Super high-strength flux cored arc welded joint having excellent impact toughness, and welding wire for manufacturing same
An ultra high-strength flux-cored arc welded joint having excellent impact toughness comprises: 0.01 wt % to 0.06 wt % of carbon (C), 0.1 wt % to 0.5 wt % of silicon (Si), 1.5 wt % to 3.0 wt % of manganese (Mn), 2.5 wt % to 3.5 wt % of nickel (Ni), 0.5 wt % to 1.0 wt % of molybdenum (Mo), 0.4 wt % to 1.0 wt % of copper (Cu), 0.4 wt % to 1.0 wt % of chromium (Cr), 0.01 wt % to 0.1 wt % of titanium (Ti), 0.003 wt % to 0.007 wt % of boron (B), 0.001 wt % to 0.006 wt % of nitrogen (N), 0.02 wt % (excluding 0) or less of phosphorus (P), 0.01 wt % (excluding 0) or less of sulfur (S), 0.03 wt % to 0.07 wt % of oxygen (O), and remaining iron (Fe) as well as unavoidable impurities.
1. A flux-cored arc welded joint, comprising:
0.01 wt % to 0.06 wt % of carbon (C), 0.1 wt % to 0.5 wt % of silicon (Si), 1.5 wt % to 3.0 wt % of manganese (Mn), 2.5 wt % to 3.5 wt % of nickel (Ni), 0.5 wt % to 1.0 wt % of molybdenum (Mo), 0.4 wt % to 1.0 wt % of copper (Cu), 0.4 wt % to 1.0 wt % of chromium (Cr), 0.035 wt % to 0.1 wt % of titanium (Ti), 0.003 wt % to 0.007 wt % of boron (B), 0.001 wt % to 0.006 wt % of nitrogen (N), 0.02 wt % (excluding 0) or less of phosphorus (P), 0.01 wt % (excluding 0) or less of sulfur (S), 0.03 wt % to 0.07 wt % of oxygen (O), and remaining iron (Fe) as well as unavoidable impurities; and
a mixed microstructure including acicular ferrite, bainite and martensite, wherein the mixed microstructure comprises: 40 area % or more of the acicular ferrite, and a 40-50% of the bainite and the martensite in an area fraction.
2. The flux-cored arc welded joint of claim 1 , further comprising:
at least one selected from the group consisting of 0.001 wt % to 0.1 wt % of niobium (Nb), 0.001 wt % to 0.1 wt % of vanadium (V), 0.05 wt % to 0.50 wt % of tungsten (W), and 0.005 wt % to 0.5 wt % of zirconium (Zr); and
at least one selected from the group consisting of 0.0005 wt % to 0.005 wt % of calcium (Ca), and 0.005 wt % to 0.05 wt % of a rare earth metal (REM).
3. The flux-cored arc welded joint of claim 2 , wherein a carbon equivalent (Ceq) value satisfies 0.73-0.85% as defined by Formula 1 below:
Ceq=C+Si/24+Mn/6+Ni/40+Cr/5+Mo/4+V/14. <Formula 1>
4. The flux-cored arc welded joint claim 2 , wherein a weld crack susceptibility index Pcm value satisfies 0.35% or less as defined by Formula 2 below:
Pcm =C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B. <Formula 2>
5. The flux-cored arc welded joint of claim 1 , having impact toughness of 80 J or more at a temperature of −5° C.
6. The flux-cored arc welded joint of claim 1 , having tensile strength of 900 MPa or more.