Hot rolled advantages
The advantages of hot rolling are that the casting structure of steel ingot can be destroyed, the grain of steel can be refined, and the defects of microstructure can be eliminated, so that the structure of steel is compact and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent. Bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.
Hot rolled shortcomings
First, after hot rolling, the non-metallic inclusions (mainly sulphides and oxides, and silicates) in the steel are pressed into thin slices, resulting in stratification (interlayer) phenomenon. Delamination greatly deteriorates the tensile properties of steel along the thickness direction and may cause interlaminar tearing during weld shrinkage. The local strain induced by weld shrinkage is often several times that of yield point strain, which is much larger than that caused by load.
The second is the residual stress caused by uneven cooling. The residual stress is the internal self-phase equilibrium stress without external force. All kinds of hot rolled section steel have this kind of residual stress. The larger the section size of general section steel is, the greater the residual stress is. Although the residual stress is self-phase equilibrium, it has a certain effect on the performance of steel member under external force. Such as deformation, stability, fatigue resistance and other aspects may have adverse effects.
