| 摘要 |
PURPOSE: A method for manufacturing a high strength steel plate having a composite precipitate of TiN and MnS is provided, in which TiN that is precipitated by nitriding treatment is surrounded by MnS to minimize toughness difference between base metal and weld heat-affected zone. CONSTITUTION: The method for manufacturing the high strength steel plate for welded structure comprises the processes of casting a steel slab comprising 0.03 to 0.17 wt.% of C, 0.01 to 0.5 wt.% of Si, 1.0 to 2.5 wt.% of Mn, 0.005 to 0.2 wt.% of Ti, 0.0005 to 0.1 wt.% of Al, 0.005 wt.% or less 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, 0.003 to 0.05wt.% of S, 0.005 wt.% or less of O, a balance of Fe and other inevitable impurities wherein the ratio of Mn against S is as follows: 220<=Mn/S<=400; nitriding the steel slab in the temperature range of 1000 to 1250°C for 60-180 minutes wherein nitrogen content in the steel plate is kept within the range of 0.008 to 0.03% while satisfying 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 40% over austenite recrystallization zone; and cooling the hot rolled steel sheet to a ferrite transformation finish temperature±10°C at a cooling rate of higher than 1°C/min.
|
