Importance

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Abstract

An ultrahigh-strength welded joint with superior strength and toughness, and a method for producing the ultrahigh-strength welded joint by means of single-pass welding by using laser hybrid welding, are provided, wherein the welded joint comprising a steel plate having a plate thickness of 4 mm to 12 mm and including weld metal of almost full martensite structure, wherein, in a cross-section of the welded joint in a direction perpendicular to a welding direction, a cross-sectional shape of the weld metal has a width W1 of 2.0 to 7.0 mm at a surface of the steel plate and a width W2 of 0.5 to 2.4 mm at a position where is separated from the surface by three-quarters of the plate thickness, wherein the weld metal comprises, by mass %, C: over 0.09% to 0.24%; Si: 0.2% to 1.0%; Mn: 0.5% to 2.5%; P: 0.02% or less; S: 0.02% or less; Al: 0.004% to 0.08%; Ti: 0.005% to 0.15%; O: 0.005% to 0.05%; and Ni: 1.0% to 9%, and wherein a carbon equivalent (Ceq) is 0.40% to 1.00%, a value Y as defined by equation (([Si]+[Mn])/40+[Al]+[Ti]) is 0.07% to 0.20%.

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First Claim