LOWER STIFFENER WITH A FUNCTION 2000MPa TENSILE STRENGTH AND IT'S MANUFACTURING METHOD

摘要

PURPOSE: A lower stiffener with tensile strength of 2000MPa manufactured using hot forming and a manufacturing method thereof are provided to obtain carbon steel with improved yield strength and tensile strength by employing Mn of 3.0% or less to increase strength without reduction of toughness. CONSTITUTION: A method for manufacturing a lower stiffener using hot forming comprises the steps of: preparing a steel pipe, which comprises C of 0.34-0.36wt.%, Mn of 3.0wt.% or less, P of 0.003wt.% or less, S of 0.003wt.% or less, Cr of 0.29-0.31wt.%, Mo of 0.34-0.36wt.%, B of 0.004wt.% or less, and Fe and inevitable impurities of the remaining amount(ST100), cutting the steel pipe to the length of a lower stiffener(ST200), heating the cut steel pipe through induction heating(ST300), and hot forming the heated steel pipe into a lower stiffener product and quenching the product(ST400).