Hot rolled seamless steel pipe: compared with cold rolling, cold rolling is rolling below the recrystallization temperature, and hot rolling is rolling above the recrystallization temperature.
Advantages:
it can destroy the casting structure of ingot, refine the grain of steel and eliminate the defects of microstructure, so as to make the steel compact and improve the mechanical properties. 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 pouring can also be welded under the action of high temperature and pressure.
Disadvantages:
1. After hot rolling, the non-metallic inclusions (mainly sulfide, oxide and silicate) in the steel are pressed into thin sheets, resulting in delamination (interlayer). Delamination greatly deteriorates the tensile properties of steel along the thickness direction, and interlayer tear may occur when the weld shrinks. The local strain induced by weld shrinkage often reaches several times of the yield point strain, which is much larger than that caused by load;
2. Residual stress caused by uneven cooling. Residual stress is the internal self-equilibrium stress without external force. Hot rolled sections of various sections have this kind of residual stress. Generally, the larger the section size of section steel, the greater the residual stress. Although the residual stress is self balanced, it still has a certain impact on the performance of steel members under external force. For example, it may have adverse effects on deformation, stability and fatigue resistance.
Post time: Jan-10-2022