Rectangular square pipe(RHS) is a kind of closed section steel with wide application. Compared with circular pipe with the same section area, it has the advantages of high strength, large modulus of bending section, easy assembly, stability and beauty. It is widely used in vehicle, subway, shipbuilding and other industries. Especially in the construction industry, large-sized square and rectangular pipes become the main load-bearing structural components in steel structure buildings. Square rectangular tube is a typical closed section steel. In the manufacturing process, every machining process will leave residual stress. Different processing technology will produce different degrees of residual stress.
The cold bending square tube forming has two ways: “directly forming the square” and “forming the square”. In order to study the different effects of forming process on the products, the scholars of Northern University of Technology measured the residual stresses of the square tubes with 100 mm The results show that different forming processes have great influence on the distribution of longitudinal residual stress, and the residual stress at the weld is the largest. The width of HAZ is smaller than that of HAZ under the condition of direct reciprocating, and the growth of austenite grains is restrained. Fine and uniform grains are obtained after cooling.