Nippon Steel Corporation

Masakazu Oshimi

Naoki Yoshinaga

Osamu Akisue

Kohsaku Ushioda

Tomohisa Katayama

A process for producing a non-aging galvanized steel sheet having good formability in a continuous galvanizing production line, which comprises heating a low carbon, Al-killed cold rolled steel sheet at a temperature not lower than a recrystallizing temperature, reducing the surface of the steel sheet thus heated in a reducing atmosphere, cooling the steel sheet to a temperature (T.sub.E) ranging from 200.degree. to 350.degree. C. from a temperature not lower than 600.degree. C. at a cooling rate not less than 30.degree. C/s, holding the steel sheet at the temperature (T.sub.E) for 0 to less than 10 seconds, reheating the steel sheet to a temperature ranging from 430.degree. to 500.degree. C. at a heating rate not less than 10.degree. C/s, immersing the steel sheet into a molten zinc bath, cooling the steel sheet thus galvanized to a temperature not higher than 370.degree. C., and subjecting the steel sheet to an overaging treatment to a temperature range from 250.degree. to 320.degree. C. for not shorter than 40 seconds. A modified process according to the present invention further comprises reheating the galvanized steel sheet to a temperature raning from 480.degree. to 600.degree. C. at a heating rate not lower than 10.degree. C/s, and holding the sheet in this temperature range to perform alloying of the zinc coating layer with the steel substrate.

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Sagamihara, Japan

Masakazu Oshimi