Patent ID: 7938917

Claim:
A method for controlling cooling of a steel sheet characterized in that the steel sheet contains, by mass %, C: 0.30% or less, Si: 2.0% or less, Al: 2.0% or less Mn: 0.1% to 5.0%, P: 0.2% or less, S: 0.0005% to 0.02%, and N: 0.02% or less and a balance of iron and unavoidable impurities, and has mass % of C, Mn, Si, and Al satisfying formula (2); the method characterized by controlling the end-of-cooling temperature in a cooling process from the Ae 3 or above temperature of the steel sheet, during which obtaining in advance enthalpies (Hγ and Hα) of an austenite phase and ferrite phase respectively at some temperatures, obtaining a dynamic enthalpy (Hsys) defined by formula (1) with an untransformed fraction (Xγ) of austenite as a function of temperature in accordance with a target temperature pattern, predicting the temperature by using a gradient of this dynamic enthalpy with respect to temperature as a dynamic specific heat, and controlling the cooling of the steel sheet: H sys= H γ( X γ)+ H α(1 −X γ) formula (1) (C)+0.2×(Mn)−0.1×(Si+2×Al)≧0.15 formula (2) wherein the target temperature pattern contains a region of ⅓ or more thereof in which a cooling rate is 10° C./s to 300° C./s.