Parts with a bainitic structure having high strength properties and manufacturing process

1. A part comprising:

a composition including, with the contents being expressed as weight-percent:

0.10≤C≤0.30,

1.6≤Mn≤2.1,

0.5≤Cr≤1.7,

0.5≤Si≤1.0,

0.065≤Nb≤0.15,

0.0010≤B≤0.0050,

0.0010≤N≤0.0130,

0≤Al≤0.060,

0≤Mo≤1.00,

0≤Ni≤1.0,

0.01≤Ti≤0.07,

0≤V≤0.3,

0≤P≤0.050,

0.01≤S≤0.1,

0≤Cu≤0.5,

0≤Sn≤0.1; and

a balance of the composition including iron and unavoidable impurities resulting from processing; and

a microstructure including, in surface proportions, from 100% to 70% bainite, less than 30% of residual austenite, and less than 5% ferrite;

wherein the part exhibits a mechanical strength greater than or equal to 1100 MPa, an elastic limit greater than or equal to 700 MPa, and a breaking elongation greater than or equal to 12%, with a constriction at break greater than 30%.

2. The part according to the claim 1 , wherein the contents of niobium, vanadium, molybdenum, titanium and aluminum are such that:

0.1≤ S 1≤0.4,

wherein S1=Nb+V+Mo+Ti+Al.

3. The part according to claim 2 , wherein the contents of carbon, nitrogen, chromium, silicon, manganese, sulfur, and nickel are such that:

0.5≤ S 2≤1.8,

0.7≤ S 3≤1.6, and

0.3≤ S 4≤1.5,

wherein,

S 2=C+N+Cr/2+( S 1)/6+(Si+Mn−4* S )/10+Ni/20,

S 3= S 2+⅓×Vr600, and

S 4= S 3−Vr400, and

Vr400 and Vr600 being expressed in ° C./s, with Vr400 representing a cooling rate of the part in a first temperature range between 420° C. and 380° C. and Vr600 representing the cooling rate of the part in a second temperature range between 620° C. and 580° C.

4. The part according to claim 1 , wherein the composition comprises, with the content being expressed in weight-percent, 0.15≤C≤0.27.

5. The part according to claim 1 , wherein the composition comprises, with the content being expressed in weight-percent, 1.7<Mn≤2.0.

6. The part according to claim 1 , wherein the composition comprises, the content being expressed in weight-percent 1.0%≤Cr≤1.5.

7. The part according to claim 1 , wherein the composition comprises, the content being expressed in weight-percent, 0.75≤Si≤0.9.

8. The part according to claim 1 , wherein the composition comprises, the content being expressed in weight-percent, 0.065≤Nb≤0.110.

9. The part according to claim 1 , wherein the composition comprises, the content being expressed in weight-percent, 0.0020≤B≤0.0030.

10. The part according to claim 1 , wherein the composition comprises, the content being expressed in weight-percent, 0.0050≤N≤0.0120.

11. The part according to claim 1 , wherein the composition comprises, the content being expressed in weight-percent, 0.003≤Al≤0.015.

12. The part according to claim 1 , wherein the composition comprises, the content being expressed in weight-percent, 0≤Ni≤0.55.

13. The part according to claim 1 , wherein the composition comprises, the content being expressed in weight-percent, 0<V≤0.2.

14. The part according to claim 1 , wherein the composition comprises, the content being expressed in weight-percent, 0.03<Mo≤0.15.

15. The part according to claim 1 , wherein the microstructure comprises 0% ferrite.

16. The part according to claim 1 , wherein the microstructure comprises ferrite.

17. The part according to claim 1 , wherein the part comprises carbonitrides.

18. The part according to claim 1 , wherein the composition comprises Sn.

19. The part according to claim 1 , wherein the part is a bar or a wire.

20. The part according to claim 1 , wherein the microstructure comprises 5% or less martensite.

21. The part according to claim 1 , wherein the microstructure is free of martensite.