High-strength alloyed hot-dip galvanized steel sheet and manufacturing method therefor

A high-strength hot-dip galvannealed steel sheet, comprising:

• a plating layer on a surface of a base steel sheet,
• wherein the base steel sheet comprises, in mass %,
• C in a range of 0.19 to 0.30%,
• Si in a range of more than 0 to 0.1%,
• Mn in a range of 1.8 to 3.0%,
• P in a range of more than 0 to 0.020%,
• S in a range of more than 0 to 0.05%,
• Al in a range of 0.015 to 0.060%,
• Cr in a range of 0.05 to 0.8%,
• Ti in a range of 0.015 to 0.080%,
• B in a range of 0.0010 to 0.0150%;
• Mo in a range of more than 0 to 0.40%,
• N in an amount of 0.0100% or less,
• O in an amount of 0.0030% or less, and
• the balance including iron and unavoidable impurities,
• wherein the base steel sheet satisfies
• 2
• ×
• [
• Cr
• ]
• -
• [
• Si
• ]
• ≥
• 0
• .
• 1
• ,
• [Cr] being a mass percentage of Cr and [Si] being a mass percentage of Si,
• wherein the base steel sheet has a metallographic structure in which a volume ratio of martensite, which has both tempered martensite and self-tempered martensite, is 82 vol % or more,
• wherein the base steel sheet has a metallographic structure in which a volume ratio of ferrite, pearlite and bainite is 13 vol % or less in total,
• wherein the base steel sheet has a metallographic structure in which a volume ratio of retained austenite is 5 vol % or less,
• wherein, in an image obtained by observing the metallographic structure of the base steel sheet with a scanning electron microscope, a number of laths at a total length of 300 μm, the number being measured by an intercept method is 200 or more,
• wherein the high-strength hot-dip galvannealed steel sheet has a yield strength of 970 MPa or more, and
• wherein the high-strength hot-dip galvannealed steel sheet has a tensile strength of 1,470 MPa or more.