Ultrahigh-strength welded joint and production method thereof

An ultrahigh-strength welded joint with a tensile strength of 1138 MPa or more and an absorbed energy in a 2 mm V-notch Charpy impact test at −40° C. (vE-40) of 27 J/cm2 or more, comprising a steel plate having a plate thickness of 4 mm to 12 mm and including a weld metal with an 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 at a surface of the steel plate and a width W2 at a position which is separated from the surface by three-quarters of the plate thickness, the width W1 being 2.0 mm to 7.0 mm and the width W2 being 0.5 mm to 2.4 mm, and

• 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%,
• wherein a carbon equivalent (Ceq) as defined by equation (1) is 0.40% to 1.00%, a value Y as defined by equation (2) is 0.07% to 0.20%, and a balance of the weld metal is constituted by unavoidable impurities and Fe:
• Ceq=[C]+[Si]/24+[Mn]/6+[Ni]/40+[Cr]/5+[Mo]/4+[V]/14 (1)
• Y=([Si]+[Mn])/40+[Al]+[Ti] (2), and
• wherein in equations (1) and (2), elements with “[ ]” represent contents (mass %) of respective elements.