HOT-ROLLED STEEL SHEET AND PROCESS FOR MANUFACTURING SAME

摘要

The present invention pertains to a process for manufacturing a hot-rolled steel sheet which comprises: heating a steel raw material that contains, in mass%, 0.055 to 0.15% of C, at most 0.2% of Si, at most 1.3% of Mn, at most 0.03% of P, at most 0.007% of S, at most 0.1% of Al, at most 0.01% of N and 0.14 to 0.30% of Ti so as to satisfy the relationship 1.0 <= ([C]/12)/([Ti*]/48) (wherein [Ti*] = [Ti]-3.4×[N]-1.5×[S]) to a temperature (T) (°C) which is equal to or higher than 1150°C and which satisfies the relationship [Ti*] < 10{-7000/(T+273)+2.75/[C]; keeping the steel raw material in a temperature range down to 1150°C for at least 15 minutes; subjecting the resulting steel raw material to hot rolling wherein the total rolling reduction in a temperature range up to 980°C is 40% or less and the finish rolling temperature is 880°C or higher; cooling the hot-rolled steel sheet at a cooling rate of 40 to 200°C/s within three seconds after the completion of the finish rolling; and winding up the cooled steel sheet in a temperature range of 500 to 680°C.