Hot and Cold Rolling of Stainless Steel
Hot and cold rolling are processes of forming steel plates. They have a great influence on the microstructure and properties of steel. The rolling of steel is mainly hot rolling, and cold rolling is only used to produce small-size steel and thin plate.
Hot rolling of stainless steel
Advantages: it can destroy the cast structure of the ingot, refine the grain of the steel, and eliminate the defects of microstructure, so as to make the steel structure compacted and improve its mechanical properties. The improvement is mainly along the rolling direction so that the steel is no longer isotropic to some extent. Bubbles, cracks and looseness formed during pouring can also be welded under high temperature and pressure.
1. After hot rolling, non-metallic inclusions (mainly sulphides and oxides, as well as silicates) inside the steel are pressed into thin sections, resulting in stratification (interlayer). Delamination greatly worsens the tensile properties of steel along the thickness direction and may lead to tears during weld contraction. Local strain induced by weld contraction often reaches several times of yield point strain and is much larger than that caused by load.
2. Residual stress caused by inhomogeneous cooling.
The residual stress is the internal self phase equilibrium stress without external force, and all kinds of hot rolled steel sections have this kind of residual stress. The larger the size of the general steel section, the greater the residual stress. Although the residual stress is self - balanced, it has certain effect on the performance of steel members under external force. Such as deformation, stability, anti fatigue and other aspects may have an adverse effect.
2. Cold rolling refers to the processing of steel plate or strip into various types of steel through cold drawing, cold bending, cold drawing and other cold processing at room temperature.
Advantages: rapid molding speed, high production, and no damage to the coating, it can be made into a variety of cross-section forms to meet the needs of the use conditions; Cold rolling can cause large plastic deformation of steel, thus improving the yield point of steel.
Disadvantages: 1) Although there is no thermal plasticity compression in the forming process, there is still residual stress in the section, which inevitably affects the overall and local buckling characteristics of steel.
2) The cold-rolled steel profile is generally an open section, which makes the free torsion stiffness of the section lower. Torsion is easy to occur when bending, bending and torsion is easy to occur when under pressure, and the torsion resistance is poor.
3) The wall thickness of cold-rolled formed steel is small, and there is no extra thickness in the corner where the plate meets. The ability of bearing local concentrated load is weak.
3. Main differences between hot rolling and cold rolling are as follows:
1) Local buckling is allowed in the section of cold-rolled formed steel, so that the bearing capacity of the bar can be fully utilized; However, local buckling of hot rolled steel section is not allowed.
2) There are different reasons for the residual stress of hot rolled and cold rolled steel, so the distribution on the section is also very different. The residual stress distribution on the cold-formed thin-walled steel section is curved, while the residual stress distribution on hot-formed steel or welded steel section is thin film.
3) The free torsion stiffness of hot-rolled steel is higher than that of cold-rolled steel, so the torsion resistance of hot-rolled steel is better than that of cold-rolled steel.