ROUND STEEL TUBE AND METHOD FOR PRODUCING ROUND STEEL TUBE

摘要

PROBLEM TO BE SOLVED: To provide a round steel tube which can be be obtained without performing manual refining operation even if the the round steel tube has a thick thickness and a large diameter, has the improved quality of its welded part, nearly free from residual stress and has sufficient toughness, and to provide a method for producing the round steel tube.;SOLUTION: A steel sheet 1 is bent by press-formation, mutually abutted edge portions 2 of the steel sheet are then joined by welding to form a semi-formed round steel tube 5 in which a straight parts 5a, 5b remain in the edge portions and a prescribed portions and the portions between the straight parts 5a, 5b are formed into arc parts 5c. The semi-formed round steel tube 5 is hot formed with a forming means 20 to obtain the round steel tube through the few number of times of the press-formations and the hot-formations. The round steel tube 6 is efficiently obtained in a short period of time without performing the manual refining operation. The round steel tube has improved quality of the welded part, nearly free from the residual stress, has high buckling strength, excellent secondary weldability and sufficient toughness and is suitable for columnar material for building in particular.;COPYRIGHT: (C)2004,JPO&NCIPI