| 摘要 |
PURPOSE: A thick steel plate for line pipe having excellent the low temperature drop weight tear test percent ductile fracture and a manufacturing method thereof are provided to manufacture the ferrite of 40 to 60% and the bainite complex structure steel of 40 to 60%, which have the effective grain size of 11μm less than, at the entire central portion of steel plate. CONSTITUTION: A thick steel plate for line pipe having excellent the low temperature drop weight tear test percent ductile fracture includes carbon (C) of 0.03 to 0.10 wt%, manganese (Mn) of 1.3-1.7 wt%, silicone of 0.2 to 0.3 wt%, aluminum (Sol.Al) of 0.2 to 0.6 wt%, niobinm (Nb) of 0.03 to 0.06 wt%, titanium (Ti) of 0.01 to 0.03 wt%, nickel (Ni) of 0.05 to 0.30 wt%, nitrogen (N) of 0.004% or less, phosphorus (P) of 0.012% or less, sulfur of 0.003% or less, remaining iron, and the other unavoidable impurities, and further includes selected at least one or two groups consisting of molybdenum (Mo) of 0.1 wt% or less, vanadium (V) of 0.1 wt% or less, copper (Cu) of 0.3 wt% or less, and chrome (Cr) of 0.3 wt% or less. The modified structure of steel plate includes the ferrite of 40 to 60 % and the bainite complex structure of 40 to 60 % based on the area faction. The effective average grain size of complex structure is 11μm or less. |
