| 摘要 |
PURPOSE: A steel plate for welded structure is provided which minimizes a toughness difference between a base metal and a weld heat-affected zone using TiN and Ti-Zr composite oxides and accomplishes high strengthening of the base metal at the same time, and a method for manufacturing the steel plate is provided. CONSTITUTION: The high strength steel plate for welded structure having superior toughness in weld heat-affected zone comprises 0.03 to 0.17 wt.% of C, 0.01 to 0.5 wt.% of Si, 0.4 to 2.0 wt.% of Mn, 0.005 to 0.2 wt.% of Ti, 0.0005 to 0.1 wt.% of Al, 0.008 to 0.030 wt.% of N, 0.0003 to 0.01 wt.% of B, 0.001 to 0.2 wt.% of W, 0.03 wt.% or less of P, 0.03 wt.% or less of S, 0.002 to 0.03 wt.% of O and 0.005 to 0.1 wt.% of Zr satisfying 1.2<=Ti/N<=2.5, 10<=N/B<=40, 2.5<=Al/N<=7, 6.5<=(Ti+2Al+4B)/N<=14, 4<=Ti/O<= 10, 3<=Zr/O<=8 and 7<=(Ti+Zr)/O<=14, and a balance of Fe and other impurities comprising 30 to 80 wt.% of bainite and a balance of ferrite which is 20 microns or less. The method for manufacturing the high strength steel plate for welded structure having superior toughness in weld heat-affected zone comprises the processes of heating a slab comprising 0.03 to 0.17 wt.% of C, 0.01 to 0.5 wt.% of Si, 0.4 to 2.0 wt.% of Mn, 0.005 to 0.2 wt.% of Ti, 0.0005 to 0.1 wt.% of Al, 0.008 to 0.030 wt.% of N, 0.0003 to 0.01 wt.% of B, 0.001 to 0.2 wt.% of W, 0.03 wt.% or less of P, 0.03 wt.% or less of S, 0.002 to 0.03 wt.% of O and 0.005 to 0.1 wt.% of Zr satisfying 1.2<=Ti/N<=2.5, 10<=N/B <=40, 2.5<=Al/N<=7, 6.5<=(Ti+2Al+4B)/N<=14, 4<=Ti/O<=10, 3<=Zr/O<=8 and 7<=(Ti+Zr)/O <=14, and a balance of Fe and other impurities to the temperature range of 1000 to 1250 deg.C for 60 to 180 minutes; hot rolling the heated slab to a rolling ratio of 40% or more in the Austenite recrystallization zone; and cooling the hot rolled steel slab to the bainite transformation finishing temperature±10 deg.C in a cooling rate of 5 to 20 deg.C/sec.
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