1. Mechanical properties of steel: The mechanical properties of structural steel include: yield point, tensile strength, elongation, low temperature impact toughness. All indicators should meet the requirements of the "Code for Design of Steel Structures", but the low temperature impact toughness can only be tested when the structure works in a low temperature environment. The determination of the mechanical index of steel must comply with the "Sampling Regulations for Mechanical and Technological Properties of Steel" (GB2975-82)
2. Chemical composition of steel: It is related to the machinability, toughness and durability of steel. The carbon content is the main component, and the alloying element content and the limits of impurity elements such as sulfur and phosphorus should comply with the provisions of GB222-84.
3. Process performance: Process performance mainly includes weldability and processability. Weldability is related to carbon content or carbon equivalent (low alloy steel) and can be identified through weldability tests. Machinability is determined by cold bending tests. According to (GB232-88) as the standard.
4. Geometrical size deviation: The deviation between the external size and theoretical size of steel (steel plate, section steel, round steel, steel pipe) should be within the allowable range. The allowable deviation value can refer to national standards GB709-88, GB706-88, GB787-88, GB978-88, GB707-88, GB816-87, etc.
5. Steel shape defects: There should be no bubbles, scars, cracks, cracks, wrinkles, inclusions and pressed iron oxide scales on the steel surface. These defects must be removed, and the depth of the depression at the location after removal shall not be greater than the negative deviation value of the steel thickness. In addition, when there are defects such as rust, pitting or scratches on the surface of the steel, the depth shall not be greater than 1/2 of the negative deviation value of the thickness of the steel.
6. Mechanical cutting: cutting by mechanical force (shearing, sawing, grinding), the corresponding machinery includes shearing machine, sawing machine, grinder, etc., which is more suitable for straight-line cutting of steel plates or profiles below 12~16mm.
7. Gas cutting: use flame to heat and melt metal, such as oxygen-acetylene, propane, liquefied gas, etc., and use compressed air to blow off the metal liquid to separate the metal, which is suitable for curve cutting and multi-head cutting.
8. Plasma cutting: The plasma arc is used to realize the cutting, which is suitable for the cutting of high melting point materials such as stainless steel.
9. Hot forming processing: refers to heating the steel to a certain temperature before processing. This method is suitable for workpieces that cannot be formed, bent and corrected at normal temperature. The termination temperature of hot working shall not be lower than 700℃. When the heating temperature is 200~300℃, the steel will be blue brittle, and it is strictly forbidden to hammer and bend. Steels with carbon content beyond the range of low carbon steels generally cannot be hot worked.
10. Cold forming processing: It is carried out at room temperature. If the external force exceeds the yield strength of the material, the material will be permanently deformed, or some part of the material will be detached from the material as required due to the external force exceeding the ultimate strength of the material. Cold working has a tendency to make the material hard and brittle. Heat treatment can restore the steel to its normal state, and it can also chip away hardened edges. Carbon steel should not be cold worked when the ambient temperature is lower than -16°C. When the temperature is lower than -12℃, low alloy steel shall not be processed.
11. Bending processing: According to the design requirements, using processing equipment and certain molds, the processing method of bending plate or section steel into a certain shape. Cold bending is suitable for thin plates and small steels; hot bending is suitable for thicker plates and more complex components and shaped steels, and the hot bending temperature is 950-1100 °C.
12. Coiled plate processing: The outer layer fibers of the flat steel plate are stretched under the action of external force, and the inner layer fibers are shortened, resulting in bending deformation. Rolling is done by a rolling machine. According to the different material temperature, it is divided into cold coil and hot coil. Coiled plates are mainly used for welding round pipe strings, pipes, air bags, etc.
