Abstract: A composite zinc-silica electro-galvanized steel sheet excellent in corrosion resistance, having on at least one surface thereof a zinciferous plating layer, preferably in an amount of from 5 to 100 g/m.sup.2 per side thereof, into which silica particles are dispersed. The above-mentioned plating layer consists essentially of:silica particles: from 0.1 to 20 wt. %,nitrogen compounds: from 0.0005 to 0.5 wt. % as converted into nitrogen,and the balance being zinc and incidental impurities.The above-mentioned plating layer further additionally contains as required at least one element selected from the group consisting of:iron: from 2 to 80 wt. %,nickel: from 2 to 25 wt. %,cobalt: from 0.1 to 5 wt. %, andchromium: from 0.5 to 20 wt. %.The total amount of the above-mentioned at least one element thus additionally contained is limited to up to 80 wt. %.

Abstract: A steel strip heated to a temperature above a recrystallization temperature is passed through a cooling unit including a plurality of cooling rollers cooled by cooling water flowing through the interior thereof. The steel strip is caused to pass alternately about upper and lower surfaces of the cooling rollers. By raising and lowering alternate cooling rollers, the contact angle and therefore the contact area, i.e., the contact time between the strip and the cooling rollers is varied to change the cooling rate. When the cooling rollers are separated from the strip. Cooling water is filled into the cooling unit to directly cool the strip. Cooling gas may be ejected against the strip before it enters into the cooling unit.