| 摘要 |
PURPOSE: A method for manufacturing a steel product for welded structure is provided which improves toughness in weld heat-affected zone by uniformly distributing fine TiN precipitates. CONSTITUTION: In a method for manufacturing a steel product 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, 0.005 wt.% or less of O and a balance of Fe and other impurities, and satisfying 1.2<=Ti/N<=2.5, 10<=N/B<=40, 2.5<=Al/N<=7 and 6.5<=(Ti+2Al+4B)/N<=14, the method for manufacturing the steel product for welded structure having superior toughness in weld heat-affected zone comprises the steps of manufacturing a slab by casting the molten steel after injecting a deoxidizing element having a larger deoxidizing power than Ti into molten steel before injecting Ti so that the molten steel is deoxidized to a dissolved oxygen of 30 ppm or less, and adding Ti to the molten steel within 10 minutes thereafter so that 0.005 to 0.2 wt.% of Ti is contained in the molten steel; and hot rolling the heated slab to a rolling ratio of 40 % or more in the austenitic recrystallization region after heating the slab in the temperature range of 1100 to 1250 deg.C for 60 to 80 minutes, and cooling the hot rolled slab to a temperature of ferrite transformation finishing temperature±10 deg.C at a cooling rate of 1 deg.C/min or more.
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