| 摘要 |
PURPOSE: A non-heat treated bainite steel plate is provided which is capable of improving toughness of heat affected zone when high heat input welding a bainite steel plate in which fine TiN precipitate is uniformly distributed, and a method for manufacturing the same is provided. CONSTITUTION: The method comprises a step of heating a slab comprising 0.001 to 0.03 wt.% of C, 0.01 to 0.5 wt.% of Si, 1.0 to 3.0 wt.% of Mn, 0.005 to 0.2 wt.% of Nb, 0.005 to 0.2 wt.% of Ti, 0.005 to 0.1 wt.% of Al, 0.0005 to 0.01 wt.% of B, 0.008 to 0.030 wt.% of N, 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 the following relations: 1.2<=Ti/N<=2.5, 2<=N/B<=20, 2.5<=Al/N<=7, 3<=Nb/N<=10 and 10<=(Ti+2Al+4B+Nb)/N<=20 in the temperature range of 1,000 to 1,250 deg.C for 60 to 180 minutes; a step of hot rolling the heated slab at a reduction ratio of 40% or more in the austenite non-recrystallization region; and a step of air cooling the hot rolled steel plate to an ordinary temperature or cooling the hot rolled steel plate to an ordinary temperature in a cooling rate of 10 deg.C/sec or less.
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