METHOD FOR MANUFACTURING NON-HEAT TREATED HIGHLY ELONGATED HYDROFORMING STEEL PIPE BY USING HIGH ELONGATION HOT ROLLED STEEL SHEET AND CONTROLLING ROLL FORMING CONDITIONS

摘要

PURPOSE: To provide a method for manufacturing a non-heat treated hydroforming steel pipe by selecting an optimum high elongation hot rolled steel sheet and minimizing work hardening in the steel pipe manufacturing process through adoption of W-bending break down roll, decreasing of pipe-forming speed and adjustment of squeeze roll gap. CONSTITUTION: The method for manufacturing a non-heat treated highly elongated hydroforming steel pipe comprises the steps of heat treating a hot rolled strip skelp containing 0.05 to 0.09 wt.% of C, 0.30 to 0.65 wt.% of Mn, 0.02 wt.% or less of P, 0.015 wt.% or less of S, 0.02 to 0.04 wt.% of Al and the balance being Fe and a trace of impurities at a coiling temperature of 630 to 670 deg.C; roll forming the strip skelp by a W-bending break down roll used instead of a first break down roll in break down rolls constructed in four stages; performing pipe-forming operation by welding both edges of the roll formed skelp at a reduced pipe-forming speed of 35 to 50 MPM; and adjusting a gap between respective squeeze rolls for pressing the both edges of the skelp so that generation of work hardening on a matrix part of the steel pipe is minimized.