Steel for cold forging
View Patent ↗A steel contains, in a chemical composition, C, Si, Mn, and Al, and contains pearlite as a metallographic structure, and a value obtained by dividing an Mn content in a cementite in the pearlite in terms of at % by an Mn content in a ferrite in the pearlite in terms of at % is higher than 0 and equal to or lower than 5.0.
1. A steel comprising, in a chemical composition, by mass %:
C: 0.005% to 0.60%,
Si: 0.01% to 0.50%,
Mn: 0.20% to 1.80%,
Al: 0.01% to 0.06%,
P: 0.04% or less,
S: 0.05% or less,
N: 0.01% or less,
Cr: 0% to 1.50%,
Mo: 0% to 0.50%,
Ni: 0% to 1.00%,
V: 0% to 0.50%,
B: 0% to 0.0050%,
Ti: 0% to 0.05%, and
a remainder of Fe and impurities,
wherein a metallographic structure contains a pearlite, and
a value obtained by dividing an Mn content in a cementite in the pearlite in terms of at % by an Mn content in a ferrite in the pearlite in terms of at % is higher than 0 and equal to or lower than 5.0.
2. The steel according to claim 1 ,
wherein the steel is a steel wire rod.
3. The steel according to claim 1 ,
wherein when a carbon content in the chemical composition by mass % is defined as C, the steel has a tensile strength of 530×C+300 or lower in the unit of MPa and a reduction of area of −35×C+89 or higher in the unit of % after a spheroidizing treatment by which an aspect ratio of the cementite in the steel becomes 5 or lower.
4. The steel according to claim 1 ,
wherein the metallographic structure consists of the pearlite, wherein the pearlite contains cementite and ferrite.
5. The steel according to claim 4 ,
wherein when a carbon content in the chemical composition by mass % is defined as C, the steel has a tensile strength of 530×C+300 or lower in the unit of MPa and a reduction of area of −35×C+89 or higher in the unit of % after a spheroidizing treatment by which an aspect ratio of the cementite in the steel becomes 5 or lower.
6. The steel according to claim 4 ,
wherein the steel is a steel wire rod.
7. The steel according to claim 1 ,
wherein the metallographic structure further contains proeutectoid ferrite or bainite, and
when a carbon content in the chemical composition by mass % is defined as C, in a cross section perpendicular to a longitudinal direction of the steel, an area fraction of the pearlite is equal to or higher than 130×C % and lower than 100%, and an area fraction of a sum of the proeutectoid ferrite and the bainite is higher than 0% and equal to or lower than 100-130×C %.
8. The steel according to claim 7 ,
wherein when a carbon content in the chemical composition by mass % is defined as C, the steel has a tensile strength of 530×C+300 or lower in the unit of MPa and a reduction of area of −35×C+89 or higher in the unit of % after a spheroidizing treatment by which an aspect ratio of the cementite in the steel becomes 5 or lower.
9. The steel according to claim 7 ,
wherein the steel is a steel wire rod.
10. The steel according to claim 1 comprising, in the chemical composition, by mass %:
Cr: 0.02% to 1.50%,
wherein a value obtained by dividing a Cr content in the cementite in the pearlite in terms of at % by a Cr content in the ferrite in the pearlite in terms of at % is higher than 0 and equal to or lower than 3.0.
11. The steel according to claim 10 ,
wherein the steel is a steel wire rod.
12. The steel according to claim 10 ,
wherein when a carbon content in the chemical composition by mass % is defined as C, the steel has a tensile strength of 530×C+300 or lower in the unit of MPa and a reduction of area of −35×C+89 or higher in the unit of % after a spheroidizing treatment by which an aspect ratio of the cementite in the steel becomes 5 or lower.
13. The steel according to claim 10 ,
wherein the metallographic structure further contains proeutectoid ferrite or bainite, and
when a carbon content in the chemical composition by mass % is defined as C, in a cross section perpendicular to a longitudinal direction of the steel, an area fraction of the pearlite is equal to or higher than 130×C % and lower than 100%, and an area fraction of a sum of the proeutectoid ferrite and the bainite is higher than 0% and equal to or lower than 100-130×C %.
14. The steel according to claim 13 ,
wherein the steel is a steel wire rod.
15. The steel according to claim 13 ,
wherein when a carbon content in the chemical composition by mass % is defined as C, the steel has a tensile strength of 530×C+300 or lower in the unit of MPa and a reduction of area of −35×C+89 or higher in the unit of % after a spheroidizing treatment by which an aspect ratio of the cementite in the steel becomes 5 or lower.
16. The steel according to claim 15 ,
wherein the steel is a steel wire rod.
17. The steel according to claim 10 ,
wherein the metallographic structure consists of the pearlite, wherein the pearlite contains cementite and ferrite.
18. The steel according to claim 17 ,
wherein the steel is a steel wire rod.
19. The steel according to claim 17 ,
wherein when a carbon content in the chemical composition by mass % is defined as C, the steel has a tensile strength of 530×C+300 or lower in the unit of MPa and a reduction of area of −35×C+89 or higher in the unit of % after a spheroidizing treatment by which an aspect ratio of the cementite in the steel becomes 5 or lower.
20. The steel according to claim 19 ,
wherein the steel is a steel wire rod.