FIELD: rolled stock production, namely manufacture of welded straight-seam tubes. SUBSTANCE: method comprises steps of shaping rectangular tubes of round cross section tubes by two transitions in rough and finish four-roll grooved passes; in rough pass shaping tube with convex rectangular cross section; in finish pass shaping tube with regular rectangular cross section; forming tube in rough pass by means of concave rolls with concavity radius R =(3.1 - 4.1)A, where A - respective side of ready rectangular tube; forming large sides of tube in finish pass by means of concave rolls with concavity degree 0.2 -0.4 mm and forming small sides of rectangular tube by means of cylindrical rolls. Invention prevents concavity of sides of rectangular tubes. EFFECT: improved strength of rolls in rough and finish passes, increased efficiency of method, enhanced quality of rectangular tubes. 1 tbl, 1 ex
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