The rectangular tube is a kind of hollow long steel, also known as the flat tube, flat square tube, or square flat tube. When the bending resistance and torsional strength are the same, the weight is lighter, so it is widely used in the manufacture of mechanical parts and engineering structures. The rectangular tube is a kind of hollow square section light thin-walled steel tube, also known as steel cold bending section. It is made of the Q235 hot-rolled or cold-rolled strip or coil as the base material, which is formed by cold bending and then high-frequency welding. In addition to the thickening of the wall thickness of the hot-rolled extra-thick-walled square tube, its corner size and edge straightness have reached or even exceeded the level of the resistance-welded cold-formed square tube.