Cold-rolled steel sheet, galvanized cold-rolled steel sheet and method of manufacturing the same

1. A cold-rolled steel sheet, comprising:

a chemical composition expressed by, in mass %:

Si: 0.01% to 0.50%;

Mn or Cr, or both thereof: 0.70% to 1.50% in total;

C: 0.030% to 0.060% when Cr: “0” (zero) % or more and less than 0.30%, 0.030% to 0.080% when Cr: 0.30% or more and 1.50% or less;

Al: 0.800% to 2.000%;

P: 0.030% or less;

S: 0.0100% or less;

Mo: 0.10% to 0.50%;

O: 0.0070% or less;

N: 0.0070% or less;

B: “0” (zero) % to 0.0020%;

Ti: “0” (zero) % to 0.050%;

Nb: “0” (zero) % to 0.050%;

V: “0” (zero) % to 0.050%;

Ni: “0” (zero) % to 1.00%;

Cu: “0” (zero) % to 1.00%;

Ca or REM, or both thereof: “0” (zero) % to 0.0300% in total;

W: “0” (zero) % to 1.000%;

Mg: “0” (zero) % to 0.010%;

Zr: “0” (zero) % to 0.200%;

As: “0” (zero) % to 0.500%;

Co: “0” (zero) % to 1.000%;

Sn: “0” (zero) % to 0.200%;

Pb: “0” (zero) % to 0.200%;

Y: “0” (zero) % to 0.200%;

Hf: “0” (zero) % to 0.2000%; and

the balance: Fe and impurities; and

a structure expressed by:

an area fraction of ferrite: 95% or more;

an area fraction of retained austenite and an area fraction of martensite: 1% to 3% in total;

a product of the area fraction of retained austenite and a carbon concentration in retained austenite: 1 or more;

a value of I(111)/{I(100)+I(110)} at a region where a depth from a surface is ¼ of a thickness of the cold-rolled steel sheet when intensity of a (hkl) plane is expressed by I(hkl): 2 or less.

2. The cold-rolled steel sheet according to claim 1 , wherein the chemical composition satisfies:

Cr: 0.30% to 0.80%; or

Mn: 0.40% to 1.00%; or

both thereof.

3. The cold-rolled steel sheet according to claim 1 , wherein the chemical composition satisfies:

B: 0.0003% to 0.0020%;

Ti: 0.005% to 0.050%;

Nb: 0.005% to 0.050%; or

V: 0.005% to 0.050%; or

any combination thereof.

4. The cold-rolled steel sheet according to claim 1 , wherein the chemical composition satisfies:

Ni: 0.01% to 1.00%; or

Cu: 0.01% to 1.00%; or

both thereof.

5. The cold-rolled steel sheet according to claim 1 , wherein the chemical composition satisfies

Ca or REM, or both thereof: 0.0005% to 0.0300% in total.

6. The cold-rolled steel sheet according to claim 1 , wherein the chemical composition satisfies:

W: 0.001% to 1.000%;

Mg: 0.0001% to 0.010%;

Zr: 0.0001% to 0.200%;

As: 0.0001% to 0.500%;

Co: 0.0001% to 1.000%;

Sn: 0.0001% to 0.200%;

Pb: 0.0001% to 0.200%;

Y: 0.0001% to 0.200%; or

Hf: 0.0001% to 0.2000%; or

any combination thereof.

7. A galvanized cold-rolled steel sheet, comprising:

the cold-rolled steel sheet according to claim 1 ; and

a hot-dip galvanized layer or an alloyed hot-dip galvanized layer on a surface of the cold-rolled steel sheet.

8. A method of manufacturing the cold-rolled steel sheet according to claim 1 , comprising:

performing hot-rolling of a slab heated to a temperature of 1250° C. or less to obtain a hot-rolled sheet;

coiling the hot-rolled sheet at a temperature of 650° C. or less;

then, performing cold-rolling of the hot-rolled sheet with a reduction ratio of 70% or more to obtain a cold-rolled sheet; and

performing continuous annealing of the cold-rolled sheet at a temperature of 750° C. to 900° C.,

wherein

the performing the hot-rolling comprises performing finish-rolling at a temperature of 850° C. to 1000° C. under a state in which two phases of ferrite and austenite exist,

a total reduction ratio at last three stands is 60% or more in the finish-rolling,

cooling is started within one second from an end of the finish-rolling, and

the slab comprises a chemical composition expressed by, in mass %,

Si: 0.01% to 0.50%;

Mn or Cr, or both thereof: 0.70% to 1.50% in total;

C: 0.030% to 0.060% when Cr: “0” (zero) % or more and less than 0.30%, 0.030% to 0.080% when Cr: 0.30% or more and 1.50% or less;

Al: 0.800% to 2.000%;

P: 0.030% or less;

S: 0.0100% or less;

Mo: 0.10% to 0.50%;

O: 0.0070% or less;

N: 0.0070% or less;

B: “0” (zero) % to 0.0020%;

Ti: “0” (zero) % to 0.050%;

Nb: “0” (zero) % to 0.050%;

V: “0” (zero) % to 0.050%;

Ni: “0” (zero) % to 1.00%;

Cu: “0” (zero) % to 1.00%;

Ca or REM, or both of them: “0” (zero) % to 0.0300% in total;

W: “0” (zero) % to 1.000%;

Mg: “0” (zero) % to 0.010%;

Zr: “0” (zero) % to 0.200%;

As: “0” (zero) % to 0.500%;

Co: “0” (zero) % to 1.000%;

Sn: “0” (zero) % to 0.200%;

Pb: “0” (zero) % to 0.200%;

Y: “0” (zero) % to 0.200%;

Hf: “0” (zero) % to 0.2000%; and

the balance: Fe and impurities.

9. The method of manufacturing the cold-rolled steel sheet according to claim 8 , wherein in the chemical composition satisfies:

Cr: 0.30% to 0.80%; or

Mn: 0.40% to 1.00%; or

both thereof.

10. The method of manufacturing the cold-rolled steel sheet according to claim 8 , wherein the chemical composition satisfies:

B: 0.0003% to 0.0020%;

Ti: 0.005% to 0.050%;

Nb: 0.005% to 0.050%; or

V: 0.005% to 0.050%; or

any combination thereof.

11. The method of manufacturing the cold-rolled steel sheet according to claim 8 , wherein the chemical composition satisfies:

Ni: 0.01% to 1.00%; or

Cu: 0.01% to 1.00%; or

both thereof.

12. The method of manufacturing the cold-rolled steel sheet according to claim 8 , wherein the chemical composition satisfies

Ca or REM, or both thereof: 0.0005% to 0.0300% in total.

13. The method of manufacturing the cold-rolled steel sheet according to claim 8 , wherein the chemical composition satisfies:

W: 0.001% to 1.000%;

Mg: 0.0001% to 0.010%;

Zr: 0.0001% to 0.200%;

As: 0.0001% to 0.500%;

Co: 0.0001% to 1.000%;

Sn: 0.0001% to 0.200%;

Pb: 0.0001% to 0.200%;

Y: 0.0001% to 0.200%; or

Hf: 0.0001% to 0.2000%; or

any combination thereof.

14. A method of manufacturing a galvanized cold-rolled steel sheet, comprising:

manufacturing a cold-rolled steel sheet by the method according to claim 8 ; and

forming a hot-dip galvanized layer or an alloyed hot-dip galvanized layer on a surface of the cold-rolled steel sheet.