Galvannealed steel sheet and producing method thereof

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, an amount equal to or less than 2 mass % of at least one of Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, and rare earth elements as needed, and a balance composed of Zn and inevitable impurities; and

a composite oxide layer of Mn, Zn, and P which is formed on a surface of the galvannealed layer, includes an amount equal to or more than 0.1 mg/m 2 and equal to or less than 100 mg/m 2 of Mn, an amount equal to or more than 1 mg/m 2 and equal to or less than 100 mg/m 2 of P, and Zn, has a P/Mn ratio of equal to or higher than 0.3 and equal to or lower than 50,

wherein the galvannealed layer includes a flat portion having an area ratio of equal to or higher than 10% and equal to or lower than 70% and a rough portion which is at a position closer to the steel sheet than the flat portion at an interface of the galvannealed layer and the composite oxide layer,

the composite oxide layer of Mn, Zn, and P contains an amorphous compound;

a surface roughness Ra of the rough portion is equal to or higher than 0.5 μm and equal to or lower than 10 μm, and

a surface roughness Ra of the flat portion is equal to or higher than 0.01 μm and lower than 0.5 μm.

2. The galvannealed steel sheet according to claim 1 , wherein a thickness of the composite oxide layer of Mn, Zn, and P is equal to or higher than 0.1 nm and lower than 100 nm.

3. The galvannealed steel sheet according to claim 1 , wherein a thickness of the composite oxide layer of Mn, Zn, and P is equal to or higher than 0.1 nm and lower than 10 nm.

4. The galvannealed steel sheet according to claim 1 or 2 , wherein the composite oxide layer of Mn, Zn, and P includes at least one of phosphoric acid group, phosphorous acid group, and hypophosphorous acid group.

5. The galvannealed steel sheet according to claim 1 or 2 ,

wherein a ratio Iη/ISi of an X-ray diffraction intensity Iη of an interplanar spacing d of the galvannealed layer of 1.237 Å to an X-ray diffraction intensity ISi of an interplanar spacing d of an Si powder standard of 3.13 Å is equal to or lower than 0.0006,

a ratio Iζ/ISi of an X-ray diffraction intensity Iζ of an interplanar spacing d of the galvannealed layer of 1.26 Å to the X-ray diffraction intensity ISi of the interplanar spacing d of the Si powder standard of 3.13 Å is equal to or higher than 0.0005, and

a ratio IΓ/ISi of an X-ray diffraction intensity IΓ of an interplanar spacing d of the galvannealed layer of 1.222 Å to the X-ray diffraction intensity ISi of the interplanar spacing d of the Si powder standard of 3.13 Å is equal to or lower than 0.004.

6. The galvannealed steel sheet according to claim 1 or 2 , wherein the steel sheet includes by mass an amount equal to or more than 0.0001% and equal to or less than 0.004% of C, an amount equal to or more than 0.001% and equal to or less than 0.15% of Si, an amount equal to or more than 0.01% and equal to or less than 1.0% of Mn, an amount equal to or more than 0.001% and equal to or less than 0.1% of P, an amount equal to or less than 0.015% of S, an amount equal to or more than 0.001% and equal to or less than 0.1% of Al, an amount equal to or more than 0.002% and equal to or less than 0.10% of Ti, an amount equal to or more than 0.0005% and equal to or less than 0.0045% of N, and a balance composed of Fe and inevitable impurities.

7. The galvannealed steel sheet according to claim 6 , wherein the steel sheet further includes by mass an amount equal to or more than 0.002% and equal to or less than 0.10% of Nb.

8. The galvannealed steel sheet according to claim 6 , wherein the steel sheet further includes an amount by mass equal to or more than 0.0001% and equal to or less than 0.003% of B.

9. The galvannealed steel sheet according to claim 6 , wherein an r-value of the steel sheet is equal to or higher than 1.6 and equal to or lower than 2.2.

10. The galvannealed steel sheet according to claim 1 or 2 , wherein the steel sheet includes by mass an amount more than 0.004% and equal to or less than 0.3% of C, an amount equal to or more than 0.001% and equal to or less than 2% of Si, an amount equal to or more than 0.01% and equal to or less than 4.0% of Mn, an amount equal to or more than 0.0001% and equal to or less than 0.15% of P, an amount equal to or less than 0.0015% of S, an amount equal to or less than 2% of Al, an amount equal to or more than 0.0005% and equal to or less than 0.004% of N, and a balance composed of Fe and inevitable impurities.

11. The galvannealed steel sheet according to claim 1 or 2 , wherein the composite oxide layer of Mn, Zn, and P includes an aqueous P compound.

12. A producing method of the galvannealed steel sheet according to claim 1 , the method comprising:

performing hot dip galvanization of the steel sheet;

forming a galvannealed layer including an amount equal to or more than 0.05% and equal to or less than 0.5% of Al and an amount equal to or more than 6% and equal to or less than 12% of Fe by alloying; and

after performing skin pass rolling, forming a composite oxide layer of Mn, Zn, and P on a surface of the galvannealed layer by controlling a treatment liquid so that an amount equal to or more than 0.1 mg/m 2 and equal to or less than 100 mg/m 2 of Mn and an amount equal to or more than 1 mg/m 2 and equal to or less than 100 mg/m 2 of P are included and a P/Mn ratio is 0.3 to 50.

13. The producing method of the galvannealed steel sheet according to claim 12 , wherein the skin pass rolling is performed to achieve an elongation ratio of equal to or higher than 0.3% and equal to or lower than 2.0%.

14. The producing method of the galvannealed steel sheet according to claim 12 or 13 , wherein the treatment liquid is applied to the surface of the galvannealed layer using a coating coater.