SQUARE STEEL PIPE AND MANUFACTURING METHOD FOR SQUARE STEEL PIPE

摘要

PROBLEM TO BE SOLVED: To provide a square steel pipe in which proof strength and toughness are improved while keeping effects generated by hot forming. SOLUTION: A semi-formed square steel pipe 5 is formed by welding after folding a steel plate 1 containing vanadium V as a chemical component. The square steel pipe is obtained by hot-forming the semi-formed square pipe 5 at the vicinity of an A3transformation point and then cooling it. The heated semi-formed square steel pipe can be hot-formed so as to be finished into the regular size and shape. The shape of each corner part, namely, the outer peripheral radius of the square steel pipe is formed in a uniform shape sharply. The square steel pipe can obtain high buckle strength with almost no residual stress by the hot forming. It has excellent secondary weldability. The square steel pipe has the improved proof strength and toughness by using the steel plate containing vanadium. The square steel pipe with the thinner plate thickness and the smaller size or the like can be adopted while obtaining sufficient design strength corresponding to the architecture. As a result, the reduction of weight and costs can be realized. COPYRIGHT: (C)2005,JPO&NCIPI