| 摘要 |
PURPOSE: A method for manufacturing an ultra high strength 80kg-grade hydroforming steel pipe is provided to achieve quality products by using a mold designed based on analysis of hydrofoaming process on the preformed hydrofoaming steel pipe and vehicle sub frame. CONSTITUTION: A method for manufacturing an ultra high strength 80kg-grade hydroforming steel pipe is as follows. An ultra-low carbon hot-rolled steel sheet coil is heated for a certain time and rapidly cooled to produce high strength steel, where the ultra-low carbon hot-rolled steel sheet coil is composed of C:0.06~0.08%, Si:1.00~1.20%, Mn:2.20~2.50%, P and S:0.02% or less, Al:0.01~0.09%, and the remnant Fe and inevitable impurities. By applying high frequency resistance welding method using the high strength steel, the existing 4-stage breakdown roll is reconstructed into 5-stage structure. As to the first-stage breakdown roll of the 5-stage breakdown roll, the formation of initial skelp edge is minimized. A forming method for precise formation and strain hardening reduction is applied at the same time. Therefore, the optimum high frequency welding condition is obtained.
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