| 摘要 |
PURPOSE:To produce steel for large heat input welded construction having excellent toughness and tensile strength by subjecting a billet consisting of the specific compsn. which is controlled in the relation between the content of N and the content of Ti and carbon equiv. to hot rolling then to direct hardening and tempering under specific conditions. CONSTITUTION:The billet which consists, by wt%, of 0.01-0.18% C, <=0.8% Si, 0.5-2.0% Mn, 0.005-0.1% Al, 0.0003-0.0020% B, <=0.02% Ti and the balance iron and unavoidable impurities, contains >=5ppm N-0.3Ti and <=25ppm N-0.5Ti and satisfies the relation Ceq=C+Si/24+Mn/6+Ni/40+Cr/5+Mo/4+V /14<=0.36% is heated and hot rolled. The rolled steel is subjected to the direct hardening from the temp. above the Ar3 point down to <=300 deg.C then to tempering at the temp. below the Ac1 point. The 60kgf/mm<2> tensile strength class steel for welded construction having the excellent toughness in the weld heat affected zone even if subjected to large heat input welding is thus obtd.
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