| 摘要 |
PROBLEM TO BE SOLVED: To provide a laser beam-welded joint excellent in ductility of a weld metal portion and suitable for welded structures such as bridges to be built using a steel material having a tensile strength of 780 MPa or higher.SOLUTION: The weld metal contains, by mass, 0.02-0.14% C, 0.008-0.05% Ti, ≤0.02% Al and 0.02-0.05% O, has a component composition satisfying 0.33-0.53% Ceq (=C+Mn/6+Si/24+Ni/40+Cr/5+Mo/4+V/14) [wherein Ceq is a carbon equivalent (mass%); and C, Mn, Si, Ni, Cr, Mo and V are the contents of respective alloy elements (mass%)], and comprises a microstructure including an acicular ferrite phase having 2×10pieces/1 mmor more of Ti-containing oxide particles which have a circle-equivalent diameter of 2 μm or less. |
