Square tube is a kind of hollow square section light thin-walled steel pipe, also known as steel cold-formed section. It is made of Q235 hot-rolled or cold-rolled strip or coil as the base material, which is formed by cold bending and then welded by high-frequency welding. In addition to wall thickness thickening, the corner size and edge straightness of hot-rolled ultra-thick square tubes have reached or even exceeded the level of resistance welding cold-formed square tubes. Good comprehensive mechanical properties, weldability, cold and hot workability and corrosion resistance, and good low-temperature toughness.