| 摘要 |
PURPOSE:To improve the low-temp. tougness of weld metal by forming the weld metal of a welded joint with a steel of decreased oxygen content and applying heat treatment under specific conditions. CONSTITUTION:Weld metal is formed of the steel of the undermentioned composition. The steel contg. <0.15% C, 0.05-0.50% Si, 0.30-3.0% Mn, 0.01-0.08% Al, <0.020% P, <0.020% S, <0.025% O2, 0.30-0.60% in carbon equiv. expressed by the following formula, or further cont. one or two or more kinds of < 0.30% Cu, <5.5% Ni, <1.2% Cr, <0.5% Mo, <0.05% V, <0.10% Nb, < 0.0020% B, <0.04% Ti is used. Carbon equiv.=C+Si/24+Mn/6+Ni/40+Cr/5+ Mo/4+V/14. The content of O2 is decreased by controlling the basicity or CaF2 amount of welding materials or using shielding gas. This weld metal is heated and held for 1-20min at austenitization temp., after which it is cooled and is further heated and held for 1-20min at temp. right under the Acl transformation point, after which it is cooled. |
