Hot-dip galvanized steel sheet and manufacturing method thereof

1. A hot-dip galvanized steel sheet comprising:

a steel sheet; and

a hot-dip galvanized layer arranged on the steel sheet,

wherein a component of the steel sheet includes, by mass %,

C: 0.05% to 0.13%,

Si: 0.2% to 0.8%,

Mn: 1.5% to 3.1%,

P: 0.001% to 0.06%,

S: 0.001% to 0.01%,

N: 0.0005% to 0.01%,

Al: 0.121% to 0.7%, and

a balance comprising Fe and unavoidable impurities,

wherein a content of the Si and a content of the Al by mass % satisfy a following Equation A,

wherein the steel sheet has a tensile strength TS of 800 MPa or more and a hole expansion ratio λ×TS is 60,000% MPa or more, and a metallographic structure of the steel sheet includes a ferrite and a martensite as quenched,

wherein, a fraction of the ferrite is 20 area % to 60 area % and a fraction of the martensite is 30 area % to 60 area %, when TS is 800 MPa to 1100 MPa, and

wherein, the fraction of the ferrite is 30 area % or less and the fraction of the martensite is 40 area % or more, when TS exceeds 1100 MPa; and

wherein the metallographic structure satisfies a following Equation B,

wherein n 1 represents a number of a MnS per 0.1 mm 2 on a surface portion of the steel sheet which is a region of ⅛ to 2/8 in a sheet thickness direction,

d 1 represents, in μm, an average equivalent circle diameter of the MnS on the surface portion of the steel sheet,

H 1 represents, in GPa, a hardness of the martensite of the surface portion of the steel sheet,

n 2 represents the number of the MnS per 0.1 mm 2 on a center portion of the steel sheet which is a region of ⅜ to ⅝ in the sheet thickness direction,

d 2 represents, in μm, the average equivalent circle diameter of the MnS on the center portion of the steel sheet, and

H 2 represents, in GPa, the hardness of the martensite of the center portion of the steel sheet:

0.5<Si+Al<1.0  (Equation A);

{( n 2 ) 2/3 ×d 2 }/{( n 1 ) 2/3 ×d 1 }×ln( H 2 /H 1 )<0.3  (Equation B).

2. The hot-dip galvanized steel sheet according to claim 1 ,

wherein the component of the steel sheet further includes, by mass %, at least one of

B: 0.0005% to 0.002%,

Mo: 0.01% to 0.5%,

Cr: 0.01% to 0.5%,

V: 0.001% to 0.1%,

Ti: 0.001% to 0.1%,

Nb: 0.001% to 0.05%,

Ca: 0.0005% to 0.005%, and

Rare Earth Metal: 0.0005% to 0.005%.

3. The hot-dip galvanized steel sheet according to claim 2 ,

wherein the steel sheet is a cold rolled steel sheet.

4. The hot-dip galvanized steel sheet according to claim 1 ,

wherein the steel sheet is a cold rolled steel sheet.

5. A manufacturing method of the hot-dip galvanized steel sheet according to claim 1 ,

wherein, when a total number of stands on a hot finish rolling is n stage, and r i % is a rolling reduction at the i th stand, the hot finish rolling satisfies a following Equation C,

( r 1 +r 2 +r 3 )/( r n-2 +r n-1 +r n )>1.6  (Equation C).

6. A manufacturing method of the hot-dip galvanized steel sheet according to claim 2 ,

wherein, when a total number of stands on a hot finish rolling is n stage, and r i % is a rolling reduction at the i th stand, the hot finish rolling satisfies a following Equation C,

( r 1 +r 2 +r 3 )/( r n-2 +r n-1 +r n )>1.6  (Equation C).

7. A manufacturing method of the hot-dip galvanized steel sheet according to claim 3 ,

wherein, when a total number of stands on a hot finish rolling is n stage, and r i % is a rolling reduction at the i th stand, the hot finish rolling satisfies a following Equation C,

( r 1 +r 2 +r 3 )/( r n-2 +r n-1 +r n )>1.6  (Equation C).

8. A manufacturing method of the hot-dip galvanized steel sheet according to claim 4 ,

wherein, when a total number of stands on a hot finish rolling is n stage, and r i % is a rolling reduction at the i th stand, the hot finish rolling satisfies a following Equation C,

( r 1 +r 2 +r 3 )/( r n-2 +r n-1 +r n )>1.6  (Equation C).