From the perspective of welding materials, seamless square rectangular pipes generally require an impact absorption energy of -45 ℃ ≥ 28J or 36J. Welding materials should be lower than the mechanical performance requirements of the product weld seam. In addition, while requiring high toughness, it is also required that the strength of the weld metal cannot exceed the actual strength of the base metal, which is limited. In the submerged arc welding of thick walled square pipes with butt welds not exceeding the actual value of the base metal by 100MPa and fillet welds not exceeding the actual value of the base metal by 120MPa, the flux plays a decisive role in the mechanical properties of the weld seam. Therefore, the performance of the flux should be required in multiple aspects. Structural support: Square rectangular tubes have good rigidity and strength, and can be used as structural support. For example, in the fields of architecture, bridges, ships, etc., rectangular tubes are…