Heat-treated steel material and method of manufacturing the same

1. A heat-treated steel material comprising:

a chemical composition comprising, in mass %:

C: 0.16% to 0.38%;

Mn: 0.6% to 1.5%;

Cr: 0.4% to 2.0%;

Ti: 0.01% to 0.10%;

B: 0.001% to 0.010%;

Si: 0.20% or less;

P: 0.05% or less;

S: 0.05% or less;

N: 0.010% or less;

Ni: 0% to 2.0%;

Cu: 0% to 1.0%;

Mo: 0% to 1.0%;

V: 0% to 1.0%;

Al: 0% to 1.0%;

Nb: 0% to 1.0%;

REM: 0% to 0.1%; and

the balance: Fe and impurities; and

a structure consisting of:

retained austenite: 1.5 volume % or less; and

the balance: martensite;

wherein a yield ratio of the steel material is 0.70 or more.

2. The heat-treated steel material according to claim 1 , wherein C: 0.16 to 0.25% in the chemical composition.

3. The heat-treated steel material according to claim 1 , wherein the chemical composition comprises Al: 0.01%-2.0%.

4. The heat-treated steel material according to claim 1 , wherein the chemical composition satisfies at least one of:

Ni: 0.1% to 2.0%;

Cu: 0.1% to 1.0%;

Mo: 0.1% to 1.0%;

V: 0.1% to 1.0%;

Al: 0.01% to 1.0%;

Nb: 0.01% to 1.0%; or

REM: 0.001% to 0.1%.

5. A method of manufacturing the heat-treated steel material of claim 1 , comprising:

heating a steel sheet to a temperature of an Ac 3 point or higher;

next cooling the steel sheet to a Ms point at a cooling rate equal to a critical cooling rate or more; and

next cooling the steel sheet from the Ms point to 100° C. at a 35° C./second average cooling rate or more, wherein

the steel sheet comprises a chemical composition comprising, in mass %:

C: 0.16% to 0.38%;

Mn: 0.6% to 1.5%;

Cr: 0.4% to 2.0%;

Ti: 0.01% to 0.10%;

B: 0.001% to 0.010%;

Si: 0.20% or less;

P: 0.05% or less;

S: 0.05% or less;

N: 0.010% or less;

Ni: 0% to 2.0%;

Cu: 0% to 1.0%;

Mo: 0% to 1.0%;

V: 0% to 1.0%;

Al: 0% to 1.0%;

Nb: 0% to 1.0%;

REM: 0% to 0.1%; and

the balance: Fe and impurities; and

a structure consisting of:

retained austenite: 1.5 volume % or less; and

the balance: martensite;

wherein a yield ratio of the steel material is 0.70 or more.

6. The method of manufacturing the heat-treated steel material according to claim 5 , wherein C: 0.16 to 0.25% in the chemical composition.

7. The method of manufacturing the heat-treated steel material according to claim 5 , wherein the chemical composition satisfies:

Ni: 0.1% to 2.0%;

Cu: 0.1% to 1.0%;

Mo: 0.1% to 1.0%;

V: 0.1% to 1.0%;

Al: 0.01% to 1.0%;

Nb: 0.01% to 1.0%; or

REM: 0.001% to 0.1%; or

any combination thereof.

8. The method of manufacturing the heat-treated steel material according to claim 5 , comprising forming the steel sheet after the heating the steel sheet to the temperature of the Ac 3 point or higher before a temperature of the steel sheet reaches the Ms point.