| 摘要 |
PROBLEM TO BE SOLVED: To provide a structural steel usable for a steel structure of building, and the like, having a yield strength of 14 kgf/mm2 or less (137 MPa or less) and excellent in toughness, and to provide its production method. SOLUTION: This structural steel low in yield strength and excellent in toughness, is composed of, by weight %, C of 0.005% or below, Si of 0.04% or below, Mn of 0.20% or below, P of 0.02% or below, S of 0.02% or below, Al of 0.015% or below, N of 0.004% or below, Ti of below 0.01-0.03% and Mg of 0.0005-0.0050% or below, and further one or two of Nb of below 0.002-0.01% and V of below 0.002-0.05%, and the balance Fe with inevitable impurities, wherein the total of solid soluble C and solid soluble N is 0.006% or below, and TiN composite particles, which are deposited in scale of 0.2μm or less on MgO or MgO/Al2O3, are present in an average spacing between particles of 0.5μm or less in this steel.
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