| 摘要 |
PROBLEM TO BE SOLVED: To provide a galvannealed steel sheet superior in the image clarity of a coating and press formability, and to manufacture the galvannealed steel sheet with an easy method without needing a roll having a special roughness and a control for the roll when temper-rolling a plated steel sheet. SOLUTION: A composition of a plating bath includes, by mass%, 6 to 13% Fe, 0.25 to 1% Al, 0.25 to 1% Ni and the balance Zn with unavoidable impurities. The galvannealed steel sheet superior in the image clarity of the coating and the press formability has mean waviness (Wca) of 0.5μm or less and mean roughness (Ra) of 0.4μm or more. The galvannealed steel sheet preferably satisfies the relationship of Ra>2×Wca. The manufacturing method includes: preparing a cold-rolled steel sheet which has been annealed and temper-rolled; pre-plating the steel sheet with Ni; heating the steel sheet to 500°C or lower; galvanizing the steel sheet in a hot-dip galvanizing bath; wiping the plated film; heating the steel sheet to alloy the plated film; and temper-rolling the steel sheet at a rolling reduction of 0.1% or more. COPYRIGHT: (C)2008,JPO&INPIT
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