| 摘要 |
<p>PURPOSE: A steel sheet with low yield ratio treated in a BAF(Batch Annealing Furnace) for a roof panel of a bus and a manufacturing method thereof are provided to obtain high elongation ratio of a steel sheet by cooling the steel sheet for 4 hours in a furnace and then cooling the steel sheet for 22 hours. CONSTITUTION: A method for manufacturing a steel sheet treated in a BAF for a roof panel of a bus comprises the steps of: preparing a steel sheet, which comprises C of 0.02-0.055wt.%, Si of 0-0.03wt.% Mn of 0.15-0.3wt.%, P of 0-0.02wt.%, S of 0-0.02wt.%, N of 0.002-0.008wt.%, S(Soluble)-Al of 0.02-0.06wt.%, and Fe inevitable impurities, inserting the steel sheet in a BAF and heating the steel sheet to 680±50°C(S110), implementing batch annealing at 680±50°C(S120), and cooling the steel sheet for 4±1 hours in the furnace and then cooling the steel sheet for 22±1 hours to 80±5°C(S130).</p> |
