Disadvantages of hot rolled 20 #
straight seam steel pipe:
1. Residual stress caused by uneven cooling. Residual stress is the stress of internal self-phase balance without external force. Hot-rolled steel sections of various cross sections have this type of residual stress. The larger the section size of general steel section, the greater the residual stress. Although the residual stress is self-balanced, it still has a certain influence on the performance of the steel member under the action of external forces. Such as deformation, stability, fatigue resistance, etc. may have adverse effects.
2. After welding, the non-metallic inclusions in the straight seam steel pipe are pressed into thin slices, and the delamination phenomenon occurs. The delamination greatly deteriorates the performance of the 20 # straight seam steel tube in the thickness direction, and there may be interlayer tearing when the weld shrinks. The local strain induced by shrinkage of the weld often reaches several times the yield point strain, which is much larger than the strain caused by the load.
Submerged arc welding straight seam steel pipe advantages: it can destroy the casting structure of the steel ingot, refine the grain of the steel, and eliminate the defects of the microstructure, so that the steel structure is compact and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the 20 # straight seam steel tube is no longer an isotropic body to a certain extent; bubbles, cracks and looseness formed during casting can also be affected by high temperature and pressure Welding.
