Method of cooling hot steel plates

In a method of cooling hot steel plate as delivered from a preceding hot rolling line and passed longitudinally through pairs of top and bottom rollers disposed in the direction in which the steel plate travels by supplying cooling water to the top and bottom surfaces thereof from nozzles on a plurality of cooling units disposed in the same longitudinal direction, each cooling unit being interposed between adjoining pairs of said top and bottom rollers and at least some of the nozzles being disposed so as to direct cooling water onto a bottom side of the steel plate, which comprises the steps of:

• determining the temperature distribution in the steel plate before starting cooling;
• setting a desired mean cooling rate;
• determining the distance from the plate side edges over which the supply of the cooling water at least to the bottom side of the steel plate is to be cut off on the basis of said temperature distribution and mean cooling rate so that the temperature of inner edge portions of the steel plate which are inside outer edge portions which are adjacent the plate edges, and outside a middle portion, are kept above the temperature of the middle portion so as to ensure that an Ar.sub.3 transformation in the inner edge portions occurs simultaneously with or after an Ar.sub.3 transformation in the middle portion;
• and
• cutting off the direct supply of the cooling water to the inner and outer edge portions of the steel plate at the bottom side of the steel plate over the distance determined in said distance determining step by shielding an appropriate number of nozzles thereon.