| 摘要 |
PURPOSE: A method for manufacturing 50 kg/mm¬2 class high strength steel sheet for use in automobile panel is provided, which is characterized in that P content is decreased to improve secondary working brittleness resistance while Ti, along with Nb which gives strength to steel, is added to fix N as S as carbide, nitride and sulfide. CONSTITUTION: The method includes the steps of soaking an aluminum killed steel slab comprising 0.01 wt.% or less of C, Mn 1.0 to 3.0 wt.%, 0.03 wt.% or less of P, Si 0.3 to 0.8 wt.%, 0.015 wt.% or less of S, 0.06 wt.% or less of sol.Al, 0.005 wt.% or less of N, Cu 0.5 to 1.0 wt.%, Ti 0.01 to 0.04 wt.%, 6.63£C|+0.02 wt.%<=Nb<=6.63£C|+0.04 wt.%, a balance of Fe and incidental impurities at 1200 to 1250 deg.C; hot rolling the aluminum killed steel slab in such a manner that finish hot rolling temperature is higher than Ar3 transformation point; coiling the hot rolled aluminum killed steel sheet at 550 to 700 deg.C, followed by cold rolling; continuous annealing the cold rolled aluminum killed steel sheet at higher than 800 deg.C; and temper rolling.
|
