| 摘要 |
PURPOSE:To make advantageous production of a titled steel sheet without generating the exfoliation of a plating layer even under severe working conditions by specifying not only the component compsn. of a stock but also plating conditions and above all alloying treatment conditions and controlling the concn. of iron in the alloyed plating layer. CONSTITUTION:A hot rolled sheet consisting, by weight, of <=0.009% C, <=0.5% Si, 0.3-1.0% Mn, Nb%/C%=3-15 Nb, 0.0005-0.005% B, 0.010-0.10% Al, <=0.0050% N, <=0.15% P, <=0.010% S, and the balance Fe is prepd. The steel sheet formed by finishing such rolled sheet by FDT of the Ar3 transformation point - Ar3+100 deg.C then cold rolling the sheet is heated to 400-550 deg.C and is subjected to hot dip zinc coating. Such steel sheet is then subjected to the alloying treatment in the temp. range of 800 deg.C - Ac3 transformation point and is quickly cooled at a cooling rate of >=5 deg.C/s down to <=400 deg.C from the holding temp. thereof. The titled steel sheet consisting of ferrite and bainite or acicular ferrite and having 15-35% concn. of the iron in the alloyed galvanizing layer on the surface of the base material consisting of the cold rolled steel sheet is obtd.
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