Steel plate having TiN+CuS precipitates for welded structures, method for manufacturing same and welded structure made therefrom
AssigneePosco
InventorsHong-Chul Jeong, Hae-Chang Choi
Life of this patent
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Abstract
A weldable structural steel product having fine complex precipitates of TiN and CuS is provided which contains, in terms of percent by weight, 0.03 to 0.17%C, 0.01 to 0.05% Si, 0.4 to 2.0% Mn, 0.005 to 0.2% Ti, 0.0005 to 0.1% Al, 0.008 to 0.030% N, 0.0003 to 0.01% B, 0.001 to 0.2% W, 0.1 to 1.5% Cu, at most 0.03% P, 0.003 to 0.05% S, at most 0.005% O, and balance Fe and incidental impurities while satisfying conditions of 1.2≦Ti/N≦2.5, 10≦N/B≦40, 2.5≦Al/N≦7, 6.5≦(Ti+2Al+4B)/N≦14, and 10≦Cu/S≦90, and having a microstructure essentially consisting of a complex structure of ferrite and pearlite having a grain size of 20 μm or less.
Claims25
A welding structural steel product having fine complex precipitates of TiN and CuS, consisting essentially of, in terms of percent by weight, 0.03 to 0.17% C, 0.01 to 0.5% Si, 0.4 to 2.0% Mn, 0.005 to 0.2% Ti, 0.0005 to 0.1% Al, 0.008 to 0.030% N, 0.0003 to 0.01% B, 0.001 to 0.2% W, 0.1 to 1.5% Cu, 0 to 0.2% V, 0 to 3.0% Ni, 0 to 0.1% Nb, 0 to 1.0% Mo, 0 to 1.0% Cr, 0 to 0.005% Ca, 0 to 0.05% REM, at most 0.03% P, 0.003 to 0.05% S, at most 0.005% O, and balance Fe and incidental impurities while satisfying conditions of 1.2≦Ti/N≦2.5, 10≦N/B≦40, 2.5≦Al/N≦7, 6.5≦(Ti+2Al+4B)/N≦14, and 10≦CU/S≦90, and having a microstructure consisting essentially of a complex structure of ferrite and pearlite having a grain size of 20 μm or less.
A method for manufacturing a welding structural steel product having fine complex precipitates of TiN and CuS, comprising the steps of:
- preparing a steel slab, consisting essentially of, in terms of percent by weight, 0.03 to 0.17,% C, 0.01 to 0.5 T Si, 0.4 to 2.0% Mn, 0.005 to 0.2 T Ti, 0.0005 to 0.1% Al, 0.008 to 0.030% N, 0.0003 to 0.01% B, 0.001 to 0.2% W, 0.1 to 1.5% Cu, 0 to 0.2% V, 0 to 3.0% Ni, 0 to 0.1% Nb, 0 to 1.0% Mo, 0 to 1.0% Cr, 0 to 0.005% Ca, 0 to 0.05% REM, at most 0.03% P, 0.003 to 0.05% S, at most 0.005% O, and balance Fe and incidental impurities while satisfying conditions of 1.2≦Ti/N≦2.5, 10≦N/B≦40, 2.5≦Al/N≦7, 6.5≦(Ti+2Al+4B)/N≦14, and 10≦Cu/S≦90;
- heating the steel slab at a temperature ranging from 1,100° C. to 1,250° C. for 60 to 180 minutes;
- hot rolling the heated steel slab in an austenite recrystallization range at a thickness reduction rate of 40% or more;
- and
- cooling the hot-rolled steel slab at a rate of 1° C./min to a temperature corresponding to ±10° C. from a ferrite transformation finish temperature.
A method for manufacturing a welding structural steel product having fine complex precipitates of TiN and CuS, comprising the steps of:
- preparing a steel slab consisting essentially of, in terms of percent by weight, 0.03 to 0.17% C, 0.01 to 0.5% Si, 0.4 to 2.0% Mn, 0.005 to 0.2% Ti, 0.0005 to 0.1% Al, at most 0.005 N, 0.0003 to 0.01% B, 0.001 to 0.2% W, 0.1 to 1.5% Cu, 0 to 0.2% V, 0 to 3.0% Ni, 0 to 0.1% Nb, 0 to 1.0%Mo, 0 to 1.0% Cr, 0 to 0.005% Ca, 0 to 0.05%REM, at most 0.03%P, 0.003 to 0.05% S, at most 0.005% O, and balance Fe and incidental impurities while satisfying a condition of 10≦CU/S≦90;
- heating the steel slab at a temperature ranging from 1,000° C. to 1,250° C. for 60 to 180 minutes while nitrogenizing the steel slab to control the N content of the steel slab to be 0.008 to 0.03%, and to satisfy conditions of 1.2≦Ti/N≦2.5, 10≦N/B≦40, 2.5≦Al/N≦7, and 6.5≦(Ti+2Al+4B)/N≦14;
- hot rolling the nitrogenized steel slab in an austenite recrystallization range at a thickness reduction rate of 40% or more;
- and
- cooling the hot-rolled steel slab at a rate of 1° C./min to a temperature corresponding to ±10° C. from a ferrite transformation finish temperature.
A welded structure having a superior heat affected zone toughness, manufactured using a welding structural steel product having fine complex precipitates of TiN and CuS, consisting essentially of, in terms of percent by weight, 0.03 to 0.17% C, 0.01 to 0.5% Si, 0.4 to 2.0% Mn, 0.005 to 0.2% Ti, 0.0005 to 0.1% Al, 0.008 to 0.030% N, 0.0003 to 0.01% B, 0.001 to 0.2% W, 0.1 to 1.5% Cu, 0 to 0.2% V, 0 to 3.0% Ni, 0 to 0.1% Nb, 0 to 1.0% Mo, 0 to 1.0% Cr, 0 to 0.005% Ca, 0 to 0.05% REM, at most 0.03% P, 0.003 to 0.05% S, at most 0.005% O, and balance Fe and incidental impurities while satisfying conditions of 1.2≦Ti/N≦2.5, 10≦N/B≦40, 2.5≦Al/N≦7, 6.5≦(Ti+2Al+4B)/N≦14, and 10≦Cu/S≦90, and having a microstructure consisting essentially of a complex structure of ferrite and pearlite having a grain size of 20 μm or less.
Dependencies are inferred from the claim text.