Method for manufacturing hot stamped body having vertical wall and hot stamped body having vertical wall

1. A method for manufacturing a hot stamped body, in which a DI inch value which is a quenching index and is calculated based on ASTM A255-67 is equal to or more than 3, the method comprising:

hot-rolling a slab containing chemical components which include, by mass %, 0.18% to 0.35% of C, 1.0% to 3.0% of Mn, 0.01% to 1.0% of Si, 0.001% to 0.02% of P, 0.0005% to 0.01% of S, 0.001% to 0.01% of N, 0.01% to 1.0% of Al, 0.005% to 0.2% of Ti, 0.0002% to 0.005% of B, and 0.002% to 2.0% of Cr, and the balance of Fe and inevitable impurities, to obtain a hot-rolled steel sheet;

coiling the hot-rolled steel sheet which is subjected to hot-rolling;

cold-rolling the coiled hot-rolled steel sheet to obtain a cold-rolled steel sheet;

continuously annealing the cold-rolled steel sheet which is subjected to cold-rolling to obtain a steel sheet for hot stamping; and

performing hot stamping by heating the steel sheet for hot stamping which is continuously annealed so that a heating temperature of an entire steel sheet for hot stamping is equal to or higher than Ac 3 ° C., a highest heating temperature is equal to or higher than Ac 3 ° C., and forming a vertical wall,

wherein the continuous annealing includes:

heating the cold-rolled steel sheet to a temperature range of equal to or higher than Ac 1 ° C. and lower than Ac 3 ° C.;

cooling the heated cold-rolled steel sheet from the highest heating temperature to 660° C. at a cooling rate of equal to or less than 10° C./s; and

holding the cooled cold-rolled steel sheet in a temperature range of 550° C. to 660° C. for one minute to 10 minutes.

2. The method for manufacturing a hot stamped body according to claim 1 ,

wherein the chemical components further include one or more from 0.002% to 2.0% of Mo, 0.002% to 2.0% of Nb, 0.002% to 2.0% of V, 0.002% to 2.0% of Ni, 0.002% to 2.0% of Cu, 0.002% to 2.0% of Sn, 0.0005% to 0.0050% of Ca, 0.0005% to 0.0050% of Mg, and 0.0005% to 0.0050% of REM.

3. The method for manufacturing a hot stamped body according to claim 1 , the method further comprising performing any one of a hot-dip galvanizing process, a galvannealing process, a molten aluminum plating process, an alloyed molten aluminum plating process, and an electroplating process, after the continuous annealing.

4. The method for manufacturing a hot stamped body according to claim 2 , the method further comprising performing any one of a hot-dip galvanizing process, a galvannealing process, a molten aluminum plating process, an alloyed molten aluminum plating process, and an electroplating process, after the continuous annealing.

5. A method for manufacturing a hot stamped body, in which a DI inch value which is a quenching index and is calculated based on ASTM A255-67 is equal to or more than 3, the method comprising:

hot-rolling a slab containing chemical components which include, by mass %, 0.18% to 0.35% of C, 1.0% to 3.0% of Mn, 0.01% to 1.0% of Si, 0.001% to 0.02% of P, 0.0005% to 0.01% of S, 0.001% to 0.01% of N, 0.01% to 1.0% of Al, 0.005% to 0.2% of Ti, 0.0002% to 0.005% of B, and 0.002% to 2.0% of Cr, and the balance of Fe and inevitable impurities, to obtain a hot-rolled steel sheet;

coiling the hot-rolled steel sheet which is subjected to hot-rolling;

cold-rolling the coiled hot-rolled steel sheet to obtain a cold-rolled steel sheet;

continuously annealing the cold-rolled steel sheet which is subjected to cold-rolling to obtain a steel sheet for hot stamping; and

performing hot stamping by heating the steel sheet for hot stamping which is continuously annealed so that a heating temperature of an entire steel sheet for hot stamping is equal to or higher than Ac 3 ° C., a highest heating temperature is equal to or higher than Ac 3 ° C., and forming a vertical wall,

wherein, in the hot-rolling, in finish-hot-rolling configured with a machine with 5 or more consecutive rolling stands, rolling is performed by setting a finish-hot-rolling temperature F i T in a final rolling mill F i in a temperature range of (Ac 3 −80)° C. to (Ac 3 +40)° C., by setting time from start of rolling in a rolling mill F i-3 which is a previous machine to the final rolling mill F i to end of rolling in the final rolling mill F i to be equal to or longer than 2.5 seconds, and by setting a hot-rolling temperature F i-3 T in the rolling mill F i-3 to be equal to or lower than F i T+100° C., and after holding in a temperature range of 600° C. to Ar 3 ° C. for 3 seconds to 40 seconds, coiling is performed,

the continuous annealing includes:

heating the cold-rolled steel sheet to a temperature range of equal to or higher than (Ac 1 −40)° C. and lower than Ac 3 ° C.;

cooling the heated cold-rolled steel sheet from the highest heating temperature to 660° C. at a cooling rate of equal to or less than 10° C./s; and

holding the cooled cold-rolled steel sheet in a temperature range of 450° C. to 660° C. for 20 seconds to 10 minutes.

6. The method for manufacturing a hot stamped body according to claim 5 ,

wherein the chemical components further include one or more from 0.002% to 2.0% of Mo, 0.002% to 2.0% of Nb, 0.002% to 2.0% of V, 0.002% to 2.0% of Ni, 0.002% to 2.0% of Cu, 0.002% to 2.0% of Sn, 0.0005% to 0.0050% of Ca, 0.0005% to 0.0050% of Mg, and 0.0005% to 0.0050% of REM.

7. The method for manufacturing a hot stamped body according to claim 5 , the method further comprising performing any one of a hot-dip galvanizing process, a galvannealing process, a molten aluminum plating process, an alloyed molten aluminum plating process, and an electroplating process, after the continuous annealing.

8. The method for manufacturing a hot stamped body according to claim 6 , the method further comprising performing any one of a hot-dip galvanizing process, a galvannealing process, a molten aluminum plating process, an alloyed molten aluminum plating process, and an electroplating process, after the continuous annealing.