| 摘要 |
PURPOSE: A steel tube with high strength and formability for hydroforming process is provided which reduces press process, manufacturing cost and product weight by increasing yield strength, elongation and work-hardening exponent, thereby improving hydroforming formability compared with an existing material. CONSTITUTION: The steel tube with high strength and formability for hydroforming process comprises 0.03 to 0.05 wt.% of carbon, 0.5 to 0.8 wt.% of manganese, 0.04 to 0.07 wt.% of phosphorus, less than 0.01 wt.% of sulfur, 0.03 to 0.06 wt.% of aluminum and a balance of Fe, wherein 0.03 wt.% or more of carbon (C) is added to a composition for a steel sheet for the steel tube as an element for increasing strength, and 0.05 wt.% or less of carbon is preferably contained in the composition to prevent formability deterioration of the steel sheet, 0.5 to 0.80 wt.% of manganese (Mn) is contained in the composition to increase strength of the steel sheet as a substitutional solid solution, it is not preferable that content of manganese exceeds 0.80 wt.% as formability is lowered, phosphorus (P) as a substitutional solid solution for increasing strength of the steel tube is added to the composition in an amount of 0.04 wt.% or more, the content of the phosphorus is limited to 0.07 wt.% or less as the phosphorus is deposited on the grain boundary to show brittleness if it is excessively contained in the composition, sulfur (S) is limited to less than 0.01 wt.% as it causes brittleness in the steel sheet, aluminum (Al) is added to the composition in an amount of 0.03 wt.% or more as a deoxidizer so that nonmetallic inclusions are reduced by removing oxygen in the steel sheet, and content of aluminum does not exceed 0.06 wt.% so that formability is not deteriorated.
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