Wire material for non-heat treated component, steel wire for non-heat treated component, and non-heat treated component and manufacturing method thereof

1. A wire material for a non-heat treated component used for manufacturing the non-heat treated component whose tensile strength is 900 MPa to 1300 MPa, containing, in mass %,

C: 0.20% to 0.49%, Si: 0.05% to 2.0%, Mn: 0.20% to 1.0%, being limited to contain P: 0.030% or less, S: 0.030% or less, N: 0.005% or less, F1 defined by the following expression (1) is less than 0.60, with the balance made up of Fe and inevitable impurities,

wherein a metal structure contains a pearlite structure of 64×(C %)+52% or more in a volume fraction, with the balance made up of one kind or two kinds of a pro-eutectoid ferrite structure and a bainite structure,

an average block grain diameter of the pearlite structure at a region from a surface layer to 0.1 D is 15 μm or less when a diameter of the wire material is set to be D, and (the average block grain diameter of the pearlite structure at the region from the surface layer to 0.1 D)/(an average block grain diameter of the pearlite structure at a range from 0.25 D to a center) is less than 1.0,

F1=C (%)+Si (%)/24+Mn (%)/6  (1)

2. The wire material for the non-heat treated component according to claim 1 , further containing, in mass %,

one kind or two or more kinds from among Al: 0.003% to 0.050%, Ca: 0.001% to 0.010%, Mg: 0.001% to 0.010%, Zr: 0.001% to 0.010%.

3. The wire material for a non-heat treated component according to claim 1 , wherein an area ratio of a structure made up of a pearlite block whose aspect ratio is 2.0 or more is 70% or more relative to a whole pearlite structure at a region from a surface layer to 1.0 mm at a cross section in parallel to an axial direction of a steel wire which is manufactured by performing wire drawing at a total reduction of area of 15 to 800%.

4. The wire material for a non-heat treated component according to claim 1 , wherein

Cr, Mo, Ni, Ti, Nb, and V are contained as the impurities, and

F1 is defined as C (%)+Si (%)/24+Mn (%)/6+(Cr (%)+Mo (%))/5+Ni (%)/40+(Ti (%)+Nb (%)+V (%))/5.

5. The wire material for the non-heat treated component according to claim 1 ,

wherein a C content is 0.48% or less.

6. The wire material for a non-heat treated component according to claim 1 , having a wire diameter of 8.0 mm to 15.0 mm.

7. A manufacturing method of the wire material for a non-heat treated component according to claim 1 , comprising:

heating a steel billet containing, in mass %, C: 0.20% to 0.490%, Si: 0.05% to 2.0%, Mn: 0.20% to 1.0%, being limited to contain P: 0.030% or less, S: 0.030% or less, N: 0.005% or less, F1 defined by the following expression (1) is less than 0.60, with the balance made up of Fe and inevitable impurities;

hot-rolling into a wire material shape;

coiling at a coiling temperature of 800° C. to 900° C.;

cooling at a cooling rate of 20° C./s to 100° C./s from a coiling finish temperature to 600° C., further cooling at the cooling rate of 20° C./s or less from 600° C. to 550° C.;

thereafter, isothermally holding in a molten salt tank 1 at 400° C. to 600° C. and a successive molten salt tank 2 at 500° C. to 600° C. for 5 seconds to 150 seconds each; and

subsequently cooling,

F1=C(%)+Si (%)/24+Mn (%)/6  (1)

8. A steel wire for a non-heat treated component used for manufacturing the non-heat treated component whose tensile strength is 900 MPa to 1300 MPa, containing, in mass %,

C: 0.20% to 0.490%, Si: 0.05% to 2.0%, Mn: 0.20% to 1.0%, being limited to contain P: 0.030% or less, S: 0.030% or less, N: 0.005% or less, F1 defined by the following expression (1) is less than 0.60, with the balance made up of Fe and inevitable impurities,

wherein a metal structure contains a pearlite structure of 64×(C %)+52% or more in a volume fraction, with the balance made up of one kind or two kinds of a pro-eutectoid ferrite structure and a bainite structure,

an average block grain diameter of the pearlite structure at a region from a surface layer to 0.1 D is 15 μm or less when a diameter of the steel wire is set to be D, and (the average block grain diameter of the pearlite structure at the region from the surface layer to 0.1 D)/(an average block grain diameter of the pearlite structure at a range from 0.25 D to a center) is less than 1.0, and

an area ratio of a structure made up of a pearlite block whose aspect ratio is 2.0 or more is 70% or more relative to a whole pearlite structure at a region from a surface layer to 1.0 mm at a cross section in parallel to an axial direction of the steel wire,

F1=C(%)+Si (%)/24+Mn (%)/6  (1)

9. The steel wire for the non-heat treated component according to claim 8 , further containing, in mass %,

one kind or two or more kinds from among Al: 0.003% to 0.050%, Ca: 0.001% to 0.010%, Mg: 0.001% to 0.010%, Zr: 0.001% to 0.010%.

10. The steel wire for a non-heat treated component according to claim 8 , wherein

Cr, Mo, Ni, Ti, Nb, and V are contained as the impurities, and

F1 is defined as C (%)+Si (%)/24+Mn (%)/6+(Cr (%)+Mo (%))/5+Ni (%)/40+(Ti (%)+Nb (%)+V (%))/5.

11. The steel wire for the non-heat treated component according to claim 8 ,

wherein a C content is 0.48% or less.

12. The steel wire for the non-heat treated component according to claim 8 ,

wherein a maximum stress at distortion of 1.0 obtained by a compression test is 1200 MPa or less.

13. A manufacturing method of the steel wire for a non-heat treated component according to claim 8 , comprising:

heating a steel billet containing, in mass %, C: 0.20% to 0.49%, Si: 0.05% to 2.0%, Mn: 0.20% to 1.0%, being limited to contain P: 0.030% or less, S: 0.030% or less, N: 0.005% or less, F1 defined by the following expression (1) is less than 0.60, with the balance made up of Fe and inevitable impurities;

hot-rolling into a wire material shape;

coiling at a coiling temperature of 800° C. to 900° C.;

cooling at a cooling rate of 20° C./s to 100° C./s from a coiling finish temperature to 600° C., further cooling at the cooling rate of 20° C./s or less from 600° C. to 550° C.;

thereafter, isothermally holding in a molten salt tank 1 at 400° C. to 600° C. and a successive molten salt tank 2 at 500° C. to 600° C. for 5 seconds to 150 seconds each;

subsequently cooling; and

thereafter, performing wire drawing at a total reduction of area of 15% to 80%,

F1=C(%)+Si (%)/24+Mn (%)/6  (1)

14. A non-heat treated component whose tensile strength is 900 MPa to 1300 MPa, manufactured by cold-working a steel wire containing, in mass %, C: 0.20% to 0.49%, Si: 0.05% to 2.0%, Mn: 0.20% to 1.0%, being limited to contain P: 0.030% or less, S: 0.030% or less, N: 0.005% or less, F1 defined by the following expression (1) is less than 0.60, with the balance made up of Fe and inevitable impurities,

wherein a metal structure contains a pearlite structure of 64×(C %)+52% or more in a volume fraction, with the balance made up of one kind or two kinds of a pro-eutectoid ferrite structure and a bainite structure,

an average block grain diameter of the pearlite structure at a region from a surface layer to 0.1 D is 15 μm or less when a diameter of the steel wire is set to be D, and (the average block grain diameter of the pearlite structure at the region from the surface layer to 0.1 D)/(an average block grain diameter of the pearlite structure at a range from 0.25 D to a center) is less than 1.0,

an area ratio of a structure made up of a pearlite block whose aspect ratio is 2.0 or more is 70% or more relative to a whole pearlite structure at a region from a surface layer to 1.0 mm at a cross section in parallel to an axial direction of the steel wire,

F1=C(%)+Si (%)/24+Mn (%)/6  (1)

15. The non-heat treated component according to claim 14 , further containing, in mass %,

one kind or two or more kinds from among Al: 0.003% to 0.050%, Ca: 0.001% to 0.010%, Mg: 0.001% to 0.010%, Zr: 0.001% to 0.010%.

16. The non-heat treated component according to claim 14 , wherein

Cr, Mo, Ni, Ti, Nb, and V are contained as the impurities, and

F1 is defined as C (%)+Si (%)/24+Mn (%)/6+(Cr (%)+Mo (%))/5+Ni (%)/40+(Ti (%)+Nb (%)+V (%))/5.

17. The non-heat treated component according to claim 14 ,

wherein a C content is 0.48% or less.

18. A manufacturing method of the non-heat treated component according to claim 14 , comprising:

heating a steel billet containing, in mass %, C: 0.20% to 0.49%, Si: 0.05% to 2.0%, Mn: 0.20% to 1.0%, being limited to contain P: 0.030% or less, S: 0.030% or less, N: 0.005% or less, F1 defined by the following expression (1) is less than 0.60, with the balance made up of Fe and inevitable impurities;

hot-rolling into a wire material shape;

coiling at a coiling temperature of 800° C. to 900° C.;

cooling at a cooling rate of 20° C./s to 100° C./s from a coiling finish temperature to 600° C., further cooling at the cooling rate of 20° C./s or less from 600° C. to 550° C.;

thereafter, isothermally holding in a molten salt tank 1 at 400° C. to 600° C. and a successive molten salt tank 2 at 500° C. to 600° C. for 5 seconds to 150 seconds each;

subsequently cooling;

thereafter, performing wire drawing at a total reduction of area of 15% to 80%; and

further, performing cold-working,

F1=C(%)+Si (%)/24+Mn (%)/6  (1)

19. The manufacturing method of the non-heat treated component according to claim 18 ,

wherein after the wire drawing is performed, cold-working is performed without performing a softening heat treatment.

20. The manufacturing method of the non-heat treated component according to claim 18 , further comprising:

holding at 200° C. to 600° C. for 10 minutes or more after the cold-working is performed.