Hardened martensitic steel having a low or zero content of cobalt, method for producing a component from this steel, and component obtained in this manner

1. Method for producing a component from steel, wherein the steel comprises the following steps prior to the finishing of the component which confers the definitive shape thereon:

the preparation of a steel having a composition, in percentages by weight:

C=0.20 to 0.30%

Co=trace levels to 1%

Cr=2 to 5%

Al=1 to 2%

Mo+W/2=1 to 4%

V=trace levels to 0.3%

Nb=trace levels to 0.1%

B=trace levels to 30 ppm

Ni=11 to 16%

Si=trace levels to 1.0%

Mn=trace levels to 2.0%

Ca=trace levels to 20 ppm

rare earths=trace levels to 100 ppm,

if N≦10 ppm, Ti+Zr/2=trace levels to 100 ppm with Ti+Zr/2≦10×N

if 10 ppm<N≦20 ppm, Ti+Zr/2=trace levels to 150 ppm

O=trace levels to 50 ppm

N=trace levels to 20 ppm

S=trace levels to 20 ppm

Cu=trace levels to 1%

P=trace levels to 200 ppm,

the remainder being iron and inevitable impurities resulting from the production operation, and wherein the composition of the steel simultaneously satisfies the relationship Ni≧7+(3.5×Al);

at least one operation for shaping this steel;

a softening tempering operation at 600-675° C. for from 4 to 20 hours followed by cooling in air;

a solution heat treatment at 900-1000° C. for at least 1 hour, followed by cooling in oil or air which is sufficiently rapid to prevent the precipitation of intergranular carbides in the austenite matrix;

a hardening ageing operation at 475-600° C. for from 5-20 hours.

2. Method for producing a component from steel according to claim 1 , further comprising a cryogenic processing operation at −50° C. or lower, preferably at −80° C. or lower, in order to convert all the austenite into martensite, the temperature being 150° C. or more less than measured Ms, at least one of the processing operations lasting at least 4 hours and a maximum of 50 hours.

3. Method for producing a component from steel according to claim 1 , further comprising a processing operation for softening the coarse martensite involving annealing carried out at 150-250° C. for from 4-16 hours, followed by cooling in still air.

4. Method for producing a component from steel according to claim 1 , wherein the component is also subjected to a carburizing operation or a nitriding or a carbonitriding operation.

5. Method for producing a component from steel according to claim 4 , wherein the nitriding or carburizing operation is carried out during a thermal cycle prior to or at the same time as the solution heat treatment.

6. Method for producing a component from steel according to claim 4 , wherein the nitriding operation is carried out during an ageing cycle.

7. Method for producing a component from steel according to claim 6 , wherein the nitriding is carried out between 490 and 525° C. for from 5 to 100 hours.

8. Method for producing a component from steel according to claim 1 , wherein the hardening ageing operation is conducted at 490-525° C. for from 5-20 hours.

9. Method for producing a component from steel according to claim 1 , wherein the steel contains C=0.20 to 0.25%.

10. Method for producing a component from steel according to claim 1 , wherein the steel contains Cr=2 to 4%.

11. Method for producing a component from steel according to claim 1 , wherein the steel contains Al=1 to 1.6%.

12. Method for producing a component from steel according to claim 1 , wherein the steel contains Mo=1 to 4%.

13. Method for producing a component from steel according to claim 1 , wherein the steel contains Mo+W/2=1 to 2%.

14. Method for producing a component from steel according to claim 1 , wherein the steel contains V=0.2 to 0.3%.

15. Method for producing a component from steel according to claim 1 , wherein the steel contains Ni=12 to 14%, with Ni≧7+3.5 Al.

16. Method for producing a component from steel according to claim 1 , wherein the steel contains Nb=trace levels to 0.05%.

17. Method for producing a component from steel according to claim 1 , wherein the steel contains Si=trace levels to 0.25%.

18. Method for producing a component from steel according to claim 1 , wherein the steel contains 0=trace levels to 10 ppm.

19. Method for producing a component from steel according to claim 1 , wherein the steel contains N=trace levels to 10 ppm.

20. Method for producing a component from steel according to claim 1 , wherein the steel contains S=trace levels to 10 ppm.

21. Method for producing a component from steel according to claim 1 , wherein the steel contains P=trace levels to 100 ppm.

22. Method for producing a component from steel according to claim 1 , wherein the steel contains Al=1.4 to 1.6%.

23. Method for producing a component from steel according to claim 1 , wherein the steel contains Si=trace levels to 0.10%.

24. Method for producing a component from steel according to claim 1 , wherein the steel contains S=trace levels to 5 ppm.

25. Method for producing a component from steel according to claim 1 , wherein the component is a mechanical component or component for a structural element.

26. Method for producing a component from steel according to claim 1 , wherein the mechanical component or component for a structural element is an engine transmission shaft, an engine suspension device, a landing gear element, a gearbox element or a bearing shaft.

27. Method for producing a component from steel according to claim 1 , wherein a measured martensitic transformation temperature Ms thereof is greater than or equal to 100° C.

28. Method for producing a component from steel according to claim 27 , wherein the measured martensitic transformation temperature Ms thereof is greater than or equal to 140° C.