| 摘要 |
PURPOSE: A method for manufacturing high strength steel plate having superior toughness in weld heat-affected zone by controlled rolling at two phase regions is provided. CONSTITUTION: The method for manufacturing the steel plate for welded structure comprises the processes of heating a steel 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.% of S, 0.005 wt.% or less of O, a balance of Fe and other inevitable impurities in the temperature range of 1000 to 1250°C for 60-180 minutes wherein the steel slab satisfies the following inequalities: 1.2<=Ti/N<=2.5, 10<=N/B<=40, 2.5<=Al/N<=7, 6.5<=(Ti+2Al+4B)/N<=14; hot rolling the heated steel slab at a reduction ratio of higher than 50% over austenite recrystallization zone; cooling the hot rolled steel sheet to the temperature range of Ar3 to Ae3 at a cooling rate of higher than 5°C/sec; hot rolling the steel slab at a reduction ratio of higher than 40%; again hot rolling the steel slab at a reduction ratio of higher than 40%; and cooling the hot rolled steel sheet to ambient temperature at a cooling rate of 5 to 10°C/sec.
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