High-strength hot-dip galvanized steel sheet and high-strength alloyed hot-dip galvanized steel sheet having excellent plating adhesion, formability, and hole expandability with tensile strength of 980 MPa or more and manufacturing method therefor

1. A high-strength alloyed hot-dip galvanized steel sheet having excellent plating adhesion, formability, and hole expandability with an ultimate tensile strength of 980 MPa or more, the alloyed hot-dip galvanized steel sheet comprising an alloyed hot-dip galvanized layer formed on a surface of a base steel sheet,

wherein the base steel sheet contains: by mass %,

C: 0.05% to 0.4%;

Si: 0.01% to 3.0%;

Mn: 0.1% to 3.0%;

Al: 0.01 to 2.0%; in which Si+Al>0.5%

P: limited to 0.04% or less;

S: limited to 0.05% or less;

N: limited to 0.01% or less; and

a balance including Fe and inevitable impurities,

a microstructure of the base steel sheet contains 40% or more by total volume fraction of martensite and bainite, 8% or more by volume fraction of residual austenite, and a balance of the microstructure being ferrite or ferrite and 10% or less by volume fraction of pearlite,

the martensite contains 10% or more by total volume fraction of two or more kinds of martensites (1), (2), and (3) below, and

the alloyed hot-dip galvanized layer contains 7 to 15 mass % of Fe,

the martensite (1): C concentration (when there is a cementite precipitation, also including C in cementite); carbon concentration in the martensite (CM1) is less than 0.8 mass %, and nano-indentation test hardness Hit1 satisfies Expression 1:

Hit1/{−982.1×(CM1) 2 +1676×CM1+189}≦0.50  Expression 1

the martensite (2): C concentration (when there is a cementite precipitation, also including C in cementite); carbon concentration in the martensite (CM2) is 0.8 mass% or more, and nano-indentation test hardness Hit2 satisfies Expression 2:

Hit2/{−982.1×(CM2) 2 +1676×CM2+189}≦0.50  Expression 2

the martensite (3): C concentration (when there is a cementite precipitation, also including C in cementite); carbon concentration in the martensite (CM3) is 0.8 mass % or more, and nano-indentation test hardness Hit3 satisfies Expression 3:

0.5<Hit3/{−982.1×(CM3) 2 +1676×CM3+189}≦0.80  Expression 3.

2. The high-strength alloyed hot-dip galvanized steel sheet having the excellent plating adhesion, formability, and hole expandability with the ultimate tensile strength of 980 MPa or more according to claim 1 , wherein the base steel sheet further contains one or more of: by mass %,

Cr: 0.05 to 1.0%;

Mo: 0.05 to 1.0%;

Ni: 0.05 to 1.0%; and

Cu: 0.05 to 1.0%.

3. The high-strength alloyed hot-dip galvanized steel sheet having the excellent plating adhesion, formability, and hole expandability with the ultimate tensile strength of 980 MPa or more according to claim 1 , wherein the base steel sheet further contains one or more of: by mass %,

Nb: 0.005 to 0.3%;

Ti: 0.005 to 0.3%; and

V: 0.01 to 0.5%.

4. The high-strength alloyed hot-dip galvanized steel sheet having the excellent plating adhesion, formability, and hole expandability with the ultimate tensile strength of 980 MPa or more according to claim 1 , wherein the base steel sheet further contains B: 0.0001 to 0.1% by mass %.

5. The high-strength alloyed hot-dip galvanized steel sheet having the excellent plating adhesion, formability, and hole expandability with the ultimate tensile strength of 980 MPa or more according to claim 1 , wherein the base steel sheet further contains one or more of: by mass %,

Ca: 0.0005 to 0.01%;

Mg: 0.0005 to 0.01%; and

REM: 0.0005 to 0.01%.

6. A manufacturing method of a high-strength alloyed hot-dip galvanized steel sheet having excellent plating adhesion, formability, and hole expandability with an ultimate tensile strength of 980 MPa or more, the manufacturing method comprising:

with respect to a steel billet containing: by mass %,

C: 0.05% to 0.4%;

Si: 0.01% to 3.0%;

Mn: 0.1% to 3.0%;

Al: 0.01 to 2.0%; in which Si+Al>0.5%

P: limited to 0.04% or less;

S: limited to 0.05% or less;

N: limited to 0.01% or less; and

a balance including Fe and inevitable impurities,

heating to 1200° C. or higher and performing hot rolling at an Ar3 transformation temperature or higher;

performing cold rolling on a base steel sheet after the hot rolling at a reduction ratio of 40 to 70%;

annealing the base steel sheet after the cold rolling at 730 to 900° C.;

cooling the base steel sheet after the annealing to a temperature of 650 to 750° C. at an average cooling rate of 0.1 to 200° C/second, and cooling the base steel sheet to 450° C. or lower from the temperature of 650 to 750° C. at an average cooling rate of 20° C/second or faster;

holding the base steel sheet cooled to the 450° C. or lower in a range of 350 to 450° C. for 120 seconds or longer;

cooling the base steel sheet held in the range of 350 to 450° C. to 70° C. or lower at an average cooling rate of 5° C./second or faster;

rolling the base steel sheet cooled to the room temperature at an elongation percentage of 0.2 to 2%;

heating the rolled base steel sheet to “temperature of hot-dip galvanizing bath −40”° C. to “temperature of hot-dip galvanizing bath +50”° C. at an average temperature rising rate of 10° C./second or faster;

dipping and hot-dip galvanizing the base steel sheet heated to the “temperature of hot-dip galvanizing bath −40”° C. to “temperature of hot-dip galvanizing bath +50”° C. into a hot-dip galvanizing bath and performing alloying-heating treatment at “temperature of hot-dip galvanizing bath −40”° C. or higher and 560° C. or lower within 40 seconds; and

cooling the alloyed hot-dip galvanized steel sheet, which is subjected to the alloying-heating treatment, to 70° C. or lower at an average cooling rate of 5° C/second or faster.

7. The manufacturing method of the high-strength alloyed hot-dip galvanized steel sheet having the excellent plating adhesion, formability, and hole expandability with the ultimate tensile strength of 980 MPa or more according to claim 6 , wherein a hot-dip galvanizing bath flows at a flow rate of 10 m/min or more and 50 m/min or less at the time of the hot-dip galvanizing.

8. The manufacturing method of the high-strength alloyed hot-dip galvanized steel sheet having the excellent plating adhesion, formability, and hole expandability with the ultimate tensile strength of 980 MPa or more according to claim 6 , wherein before being heated to the “temperature of hot-dip galvanizing bath −40”° C. to “temperature of hot-dip galvanizing bath +50”° C., the base steel sheet is subjected to pickling, and then a surface of the base steel sheet is polished and removed to a depth of 0.1 μm or more and is pre-plated with 0.2 to 2 g/m 2 of Ni.