Hot-stamped part and method of manufacturing the same

1. A hot-stamped part comprising:

a chemical composition represented by, in mass %:

C: 0.120% to 0.400%;

Si: 0.005% to 2.000%;

Mn or Cr, or both thereof: 1.00% to 3.00% in total;

Al: 0.005% to 0.100%;

B: 0.0003% to 0.0020%;

P: not more than 0.030%;

S: not more than 0.0100%;

O: not more than 0.0070%;

N: not more than 0.0070%;

Ti: 0% to 0.100%;

Nb: 0% to 0.100%;

V: 0% to 0.100%;

Ni: 0% to 2.00%;

Cu: 0% to 2.00%;

Mo: 0% to 0.50%;

Ca or REM, or both thereof: 0% to 0.0300% in total; and

the balance: Fe and impurities; and

a structure represented by:

an area fraction of martensite or bainite, or both thereof: not less than 95% in total;

a coverage factor of prior austenite grain boundary by iron-based carbides: not more than 80%; and

a number density of iron-based carbides in prior austenite grains: not less than 45/μm 2 .

2. The hot-stamped part according to claim 1 , wherein the chemical composition satisfies:

Ti: 0.005% to 0.100%;

Nb: 0.005% to 0.100%; or

V: 0.005% to 0.100%; or

any combination thereof.

3. The hot-stamped part according to claim 1 , wherein the chemical composition satisfies:

Ni: 0.05% to 2.00%;

Cu: 0.05% to 2.00%; or

Mo: 0.05% to 0.50%; or

any combination thereof.

4. The hot-stamped part according to claim 1 , wherein the chemical composition satisfies

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

5. A method of manufacturing a hot-stamped part, comprising the steps of:

heating a steel sheet to a temperature of not less than Ac3 point and not more than 950° C. at an average heating rate of not less than 2° C./sec;

then, cooling the steel sheet through a temperature range from a Ar3 point to (Ms point−50)° C. at an average cooling rate of not less than 100° C./sec while performing hot pressing;

changing the average cooling rate at a temperature of (Ms point−50)° C.; and

then, cooling the steel sheet through a temperature range from (Ms point−50)° C. to 100° C. at an average cooling rate of not more than 50° C./sec,

wherein the steel sheet comprises a chemical composition represented by, in mass %:

C: 0.120% to 0.400%;

Si: 0.005% to 2.000%;

Mn or Cr, or both thereof: 1.00% to 3.00% in total:

Al: 0.005% to 0.100%:

B: 0.0003% to 0.0020%:

P: not more than 0.030%;

S: not more than 0.0100%;

O: not more than 0.0070%;

N: not more than 0.0070%;

Ti: 0% to 0.100%;

Nb: 0% to 0.100%;

V: 0% to 0.100%;

Ni: 0% to 2.00%:

Cu: 0% to 2.00%;

Mo: 0% to 0.50%;

Ca or REM, or both thereof: 0%-0.0300% in total; and the balance: Fe and impurities, and

a maximum cooling rate is not more than 70° C./sec and a minimum cooling rate is not less than 5° C./sec in a temperature range from (Ms point−120)° C. to 100° C., thereby producing the hot-stamped part of claim 1 .

6. The method of manufacturing the hot-stamped part according to claim 5 , wherein the chemical composition satisfies:

Ti: 0.005%-0.100%;

Nb: 0.005%-0.100%; or

V: 0.005%-0.100%; or

any combination thereof.

7. The method of manufacturing the hot-stamped part according to claim 5 , wherein the chemical composition satisfies:

Ni: 0.05%-2.00%;

Cu: 0.05%-2.00%; or

Mo: 0.05%-0.50%; or

any combination thereof.

8. The method of manufacturing the hot-stamped part according to claim 5 , wherein the chemical composition satisfies

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