Galvannealed steel sheet and method of manufacturing the same

A galvannealed steel sheet comprising:

• a steel sheet;
• a coating layer on a surface of the steel sheet;
• and
• a mixed layer formed between the steel sheet and the coating layer,
• wherein the steel sheet contains, in terms of mass %,
• C:
• 0.050% or more and 0.50% or less, and
• Mn:
• 0.01% or more and 3.00% or less,
• further contains, in terms of mass%, one type or two or more types of
• Si:
• 0.01% or more and 3.00% or less,
• Al:
• 0.010% or more and 2.00% or less, and
• Cr:
• 0.01% or more and 2.00% or less,
• limits amounts of P, S, O, N, Ti, Nb, Mo, Cu, Ni, and B, in terms of mass %, to
• P:
• 0.100% or less,
• S:
• 0.0200% or less,
• O:
• 0.0100% or less,
• N:
• 0.0100% or less,
• Ti:
• 0.150% or less,
• Nb:
• 0.150% or less,
• Mo:
• 1.00% or less,
• Cu:
• 2.00% or less,
• Ni:
• 2.00% or less, and
• B:
• 0.0100% or less,
• satisfies [Mn]+[Si]+[Al]+[Cr]≧0.4, wherein the Mn content, the Si content, the Al content, and the Cr content are respectively expressed by [Mn], [Si], [Al], and [Cr] in terms of mass %, and
• contains a remainder including Fe and unavoidable impurities,
• the coating layer is a galvannealed layer containing, in terms of mass %,
• Fe:
• 7.0% or more and 15.0% or less,
• Al:
• 0.01% or more and 1.00% or less, and
• a remainder including Zn and unavoidable impurities,
• the mixed layer includes
• a base iron portion having fine grains having a size of greater than 0 μm and equal to or smaller than 2 μm,
• a Zn—Fe alloy phase, and
• oxides containing one or more types of Mn, Si, Al, and Cr, and
• in the mixed layer, the oxides and the Zn—Fe alloy phase are present in grain boundaries that form the fine grains, and the Zn—Fe alloy phase is tangled with the base iron portion.