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    • 9. 发明申请
    • METHOD FOR MANUFACTURING HOT-ROLLED SHEET HAVING FINE-GRAINED FERRITE, AND HOT-ROLLED SHEET
    • US20100089505A1
    • 2010-04-15
    • US12525094
    • 2007-02-02
    • Suguhiro FukushimaManabu EtoTamotsu SasakiKaori KawanoMasayuki Wakita
    • Suguhiro FukushimaManabu EtoTamotsu SasakiKaori KawanoMasayuki Wakita
    • C21D8/02C22C38/00C22C38/04
    • C22C38/06B21B1/38B21B3/00C21D8/02C22C38/001C22C38/02C22C38/04
    • The present invention provides a method for manufacturing the hot-rolled sheet, which includes: a step A including 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 including 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 including 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.}.