Galvannealed steel sheet having excellent formability and exfoliation resistance after adhesion and production method thereof

摘要

The galvannealed steel sheet includes: a galvannealed layer formed on at least one surface of a steel sheet and contains includes an amount of 0.05 mass % to 0.5 mass % of Al, an amount of 6 mass % of 12 mass % of Fe, and the balance composed of Zn and inevitable impurities; and a mixed layer formed on a surface of the galvannealed layer and includes a composite oxide of Mn, Zn, and P and an aqueous P compound, wherein the composite oxide includes 0.1 mg/m2 to 100 mg/m2 of Mn, an amount of 1 mg/m2 to 100 mg/m2 of P, and Zn, and a P/Mn ratio is 0.3 to 50, and wherein the total size of an area of the mixed layer in which an attached amount of P is equal to or more than 20 mg/m2 is 20% to 80% of a surface area of the mixed layer.

主权项

1. A galvannealed steel sheet comprising:
a steel sheet; a galvannealed layer which is formed on at least one surface of the steel sheet and includes an amount equal to or more than 0.05 mass % and equal to or less than 0.5 mass % of Al, an amount equal to or more than 6 mass % and equal to or less than 12 mass % of Fe, and optionally a total amount equal to or less than 2 mass % of at least one of Pb, Sb, Si, Fe, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, and rare earth elements, and the balance composed of Zn and inevitable impurities; and a mixed layer which is formed on a surface of the galvannealed layer and includes a composite oxide of Mn, Zn, and P and an aqueous P compound, wherein the composite oxide includes an amount equal to or more than 0.1 mg/m2 and equal to or less than 100 mg/m2 of Mn, an amount equal to or more than 1 mg/m2 and equal to or less than 100 mg/m2 of P, and Zn, and has a P/Mn ratio of equal to or higher than 0.3 and equal to or lower than 50, and wherein the mixed layer includes a first applied part and a second applied part, an attached amount of P in the second applied part being larger than an attached amount of P in the first applied part, the attached amount of P in the second applied part being equal to or more than 20 mg/m2, and a total surface area of the second applied part is equal to or higher than 20% and equal to or lower than 80% of a surface area of the mixed layer; wherein the total size of an area of the mixed layer in which the P/Mn ratio is equal to or higher than 3 is equal to or higher than 1% and equal to or lower than 50% of the surface area of the mixed layer.