| 摘要 |
PURPOSE: A method of manufacturing high strength steel sheets with a tensile strength of 150 kgf/mm¬2 for use in the manufacture of armor plate for armored motorcars by controlled rolling and direct quenching process is provided. CONSTITUTION: The passivation method of pickled stainless cold rolled steel sheets includes the steps of reheating a slab comprising C 0.14 to 0.18 wt.%, Mn 0.5 to 1.5 wt.%, Si 0.15 to 0.35 wt.%, 0.02 wt.% or less of P, 0.008 wt.% or less of S, Ni 2.5 to 3.5 wt.%, Cr 0.5 to 1.0 wt.%, Mo 0.15 to 0.45 wt.%, Nb 0.01 to 0.04 wt.%, Sol-Al 0.02 to 0.06 wt.% at 1150 to 1300°C; controlled-rolling the slab at an accumulation reduction ratio of greater than 50 % in nonrecrystallization region; water cooling the hot rolled steel sheet at a cooling rate of 10 to 50°C/sec to ambient temperature; tempering the cooled steel sheet at 150 to 350°C.
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