PURPOSE: To produce a galvannealed steel sheet excellent in plating adhesion by alloying in a short time by forming a film essentially consisting of FeS on the surface of a common steel sheet, subjecting the same to heat treatment and thereafter executing galvanizing and allaying treatment under heating.
CONSTITUTION: On the surface of a common steel sheet, a film essentially consisting of FeS is formed, and heat treatment is executed. Preferably, the formation of this film is executed by heating the steel sheet at about 200 to 600°C for about 7sec in an atmosphere mixed with H2S, e.g. an atmosphere of about 20 to 200ppm gaseous H2S, 3 to 25% gaseous H2, and the balance gaseous N2. Thus, the same film can easily and securely be formed into about 20 to 250 thickness. Furthermore, the formation of this film is executed preferably before or in the initial stage of the heat treatment for the steel sheet. After this heat treatment, the steel sheet is immersed in a plating bath, is galvanized and is moreover alloyed under heating.
MORI MASAAKI
OGAWA YUTAKA
ITOMI MAKOTO
