HOT-ROLLED STEEL SHEET AND A MANUFACTURING METHOD THEREOF, CAPABLE OF IMPROVING A TENSILE STRENGTH THEREOF OVER 600 MPa WITH ADDING CHROME TO THE SAME

摘要

PURPOSE: A hot-rolled steel sheet and a manufacturing method thereof are provided to add Cr to the same, thereby improving a tensile strength thereof over 600 MPa and an elongation thereof over 15%.;CONSTITUTION: A manufacturing method of a hot-rolled steel sheet includes: a step (S105) of re-dissolving elements and precipitates, which are segregated in casting, through reheating a half-finished slab sheet material at a temperature of 1150 to 1300°C about for one to three hours; a step (S110) of hot-rolling the sheet material at a finishing delivery temperature (FDT) of 820 to 860°C; and a step (S120) of cooling the hot-rolled sheet material, and then coiling the sheet material at a coiling temperature (CT) of 640 to 680°C. The sheet material includes 0.33 to 0.37 wt% of C, below 0.25 wt% of Si, 0.6 to 0.8 wt% of Mn, below 0.02 wt% of P, below 0.005 wt% of S, and below 1.0 wt% of Cr, and further includes at least one of below 0.5 wt% of Ni and below 0.25 wt% of Mo, and remnants Fe and inevitable impurities. The sum of Cr, Ni, and Mo is below 1.0 wt%.;COPYRIGHT KIPO 2013;[Reference numerals] (AA) Start; (BB) End; (S105) Reheat a slab (SRT: 1150-1300°); (S110) Hot rolling (FDT: 820-860°); (S120) Cooling/winding (CT: 640-680°)