1. Ordinary carbon structural steel

Ordinary carbon structural steel follows the "Carbon structural steel" GB/T700-2006 standard. Due to its affordable price and large output, this type of steel is widely used in the field of gold structure and general mechanical parts. According to the different uses, ordinary carbon structural steel can be divided into ordinary carbon steel for general purposes and special ordinary carbon steel.

In the production process, ordinary carbon structural steel can be divided into five grades according to the carbon content and yield strength: Q195, Q215, Q235, Q255, Q275. Among them, the steel structure mainly uses Q235 steel. Although Q215 and Q255 can also be used as structural steel, their production and dosage are relatively small. When using the standard steel number, the following points should be noted: (1) The standard steel number is mainly used for engineering and general structural steel; (2) The standard steel mainly includes steel, steel strip and section steel in the use of varieties; (3) The standard steel number can be used as steel for welding and bolted structures, but Q235-A grade steel should not be used for welding bearing steel structures; (4) The standard steel number is generally delivered and used in the hot rolled state.

2. Weathering steel

Weathering steel follows the standards of "Weathering Steel for Welding Structures" GB/T4172-2000 and "High Weathering Structural Steel" GB/T4171-2000. This kind of steel by adding a small amount of alloying elements in the smelting process, so that the basic surface of the metal to form a protective layer, so as to improve the atmospheric corrosion resistance of steel. Weathering steel can be divided into high weathering structural steel and welded structural weathering steel, of which the welded structural weathering steel is divided into Q235NH, Q295NH, Q355NH, Q460NH four grades.

3. Low alloy high strength structural steel

Low-alloy high-strength structural steel follows the "low-alloy high-strength Structural steel" -GB/T1591-2008 standard. In the process of steelmaking, some alloying elements are added to improve the strength of steel significantly. This kind of steel can play a full role in the three main control indicators of the strength, stiffness and stability of the steel structure members, especially in the large-span or heavy-load structure. In general, compared with carbon structural steel, this type of steel can save about 20% of the steel used. According to the yield strength, low-alloy high-strength structural steel can be divided into 8 grades, of which Q345 is the most commonly used steel structure.

4. Steel plate for building structure

The steel plate for building structure follows the GB/T19879-2005 standard of "Steel Plate for Building Structure". This standard is the national standard after the revision and upgrade of the original metallurgical industry standard "Steel plate for high-rise buildings" (YB4104-2000). The standard provides five grades of steel plates, such as Q235G, Q345GJ, Q390GJ, Q420GJ and Q460GJ. The comprehensive performance of these steel plates is better than that of ordinary carbon structural steel and low-alloy high-strength structural steel, and the quality of steel is higher. To be specific:

1) To be able to withstand the damage of the earthquake force, it is necessary to be earthquake-proof and earthquake-proof, so that the steel plate has sufficient strength at the same time, but also has a low yield ratio. Low yield ratio can make the material have good cold deformation ability and high plastic deformation ability, even if the local overload instability will not occur sudden fracture.

2) The steel plate should have a narrow fluctuation range of yield strength. If the yield strength of the steel plate fluctuates greatly, when the building is subjected to an earthquake, the plasticity will be transferred, and the damage degree can not be controlled according to the design objective.

3) The steel plate should have lamellar tearing ability (thickness direction performance). High-rise steel structure in the beam-column connection and box column corner weld, due to the local structure, the formation of high constraints, welding is easy to cause lamellar tearing along the plate thickness direction, therefore, such steel plate must have a certain level of thickness direction performance.

4) Good welding performance, clearly specify the welding carbon equivalent and welding grain sensitivity index.

5. Structural steel for Bridges

Structural steel for Bridges follows the GB/T714-2008 standard of Structural Steel for Bridges. Corresponding to 4 strength classes: Q235g (C, D), Q345g (C, D, E), Q370(C, D, E), Q420g (C, D, E). Compared with the 2008 version, the 2000 version added Q460q, Q500g, Q550, 620g, and 690q grades. The chemical composition requirements are more stringent, and the harmful elements of sulfur and phosphorus are lower in alloy structural steel. Low carbon equivalent alloy structural steel is low. The smelting method requires off-furnace refining.