The selection of steel is very important in steel structure engineering. In order to achieve the purpose of safety and reliability, meet the use requirements and economic and reasonable purposes, the following factors should be comprehensively considered when selecting steel grades and material properties:

 1、 The importance of structures, structures and components can be divided into important, general and minor categories according to their use, location and severity of damage consequences. Different types of structures or components should first use different steels. For important structures such as heavy industrial building structures, long-span steel structures, high-rise or super-high-rise civil building structures or structures, high-quality steel should be usedFor general industrial and civil building structures, ordinary quality steel can be selected according to the nature of work. 

2、 For steel load, the load can be divided into static load and dynamic load. Steel with good comprehensive performance should be selected for the structure directly bearing dynamic load and structure in strong earthquake area, while Q235 steel with lower price can be selected for structure bearing static load.

 3、 There are two connection methods of steel structure: welding and non welding. Welding deformation, welding stress and other welding defects, such as undercut, porosity, crack and slag inclusion, may cause cracks or brittle fracture of the structure.Therefore, the requirements of welding structure on material should be strict. For example, in terms of chemical composition, the limit content of carbon, sulfur and phosphorus must be strictly controlled in welding structure, while the requirement of variable reduction of carbon content in non welded structure is required. 

  4、 Due to the temperature and environment in which the structure is located, the steel is easy to be cold brittle when it is at low temperature. Therefore, the stabilizing steel with good resistance to low temperature brittle fracture should be selected for the structure working at low temperature, especially the welded steel structure.In addition, the steel of open-air structure is easy to produce aging, and the steel with harmful medium is easy to corrode, fatigue and fracture. 

5、 Steel thickness, thick steel not only has low strength, but also has poor plasticity, impact toughness and welding performance. Therefore, the welding structure with large thickness should adopt steel with good material.