| 摘要 |
PURPOSE: A hot rolled steel sheet, a cold rolled steel sheet with high carbon and a production method thereof are provided to supply the excellent hot rolled steel sheet with high carbon having high strength and high hardness simultaneously and to improve the quality of surface preventing decarburization. CONSTITUTION: The production method of a hot-rollled steel sheet and a cold-rolled steel sheet with high carbon executes the following steps. A rolled steel with high carbon is prepared being composed of 0.15-0.7 weight% of C; less than 0.5 weight% of Si; 0.1-1.5 weight% of Mn; less than 0.05 weight% of P; less than 0.03 weight% of S; one or more element selected from less than 0.5 weight% of Mo, less than 0.15 weight% of Nb, less than 0.15 weight% of V; less than 1.5 weight% of one or more element selected from a group of Cr, Ni, Cu; the remaining weight% of Fe; and inevitable impurities. A steel sheet is produced executing hot rolling in an austenite region. The steel sheet is rapidly cooled to 520-660 degreeC before starting a phase change in a run-out table[ROT]. A cooling temperature maintained is kept flat. The rolled steel is wrapped in the cooling temperature maintained. [Reference numerals] (AA) Hot-rolling(perlite); (BB) Souring; (CC) Annealing into spherical shape; (DD) First cold-rolling; (EE) Heat-processing(fine perlite); (FF, JJ) Polishing/souring; (GG) Second cold-rolling; (HH) Hot-rolling(fine perlite); (II) Removing post-processes; (KK) Cold-rolling |
