| 摘要 |
PURPOSE: A process for preparing the subject steel having high strength while having the same weldability as conventional steel by minimizing ferrite particles in low carbon steel without adding a large quantity of an alloy is provided, thereby producing steel for structural having excellent weldability. CONSTITUTION: This steel for structural comprises C:0.05 to 0.2%, Mn:0.5 to 2.0%, Si:0.01 to 0.5%, Al:0.005 to 0.1%, Nb and Ti alone or composite:0.01 to 0.03%, P:0.03% or less, S:0.03% or less, N;0.03 to 0.014% and the balance of Fe with other inevitable impurities, wherein a fine structure is a composite structure of ferrite+ferrite or ferrite+bainite and the ferrite has a particle size of 5 to 7 micrometer.
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