properties.
Application of steel silo industry
Compared with the original traditional storage container, the steel silo has the advantages of fast construction speed, good air tightness, high strength, less floor space, low cost, novel structure and beautiful appearance. More than 80% of the steel used in the manufacture of the granary is hot-rolled galvanized steel strip with a thickness of 1.0-1.4mm and a width of 495mm (2.5-4mm accounts for 75%), the material is Q215-235, and the amount of galvanizing is >275g/square meter. The sewage treatment tanks of urban and industrial sewage treatment systems mainly use 4.0mm galvanized sheets.
The hot-rolled galvanized sheet is 3.0X480 galvanized sheet and strip on the highway guardrail, and the material is Q235. According to the forecast of the transportation planning department, in the next ten years, an average of more than 2,000 kilometers of expressways will be built in the country every year, and the required galvanized sheet will be 136,000 tons. Plate more than 150,000 tons.
Application in railway passenger car manufacturing industry
1.0-3.0mm hot-rolled or cold-rolled galvanized sheet is required to manufacture the outer shell, inner shell, roof and floor of passenger cars. The hot-rolled galvanized sheet replaces the cold-rolled sheet, which simplifies the process, speeds up the manufacturing cycle of the vehicle, and at the same time prolongs the service life of the vehicle. The average consumption of hot-rolled galvanized sheet for each passenger car is 15 tons, of which 1-2.75mm is 4.5 tons. The country's annual passenger car manufacturing capacity is about 10,000 vehicles, and it is estimated that about 45,000 tons of hot-rolled galvanized sheets will be needed.
Applications in the automotive industry
In developed countries, the amount of coated steel plates for automobiles has accounted for more than 60% of the amount of thin plates. In recent years, my country's automobile industry has developed rapidly. It is an inevitable trend to widely use plated sheets as car body coverings to improve anti-corrosion performance. Judging from the use of galvanized sheet in automobiles, it has many specifications and a relatively large amount. It is mainly used in the bottom plate of the car, various beams, beam reinforcement plates, supports, brackets and connecting plates. Since it is used in hidden parts, it does not require high surface quality and deep drawing performance, so some parts can be replaced by hot-dip galvanized sheet processing. The specifications of hot-dip galvanized sheet for automobile consumption are mainly 1.5-3.0mm.
Instead of cold rolled galvanized sheet
At present, domestic galvanizing manufacturers produce 120,000-140,000 tons/year of galvanizing above 1.2mm. According to relevant experts, there is little difference in performance between cold-rolled galvanized sheet and hot-dip galvanized sheet, while hot-rolled galvanized sheet has little difference in performance. The galvanized substrate has obvious cost advantages. In theory, hot-dip galvanizing can completely replace cold-substrate galvanizing products.
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