Patent ID: 8404060

Claim:
A method for manufacturing hot-rolled sheet, the method comprising: a step A comprising a first rolling in which a steel sheet containing 0.04-0.20% C, 0.01-2.0% Si, 0.5-3.0% Mn by mass, and the reminder being Fe and inevitable impurities, is rolled by successive multi-pass rolling at a total rolling reduction of 80% or more while keeping the steel sheet at temperatures not lower than the para-equilibrium transformation temperature Ae3; a step B comprising a second rolling in which a single-pass rolling is carried out at a rolling reduction of 30-55% when an entry side temperature is not lower than the para-equilibrium transformation temperature Ae3; a step C comprising a third rolling in which a single-pass rolling is carried out at a rolling reduction of 35-70% when an entry side temperature is set within a predetermined range; and a step D in which within 0.2 seconds after the third rolling, the rolled sheet is cooled at a cooling rate of 600 degree C/sec or higher to a temperature not higher than {(the para-equilibrium transformation temperature Ae3) −130 degree C.}, in the step C, the third rolling being carried out: within 0.6 seconds after the second rolling when the predetermined temperature range is {(the para-equilibrium transformation temperature Ae3) −60 degree C.} or more and below {(the para-equilibrium transformation temperature Ae3) −30 degree C.}; within 0.5 seconds after the second rolling when the predetermined temperature range is {(the para-equilibrium transformation temperature Ae3) −30 degree C.} or more and below {(the para-equilibrium transformation temperature Ae3) −5 degree C.}; and within 0.3 seconds after the second rolling when the predetermined temperature range is {(the para-equilibrium transformation temperature Ae3) −5 degree C.} or more and below {(the para-equilibrium transformation temperature Ae3) +20 degree C.}.