High-strength galvanized steel sheet and method for manufacturing the same

A high-strength galvanized steel sheet having

• a chemical composition containing, by mass %, C:
• 0.05% or more and 0.15% or less, Si:
• 0.01% or more and 1.00% or less, Mn:
• 1.5% or more and 4.0% or less, P:
• 0.100% or less, S:
• 0.02% or less, Al:
• 0.01% or more and 0.50% or less, Cr:
• 0.010% or more and 2.000% or less, Nb:
• 0.005% or more and 0.100% or less, Ti:
• 0.005% or more and 0.100% or less, B:
• 0.0005% or more and 0.0050% or less, and the balance being Fe and inevitable impurities, in which K, which is expressed by equation (1) below, is 3.0 or more and
• a metallographic structure including, in terms of area ratio determined by performing structure observation at a position located at ¼ of the thickness in a cross section at a right angle to the surface of the steel sheet, ferrite:
• 10% or less, bainitic ferrite:
• 2% or more and 30% or less, and martensite:
• 60% or more and 98% or less, wherein the proportion of retained austenite determined by using an X-ray diffraction method is less than 2%, an average grain diameter of martensite adjacent to bainite is 15 μm or less, the proportion of massive martensite adjacent only to bainite to the whole metallographic structure is 10% or less, and a value (ΔHv) calculated by subtracting the Vickers hardness at a position located at 20 μm from the surface of the steel sheet from the Vickers hardness at a position located at 100 μm from the surface of the steel sheet is 30 or more:
• K=−0.4×[Si]+1.0×[Mn]+1.3×[Cr]+200×[B] (1),
• where, in equation (1) above, [Si] denotes the content [mass %] of Si, [Mn] denotes the content [mass %] of Mn, [Cr] denotes the content [mass %] of Cr, and [B] denotes the content [mass %] of B.