High-strength high-toughness thick steel plate and manufacturing method therefor
The objective of one aspect of the present invention is to provide: a thick steel plate having high strength and high toughness without carrying out accelerated cooling using water cooling, in the manufacturing, by means of a thermomechanical control process (TMCP), of a thick steel having a thickness of 15 mmt and over; and a method for manufacturing the same.
1 . A steel plate, by weight %, comprising: 0.02 to 0.10% of carbon (C), 0.6 to 1.7% of manganese (Mn), 0.5% or less of silicon (Si) (excluding 0%), 0.02% or less of phosphorus (P), 0.015% or less of sulfur(S), 0.005 to 0.05% of niobium (Nb), 0.005 to 0.08% of vanadium (V), a balance of iron (Fe) and inevitable impurities, and having a microstructure consisting of 85 to 95% of ferrite and 5 to 15% of pearlite by an area fraction,
wherein a grain size of austenite is ASTM grain size number of 10 or more and a grain size of ferrite is ASTM grain size number of 9 or more,
the thickness of the steel plate is 15 to 75 mm,
the steel plate has a yield ratio (yield strength (MPa)/tensile strength (MPa)) of 80 to 92%, and impact toughness at −70° C. of 300J or more, and
the steel plate has the tensile strength of 470 to 525 MPa.
2 . The steel plate of claim 1 , wherein the steel plate further comprises, by weight %, one or more of 0.5% or less of Ni and 0.5% or less of Cr.
3 . The steel plate of claim 1 , wherein the steel plate further comprises, by weight %, 0.05% or less of Ti.
4 . The steel plate of claim 1 , wherein the steel plate further comprises, by weight %, 0.001% or more and 0.5% or less of Ni.
5 . The steel plate of claim 1 , wherein the steel plate further comprises, by weight %, 0.15% or more and 0.5% or less of Ni.
6 . The steel plate of claim 1 , wherein the steel plate further comprises, by weight %, 0.40% or more and 0.5% or less of silicon (Si).
7 . The steel plate of claim 1 , wherein the steel plate further comprises, by weight %, 0.046 to 0.08% of vanadium (V).