Galvannealed steel sheet and production method thereof

A galvannealed steel sheet, obtained by subjecting a base steel sheet to hot-dip galvanization and then alloying the galvanization layer, wherein a base steel sheet of the galvannealed steel sheet is obtained by hot rolling a steel,

• a steel of the galvannealed steel sheet, comprising:
• Fe;
• inevitable impurities;
• and
• carbon (C) in a content of 0.02 to 0.25 percent by mass;
• silicon (Si) in a content of 0.5 to 3 percent by mass;
• manganese (Mn) in a content of 1 to 4 percent by mass;
• chromium (Cr) in a content of 0.03 to 1 percent by mass;
• aluminum (Al) in a content of 1.5 percent by mass or less, exclusive of 0 percent by mass;
• phosphorus (P) in a content of 0.03 percent by mass or less, exclusive of 0 percent by mass;
• sulfur (S) in a content of 0.03 percent by mass or less, exclusive of 0 percent by mass;
• titanium (Ti) in a content of 0.003 to 1 percent by mass;
• copper (Cu) in a content of 0.25 to 5.0 percent by mass;
• and
• nickel (Ni) in a content of 0.05 to 1.0 percent by mass,
• wherein the copper and nickel contents satisfy following Condition (1):
• [Cu]/[Ni]≧5 (1)
• wherein [Cu] and [Ni] represent the contents, as a percent by mass, of Cu and Ni, respectively.