Hot-rolled steel sheet and method for manufacturing the same

1. A hot-rolled steel sheet having a tensile strength of 900 MPa or more, the hot-rolled steel sheet consisting of, in mass %,

C: greater than 0.050% and less than or equal to 0.10%,

Si: greater than or equal to 0.1% and less than or equal to 2.0%,

Mn: greater than or equal to 1.0% and less than or equal to 3.0%,

P: less than or equal to 0.1%,

S: less than or equal to 0.01%,

Al: greater than or equal to 0.005% and less than or equal to 0.05%,

N: less than or equal to 0.01%,

Ti: greater than or equal to 0.10% and less than or equal to 0.20%,

Nb: greater than or equal to 0% and less than or equal to 0.06%,

B: greater than or equal to 0% and less than or equal to 0.03%,

Ca: greater than or equal to 0% and less than or equal to 0.005%, and

the balance: Fe and impurities,

wherein an average crystal grain size is less than or equal to 7.0 μm, and

wherein an X-ray random intensity ratio in {211} <011> orientation that is parallel to a rolled surface and a rolling direction is less than or equal to 2.5.

2. The hot-rolled steel sheet according to claim 1 , including one or more selected from the group consisting of, in mass %,

Nb: greater than or equal to 0.001% and less than or equal to 0.06%,

B: greater than or equal to 0.0005% and less than or equal to 0.03%, and

Ca: greater than or equal to 0.0005% and less than or equal to 0.005%.

3. The hot-rolled steel sheet according to claim 1 , further comprising:

a Zn-plating layer or an Fe—Zn-alloy-plating layer on a surface of the hot-rolled steel sheet.

4. The hot-rolled steel sheet according to claim 2 , further comprising:

a Zn-plating layer or an Fe—Zn-alloy-plating layer a surface of the hot-rolled steel sheet.

5. A method for manufacturing a hot-rolled steel sheet, the method comprising:

performing hot-rolling on a slab having a chemical composition according to claim 1 at a temperature of higher than or equal to 1200° C. and lower than or equal to 1350° C.;

ending the hot-rolling at a temperature of higher than or equal to 960° C. and lower than or equal to 1100° C.;

within 1.0 second after the ending of the hot-rolling, starting quenching;

quenching the hot-rolled steel sheet at an average cooling speed of greater than or equal to 80° C./second until the temperature becomes lower than the temperature at the ending of the hot-rolling by 50° C. to 200° C.; and

winding up the hot-rolled steel sheet at a temperature of higher than or equal to 400° C. and lower than or equal to 600° C.,

wherein a cooling after the ending of the quenching until the winding is performed at an average cooling speed of 20° C./second or more.

6. A method for manufacturing a hot-rolled steel sheet, the method comprising:

performing hot-rolling on a slab having a chemical composition according to claim 2 at a temperature of higher than or equal to 1200° C. and lower than or equal to 1350° C.;

ending the hot-rolling at a temperature of higher than or equal to 960° C. and lower than or equal to 1100° C.;

within 1.0 second after the ending of the hot-rolling, starting quenching;

quenching the hot-rolled steel sheet at an average cooling speed of greater than or equal to 80° C./second until the temperature becomes lower than the temperature at the ending of the hot-rolling by 50° C. to 200° C.; and

winding up the hot-rolled steel sheet at a temperature of higher than or equal to 400° C. and lower than or equal to 600° C.,

wherein a cooling after the ending of the quenching until the winding is performed at an average cooling speed of 20° C./second or more.

7. The method for manufacturing a hot-rolled steel sheet according to claim 5 , further comprising:

after the winding up, removing scale by acid cleaning and performing Zn-plating to form a Zn-plating layer.

8. The method for manufacturing a hot-rolled steel sheet having a tensile strength of 900 MPa or more, the method comprising:

after the winding up of the hot-rolled steel sheet manufactured by the method according to claim 5 , removing scale by acid cleaning;

heating the hot-rolled steel sheet at a temperature of higher than or equal to 500° C. and lower than or equal to 650° C. in a reduction atmosphere to activate a surface of the hot-rolled steel sheet;

immersing the hot-rolled steel sheet in a molten Zn bath at a bath temperature of higher than or equal to 430° C. and lower than or equal to 490° C. in a state in which a temperature at the time of the immersing is higher than or equal to 420° C. and lower than or equal to 500° C.; and

adjusting a deposited amount of the Zn-plating by gas wiping.

9. The method for manufacturing a hot-rolled steel sheet having a tensile strength of 900 MPa or more, the method comprising:

after the winding up of the hot-rolled steel sheet manufactured by the method according to claim 5 , removing scale by acid cleaning;

plating the hot-rolled steel sheet with Ni in greater than or equal to 0.05 g/m 2 and less than or equal to 3 g/m 2 by electrolysis;

heating the hot-rolled steel sheet at a temperature of higher than or equal to 420° C. and lower than or equal to 500° C. in a reduction atmosphere;

immersing the hot-rolled steel sheet in a molten Zn bath at a bath temperature of higher than or equal to 430° C. and lower than or equal to 490° C.; and

adjusting a deposited amount of the Zn-plating by gas wiping.

10. The method for manufacturing a hot-rolled steel sheet according to claim 8 , further comprising:

after the gas wiping, heating the hot-rolled steel sheet at a temperature of higher than or equal to 500° C. and lower than or equal to 650° C. to form an Fe—Zn-plating layer.

11. The method for manufacturing a hot-rolled steel sheet according to claim 9 , further comprising:

after the gas wiping, heating the hot-rolled steel sheet at a temperature of higher than or equal to 500° C. and lower than or equal to 650° C. to form an Fe—Zn-plating layer.