By definition, ingot and billet at room temperature is very difficult to deformation, not easy processing, general rolling heating to 1100 ~ 1250 ℃, the rolling technology called hot rolled.
Hot end temperature is 800 ~ 900 ℃, generally in the air after cooling, and hot rolling state is equivalent to normalizing treatment.
Most steel is rolled by hot rolling. Hot rolled steel, due to high temperature, the surface of a layer of oxidized iron sheet, so a certain corrosion resistance, open storage.
But the rough surface layer of tin oxide also make hot rolled steel, size volatile, so the surface is bright and clean, precise size and good mechanical properties of steel, with hot rolled semi-finished or finished products as raw materials to cold rolling production.
With high forming speed, high yield and no damage to the coating, it can be made into a variety of cross-section forms to meet the requirements of using conditions. Cold rolling can cause great plastic deformation of steel, thus increasing the yield point of steel.
1. Although there is no thermal plastic compression during the molding process, there is still residual stress in the section, which will inevitably affect the overall and local buckling characteristics of the steel.
2. Cold-rolled section steel generally has an open section, which makes the section free torsion stiffness lower. Torsion is easy to occur when bending, bending and torsion buckling are easy to occur when pressing, and the torsion resistance is poor.
3. The wall thickness of cold-rolled section steel is small, and it is not thickened at the corner where the plates connect, so it has a weak ability to withstand local concentrated load.