Steel sheet for hot stamping, method of manufacturing the same, and hot stamped steel sheet member

1. A cold-rolled steel sheet for hot stamping, comprising

a chemical composition expressed by, in mass%:

C: 0.08% or more and less than 0.20%;

Si: 0.003% to 0.2%;

Mn: 1.6% to 3.5%;

sol. Al: 0.0002% to 2.0%;

B: 0.0003% to 0.01%;

P: 0.1% or less;

S: 0.004% or less;

N: 0.01% or less;

Ti: 0% to 0.04 +48/14 × [N] % when an N content is expressed by [N];

Cr: 0% to 1.00%;

Bi: 0% to 0.5%;

Ca: 0% to 0.05%;

Mg: 0% to 0.05%;

REM: 0% to 0.05%;

Mo: 0% to 1%;

Cu: 0% to 1%;

Ni: 0% to 1%;

W: 0% to 1%;

Nb: 0% to 1%;

V: 0% to 1%;

balance: Fe and impurities,

wherein:

an expression (1) is satisfied when an Mn content is represented by [Mn] and a C content is represented by [C],

where [Mn]+6.67×[C]−2.73≥0  (1); and

the cold rolled steel sheet comprises a steel structure consisting of, in an area ratio:

bainite: 20% to 95%;

ferrite: 5% to 80%; and

balance: one or two selected from the group consisting of pearlite and martensite.

2. The cold-rolled steel sheet for hot stamping according to claim 1 , wherein the chemical content contains:

Ti:48/14 ×[N]% to 0.04 +48/14×[N]%.

3. The cold-rolled steel sheet for hot stamping according to claim 1 , wherein

a Cr content is 0.01% to 1.00%, and

when the Mn content is represented by [Mn] and the Cr content is represented by [Cr], an expression (2) is satisfied,

1.6≤[Mn]+[Cr]≤3.5  (2).

4. The cold-rolled steel sheet for hot stamping according to claim 1 , wherein the chemical content contains:

Bi: 0.0001% to 0.5%.

5. The cold-rolled steel sheet for hot stamping according to claim 1 , wherein the chemical composition contains one or more selected from the group consisting of:

Ca: 0.0005% to 0.05%;

Mg: 0.0005% to 0.05%; and

REM: 0.0005% to 0.05%.

6. The cold-rolled steel sheet for hot stamping according to claim 1 , wherein the chemical composition contains one or more selected from the group consisting of:

Mo: 0.03% to 1%;

Cu: 0.01% to 1%;

Ni: 0.01% to 1%; and

W: 0.01% to 1%.

7. The cold-rolled steel sheet for hot stamping according to claim 1 , wherein the chemical composition contains one or two selected from the group consisting of:

Nb: 0.005% to 1%; and

V: 0.005% to 1%.

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

hot-rolling a steel ingot or a steel billet;

acid-pickling a steel sheet obtained by the hot-rolling;

cold-rolling a steel sheet obtained by the acid pickling; and

performing a heat treatment of a steel sheet obtained by the cold-rolling,

wherein:

the steel ingot or the steel billet comprises the chemical composition according to claim 1 ;

the hot-rolling comprises:

starting a rolling at a temperature of 1050° C. or more; and

thereafter coiling at a temperature zone of 400° C. to 700° C.; and

the performing the heat treatment comprises:

heating to a temperature zone of 700° C. to 840° C.;

thereafter cooling to a temperature of 500° C. or less at an average cooling rate of 5° C/sec to 100° C/sec; and

thereafter retaining at a temperature zone of 300° C. to 500° C. for 5 seconds to 600 seconds.

9. A method of manufacturing the cold-rolled steel sheet for hot stamping according to claim 1 , comprising:

hot-rolling a steel ingot or a steel billet;

acid-pickling a steel sheet obtained by the hot-rolling;

cold-rolling a steel sheet obtained by the acid pickling;

performing a heat treatment of a steel sheet obtained by the cold-rolling, and plating a steel sheet obtained by the heat treatment,

wherein:

the steel ingot or the steel billet comprises the chemical composition according to claim 1 ;

the hot-rolling comprises:

starting a rolling at a temperature of 1050° C. or more; and

thereafter coiling at a temperature zone of 400° C. to 700° C.;

the performing the heat treatment comprises:

heating to a temperature zone of 700° C. to 840° C.;

thereafter cooling to a temperature of 580° C. or less at an average cooling rate of 3° C/sec to 20° C/sec; and

thereafter retaining at a temperature zone of 500° C. to 570° C. for 5 seconds to 600 seconds; and

the plating comprises:

performing a hot-dip galvanizing treatment; and

thereafter performing an alloying treatment at a temperature zone of 500° C. to 650° C.

10. The method of manufacturing the cold-rolled steel sheet for hot stamping according to claim 8 ,

wherein the chemical composition contains:

Ti:48/14×[N]% to 0.04 +48/14×[N]%.

11. The method of manufacturing the cold-rolled steel sheet for hot stamping according to claim 8 ,

wherein a Cr content is 0.01% to 1.00%, and when the Mn content is represented by [Mn] and the Cr content is represented by [Cr], an expression (2) is satisfied,

1.6≤[Mn]+[Cr]≤3.5  (2).

12. The method of manufacturing the cold-rolled steel sheet for hot stamping according to claim 8 ,

wherein the chemical composition contains:

Bi: 0.0001% to 0.5%.

13. The method of manufacturing the cold-rolled steel sheet for hot stamping according to claim 8 ,

wherein the chemical composition contains one kind or two or more kinds selected from the group consisting of:

Ca: 0.0005% to 0.05%;

Mg: 0.0005% to 0.05%; and

REM: 0.0005% to 0.05%.

14. The method of manufacturing the cold-rolled steel sheet for hot stamping according to claim 8 ,

wherein the chemical composition contains one kind or two or more kinds selected from the group consisting of:

Mo: 0.03% to 1%;

Cu: 0.01% to 1%;

Ni: 0.01% to 1%; and

W: 0.01% to 1%.

15. The method of manufacturing the cold-rolled steel sheet for hot stamping according to claim 8 ,

wherein the chemical composition contains one kind or two kinds selected from the group consisting of:

Nb: 0.005% to 1%; and

V: 0.005% to 1%.

16. The method of manufacturing the cold-rolled steel sheet for hot stamping according to claim 9 ,

wherein the chemical composition contains:

Ti:48/14×[N] % to 0.04+48/14×[N]%.

17. The method of manufacturing the cold-rolled steel sheet for hot stamping according to claim 9 ,

wherein a Cr content is 0.01% to 1.00%, and when the Mn content is represented by [Mn] and the Cr content is represented by [Cr], an expression (2) is satisfied,

1.6≤[Mn]+[Cr]≤3.5  (2).

18. The method of manufacturing the cold-rolled steel sheet for hot stamping according to claim 9 ,

wherein the chemical composition contains:

Bi: 0.0001% to 0.5%.

19. The method of manufacturing the cold-rolled steel sheet for hot stamping according to claim 9 ,

wherein the chemical composition contains one kind or two or more kinds selected from the group consisting of:

Ca: 0.0005% to 0.05%;

Mg: 0.0005% to 0.05%; and

REM: 0.0005% to 0.05%.

20. The method of manufacturing the cold-rolled steel sheet for hot stamping according to claim 9 , wherein the chemical composition contains one kind or two or more kinds selected from the group consisting of:

Mo: 0.03% to 1%;

Cu: 0.01% to 1%;

Ni: 0.01% to 1%; and

W: 0.01% to 1%.

21. The method of manufacturing the cold-rolled steel sheet for hot stamping according to claim 9 ,

wherein the chemical composition contains one kind or two kinds selected from the group consisting of:

Nb: 0.005% to 1%; and

V: 0.005% to 1%.